SCXI-1104 Calibration Procedure

CALIBRATION PROCEDURE
SCXI™-1104
Introduction
This document contains information and step-by-step instructions for
verifying and calibrating the National Instruments SCXI-1104 signal
conditioning module.
What Is Calibration?
Calibration is a procedure of reading offset and gain errors from a device
and updating special analog calibration circuitry that corrects these errors.
National Instruments calibrates every SCXI-1104 module at the factory.
During the factory calibration process, the calibration constants are stored
in the non-volatile memory of the device. These values are loaded from
memory and used as needed by the device.
Why Should You Calibrate?
Offset and gain errors drift with time and temperature, which could
invalidate the factory-set calibration of a device. Calibration restores the
device to its specified accuracy.
How Often Should You Calibrate?
The measurement accuracy requirements of your application
determine how often you should calibrate your SCXI-1104 module.
National Instruments recommends you perform a complete calibration
at least once every year. You can shorten this interval to six months or
90 days, based on the demands of your application.
CVI™, LabVIEW™, National Instruments™, ni.com™, NI-DAQ™, and SCXI™ are trademarks of National Instruments Corporation. Product and company
names mentioned herein are trademarks or trade names of their respective companies.
370267A-01
© Copyright 2000 National Instruments Corp. All rights reserved.
July 2000
Equipment and Other Test Requirements
This section describes the equipment, software, documentation, and test
conditions required for calibrating the SCXI-1104.
Test Equipment
Calibration requires a high-precision voltage source with at least 50 ppm
accuracy, a multiranging 5 1/2 digit digital multimeter (DMM) with
15 ppm accuracy, and a National Instruments E Series DAQ device.
National Instruments recommends the following instruments for
calibration of an SCXI-1104:
•
Calibrator—Fluke 5700A
•
DMM—NI 4060 or HP 34401A
•
National Instruments E Series DAQ device
If these instruments are not available, use the accuracy requirements listed
above to select a substitute calibration standard.
If you do not have custom connection hardware, you will need a connector block
such as the National Instruments SCXI-1300, a shielded 68-pin connector cable, a 50-pin
ribbon cable, a 50-pin breakout box, and an SCXI adapter. These components give easy
access to the individual pins on the SCXI-1104 front and rear connectors.
Note
Software and Documentation
You will need the following software and documentation to calibrate the
SCXI-1104. You can find these on the National Instruments Web site at
ni.com/calibration:
•
The latest version of the National Instruments NI-DAQ driver
•
NI-DAQ Function Reference Online Help file
•
NI-DAQ User Manual for PC Compatibles
Software
The SCXI-1104 calibration procedure requires the latest version of the
National Instruments NI-DAQ driver on the calibration system. The driver
supports a number of programming languages, including LabVIEW,
LabWindows/CVI, Microsoft Visual C++, Microsoft Visual Basic, and
Borland C++. When you install the driver, you only need to install support
for the programming language you will use.
SCXI-1104 Calibration Procedure
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Documentation
The NI-DAQ Function Reference Online Help file and the NI-DAQ User
Manual for PC Compatibles contain detailed information on using the
NI-DAQ driver. The online help file includes detailed information on the
driver functions. You can access the online help file by clicking
Start»Programs»National Instruments DAQ»NI-DAQ Help. The user
manual provides instructions on installing and configuring
National Instruments DAQ devices. This manual also includes detailed
information on creating applications that use the NI-DAQ driver. These
are your primary references for writing your calibration utility. For further
information on the products you are calibrating, refer to your device user
manuals.
Test Conditions
Follow these guidelines to optimize the connections and the environment
during calibration:
•
Keep connections to the SCXI module as short as possible. Long
cables and wires can act as antennae, which pick up extra noise that
can affect measurements.
•
Use shielded copper wire for all cable connections to the device.
Use twisted-pair wire to eliminate noise and thermal offsets.
•
Maintain the temperature between 18 and 28 °C.
•
Keep relative humidity below 80%.
•
Allow a warm-up time of at least 15 minutes for the SCXI module and
30 minutes for the E Series device to ensure the measurement circuitry
is at a stable operating temperature.
