PIC18F87J72 Single-Phase
Energy Meter Calibration
User’s Guide
© 2011 Microchip Technology Inc.
DS51964A
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DS51964A-page 2
© 2011 Microchip Technology Inc.
PIC18F87J72 SINGLE-PHASE
ENERGY METER CALIBRATION
USER’S GUIDE
Table of Contents
Preface ........................................................................................................................... 5
Introduction............................................................................................................ 5
Document Layout .................................................................................................. 5
Conventions Used in this Guide ............................................................................ 6
Recommended Reading........................................................................................ 7
The Microchip Web Site ........................................................................................ 7
Customer Support ................................................................................................. 7
Document Revision History ................................................................................... 8
Chapter 1. Product Overview
1.1 Introduction ..................................................................................................... 9
Chapter 2. Meter Calibration
2.1 Introduction ................................................................................................... 11
2.2 Types of Calibration ..................................................................................... 11
2.3 Closed Loop Calibration ............................................................................... 12
2.4 Multipoint Calibration .................................................................................... 30
2.5 Single Point Calibration ................................................................................ 48
2.6 Creep Threshold Calibration ........................................................................ 49
2.7 Meter Specifications And Calibration Parameters ........................................ 51
Chapter 3. Microchip Energy Meter Software
3.1 Introduction ................................................................................................... 53
3.2 Main Screen ................................................................................................. 53
3.3 Debug Mode ................................................................................................. 56
Chapter 4. Communication Protocol
4.1 Protocol ........................................................................................................ 59
Worldwide Sales and Service .................................................................................... 62
© 2011 Microchip Technology Inc.
DS51964A-page 3
© 2011 Microchip Technology Inc.
DS51964A-page 4
PIC18F87J72 SINGLE-PHASE
ENERGY METER CALIBRATION
USER’S GUIDE
Preface
NOTICE TO CUSTOMERS
All documentation becomes dated, and this manual is no exception. Microchip tools and
documentation are constantly evolving to meet customer needs, so some actual dialogs
and/or tool descriptions may differ from those in this document. Please refer to our web site
(www.microchip.com) to obtain the latest documentation available.
Documents are identified with a “DS” number. This number is located on the bottom of each
page, in front of the page number. The numbering convention for the DS number is
“DSXXXXXA”, where “XXXXX” is the document number and “A” is the revision level of the
document.
For the most up-to-date information on development tools, see the MPLAB® IDE on-line help.
Select the Help menu, and then Topics to open a list of available on-line help files.
INTRODUCTION
This chapter contains general information that will be useful to know before using the
Microchip Single-Phase Energy Meter Calibration Tool. Items discussed in this chapter
include:
•
•
•
•
•
•
Document Layout
Conventions Used in this Guide
Recommended Reading
The Microchip Web Site
Customer Support
Document Revision History
DOCUMENT LAYOUT
This document describes how to use the Single Phase Energy Meter Calibration tool
in energy meter design. The manual layout is as follows:
• Chapter 1. Product Overview provides a brief overview of the calibration tool, its
features and uses.
• Chapter 2. Meter Calibration provides detail on calibration implementation and
how to calibrate the meter. The PC calibration software, included with the
reference design manual, automates the steps and calculations described in this
chapter.
• Chapter 3. Microchip Energy Meter Software provides a detailed description of
features of the calibration software tool, which is provided with the Single-Phase
Energy Meter Calibration Reference Design User’s Guide.
• Chapter 4. Communication Protocol provides the details on the protocol used
to communicate with the meter for accessing the internal registers.
© 2011 Microchip Technology Inc.
DS51964A-page 5
PIC18F87J72 Single-Phase Energy Meter Calibration User’s Guide
CONVENTIONS USED IN THIS GUIDE
This manual uses the following documentation conventions:
DOCUMENTATION CONVENTIONS
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select Enable Programmer
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DS51964A-page 6
© 2011 Microchip Technology Inc.
Preface
RECOMMENDED READING
This user’s guide describes how to use the Microchip Single-Phase Energy Meter
Calibration Tool. Other useful documents are listed below. The following Microchip
documents are available and recommended as supplemental reference resources:
User’s Guide – “PIC18F87J72 Energy Meter Reference Design”(DS51931A)
This user’s guide contains the details of energy meters internal registers and hardware
design descriptions.
PIC18F87J72 Family Data Sheet – “80-Pin, High-Performance Microcontrollers
with Dual Channel AFE, LCD Driver and nanoWatt Technology” (DS39979)
This data sheet provides detailed information regarding the PIC18F87J72 device.
AN994 – “IEC61036 Meter Design using the MCP3905A/06A Energy Metering
Devices” (DS00994)
This application note describes the design decisions related to the meter design using
the MCP390X devices and IEC compliance. These are directly related to the
PIC18F87J72 and other PIC® based energy meter designs.
THE MICROCHIP WEB SITE
Microchip provides online support via our web site at www.microchip.com. This web
site is used as a means to make files and information easily available to customers.
Accessible by using your favorite Internet browser, the web site contains the following
information:
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• General Technical Support – Frequently Asked Questions (FAQs), technical
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and distributors and factory representatives
CUSTOMER SUPPORT
Users of Microchip products can receive assistance through several channels:
•
•
•
•
Distributor or Representative
Local Sales Office
Field Application Engineer (FAE)
Technical Support
Customers should contact their distributor, representative or field application engineer
(FAE) for support. Local sales offices are also available to help customers. A listing of
sales offices and locations is included in the back of this document.
Technical support is available through the web site at: http://support.microchip.com
© 2011 Microchip Technology Inc.
DS51964A-page 7
PIC18F87J72 Single-Phase Energy Meter Calibration User’s Guide
DOCUMENT REVISION HISTORY
Revision A (June 2011)
Initial Release of this Document.
DS51964A-page 8
© 2011 Microchip Technology Inc.
PIC18F87J72 SINGLE-PHASE
ENERGY METER CALIBRATION
USER’S GUIDE
Chapter 1. Product Overview
1.1
INTRODUCTION
Energy meters are part of electricity distribution networks, which measure electricity
consumption. Usage of the energy meter in the electricity distribution network requires
the energy meters to be adaptable to various configurations. This depends on the part
of the distribution network and the type of end consumer for which the energy meters
are installed. These configurations include a wide range of voltage and current, across
which the meter should be functional, as per the specifications. The above
requirements demand the metering engine to be adaptable, so that the transducers
converting the input signal are selectable, depending on the specification, while still
recording the actual values of the input line signal.
The meter design is comprised of many components, which may vary in their
characteristics due to the various factors across the meter design.
The components that form part of the circuitry include:
•
•
•
•
•
Current Transformer (CT) or Shunt used as a current transducer
Resistive voltage divider as voltage transducer
Resistors
Capacitors
Inductors
These variations in characteristics have an impact on measured signals, which may
result in offset addition, amplitude alteration and change in signal phase.
Considering all the above factors, the standard value calibration needs to be carried
out to achieve meter output. Calibration is the process where the line parameters are
set to known values and the various signal conditioning parameters such as gain, offset
compensation, and phase compensation factors are calculated.
The calibration process should be comprehensive. The process should aid meter
design by selecting the various transducers, and should be fast enough to reduce the
production line assembly time. The calibration should be accountable for the
specifications like accuracy, class, and various parameters that need to be measured
by the meter. The above requirements necessitate that the calibration process should
be:
• Fast to aid production line calibration
• Achieve required meter specifications in one iteration
• Give information about the value of transducers required for a particular specification of the meter, aiding meter design
• Modular such that only required meter output parameter can be calibrated to
desired level of accuracy
Different types of calibrations, considering all the above factors, are described in the
following chapters.
© 2011 Microchip Technology Inc.
DS51964A-page 9
PIC18F87J72 Single-Phase Energy Meter Calibration User’s Guide
NOTES:
DS51964A-page 10
© 2011 Microchip Technology Inc.
PIC18F87J72 SINGLE-PHASE
ENERGY METER CALIBRATION
USER’S GUIDE
Chapter 2. Meter Calibration
2.1
INTRODUCTION
This chapter describes the method to calculate calibration parameters. It includes
various types of calibration suitable for different stages of meter design.
2.2
TYPES OF CALIBRATION
Based on the type of meter accuracy class, and the stages of meter development, the
different types of calibration options provided are:
• Closed Loop Calibration
• Multipoint Calibration
• Single Point Calibration
During the calibration process, the following register values are computed:
• Gain registers
- GAIN_V_RMS
- GAIN_I_RMS
- GAIN_POWER_ACT
- GAIN_POWER_REACT
- GAIN_NUMR_ENERGY_ACT
- GAIN_DENR_ENERGY_ACT
- GAIN_NUMR_ENERGY_REACT
- GAIN_DENR_ENERGY_REACT
• Offset registers
- OFFSET_I_RMS
- OFFSET_V_RMS
- OFFSET_POWER_ACT
- OFFSET_POWER_REACT
• Phase compensation register
- PHASE_COMPENSATION
• Creep threshold for No Load condition
- CREEP_THRSHOLD_MINUTE
- CREEP_THRSHOLD_SECOND
Note:
For descriptions on these registers, refer to User’s Guide – “PIC18F87J72
Energy Meter Reference Design”(DS51931)
The calibration flow charts, procedures and equation presented in this section are all
automated using Microchip’s “Single Phase Energy Meter Calibration Software”,
downloadable from the Energy Meter product page. The calibration software features
multiple tabs, offering three different calibration processes.
© 2011 Microchip Technology Inc.
DS51964A-page 11
PIC18F87J72 Single-Phase Energy Meter Calibration User’s Guide
2.2.1
Calibration Requirements
The calibration requirements for the Closed Loop, Multipoint and Single Point
Calibration process are:
• Requirement for Closed Loop Calibration
Closed loop calibration requires a reference meter. The reference meter is an accurate
measurement source capable of measuring the line parameters and the output of the
meter under calibration simultaneously, and gives the percentage difference.
Calibration using a reference meter is common practice in the industry, which is
adopted in the Closed Loop Calibration. To measure the output of the meter under
calibration, the calibration pulse rate (CF pulse) is used, which is proportional to the
energy accumulated by the meter. The rate of CF pulse of the meter and the reference
meter are compared to calculate this percentage error (Error %). This Error % is used
as feedback to calibrate the meter. The Closed Loop Calibration method reads the
meter output as an average value over a period. Therefore, even if the line input is not
from a highly accurate input source, it will not be a limitation during the closed loop
calibration.