Calibration
The calibration process consists of the following steps:
1.
Setting up the module for testing.
2.
Verifying the existing operation of the module to determine whether
your module is operating within its specifications.
3.
Adjusting your module with respect to a known voltage source.
4.
Verifying that the module is operating within its specifications after
adjustments.
© National Instruments Corporation
3
SCXI-1104 Calibration Procedure
Setting Up Your Module
Complete the following steps to set up your module for verification:
1.
Install your SCXI-1104 in slot 1 of your SCXI chassis.
2.
Connect a 68-to-68-pin cable between your SCXI module and E Series
DAQ device.
3.
Configure the hardware with Measurement & Automation Explorer.
If your need more information on configuring the system, refer to the
E Series device and SCXI module documentation.
Verifying the Operation of Your Module
The verification procedure determines how well the SCXI-1104 module is
meeting its specifications. You can use this information to select the
appropriate calibration interval for your application.
Complete the following steps to verify the operation of your SCXI-1104:
1.
Read the Test Conditions section earlier in this document.
2.
Refer to Table 1 at the end of this document to see the test
specifications.
National Instruments recommends you verify all ranges and gains.
However, you can save time by checking only those ranges that you use
in your application.
3.
Connect the E Series device to the SCXI-1104.
4.
Call Calibrate_E_Series to minimize the uncertainty associated
with the E Series device. Set the following parameters:
5.
SCXI-1104 Calibration Procedure
•
deviceNumber—The value obtained from Measurement &
Automation Explorer
•
calOp—ND_SELF_CALIBRATE
•
setOfCalConstants—ND_USER_EEPROM_AREA
•
calRefVolts—0.0
Call AI_Configure to put the E Series device in bipolar mode. Set the
following parameters:
•
deviceNumber—The value obtained from Measurement &
Automation Explorer
•
chan—0
•
inputMode—0
•
inputRange—0
•
polarity—0
•
driveAIS—0
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6.
Call MIO_Config to enable dithering on your E Series device. Set the
following parameters:
•
deviceNumber—The value obtained from Measurement &
Automation Explorer
•
dither—1
•
useAMUX—0
7.
Connect the calibrator to the appropriate analog input, starting with
channel 0. Refer to Figure 1 to determine the pins on the 96-pin front
connector that correspond to the positive and negative inputs of the
specified channel. For example, the positive input for channel 0
(CH0+) is pin C32. The negative input for channel 0 (CH0–) is pin
B32. If you are using an SCXI-1300 breakout module connected to the
SCXI-1104, connect your calibrator to the CH0+ and CH0– inputs.
8.
Call SCXI_Single_Chan_Setup to configure the module for
single-channel measurements. Set the following parameters:
9.
•
SCXIchassisID—The value obtained from Measurement &
Automation Explorer
•
moduleSlot—1
•
moduleChan—The channel you are verifying
•
DAQdeviceNumber—The device number assigned by
Measurement & Automation Explorer for the E Series DAQ
device
Set your calibrator to output the test point voltage from Table 1.
10. Call DAQ_Op. Set the following parameters:
•
deviceNumber—The device number of the DAQ device
•
channel—0
•
gain—1 for 16-bit E Series devices or –1 for 12-bit E Series
devices
•
count—100
•
sampleRate—100
11. Call SCXI_Scale. Set the following parameters:
© National Instruments Corporation
•
SCXIChassisID—The value obtained from Measurement &
Automation Explorer
•
moduleSlot—1
•
channel—The channel you are verifying
•
SCXIgain—0.1
•
TBgain—1
•
DAQboard—The device number for the DAQ device
5
SCXI-1104 Calibration Procedure
•
DAQChannel—0
•
DAQgain—0 for 16-bit devices, –1 for 12-bit devices
•
numPoints—100
•
binArray—The array returned from the DAQ_Op function
The result is a set of scaled voltages that you read from the SCXI
module.
12. Average the results returned from the SCXI_Scale function. Compare
the averaged result to the upper and lower limits in Table 1. If the result
falls within these limits, your module has passed this portion of the
test. If it does not, use the steps in the next section, Adjusting Gain and
Offset Errors and Calibration Constants, to adjust your module.