• Requirement for Multipoint and Single Point Calibration
The accurate source that feeds the line parameters precisely is used in the multipoint
and single point calibration. In this calibration process, the parameter under calibration
is measured over a definite period, under the condition that the input is precisely set to
a known value without any fluctuations. Based on this, various calibration register
values are computed theoretically. As the calibration does not involve any feedback,
the source feeding the line parameters must be highly accurate to achieve the desired
accuracy class.
2.3
CLOSED LOOP CALIBRATION
The Closed Loop Calibration process involves taking feedback from the meter output
and comparing it with the reference meter for the given parameter values. Error % in
the meter output with respect to the standard reference meter is calculated, and the
register values are adjusted until the desired level of accuracy is achieved.
Closed Loop Calibration includes two configurations, offered as a modular process:
• Power Calibration
• Energy Calibration
During these stages, various meter outputs are calibrated, and include:
•
•
•
•
•
•
•
RMS Voltage
RMS Current
Active Power
Reactive Power
Apparent Power
Active Energy
Reactive Energy
All the above meter outputs can be calibrated independently, with the few
dependencies based on the accuracy class of the meter under calibration.
The method of calibrating these separate signal flows can be combined into five
different stages in the power calibration tab, and three different stages in the energy
calibration tab. These stages consist of supplying specific voltage and current at
specific phase angles to the meter and input the Error % in energy registered in the
reference meter.
DS51964A-page 12
© 2011 Microchip Technology Inc.
Meter Calibration
Depending on the accuracy and the meter type, all calibration stages are not required
to calibrate a meter completely. In some cases, only a few calibration stages are
required. The software allows individual stages to be carried out independently, during
the calibration flow.
2.3.1
Generic Flow chart for closed Loop calibration
Figure 2-1 represents the generic calibration process followed for:
•
•
•
•
RMS Voltage
RMS Current
Active Power
Reactive Power
Start
Enter Line Parameter Value
Input to meter
NO
Is Calibrate Button
Pressed
YES
Read Meter Output Line Parameter
Compute Error Percentage with respect to
Input Line Parameter
Is Error within
Specification or 5 times Iterations
Completed?
YES
Stop
NO
Calculate Gain using Formula
(in Gain Compensation)
Write New Gain to Meter
Wait for New Gain to take Effect
FIGURE 2-1:
Generic Flow Chart for Closed Loop Calibration.
© 2011 Microchip Technology Inc.
DS51964A-page 13
PIC18F87J72 Single-Phase Energy Meter Calibration User’s Guide
2.3.2
ENERGY CALIBRATION
In energy calibration, the calibration pulse rate, proportional to the energy measured by
the meter, is used in the calibration. The calibration pulse output from the meter is probed
to the reference meter. Any error registered in the energy meter is given by the reference
meter, based on the difference in the blinking rate. This error percentage is entered as
an input to the energy calibration. Depending upon the error, necessary corrections are
made to the energy gain and phase compensation.
Energy calibration is carried out for active energy and reactive energy. Reactive energy
calibration should always be preceded by the active energy calibration. In the two
stages of active energy calibration, the phase compensation between voltage and
current is computed, which is necessary for achieving good accuracy in reactive energy
calibration.
2.3.2.1
ACTIVE ENERGY SIGNAL FLOW AND CALIBRATION
During the active energy calibration, the gain register GAIN_NUMR_ENERGY_ACT,
GAIN_DENR_ENERGY_ACT and PHASE_COMPENSATION gets computed.
Figure 2-2 shows the active energy calculation in the metering engine, the calibration
gain and the phase compensation registers.
Over 128 Samples
ADC
CURRENT
PHASE_COMPENSTATION:8 X
X
Σ
ADC
PERIOD:16
(INTERNAL REGISTER)
Φ
VOLTAGE
Digital to
Frequency
Converter
GAIN_NUMR_ENERGY_ACT:16 GAIN_DENR_ENERGY_ACT:8
GAIN_ENERGY_ACT:16
(NOT IMPLEMENTED)
ENERGY_ACT_L:64
kWh
X
Σ
X
CF OUTPUT
FREQUENCY
RAW_ENERGY_ACT:48
Over 128 Signal
Cycles
FIGURE 2-2:
DS51964A-page 14
kWh 1/METER
CONSTANT
kWh
Σ
ENERGY_ACT:32
Active Energy Calculation Signal Flow.
© 2011 Microchip Technology Inc.
Meter Calibration
2.3.2.2
ACTIVE ENERGY GAIN COMPUTATION
Active energy gain is computed as the percentage ratio of the error recorded against
the previous gain. The Error % is the difference between the input line active energy
and the meter output as recorded by the reference meter. Active energy gain is computed using Equation 2-1.
EQUATION 2-1:
ACTIVE ENERGY GAIN COMPUTATION
GAIN
( NewValue )
GAIN ( OldValue )
= -------------------------------------------⎛ Error%
------------------⎞ + 1
⎝ 100 ⎠
If GAIN > 65535
Then,
GAIN_NUMR_ENERGY_ACT (New Value) = GAIN (New Value) / 2
GAIN_DENR_ENERGY_ACT(New Value) = GAIN_DENR_ENERGY_ACT(Old Value) + 1
else,
GAIN_NUMR_ENERGY_ACT (New Value = GAIN (New Value)
GAIN_DENR_ENERGY_ACT (New Value) = GAIN_DENR_ENERGY_ACT (Old Value) )
2.3.2.3
PHASE COMPENSATION
Due to reactive components in the signal flow path, the voltage and current may not be
in phase at PF = 1.0. Therefore, the voltage and current samples measured will have
a small phase offset, that may affect the energy accuracy. To rectify the offset, phase
compensation is introduced, which shifts the voltage/current samples by corresponding
angle through an interpolation method.
2.3.2.3.1
Phase Compensation Calculation
Equations 2-2 to 2-6 shows the calculation of different stages of phase compensation.
EQUATION 2-2:
ENERGY WITH PHASE ERROR AT PF = 1.0
Energy at PF = 1.0 ( Φ= 0o):
EUPF = VRMS x IRMS x Cos( Φ+ β) x Period = VRMS x IRMS x Cos( β) x Period
Where:
Φ = Input Phase between V and I
β = Phase deviation between V and I, β Є [-90°, +90°]
EQUATION 2-3:
ENERGY WITH PHASE ERROR AT PF = 0.5 LAG
Energy at PF = 0.5 lag ( Φ= 60o):
EPF0.5_error = VRMS x IRMS x Cos( Φ + β) x Period
= VRMS x IRMS x Cos( 60 + β) x Period
Where:
Φ = Input Phase between V and I
β = Phase deviation between V and I, β Є [-90°, +90°]
© 2011 Microchip Technology Inc.
DS51964A-page 15
PIC18F87J72 Single-Phase Energy Meter Calibration User’s Guide
EQUATION 2-4:
ENERGY WITHOUT PHASE ERROR AT PF = 0.5 LAG
Actual Energy at PF = 0.5 lag ( Φ = 60o ):
EPF0.5 = VRMS x IRMS x Cos( ø ) x Period
= VRMS x IRMS x Cos( 60 ) x Period
Where:
Φ = Input Phase between V and I
EQUATION 2-5:
PHASE COMPENSATION ANGLE CALCULATION
Error = (EPF0.5 - EPF0.5_error ) * 100 / EPF0.5
Error/100 = 1 – (EPF0.5_error / EPF0.5)
Substituting equations and simplify:
Error/100 = 1 – (Cos(60 + β) / Cos(60))
= 1 – (Cos(60 + β) / 0.5)
Cos(60 + β) = 0.5 x (1 + Error/100) = n
β = [COS-1 (n) – 60] in degree is the phase compensation angle
EQUATION 2-6:
PHASE COMPENSATION FACTOR CALCULATION
PHASE_COMPENSATION = β x 128 / Angle between samples
= β x 128 / 5.529o
Angle between samples = 360o / Samples per sine cycle
= 360o / 65.1
= 5.529o
Samples per sine cycle = Sampling rate/Frequency of Signal
= 3906 / 60Hz
= 65.1 samples per cycle
Magnitude of Phase compensation factor:
PHASE_COMPENSATION (magnitude) = |PHASE_COMPENSATION |
= PHASE_COMPENSATION x 2
Note 1:
The Sign convention of Phase Compensation angle is:
• Positive, if the current leads voltage
• Negative, if the current lags voltage
2.3.2.3.2
Phase Compensation between Voltage and Current
To determine the state of the signal between the two successive samples, use the
interpolation method.
If x(Θ-N) and x(Θ) are known, where, “Θ” is the phase of signal that can vary between
0o to 360o and “N” is the angle between two successive samples = (360 * frequency of
signal/sampling rate), then it is possible to determine the state of the signal at any interval between ‘Θ-N’ and ‘Θ’ with an assumption that signal varies linearly in the
intermediate region as shown in Equation 2-7.
To apply this method to a line signal, the sampling rate has to be selected such that the
interval between successive samples is small. This ensures that the above stated
assumption holds true.
DS51964A-page 16
© 2011 Microchip Technology Inc.
Meter Calibration
EQUATION 2-7:
CALCULATIONS WITH THE INTERPOLATION METHOD
Consider, X(Θ) and X(Θ - N) as known samples
X[Θ + β] = X[Θ] + (X[Θ] - X[Θ - N] ) * PHASE_COMPENSATION (magnitude)/256
Where:
Θ-N ≤Θ+β ≤Θ
Θ = Varies between 0 and 360°
N = Angle between successive samples = (360 * frequency of signal / sampling rate)
PHASE_COMPENSATION value is derived from Equations 2-2 to 2-6.
Equation 2-7 implements the linear interpolation on the previous sample of voltage for
the phase compensation. The present or the previous sample of current is considered,
depending on the voltage lag or lead condition respectively, as explained in Case1 and
Case 2, thus accounting to compensate phase by a maximum angle of ±N/2.
Case 1: Current Leads Voltage by Angle β
Phase correction factor “PHASE_COMPENSATION” is calculated for the correction
angle ‘β’ as explained in Equation 2-5 and Equation 2-6. In this case ‘β’ is positive, therefore “PHASE_COMPENSATION” value will be positive as explained in Note 1.
As the current leads the voltage during phase compensation, the voltage sample needs
to be given a lead by an angle ‘β’. From the interpolation method, it is possible to determine X(Θ + β) from X(Θ) and X(Θ - N) and achieve a lead. The lead can only be applied
to the previous sample, but not to the present sample.
Therefore, keeping the above argument in consideration to compensate the current
lead:
• Phase compensation is carried out on the voltage sample, introducing a lead by
using the present and the previous sample of voltage. This phase lead is applied
to the previous sample of voltage.