13. Repeat steps 7 through 12 for the remaining channels.
You have now completed verifying the operation of your SCXI-1104.
If all channels fall within the upper and lower limits, your module does not need to
be adjusted.
Note
Adjusting Gain and Offset Errors and Calibration Constants
This section contains step-by-step instructions on adjusting gain and offset
errors and calibration constants.
Adjusting Gain and Offset Errors
Complete the following steps to adjust gain and offset errors in your
SCXI-1104:
1.
Read the Test Conditions section.
2.
Connect the E Series device to the SCXI-1104.
3.
Call Calibrate_E_Series to minimize the uncertainty associated
with the E series device. Set the following parameters:
4.
SCXI-1104 Calibration Procedure
•
deviceNumber—The value obtained from Measurement &
Automation Explorer
•
calOp—ND_SELF_CALIBRATE
•
setOfCalConstants—ND_USER_EEPROM_AREA
•
calRefVolts—0.0
Call AI_Configure to put the E Series device in bipolar mode. Set the
following parameters:
•
deviceNumber—The value obtained from Measurement &
Automation Explorer
•
chan—0
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5.
6.
•
inputMode—0
•
inputRange—0
•
polarity—0
•
driveAIS—0
Call MIO_Config to enable dithering on your E Series device.
Set the following parameters:
•
deviceNumber—The value obtained from Measurement &
Automation Explorer
•
dither—1
•
useAMUX—0
Call SCXI_Single_Chan_Setup to configure the module for
single-channel measurements. Set the following parameters:
•
SCXIchassisID—The value obtained from Measurement &
Automation Explorer
•
moduleSlot—1
•
moduleChan—The channel you want to calibrate
•
DAQdeviceNumber—The device number assigned by
Measurement & Automation Explorer for the E Series DAQ
device
7.
Connect the calibrator to the channel you want to adjust. Refer to
Figure 1 to determine the pins on the 96-pin front connector that
correspond to the positive and negative inputs of the specified channel.
For example, the positive input for channel 0 is pin C32 which is
labeled CH0+. The negative input for channel 0 is pin B32 which is
labeled CH0–. If you are using an SCXI-1300 breakout module
connected to the SCXI-1104, connect your calibrator to the CH0+ and
CH0– inputs.
8.
Connect your DMM to the positive output on pin 3 (MCHO+) and
negative output on pin 4 (MCHO–) on the rear panel connector.
Figure 2 shows the 50-pin rear panel connector pin assignments.
For easy access to individual pins, use a screw terminal adapter connected to a
50-pin terminal block.
Tip
9.
Set the calibrator voltage to the positive test point value in Table 1.
10. Read the voltage from the DMM. Record the actual DMM reading,
which is output1, and the calibrator output voltage, which is volt1,
for later use.
11. Set the calibrator to the negative test point value for the same gain.
Skip any input limits that are specified as 0 V. You need only upper and
lower limits for adjustment.
© National Instruments Corporation
7
SCXI-1104 Calibration Procedure
12. Read the voltage from the DMM. Record the actual DMM reading,
output2, and the calibrator output voltage, voltage2.
You now have two pairs of data points, (volt1, output1) and
(volt2, output2), where volt is the calibrator reading and output is
the DMM reading.
13. Convert the DMM voltage readings (output1 and output2) to binary
readings (binary1 and binary2) by using one of the following
equations:
output
binary reading for 12-bit E Series products (binary) =  ----------------- × 2 12
 20 
output
binary reading for 16-bit E Series praducts (binary) =  ----------------- × 2 16
 20 
For example, using a 12-bit product such as a PCI-MIO-16E-1 and
obtaining a DMM reading of –9.9 V, you would have the following
results:
binary reading = (–9.9/20) × 212 = –2027.52
14. Record binary1 with volt1 and binary2 with volt2 for later use.
15. Repeat step 4 through 14 for the remaining channels you want to
adjust.
Adjusting Calibration Constants
Complete the following steps to adjust the calibration constants on your
SCXI-1104:
1.