• As the phase lead is applied to the previous sample of voltage, the corresponding
previous sample of current is considered. This compensation brings voltage and
current in synchronization.
Case 2: Current Lags Voltage by Angle β
The phase correction factor “PHASE_COMPENSATION”, is calculated for the
correction angle ‘β’ as explained in Equation 2-5 and Equation 2-6. In this case, ‘β’ is
negative, therefore the “PHASE_COMPENSATION” value will be negative as
explained in Note 1.
As the current lags voltage during phase compensation, the voltage sample needs to
be given a lead by angle ‘N-β’. From the interpolation method, it is possible to determine X[Θ + N - β] from X(Θ) and X(Θ-N) as Θ-N ≤ Θ+ N-β ≤ Θ and achieve a lead. The
lead can only be applied to the previous sample, but not to the present sample.
Therefore, keeping the above argument in consideration in order to compensate the
current lag:
• Phase compensation is carried out on the voltage sample, introducing a lead by
using the present and the previous sample of voltage. This phase lead is applied to
the previous sample of voltage.
• As the phase lead is applied to the previous sample of voltage, the present sample of
current is considered. This compensation brings voltage and current in
synchronization.
© 2011 Microchip Technology Inc.
DS51964A-page 17
PIC18F87J72 Single-Phase Energy Meter Calibration User’s Guide
2.3.2.4
ACTIVE ENERGY CALIBRATION PROCEDURE
The active energy calibration (kWh) consists of two stages:
STAGE 1
During Stage 1, the active energy gain compensation gets computed at PF = 1.0 lag.
Depending on the type, value of voltage and current transducers, the value of gain
compensation varies to measure the standard value of energy.
1. At PF = 1.0, the active energy calibration pulse output is probed. The Error % is
entered into the Stage 1 calibration software, as shown in Figure 2-3.
2. Click Calibrate to proceed with the calibration. During this stage, the gain of the
active energy will be calibrated.
3. After completion of the process, the active energy pulse output is probed and the
Error % is recorded. If the meter output is within the specification, the active
energy calibration Stage 1 can be stopped.
FIGURE 2-3:
DS51964A-page 18
Active Energy Calibration Stage 1.
© 2011 Microchip Technology Inc.
Meter Calibration
STAGE 2
During this stage, phase compensation will be computed at PF = 0.5 lag. Due to various components in the board design, there may be a phase delay between the voltage
and the current.
1. To compensate for the phase delay, the meter line inputs are set at PF = 0.5 lag
and the active energy calibration pulse output is probed.
2. The Error % registered in the reference meter is entered as an input to Stage 2
calibration. Click Calibrate to initiate the phase compensation calibration as
shown in Figure 2-4.
3. After completion of the process, the meter active energy pulse output is probed
and the Error % is recorded. To confirm accurate phase compensation, the active
energy at various PF can be checked, during which the accuracy must be within
the specification. If the meter output is within the specification, active energy
calibration Stage 2 can be stopped.
FIGURE 2-4:
Active Energy Calibration Stage 2.
© 2011 Microchip Technology Inc.
DS51964A-page 19
PIC18F87J72 Single-Phase Energy Meter Calibration User’s Guide
2.3.3
Reactive Energy Signal Flow and Calibration
During reactive energy calibration, the gain register GAIN_NUMR_ENERGY_REACT,
GAIN_DENR_ENERGY_REACT gets computed. Figure 2-5 shows the reactive
energy calculation in the metering engine and the calibration gain register.
Over 128 Samples
ADC
CURRENT
PHASE_COMPENSTATION:8
(1)
(2)
+ α
Φ
ADC
Σ
X
X
PERIOD:16
(INTERNAL REGISTER)
VOLTAGE
Digital to
Frequency
Converter
GAIN_DENR_ENERGY_REACT:8
GAIN_NUMR_ENERGY_REACT:16
90° PHASE SHIFTER
GAIN_ENERGY_REACT:16
(NOT IMPLEMENTED)
kVARh
ENERGY_REACT_L:64
/
kVARh
Σ
X
CF OUTPUT
FREQUENCY
1/METER
CONSTANT
Σ
kVARh
RAW_ENERGY_REACT:48
Over 128 Signal
Cycles
Note 1:
2:
ENERGY_REACT:32
90° PHASE SHIFTER is implemented as a low-pass filter in cutoff band and a phase compensator.
α is a phase compensator to compensate small angles to get exact 90° phase shift in conjunction with the
low- pass filter.
FIGURE 2-5:
Reactive Energy Calculation Signal Flow.
2.3.3.1
REACTIVE ENERGY GAIN COMPUTATION
Reactive energy gain is computed as a percentage ratio of the error recorded against
the previous gain. The Error % is the difference between the input line reactive energy
and the meter output, as recorded by the reference meter. Reactive energy gain is
computed using Equation 2-8.
EQUATION 2-8:
REACTIVE ENERGY GAIN COMPUTATION
GAIN
GAIN
( OldValue )
= -------------------------------------------( NewValue )
⎛ Error%
------------------⎞ + 1
⎝ 100 ⎠
If GAIN > 65535
Then,
GAIN_NUMR_ENERGY_REACT (New Value) = GAIN (New Value) / 2
GAIN_DENR_ENERGY_REACT(New Value) = GAIN_DENR_ENERGY_REACT(Old Value) + 1
else,
GAIN_NUMR_ENERGY_REACT (New Value = GAIN (New Value)
GAIN_DENR_ENERGY_REACT (New Value) = GAIN_DENR_ENERGY_REACT (Old Value) )
DS51964A-page 20
© 2011 Microchip Technology Inc.
Meter Calibration
2.3.3.2
REACTIVE ENERGY CALIBRATION PROCEDURE
In reactive energy calibration stage, the reactive energy calibration pulse output is
probed and the percentage error (Error %) is entered as an input to the calibration
software as shown in Figure 2-6. To calibrate the reactive energy, the phase
compensation should be calibrated, which otherwise may be erroneous. The reactive
energy calibration is similar to Stage 1 of active energy calibration, during which the
gain of the reactive energy is calibrated.
1. At PF = 0.5 lag, the reactive energy calibration pulse output is probed and the
percentage error (Error %) is entered as an input to the calibration software.
2. Click Calibrate to proceed with calibration. During this stage, the gain of the
reactive energy is calibrated.
3. After the completion of the process, the meter reactive energy pulse output is
probed and the error percentage is recorded, in comparison with the reference
meter output. If the meter output is within the specification, the reactive energy
calibration can be stopped.
FIGURE 2-6:
Reactive Energy Calibration.
© 2011 Microchip Technology Inc.
DS51964A-page 21
PIC18F87J72 Single-Phase Energy Meter Calibration User’s Guide
2.3.4
Power Calibration
In Power Calibration, the line parameter measured by the reference meter, is entered
as an input to the calibration software. The difference between the output of the meter
under the calibration, and the reference meter is computed. The Error % is used as
feedback to adjust the calibration parameters accordingly.
In power calibration configuration, Active power, Reactive Power, RMS Voltage and
RMS Current get calibrated.
2.3.4.1
VOLTAGE SIGNAL FLOW AND CALIBRATION
During voltage calibration, the gain register GAIN_V_RMS gets computed. Figure 2-7
shows the voltage calculation in the metering engine and the calibration gain register.
OFFSET_V_RMS:16
X2
ADC
Σ
GAIN_V_RMS:16
Σ
V_RMS:16
X
VOLTAGE
Average
Over 128 Signal
Cycles
FIGURE 2-7:
RAW_V_RMS:16
RMS Voltage Calculation Signal Flow.
2.3.4.1.1
Voltage Gain Computation
Voltage gain is computed as a percentage ratio of the error, recorded against the
previous gain. The Error % is the difference between the input line voltage and the
meter output.
EQUATION 2-9:
VOLTAGE GAIN COMPUTATION
GAIN_V_RMS
Note:
2.3.4.1.2
( NewValue )
GAIN_V_RMS ( OldValue )
= -----------------------------------------------------------------⎛ Error%
------------------⎞ + 1
⎝ 100 ⎠
The Error % is used as an input for the calibration software.
Voltage Calibration Procedure
To calibrate the RMS voltage output of the meter, follow this procedure:
1. Enter the input line voltage value in “Calibration Voltage (V)” and click Calibrate
to initiate the calibration, as shown in Figure 2-8.
2. After completion of the process, the meter output voltage will be displayed along
with the Error % in comparison with the input line voltage.
3. If the meter output is within the specification, the voltage calibration can be
stopped.
DS51964A-page 22
© 2011 Microchip Technology Inc.
Meter Calibration
FIGURE 2-8:
Voltage Calibration.
2.3.4.2
CURRENT SIGNAL FLOW AND CALIBRATION
During the current calibration, the gain register GAIN_I_RMS gets computed.
Figure 2-9 shows the current calculation in the metering engine and the calibration gain
register.
OFFSET_I_RMS:16
ADC
X2
Σ
Σ
GAIN_I_RMS:16
X
A
I_RMS:16
CURRENT
Average
Over 128 Signal
Cycles
FIGURE 2-9:
RAW_I_RMS:16
RMS Current Calculation Signal Flow.
© 2011 Microchip Technology Inc.
DS51964A-page 23
PIC18F87J72 Single-Phase Energy Meter Calibration User’s Guide
2.3.4.2.1
Current Gain Computation
Current gain is computed as a percentage ratio of the error recorded against the
previous gain. The Error % is the difference between the input line current and the
meter output.
EQUATION 2-10:
CURRENT GAIN COMPUTATION
GAIN_I_RMS
2.3.4.2.2
( NewValue )
GAIN_I_RMS ( OldValue )
= ---------------------------------------------------------------⎛ Error%
------------------⎞ + 1
⎝ 100 ⎠
Current Calibration Procedure
To calibrate the RMS current output of the meter, follow this procedure:
1. Enter the input line current value in “Calibration Current (A)” and click Calibrate
to initiate the calibration, as shown in Figure 2-10.
2. After completion of the process, the meter output current will be displayed along
with the Error % in comparison with the input line current.
3. If the meter output is within the specification, then the current calibration can be
stopped.
FIGURE 2-10:
DS51964A-page 24
Current Calibration.
© 2011 Microchip Technology Inc.
Meter Calibration
2.3.4.3
ACTIVE POWER SIGNAL FLOW AND CALIBRATION
During Active Power Calibration, the gain registers GAIN_POWER_ACT and
PHASE_COMPENSATION get computed. Figure 2-11 shows the active power
calculation in the metering engine, the calibration gain and the phase compensation
registers.
Average
Over 128 Signal
Cycles
ADC
CURRENT
PHASE_COMPENSATION:8 X
Σ
Σ
Over 128 Samples
Φ
ADC
Σ
OFFSET_POWER_ACT:32
GAIN_POWER_ACT:16
VOLTAGE
POWER_ACT:32
FIGURE 2-11:
kW
RAW_POWER_ACT:64
X
Active Power Calculation Signal Flow
Note:
2.3.4.3.1
Stage 2 of active power calibration includes the phase compensation factor
calculation. This calibration is also included in the second stage of active
energy calibration. If the meter configuration includes both active energy
and power calibration, then it is suggested to calibrate the phase
compensation factor in the energy calibration stage and skip this step
during power calibration.
Active Power Gain Computation
Active Power Gain is computed as a percentage ratio of the error recorded against the
previous gain. The Error % is the difference between the input line active power and
the meter output, as shown in Equation 2-11.
Note:
Phase compensation is explained in Stage 2 of Energy Calibration
(Equations 2-2 to 2-6).
EQUATION 2-11:
ACTIVE POWER GAIN COMPUTATION
GAIN_POWER_ACT
( OldValue )
GAIN_POWER_ACT ( NewValue ) = ---------------------------------------------------------------------------------Error%
⎛ ------------------⎞ + 1
⎝ 100 ⎠
2.3.4.3.2
Active Power Calibration Procedure
The Active Power (W) calibration in the meter consists of two stages:
STAGE 1
1. During Stage 1 at PF = 1.0 lag, the active power read by the reference meter is
entered as an input, and the active power calibration Stage 1 is selected as
shown in Figure 2-12.
2. Click Calibrate to proceed with calibration. During this stage, the gain of the
active power will be calibrated.
3. After the completion of the process, the meter active power output will be displayed along with the Error %, in comparison with the reference meter output. If
the meter output is within the specification, the active power calibration Stage 1
can be stopped.
© 2011 Microchip Technology Inc.
DS51964A-page 25
PIC18F87J72 Single-Phase Energy Meter Calibration User’s Guide
FIGURE 2-12:
Active Power Phase 1 Calibration.
STAGE 2
During this stage, phase compensation will be computed at PF = 0.5 lag.
1. During Stage 2, meter line inputs are set at PF = 0.5 lag, with the active power
being exactly half of PF = 1.0.
2. The phase compensation calibration is initiated by selecting Stage 2 of the active
power calibration, as shown in Figure 2-13.
3. Click Calibrate to proceed with the calibration.
4. After the completion of this process, the meter active power output will be
displayed along with the Error %, in comparison with that of the reference meter
output. After the calibration, the meter output should be exactly half of the active
power value that was calibrated at the Stage 1. If the meter output is within the
specification, active power calibration Stage 2 can be stopped.
DS51964A-page 26
© 2011 Microchip Technology Inc.
Meter Calibration
FIGURE 2-13:
Active Power Phase 2 Calibration.
© 2011 Microchip Technology Inc.
DS51964A-page 27
PIC18F87J72 Single-Phase Energy Meter Calibration User’s Guide
2.3.4.4
REACTIVE POWER SIGNAL FLOW AND CALIBRATION
During Reactive Power Calibration, the gain register GAIN_POWER_REACT gets
computed. Figure 2-14 shows the reactive power calculation metering engine and the
calibration gain register.
Average
Over 128 Signal
Cycles
ADC
CURRENT
PHASE_COMPENSATION:8
+ α
ADC
Σ
X
Φ
Σ
Σ
Over 128 Samples
OFFSET_POWER_REACT:32
VOLTAGE
GAIN_POWER_REACT:16
RAW_POWER_REACT:64
90° PHASE SHIFTER
POWER_REACT:32
FIGURE 2-14:
kVAR
X
Reactive Power Calculation Signal Flow.
2.3.4.4.1
Reactive Power Gain Computation
Reactive Power Gain is computed as the percentage ratio of the error recorded against
the previous gain. The Error % is the difference between the input line reactive power
and the meter output, as shown in Equation 2-12.
EQUATION 2-12:
REACTIVE POWER GAIN COMPUTATION
GAIN_POWER_REACT ( OldValue )
GAIN_POWER_REACT ( NewValue ) = ----------------------------------------------------------------------------------------⎛ Error%
-⎞ + 1
⎝ ----------------100 ⎠
2.3.4.4.2
Reactive Power Calibration Procedure
Reactive Power Calibration mode is entered by selecting the Reactive Power (VAR)
calibration. To calibrate reactive power, phase compensation should be calibrated,
which otherwise may be erroneous. Therefore, the software does not allow users to calibrate reactive power unless the phase compensation in Stage 2 of the active power is
calibrated. The Reactive Power Calibration is similar to Stage 1 of the active power calibration, during which the gain of the reactive power will be calibrated (see
Figure 2-15).
1. Enter the reactive power value read by the reference meter as an input at PF = 0.5
lag. The reactive power calibration is selected as shown in Figure 2-15.
2. Click Calibrate to proceed with the calibration. During this stage, the gain of
reactive power will be calibrated.
3. After completion of the process, the meter reactive power output will be displayed
along with the Error %, in comparison with the reference meter output. If the
meter output is within the specification, the Reactive Power Calibration can be
stopped.
DS51964A-page 28
© 2011 Microchip Technology Inc.
Meter Calibration
FIGURE 2-15:
Reactive Power Calibration.
© 2011 Microchip Technology Inc.
DS51964A-page 29
PIC18F87J72 Single-Phase Energy Meter Calibration User’s Guide
2.4
MULTIPOINT CALIBRATION
Multipoint Calibration calculates the gain and offset theoretically, based on the input
line parameters. The line parameters are set to defined values, which are entered as
an input to the calibration software. This calibration is suitable for the development process, to get an insight on gain and offset to the gain and offset calculations for signal
conditioning.
2.4.1
IB, VB, Meter Constant and Calibration Configurations
The calibration of the single phase energy meter involves up to five different
configurations, as shown in Figure 2-16.
EXAMPLE 2-1:
Meter design with base operational condition is 5(10)A, IB = 5, IMAX = 10A.
1. Calibration Stage C1: Active Power, Energy and RMS Voltage Gain Calibration,
Gain – Basic voltage VB and basic current IB at a power factor of 1. For example,
220V and 5A.
2. Calibration Stage C2: Phase Compensation, Reactive Power and Energy Gain
Calibration – Basic 220V and 5A voltage VB and basic current IB at a power factor
of 0.5 lag.
3. Calibration Stage C3: Reactive Power Offset – Base voltage VB and 1/100 of
base current IB at PF = 0.5 lag at 220V and 50 mA.
4. Calibration Stage C4: Active Power Offset – Basic voltage VB and 1/100 of IB at
a power factor of 1. For example, 220V and 50 mA.
5. Calibration Stage C5: Current Gain and Offset Calibration – Mid-range – Basic
voltage VB and 1/10 of IB at a power factor of 1. For example, 220V and 500 mA.
DS51964A-page 30
© 2011 Microchip Technology Inc.
Meter Calibration
FIGURE 2-16:
Multipoint/Single Point Calibration Screen.
These calibration configurations are sequential steps. Configuration C1 is always the
most important stage of calibration, and must be executed in the beginning. The other
configurations require values obtained from configuration C1, but are not dependent on
the values obtained from the other configurations. In other words, C1 is the first step,
while the other configurations are optional, depending on the meter type.
The meter constant is typically measured in units of impulses per kilowatt-hour or
impulses per kilovar-hour. For example, the calibration output frequency of the calibration frequency, METER CONSTANT = 3200 imp/kWh or imp/kVARh, 6400 imp/kWh or
imp/kVARh.
Depending on the accuracy, type and output parameters of the meter, not all stages of
the calibration configuration are required to completely calibrate the meter. In some
cases, only a single point calibration is required. The software allows individual
configurations to be turned on or off, when going through the calibration flow.
2.4.2
Active Power and Energy Signal Flow and Calibration
The active power and energy signal flow leads to the CF output pulse frequency, which
is proportional to the total active energy measured by the energy meter as shown in
Figure 2-17.
Table 2-1 represents the registers that are set for active power and energy calibration.
© 2011 Microchip Technology Inc.
DS51964A-page 31
PIC18F87J72 Single-Phase Energy Meter Calibration User’s Guide
TABLE 2-1:
CALIBRATION REGISTERS GENERATED THROUGH THIS ROUTINE
Register Name
Equations
Configurations Required
Section 2.4.4.1 “Equations for Configuration
C1 Calibration – Active Energy and Active
Power”
GAIN_NUMR_ENERGY_ACT Section 2.4.4.1 “Equations for Configuration
C1 Calibration – Active Energy and Active
Power”
PHASE_COMPENSATION
Section 2.4.7.1 “Equations for Configuration
C2 Calibration – Phase Delay”
OFFSET_POWER_ACT
Section 2.4.9.1 “Equations for Configuration
C4 Calibration – Active Power Offset”
Section 2.4.4.1 “Equations for Configuration
GAIN_POWER_ACT
C1 Calibration – Active Energy and Active
Power”
GAIN_DENR_ENERGY_ACT
GAIN_ENERGY_ACT
C1 ONLY
C1 ONLY
C1, C2
C1, C4
C1 ONLY
Not Implemented
ADC
CURRENT
PHASE_COMPENSTAION:8
Not Implemented
Σ
X
Φ
ADC
OFFSET_POWER_ACT:32
GAIN_POWER_ACT:16
VOLTAGE
kW
POWER_ACT:32
RAW_POWER_ACT:48
X
GAIN_ENERGY_ACT:16 (NOT IMPLEMENTED)
PERIOD:16 (INTERNAL REGISTER)
ENERGY_ACT_L:32
kWh
X
X
RAW_ENERGY_ACT:64
Digital to
Frequency
Converter
GAIN_DENR_ENERGY_ACT:8
GAIN_NUMR_ENERGY_ACT:16
/
CF OUTPUT
FREQUENCY
Σ
kWh 1/METER
CONSTANT
kWh
ENERGY_ACT:32
FIGURE 2-17:
DS51964A-page 32
Active Power and Energy Signal Path Showing Output and Calibration Registers.
© 2011 Microchip Technology Inc.
Meter Calibration
2.4.3
RMS Current, RMS Voltage, Signal Flow and Calibration
The RMS current and voltage outputs require a two-point calibration at configurations
C1 and C5. The automated software performs these calibrations, suggested on the
calibration values entered in the text boxes, as shown in Figure 2-16.