SCXI-1104 Calibration Procedure
Call SCXI_Cal_Constants to create and store the new calibration
constants in the SCXI-1104 memory. Set the following parameters:
•
SCXIchassisID—The ID assigned by Measurement &
Automation Explorer
•
ModuleSlot—1, unless you have installed the module in a
different slot
•
channel—The channel you want to adjust
•
OpCode—2
•
calibrationArea—0
•
rangeCode—0 (not used for the SCXI-1104)
•
SCXIgain—0.1
•
DAQboard—The device number assigned by the Measurement
& Automation Explorer
•
DAQChan—0
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•
DAQGain—1 for 16-bit devices, –1 for 12-bit devices
•
Tbgain—1.0
•
volt1 and volt2—The first and second voltage readings for the
gain values that you are about to save on the SCXI-1104
•
binary1 and binary2—The first and second binary readings for
the gain values that you are about to save on the SCXI-1104
•
calConst1 and calConst2—These are return values.
2.
Repeat step 1, changing calibrationArea to 1.
3.
Repeat step 1, changing calibrationArea to 3.
4.
Repeat steps 1 through 3 for the next channel.
You have now adjusted the calibration constants.
Verifying Adjusted Values
After completing the adjustments, it is important to verify the adjusted
values by repeating the steps listed in the Verifying the Operation of Your
Module section of this document. Verifying the adjusted values ensures
your module is now operating within its specifications.
© National Instruments Corporation
9
SCXI-1104 Calibration Procedure
Front and Rear Panel Diagrams
Figure 1 shows the pin assignments for the SCXI-1104 module front panel
connector. Figure 2 shows the pin assignments for the SCXI-1104 rear
panel connector.
A
CGND
NC
NC
NC
NC
NC
NC
NC
CGND
NC
NC
NC
NC
NC
NC
NC
CGND
NC
NC
NC
NC
NC
NC
NC
NC
NC
NC
CGND
RSVD
RSVD
CGND
+5 V
32
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
B
CH0–
CH1–
CH2–
CH3–
CH4–
CH5–
CH6–
CH7–
CH8–
CH9–
CH10–
CH11–
CH12–
CH13–
CH14–
CH15–
CH16–
CH17–
CH18–
CH19–
CH20–
CH21–
CH22–
CH23–
CH24–
CH25–
CH26–
CH27–
CH28–
CH29–
CH30–
CH31–
32
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
C
CH0+
CH1+
CH2+
CH3+
CH4+
CH5+
CH6+
CH7+
CH8+
CH9+
CH10+
CH11+
CH12+
CH13+
CH14+
CH15+
CH16+
CH17+
CH18+
CH19+
CH20+
CH21+
CH22+
CH23+
CH24+
CH25+
CH26+
CH27+
CH28+
CH29+
CH30+
CH31+
32
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
Figure 1. SCXI-1104 Front Connector Pin Assignments
SCXI-1104 Calibration Procedure
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AOGND
MCH0+
NC
NC
NC
NC
NC
NC
NC
OUTREF
NC
NC
SERDATIN
DAQD*/A
SLOT0SEL*
NC
DGND
NC
SERCLK
NC
NC
RSVD
NC
NC
NC
1
3
5
2
4
6
AOGND
MCH0–
7
9
11
13
15
17
19
21
23
25
8
10
12
14
16
18
20
22
24
26
NC
NC
27
29
31
33
35
37
39
41
43
45
47
49
28
30
32
34
36
38
40
42
44
46
48
50
NC
NC
NC
NC
NC
NC
NC
NC
DGND
SERDATOUT
NC
NC
NC
SCANCLK
NC
NC
NC
NC
RSVD
NC
NC
Figure 2. SCXI-1104 Rear Panel Connector Pin Assignments
Specifications
The following table contains test specifications for the SCXI-1104 signal
conditioning module. If the device has been calibrated within the last year,
the Test Point value should fall between the Upper Limit and Lower Limit
values.
Table 1. SCXI-1104 Specifications
Ranges
© National Instruments Corporation
Gain
Test Point (V)
Upper Limit (V)
Lower Limit (V)
0.100
41.8000
41.8219
41.7781
0.0000
0.0010
–0.0010
–41.8000
–41.7781
–41.8219
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SCXI-1104 Calibration Procedure