Table 2-2 and Figure 2-18 represent the registers that are set for RMS current and
voltage calibration.
TABLE 2-2:
RMS CURRENT, RMS VOLTAGE, CALIBRATION REGISTERS
Register
Equation
Configurations Required
OFFSET_V_RMS
Section 2.4.10.1 “Equations for Configuration
C5 Calibration – RMS Voltage and Current”
C1, C5
OFFSET_I_RMS
Section 2.4.10.1 “Equations for Configuration
C5 Calibration – RMS Voltage and Current”
C1, C5
GAIN_V_RMS
Section 2.4.10.1 “Equations for Configuration
C5 Calibration – RMS Voltage and Current”
C1 ONLY
GAIN_I_RMS
Section 2.4.10.1 “Equations for Configuration
C5 Calibration – RMS Voltage and Current”
C1 ONLY
OFFSET_I_RMS:16
ADC
CURRENT
RAW_I_RMS:16
Σ
X2
A
X
I_RMS:16
RMS Current
GAIN_I_RMS:16
ADC
VOLTAGE
X2
RMS Voltage
OFFSET_V_RMS:16
GAIN_V_RMS:16
Σ
X
V
V_RMS:16
RAW_V_RMS:16
FIGURE 2-18:
RMS Current and Voltage Flow.
© 2011 Microchip Technology Inc.
DS51964A-page 33
PIC18F87J72 Single-Phase Energy Meter Calibration User’s Guide
2.4.4
Flow Chart for C1 Configuration – Active Energy, Active Power Gain
Begin Calibration
Set MODE1 register bits
and LINE_CYC register
Put meter in Calibration
Configuration C1
(VB and IB at PF=1)
Enable Calibration Mode
by setting bit 0 and 1
of CAL_CONTROL
register to 1
Is
CAL_MODE
bit 1 low?
NO
YES
Read contents of
RAW_ENERGY_ACT,
RAW_POWER_ACT
Calculate and Write
GAIN_NUMR_ENERGY_ACT,
GAIN_DENR_ENERGY_ACT,
GAIN_POWER_ACT contents
based on equations in
Section 2.4.4.1 “Equations for
Configuration C1 Calibration
– Active Energy and Active
Power”
End
DS51964A-page 34
© 2011 Microchip Technology Inc.
Meter Calibration
2.4.4.1
EQUATIONS FOR CONFIGURATION C1 CALIBRATION – ACTIVE
ENERGY AND ACTIVE POWER
Equations 2-13 to 2-17 represent the method for calculating the calibration, and the
correction factors after configuration C1. The PC calibration software processes these
calculations automatically.
Equations 2-13 to 2-16 apply for calculating the proper output frequency of the CF
output. See Section 2.4.4 “Flow Chart for C1 Configuration – Active Energy,
Active Power Gain” for the meter input conditions.
EQUATION 2-13:
Meter Constant
CF_IMP_S = ------------------------------------3600
V I
B B
⋅ ------------1000
EQUATION 2-14:
LINE_CYC_NUM = 2
LINE_CYC
EQUATION 2-15:
32
⎛
⎞
2 ⋅ CF_IMP_S
⎜ --------------------------------------------------------------------------⎟
⎝ Line Freq ⋅ Samples per Cycle⎠
GAIN = -------------------------------------------------------------------------------RAW_ENERGY_ACT ⎞
⎛ --------------------------------------------------------⎝ LINE_CYC_NUM ⋅ 256⎠
⋅ 32768
If GAIN>65535
Then,
GAIN_NUMR_ENERGY_ACT = GAIN / 2
GAIN_DENR_ENERGY_ACT = GAIN_DENR_ENERGY_ACT + 1
else,
GAIN_NUMR_ENERGY_ACT = GAIN
GAIN_DENR_ENERGY_ACT = GAIN_DENR_ENERGY_ACT
Note:
Convert to a 16-bit unsigned integer for compatibility with the energy meter
register and firmware calculations.
Equations 2-16 and 2-17 are used for calculating the proper Gain/LSb registers in
calibration.
EQUATION 2-16:
PLSb = Value from Table 2-7 based on VB and IMAX values
EQUATION 2-17:
⎛ V B ⋅ I B⎞
⎜ -------------------⎟
⎝ PLSb ⎠
GAIN_POWER_ACT = ------------------------------------------------------------RAW_POWER_ACT ⎞
⎛ -----------------------------------------------------⎝ 64 ⋅ LINE_CYC_NUM⎠
Note:
© 2011 Microchip Technology Inc.
⋅ 32768
Convert to a 16-bit unsigned integer for compatibility with the energy meter
register and firmware calculations.
DS51964A-page 35
PIC18F87J72 Single-Phase Energy Meter Calibration User’s Guide
2.4.5
Reactive Power and Energy Signal Flow and Calibration
The reactive power and the energy signal flow leads to the CF output pulse frequency,
which is proportional to the total reactive energy, measured by the energy meter as
shown in Figure 2-19.
Table 2-3 represents the registers being set during the reactive power and energy
calibration.
TABLE 2-3:
CALIBRATION REGISTERS GENERATED THROUGH THIS ROUTINE
Register Name
Equations
Configurations Required
GAIN_DENR_ENERGY_REACT
Section 2.4.6.1 “Equations for Configuration C2
Calibration – Reactive Energy and Reactive
Power”
C2 ONLY
GAIN_NUMR_ENERGY_REACT
Section 2.4.6.1 “Equations for Configuration C2
Calibration – Reactive Energy and Reactive
Power”
C2 ONLY
OFFSET_POWER_REACT
Section 2.4.8.1 “Equations for Configuration C3
Calibration – Reactive Power Offset”
C2, C3
GAIN_POWER_REACT
Section 2.4.6.1 “Equations for Configuration C2
Calibration – Reactive Energy and Reactive
Power”
C2 ONLY
GAIN_ENERGY_REACT
Not Implemented
Not Implemented
ADC
CURRENT
PHASE_COMPENSATION:8 X
Σ
+ α
Φ
OFFSET_POWER_REACT:32
VOLTAGE
GAIN_POWER_REACT:16
PHASE SHIFTER
kVAR
X
POWER_REACT:32
ADC
RAW_POWER_REACT:48
GAIN_ENERGY_REACT:16 (NOT IMPLEMENTED)
PERIOD:16 (INTERNAL REGISTER)
ENERGY_REACT_L:32
kVARh
X
X
RAW_ENERGY_REACT:64
Digital to
Frequency
Converter
GAIN_DENR_ENERGY_REACT:8
GAIN_NUMR_ENERGY_REACT:16
/
CF OUTPUT
FREQUENCY
Σ
kVARh
1/METER
CONSTANT
kVARh
ENERGY_REACT:32
FIGURE 2-19:
DS51964A-page 36
Reactive Power and Energy Signal Path Showing Output and Calibration Registers.
© 2011 Microchip Technology Inc.
Meter Calibration
2.4.6
Configuration C2 Flow Chart – Reactive Power and Energy
Begin Calibration
Set MODE1 register bits
and LINE_CYC register
Put meter in Calibration
Configuration C2
(VB and IB at PF=0.5 lag)
Enable Calibration Mode
by setting bit 0 and 1
of CAL_CONTROL
register to 1
Is
CAL_MODE
bit 1 low?
NO
YES
Read contents of
RAW_ENERGY_REACT,
RAW_POWER_REACT
Calculate and Write
GAIN_NUMR_ENERGY_REACT
GAIN_DENR_ENERGY_REACT,
GAIN_POWER_REACT contents
based on equations in
Section 2.4.6.1 “Equations for Configuration C2 Calibration – Reactive
Energy and Reactive Power”
End
© 2011 Microchip Technology Inc.
DS51964A-page 37
PIC18F87J72 Single-Phase Energy Meter Calibration User’s Guide
2.4.6.1
EQUATIONS FOR CONFIGURATION C2 CALIBRATION – REACTIVE
ENERGY AND REACTIVE POWER
Equations 2-18 to 2-22 represent the method for calculating the calibration and the
correction factors after configuration C2. The PC calibration software processes these
calculations automatically.
Equations 2-18 to Equation 2-21 applies for calculating the proper output frequency of
the CF output. See Section 2.4.6 “Configuration C2 Flow Chart – Reactive Power
and Energy” for the meter input conditions.
EQUATION 2-18:
Meter Constant
CF_IMP_S = ------------------------------------3600
V I
B B
⋅ ------------1000
EQUATION 2-19:
LINE_CYC_NUM = 2
LINE_CYC
EQUATION 2-20:
⎛ 2 32 ⋅ CF_IMP_S ⋅ SIN(60) ⎞
⎜ --------------------------------------------------------------------------⎟
⎝ Line Freq ⋅ Samples per Cycle⎠
GAIN = -------------------------------------------------------------------------------⎛ RAW_ENERGY_REACT
-----------------------------------------------------------⎞
⎝ LINE_CYC_NUM ⋅ 256 ⎠
⋅ 32768
If GAIN>65535
Then,
GAIN_NUMR_ENERGY_REACT = GAIN / 2
GAIN_DENR_ENERGY_REACT = GAIN_DENR_ENERGY_REACT + 1
else,
GAIN_NUMR_ENERGY_REACT = GAIN
GAIN_DENR_ENERGY_REACT = GAIN_DENR_ENERGY_REACT
Note:
Convert to a 16-bit unsigned integer for compatibility with the energy meter
register and firmware calculations.
Equations 2-21 and 2-22 are used for calculating the proper Gain/LSb registers in
calibration.
EQUATION 2-21:
PLSb = Value from Table 2-7 based on VB and IMAX values
EQUATION 2-22:
⎛ VB ⋅ I B ⋅ SIN(60)⎞
⎜ ----------------------------------------------⎟
PLSb
⎝
⎠
GAIN_POWER_REACT = -------------------------------------------------------------RAW_POWER_REACT⎞
⎛ -------------------------------------------------------⎝ 64 ⋅ LINE_CYC_NUM ⎠
Note:
DS51964A-page 38
⋅ 32768
Convert to a 16-bit unsigned integer for compatibility with the energy meter
register and firmware calculations.
© 2011 Microchip Technology Inc.
Meter Calibration
2.4.7
Configuration C2 Flow Chart – Phase Delay,
Set MODE1 register bits
and LINE_CYC register
Put meter in
Calibration Configuration C2
(VB and IB at PF=0.5)
Enable Calibration Mode
by setting bit 0 and 1 of
CAL_CONTROL reg to 1
Is
CAL_MODE
bit 1 low?
NO
YES
Read contents of
RAW_POWER_ACT
register
Calculate and Write
PHASE_COMPENSATION calibration register contents based on
equations in
Section 2.4.7.1 “Equations for
Configuration C2 Calibration –
Phase Delay”
End
© 2011 Microchip Technology Inc.
DS51964A-page 39
PIC18F87J72 Single-Phase Energy Meter Calibration User’s Guide
2.4.7.1
EQUATIONS FOR CONFIGURATION C2 CALIBRATION – PHASE
DELAY
For active power, Equations 2-23 to 2-27 are used to calculate the time shift delay for
a given phase.
EQUATION 2-23:
W1 = RAW_POWER_ACT @ PF = 1, Configuration C1
EQUATION 2-24:
W2 = RAW_POWER_ACT @ PF = 0.5, Configuration C2
EQUATION 2-25:
LINE_CYC_NUM_1 = LINE_CYC_NUM @ PF = 1, Configuration C1
EQUATION 2-26:
LINE_CYC_NUM_2 = LINE_CYC_NUM @ PF = 0.5, Configuration C2
EQUATION 2-27:
– 1 ⎛ ⎛ ( W2 ) ⁄ ( LINE_CYC_NUM2 )⎞ 180⎞
- ⋅ --------- – 60
⎝ ⎝ --------------------------------------------------------------------( W1 ) ⁄ ( LINE_CYC_NUM1 )⎠ PI ⎠
PHASE_COMPENSATION = -------------------------------------------------------------------------------------------------------------------------------------DEGREE
------------------------SAMPLE
COS
DS51964A-page 40
⋅ 128
Note 1:
Convert to an 8-bit signed integer for compatibility with the energy meter
register and firmware calculations.
2:
Since the 60° (default) is being subtracted from the measured quantity,
the current should lag the voltage under configuration C2.
3:
In the reference design, with a sampling rate of 3906 samples/sec,
Degree/Sample value will be equal to 5.529.
© 2011 Microchip Technology Inc.
Meter Calibration
2.4.8
Configuration C3 Flow Chart – Reactive Power Offset
Set MODE1 register bits
and LINE_CYC register
(suggest 256 Line Cycles)
Put meter in
Calibration Configuration C3
(VB and 1/100 IB at PF = 0.5 lag)
Enable Calibration Mode by
setting bit 0 and 1 of
CAL_CONTROL register to 1
Is
CAL_MODE
bit 1 low?
NO
YES
Read contents of
RAW_POWER_REACT
Register
Calculate and Write
OFFSET_POWER_REACT
register contents based on equations
in Section 2.4.8.1 “Equations for
Configuration C3 Calibration –
Reactive Power Offset”
End
© 2011 Microchip Technology Inc.
DS51964A-page 41
PIC18F87J72 Single-Phase Energy Meter Calibration User’s Guide
2.4.8.1
EQUATIONS FOR CONFIGURATION C3 CALIBRATION – REACTIVE
POWER OFFSET
For reactive power offset, Equations 2-28 to 2-32 apply for a given phase. W1 corresponds to the RAW_POWER_REACT register obtained during configuration C2.
LINE_CYC_NUM_W1 corresponds to the LINE_CYC during this measurement.
W2 corresponds to the RAW_POWER_REACT register obtained during configuration
C3. LINE_CYC_NUM_W2 is the LINE_CYC during this measurement.
EQUATION 2-28:
W1 = RAW_POWER_REACT @ I
B,
Configuration C2
EQUATION 2-29:
W2 = RAW_POWER_REACT @ 1/100 I B , Configuration C3
EQUATION 2-30:
LINE_CYC_NUM_W1 = LINE_CYC_NUM in Configuration C2
EQUATION 2-31:
LINE_CYC_NUM_W2 = LINE_CYC_NUM in Configuration C3
EQUATION 2-32:
( W1 ) ⁄ ( 100 )
W2
OFFSET_POWER_REACT = ------------------------------------------------------ – -----------------------------------------------------LINE_CYC_NUM_W1
LINE_CYC_NUM_W2
Note:
Convert to a 32-bit signed integer for compatibility with the energy meter
register and firmware calculations.
The OFFSET_POWER_REACT registers hold a signed 32-bit value. However, the
math in the microcontroller can overflow for some values near the limits. Limit check
the resulting value to make sure the value is between -2,130,706,432 and
2,130,706,431 (inclusive). Values less than -2,130,706,432 should be set to
-2,130,706,432, while values greater than 2,130,706,431 should be set to
2,130,706,431. If the value is limited, the user should be aware that the meter cannot
correct the offset completely.
It is expected that this value will always be negative. If the value is positive, it may
indicate that the user has not provided a large enough number of line cycles for
configuration C4 (where, the number of line cycles should be set to a larger value, such
as 64 or 128). This may also be true if offset does not contribute a large enough
percentage to W2 (for example, 10% to 50% or more).
DS51964A-page 42
© 2011 Microchip Technology Inc.
Meter Calibration
2.4.9
Configuration C4 Flow Chart - Active Power Offset
Set MODE1 register bits
and LINE_CYC register
(suggest 256 Line Cycles)
Put meter in
Calibration Configuration C4
(VB and 1/100 IB at PF = 1)
Enable Calibration Mode by
setting bit 0 and 1 of
CAL_CONTROL register to 1
Is
CAL_MODE
bit 1 low?
NO
YES
Read contents of
RAW_ENERGY_ACT
Register
Calculate and Write
OFFSET_POWER_ACT
register contents based on equations in
Section 2.4.9.1 “Equations for
Configuration C4 Calibration –
Active Power Offset”
End
© 2011 Microchip Technology Inc.
DS51964A-page 43
PIC18F87J72 Single-Phase Energy Meter Calibration User’s Guide
2.4.9.1
EQUATIONS FOR CONFIGURATION C4 CALIBRATION – ACTIVE
POWER OFFSET
For active power offset, Equations 2-33 to 2-37 apply for a given phase. W1 corresponds to the RAW_POWER_ACT register obtained during configuration C1.
LINE_CYC_NUM_W1 corresponds to the LINE_CYC during this measurement.
W2 corresponds to the RAW_POWER_ACT register obtained during configuration C4.
LINE_CYC_NUM_W2 is the LINE_CYC during this measurement.
EQUATION 2-33:
W1 = RAW_POWER_ACT @ I
B,
Configuration C1
EQUATION 2-34:
W2 = RAW_POWER_ACT @ 1/100 I B , Configuration C4
EQUATION 2-35:
LINE_CYC_NUM_W1 = LINE_CYC_NUM in Configuration C1
EQUATION 2-36:
LINE_CYC_NUM_W2 = LINE_CYC_NUM in Configuration C4
EQUATION 2-37:
( W1 ) ⁄ ( 100 )
W2
OFFSET_POWER_ACT = ------------------------------------------------------ – -----------------------------------------------------LINE_CYC_NUM_W1
LINE_CYC_NUM_W2
Note:
Convert to a 32-bit signed integer for compatibility with the energy meter
register and firmware calculations.
The OFFSET_POWER_ACT registers hold a signed 32-bit value. However, the math
in the microcontroller can overflow for some values near the limits. Limit check the
resulting value to make sure the value is between -2,130,706,432 and 2,130,706,431
(inclusive). Values less than -2,130,706,432 should be set to -2,130,706,432, while
values greater than 2,130,706,431 should be set to 2,130,706,431. If the value is
limited, the user should be aware that the meter cannot correct the offset completely.
It is expected that this value will always be negative. If the value is positive, it may
indicate that the user has not provided a large enough number of line cycles for
configuration C4 (where, the number of line cycles should be set to a larger value, such
as 64 or 128). This may also be true if offset does not contribute a large enough
percentage to W2 (for example, 10% to 50% or more).
DS51964A-page 44
© 2011 Microchip Technology Inc.
Meter Calibration
2.4.10
Flow Chart for RMS Calibration
Set MODE1 register bits
and LINE_CYC register
Put meter in
Calibration Configuration C5
(VB and 1/10 IB at PF = 1)
Is
CAL_MODE
bit 1 low?
NO
YES
Read contents of
RAW2_I_RMS and
RAW2_V_RMS registers
(referred to as IR2 and VR2
in equation set)
Fetch values from Calibration
Configuration C1
Calculate and Write OFFSET_I_RMS,
OFFSET_V_RMS, GAIN_I_RMS,
GAIN_V_RMS, calibration register
contents based equations in
Section 2.4.10.1 “Equations for Configuration C5 Calibration – RMS Voltage
and Current”
End
© 2011 Microchip Technology Inc.
DS51964A-page 45
PIC18F87J72 Single-Phase Energy Meter Calibration User’s Guide
2.4.10.1
EQUATIONS FOR CONFIGURATION C5 CALIBRATION – RMS
VOLTAGE AND CURRENT
Equations 2-38 to 2-49 represent the method for calculating the calibration and
correction factors for the RMS current and RMS voltage. The PC calibration software
processes these calculations automatically.
Typically, the Vmin and Imin voltages and currents will be 1/10 of the VB and IB values.
For RMS Offset, apply Equations 2-38 to 2-45:
EQUATION 2-38:
IR1 = RAW2_I_RMS @ I , Configuration C1
B
EQUATION 2-39:
VR1 = RAW2_V_RMS @ I B , Configuration C1
EQUATION 2-40:
IR2 = RAW2_I_RMS @ I , Configuration C5
B
EQUATION 2-41:
VR2 = RAW2_V_RMS @ I , Configuration C5
B
EQUATION 2-42:
I @ C1
B
I G = ---------------------I B @ C5
EQUATION 2-43:
V @ C1
B
VG = -----------------------VB @ C5
EQUATION 2-44:
IR1 – IR2 ⎞
⎛ --------------------------⎝ IG ⋅ IG – 1-⎠ – IR2
OFFSET_I_RMS = ------------------------------------------------65536
Note:
DS51964A-page 46
Convert to a 16-bit signed integer for compatibility with the energy meter
register and firmware calculations.
© 2011 Microchip Technology Inc.
Meter Calibration
EQUATION 2-45:
VR1 – VR2 ⎞
⎛ ------------------------------– VR
⎝ VG ⋅ VG – 1⎠
2
OFFSET_V_RMS = -----------------------------------------------------65536
Note:
Convert to a 16-bit signed integer for compatibility with the energy meter
register and firmware calculations.
For RMS LSb correction, apply Equations 2-46 to 2-49.
EQUATION 2-46:
ILSb = Value from Table 2-6 based on IMAX value
EQUATION 2-47:
VLSb = Value from Table 2-8 based on VB value
EQUATION 2-48:
I
B ⎞
⎛ ----------⎝ ILSb-⎠
GAIN_I_RMS = ------------------------------------------------------------------IR 1
--------------- + OFFSET_I_RMS
65536
Note:
⋅ 32768
Convert to a 16-bit unsigned integer for compatibility with the energy meter
register and firmware calculations.
EQUATION 2-49:
V
B ⎞
⎛ ------------⎝ VLSb⎠
GAIN_V_RMS = --------------------------------------------------------------------VR1
--------------- + OFFSET_V_RMS
65536
Note:
© 2011 Microchip Technology Inc.
⋅ 32768
Convert to a 16-bit unsigned integer for compatibility with the energy meter
register and firmware calculations.
DS51964A-page 47
PIC18F87J72 Single-Phase Energy Meter Calibration User’s Guide
2.5
SINGLE POINT CALIBRATION
Single Point Calibration is a subset of multipoint calibration, with the omission of a few
calibration register value calculations. With the omission, the number of stages in calibration are reduced, thus speeding the calibration process. Single Point Calibration can
be carried out if the meter accuracy class is achieved, even with the omission of a few
calibration parameter calculations, such as offset.
Single Point Calibration includes only two stages of calibration, as listed below:
1. Calibration Stage C1: Active power, energy and RMS voltage, current gain
calibration, gain - basic voltage VB and basic current IB at a power factor of unity.
For example, 220V and 5A at PF = 1.0.
The calibration parameters calculated in this stage include:
TABLE 2-4:
CALIBRATION REGISTERS GENERATED THROUGH THIS ROUTINE
Register Name
Equations
Configurations Required
GAIN_POWER_ACT
Section 2.4.4.1 “Equations for Configuration C1
Calibration – Active Energy and Active Power”
C1 ONLY
GAIN_NUMR_ENERGY_ACT
Section 2.4.4.1 “Equations for Configuration C1
Calibration – Active Energy and Active Power”
C1 ONLY
GAIN_DENT_ENERGY_ACT
Section 2.4.4.1 “Equations for Configuration C1
Calibration – Active Energy and Active Power”
C1 ONLY
GAIN_V_RMS
Section 2.4.10.1 “Equations for Configuration
C5 Calibration – RMS Voltage and Current”
C1 ONLY
GAIN_I_RMS
Section 2.4.10.1 “Equations for Configuration
C5 Calibration – RMS Voltage and Current”
C1 ONLY
2. Calibration Stage C2: Phase compensation and reactive power and energy gain
calibration - basic 220V and 5A voltage VB and basic current IB at a power factor
of 0.5 lag.
The calibration parameters calculated in this stage include:
TABLE 2-5:
CALIBRATION REGISTERS GENERATED THROUGH THIS ROUTINE
Register Name
Equations
Configurations Required
GAIN_POWER_REACT
Section 2.4.6.1 “Equations for Configuration C2 Calibration – Reactive Energy and
Reactive Power”
C2 ONLY
GAIN_NUMR_ENERGY_REACT
Section 2.4.6.1 “Equations for Configuration C2 Calibration – Reactive Energy and
Reactive Power”
C2 ONLY
GAIN_DENT_ENERGY_REACT
Section 2.4.6.1 “Equations for Configuration C2 Calibration – Reactive Energy and
Reactive Power”
C2 ONLY
DS51964A-page 48
© 2011 Microchip Technology Inc.
Meter Calibration
2.6
CREEP THRESHOLD CALIBRATION
Creep threshold represents a state below which the energy accumulation will be suppressed. Due to external noise, even under No Load condition, the meter may register a
very small value of energy. To inhibit registering of this unwanted energy, the meter needs
to be calibrated for creep threshold. Creep Threshold Calibration also accounts for the
threshold starting current, above which the energy needs to be registered.
In Creep Threshold Calibration, maximum-rated operational voltage, threshold starting
current and Meter Constant of the meter are used to compute the creep threshold timer
value. Using these parameters, the time for energy accumulation equivalent to
1/METER CONSTANT at threshold starting current, is calculated. If the energy
accumulation is less than 1/METER CONSTANT during this creep threshold time, it
represents either a No Load condition, or load current less than the threshold starting
current. In such a case, the incremental energy accumulation will be flushed, suppressing
energy accumulation.
2.6.1
Creep Threshold Computation
To accumulate energy equal to 1/METER CONSTANT at the above specified line input,
time taken is as shown in Equation 2-50.
EQUATION 2-50:
Time = ( 1kWh ) ⁄ ( METERCONSTANT ⋅ MAX_VOLTAGE ⋅ LEAST_CURRENT_DETECT )
Time is converted to equivalent minutes + seconds
CREEP_THRESHOLD_MINUTE = Creep Threshold time in minutes
CREEP_THRESHOLD_SECOND = Creep Threshold time in seconds
2.6.2
Creep Threshold Calibration procedure
Apply the following procedure for Creep Threshold Calibration:
1. Enter the maximum rated voltage of the meter in “Maximum Input Voltage (V)”
field, as shown in Figure 2-20.
2. Enter the least detectable current the of meter in “Starting Current”.
3. Set the “Meter Constant”.
4. Click Save to EEPROM to save the calibration data to EEPROM. During this
process, creep threshold values get computed and saved in the meter.
Note:
© 2011 Microchip Technology Inc.
Creep Threshold Calibration needs to be done irrespective of the type of
above mentioned calibration process.
DS51964A-page 49
PIC18F87J72 Single-Phase Energy Meter Calibration User’s Guide
FIGURE 2-20:
DS51964A-page 50
Creep Threshold Calibration.
© 2011 Microchip Technology Inc.
Meter Calibration
2.7
METER SPECIFICATIONS AND CALIBRATION PARAMETERS
This section contains the editable options for the meter design.
The resolution of the output registers are determined from these three parameters, and
are set based on the information in Table 2-6–Table 2-8.
These tables are important and are applied to calculate the resolution values used
when calculating the GAIN/LSb registers, that occur while calibrating the meter. These
values are also used to place the decimal point in the reading or results frame.
The resolutions shown in the below tables are based on the assumption that the IMAX
and VCAL voltages will be at approximately 50% of the input voltage to the A/D
converters. To change the headroom of the A/D input, simply change the maximum
current number, and the GAIN/LSb registers will scale accordingly.
TABLE 2-6:
CURRENT RESOLUTION TABLE
Maximum Current Less than or Equal To
(A)
LSb Resolution (A)
8.1
0.001
81
0.01
810
0.1
8,100
1
TABLE 2-7:
POWER RESOLUTION TABLE
Maximum Wattage Less than or Equal To
(W - IMAX times VCAL)
LSb Resolution (mW)
125
0.001
1,250
0.01
12,500
0.1
TABLE 2-8:
125,000
1
1,250,000
10
12,500,000
100
VOLTAGE RESOLUTION TABLE
Maximum Voltage Less than or Equal To (V)
LSb Resolution (V)
ALL
0.1
Note:
© 2011 Microchip Technology Inc.
The decimal point location in the reading frame is updated whenever the
VCAL, ICAL or IMAX values are changed.
DS51964A-page 51
PIC18F87J72 Single-Phase Energy Meter Calibration User’s Guide
DS51964A-page 52
© 2011 Microchip Technology Inc.
PIC18F87J72 SINGLE-PHASE
ENERGY METER CALIBRATION
USER’S GUIDE
Chapter 3. Microchip Energy Meter Software
3.1
INTRODUCTION
The energy meter software is a Graphical User interface (GUI) that enables the meter
to be monitored and debugged in the development phase. It also provides the
calibration tool used to precisely calibrate the meter.
3.2
MAIN SCREEN
The main screen contains four tabs:
• Energy Meter: This tab contains the instantaneous meter output display and a
debug window, which enables access to all the internal registers of the meter.
• Meter Parameters: This tab contains a calibration tool for Multipoint and Single
Point Calibration.
• Power Calibration: This tab is used for feedback calibration of voltage, current
and power.
• Energy Calibration: This tab is used for feedback calibration of energy.
The COM port selection option on top of the window is used to select a serial port or a
serial port emulator.
The status of the meter connection with the computer is displayed at the top of the window. This status displays the text “Meter Detected” in green if connected, and changes
its status to “Meter Disconnected” in red, if disconnected. This status is present across
all the tabs.
The tool has a feature to display the “Instantaneous Parameters”, updated in real time
(see Figure 3-1).
© 2011 Microchip Technology Inc.
DS51964A-page 53
PIC18F87J72 Single-Phase Energy Meter Calibration User’s Guide
FIGURE 3-1:
Main Screen with Active Results Frame.
The “Instantaneous Parameters” field contains the recent meter output parameters,
such as Active Power, Reactive Power, Apparent Power, RMS Current, RMS Voltage
and Frequency. The registers in this frame are continuously collected and refreshed on
the PC side periodically.
Table 3-1 shows examples of the meter readings.
TABLE 3-1:
REGISTERS READINGS OF THE METER
Meter Reading
Register
Example
POWER_ACT
101.44W
Reactive Power
POWER_REACT
17.2371 VAR
Apparent Power
POWER_APP
102.894 VA
Active Power
RMS Current Phase A
I_RMS
0.45A
RMS Voltage Phase A
V_RMS
220.6V
FREQUENCY
50 Hz
Frequency
DS51964A-page 54
© 2011 Microchip Technology Inc.
Microchip Energy Meter Software
3.2.1
Decimal Point Location
The location of the decimal point, i.e., the resolution of the power quantities, is
determined by the values introduced in the “Calibration Parameters” field on the
Calibration tab. When the meter is calibrated using the calibration methods available
with this software, the proper GAIN/LSb correction factor is calculated to ensure the
Least Significant bit (LSb), which represents the least significant digit for a given
quantity. For example, if the PHA_I_RMS register, which represents the RMS current,
contains the decimal value 4523, and the ILSb is defined to be 0.01 based on the meter
design entry, this value represents exactly 45.23A.
Another example for active power is shown in Table 3-1, where the POWER_ACT register
contains the value 101.44. For this example, the power resolution is 0.1 mW. Therefore, this
register represents exactly 101.44W.
© 2011 Microchip Technology Inc.
DS51964A-page 55
PIC18F87J72 Single-Phase Energy Meter Calibration User’s Guide
3.3
DEBUG MODE
The Debug mode feature enables access to all the internal registers of the meter. From
the Energy Meter tab, click on Enter Debug Mode on the lower right corner of the tool.
The Debug mode screen appears as shown in Figure 3-2.
Debug mode displays a complete list of all the internal registers of the meter with their
address, name, attribute, register length and value.
Each register is available for read and write in real time, when the meter is computing.
This is a convenient tool for debugging operations, giving complete access to all
internal details of the meter.
3.3.1
Monitoring Individual Registers
The tool enables the selected registers to be monitored for their real-time updates.
Monitoring can be enabled by writing “1” to column “Monitor” across a particular register, as shown in Figure 3-2. By enabling this, the GUI reads the register periodically by
bringing the real-time status. Unless monitoring is enabled, the register status is not
updated with every instantaneous refresh.
FIGURE 3-2:
DS51964A-page 56
Debug Mode in Main Screen Showing Internal Registers.
© 2011 Microchip Technology Inc.
Microchip Energy Meter Software
3.3.2
Refreshing Registers Status
To update all the internal registers, click Refresh Meter Registers at the lower right
corner, as shown in Figure 3-2. However, this will update the registers only once per
click.
3.3.3
Writing to Individual Registers
It is possible to write to individual registers for testing certain limiting conditions and fine
tuning the calibration registers. To write to a register, enter the value in hex format (as
stored in the registers) in the “Value” column across that particular register, as shown
in Figure 3-2, and press Enter to initiate the write process.
Note:
© 2011 Microchip Technology Inc.
“Value” and “Monitor” are the only two user editable columns. The remaining
sections are read only.
DS51964A-page 57
PIC18F87J72 Single-Phase Energy Meter Calibration User’s Guide
NOTES:
DS51964A-page 58
© 2011 Microchip Technology Inc.
PIC18F87J72 SINGLE-PHASE
ENERGY METER CALIBRATION
USER’S GUIDE
Chapter 4. Communication Protocol
4.1
PROTOCOL
The Universal Asynchronous Receiver and Transmitter (UART) of the PIC
Microcontroller is used to communicate with the meter. In addition to the reading and
writing of the registers, there are also dedicated commands for clearing, loading and
storing calibration registers to Flash. The first byte UART data is an ASCII character
that represents the command, and each command has a specific protocol. Each
command ends with the ASCII character “X”.
4.1.1
Command Description
The first byte of the data (byte 0) is an ASCII character E, L, S, W and R.
• E – Request for Echo Response to which meter responds with “Q” as
acknowledgment
• L – Load Calibration Registers from Flash (LOAD)
• S – Store Calibration Registers (STORE)
• W – Write Bytes (WRITE)
• R – Read Bytes (READ)
• C – Load Default Calibration Values
The last data byte is always an ‘X’ character. All commands will result in the same command being returned. The exception is the ‘R’ (READ) command which will return the
additional data in lieu of the number of bytes.
4.1.1.1
“E” ECHO: - TO DETECT THE METER CONNECTION
Example: ‘EX’.
Returns: ‘QX’
4.1.1.2
“L” LOAD: LOAD CALIBRATION REGISTERS FROM FLASH
Example: ‘LX’.
Returns: ‘LX’.
This command is used to verify that the calibration values were actually written into
flash (or EEPROM). When the software executes a ‘SX’ command, it should verify that
the values were stored by issuing a ‘LX’ command and then reading the calibration
values with an ‘R’ command.
4.1.1.3
“S” STORE: STORE CALIBRATION REGISTERS INTO FLASH
The Store command writes all the calibration values to the internal EEPROM, and this
function takes some time. During that time, the meter is not functional. The Store
command should only be used after calibrating the meter, not while it is in actual use.
Example: ‘SX’.
Returns: ‘SX’.
© 2011 Microchip Technology Inc.
DS51964A-page 59
Communication Protocol
4.1.1.4
“W” WRITE: WRITE STARTING AT SPECIFIED ADDRESS
Write the specified bytes.
Example: ‘W030000102030405060708090A0B0C0D0E0FX’.
Returns: ‘W030000102030405060708090A0B0C0D0E0FX’.
Note:
If the number of data characters is odd, the last character (the one just prior
to the ‘X’) will be ignored.
3 Address Bytes (ASCII)
Command Byte
7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0
7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0
ASCII Data
“X” (ASCII)
7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0
TABLE 4-1:
WRITE COMMAND EXAMPLES
Description
WRITE of 255d to
OFFSET_POWER_ACT
Register
FIGURE 4-1:
Command ASCII
Command Hex
“W 170 00 F F X”
57 31 37 30 30 30 46 46 58
WRITE Command Protocol.
4.1.1.5
“R” READ: READ STARTING AT SPECIFIED ADDRESS
Example: ‘R03010X’ (read 16 bytes starting at address 30h).
Returns: ‘R030000102030405060708090A0B0C0D0E0FX’.
Note:
For 16 bytes, there are 32 ASCII characters returned, or two characters per
byte.
Command Byte
7 6 5 4 3 2 1 0
3 Address Bytes (ASCII)
7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0
# Bytes to Read (2 Bytes ASCII)
7 6 5 4 3 2 1 0
TABLE 4-2:
“X” (ASCII)
7 6 5 4 3 2 1 0
7 6 5 4 3 2 1 0
READ COMMAND EXAMPLES
DESCRIPTION
READ on RAW_ENERGY_ACT Register
FIGURE 4-2:
7 6 5 4 3 2 1 0
COMMAND ASCII
COMMAND HEX
“R 0D4 06 X”
52 00 44 34 30 36 58
READ Command Protocol.
© 2011 Microchip Technology Inc.
DS51964A-page 60
Communication Protocol
NOTES:
© 2011 Microchip Technology Inc.
DS51964A-page 61
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ASIA/PACIFIC
ASIA/PACIFIC
EUROPE
Corporate Office
2355 West Chandler Blvd.
Chandler, AZ 85224-6199
Tel: 480-792-7200
Fax: 480-792-7277
Technical Support:
http://www.microchip.com/
support
Web Address:
www.microchip.com
Asia Pacific Office
Suites 3707-14, 37th Floor
Tower 6, The Gateway
Harbour City, Kowloon
Hong Kong
Tel: 852-2401-1200
Fax: 852-2401-3431
India - Bangalore
Tel: 91-80-3090-4444
Fax: 91-80-3090-4123
India - New Delhi
Tel: 91-11-4160-8631
Fax: 91-11-4160-8632
Austria - Wels
Tel: 43-7242-2244-39
Fax: 43-7242-2244-393
Denmark - Copenhagen
Tel: 45-4450-2828
Fax: 45-4485-2829
India - Pune
Tel: 91-20-2566-1512
Fax: 91-20-2566-1513
France - Paris
Tel: 33-1-69-53-63-20
Fax: 33-1-69-30-90-79
Japan - Yokohama
Tel: 81-45-471- 6166
Fax: 81-45-471-6122
Germany - Munich
Tel: 49-89-627-144-0
Fax: 49-89-627-144-44
Atlanta
Duluth, GA
Tel: 678-957-9614
Fax: 678-957-1455
Boston
Westborough, MA
Tel: 774-760-0087
Fax: 774-760-0088
Chicago
Itasca, IL
Tel: 630-285-0071
Fax: 630-285-0075
Cleveland
Independence, OH
Tel: 216-447-0464
Fax: 216-447-0643
Dallas
Addison, TX
Tel: 972-818-7423
Fax: 972-818-2924
Detroit
Farmington Hills, MI
Tel: 248-538-2250
Fax: 248-538-2260
Indianapolis
Noblesville, IN
Tel: 317-773-8323
Fax: 317-773-5453
Los Angeles
Mission Viejo, CA
Tel: 949-462-9523
Fax: 949-462-9608
Santa Clara
Santa Clara, CA
Tel: 408-961-6444
Fax: 408-961-6445
Toronto
Mississauga, Ontario,
Canada
Tel: 905-673-0699
Fax: 905-673-6509
Australia - Sydney
Tel: 61-2-9868-6733
Fax: 61-2-9868-6755
China - Beijing
Tel: 86-10-8569-7000
Fax: 86-10-8528-2104
China - Chengdu
Tel: 86-28-8665-5511
Fax: 86-28-8665-7889
China - Chongqing
Tel: 86-23-8980-9588
Fax: 86-23-8980-9500
Korea - Seoul
Tel: 82-2-554-7200
Fax: 82-2-558-5932 or
82-2-558-5934
China - Hangzhou
Tel: 86-571-2819-3180
Fax: 86-571-2819-3189
Malaysia - Kuala Lumpur
Tel: 60-3-6201-9857
Fax: 60-3-6201-9859
China - Hong Kong SAR
Tel: 852-2401-1200
Fax: 852-2401-3431
Malaysia - Penang
Tel: 60-4-227-8870
Fax: 60-4-227-4068
China - Nanjing
Tel: 86-25-8473-2460
Fax: 86-25-8473-2470
Philippines - Manila
Tel: 63-2-634-9065
Fax: 63-2-634-9069
China - Qingdao
Tel: 86-532-8502-7355
Fax: 86-532-8502-7205
Singapore
Tel: 65-6334-8870
Fax: 65-6334-8850
China - Shanghai
Tel: 86-21-5407-5533
Fax: 86-21-5407-5066
Taiwan - Hsin Chu
Tel: 886-3-6578-300
Fax: 886-3-6578-370
China - Shenyang
Tel: 86-24-2334-2829
Fax: 86-24-2334-2393
Taiwan - Kaohsiung
Tel: 886-7-213-7830
Fax: 886-7-330-9305
China - Shenzhen
Tel: 86-755-8203-2660
Fax: 86-755-8203-1760
Taiwan - Taipei
Tel: 886-2-2500-6610
Fax: 886-2-2508-0102
China - Wuhan
Tel: 86-27-5980-5300
Fax: 86-27-5980-5118
Thailand - Bangkok
Tel: 66-2-694-1351
Fax: 66-2-694-1350
Italy - Milan
Tel: 39-0331-742611
Fax: 39-0331-466781
Netherlands - Drunen
Tel: 31-416-690399
Fax: 31-416-690340
Spain - Madrid
Tel: 34-91-708-08-90
Fax: 34-91-708-08-91
UK - Wokingham
Tel: 44-118-921-5869
Fax: 44-118-921-5820
China - Xian
Tel: 86-29-8833-7252
Fax: 86-29-8833-7256
China - Xiamen
Tel: 86-592-2388138
Fax: 86-592-2388130
China - Zhuhai
Tel: 86-756-3210040
Fax: 86-756-3210049
DS51964A-page 62
Korea - Daegu
Tel: 82-53-744-4301
Fax: 82-53-744-4302
05/02/11
© 2011 Microchip Technology Inc.