SCXI-1327 Terminal Block Calibration Procedure

CALIBRATION PROCEDURE
SCXI™-1327 TERMINAL BLOCK
Introduction
This document contains information and step-by-step instructions for
verifying the temperature sensor and voltage attenuator performance of the
National Instruments SCXI-1327 terminal block.
What Is Calibration?
For SCXI-1327 terminal blocks, calibration is simply determining the
measurement accuracy of the components on the terminal block. Because
these components are not user-adjustable, calibration consists of a
verification procedure only.
Why Calibrate?
Electronic components drift with time, which can affect measurement
accuracy as the device ages. Calibration ensures that your SCXI-1327
terminal block is still meeting National Instruments standards. If the results
of the procedure indicate that your terminal block is out of specification,
return it to National Instruments for repair.
How Often Should You Calibrate?
The measurement accuracy requirements of your application
determine the calibration interval of your SCXI-1327 terminal block.
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.
National Instruments™ and SCXI ™ are trademarks of National Instruments Corporation. Product and company names mentioned herein are
trademarks or trade names of their respective companies.
370256A-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 needed for verification.
Test Equipment
Verification requires a high-precision voltage source with at least 50 ppm
accuracy, and a multiranging 5 1/2 digit digital multimeter (DMM) with
15 ppm accuracy.
National Instruments recommends you use the following instruments for
verification of an SCXI-1327:
•
Calibrator—Fluke 5700A
•
DMM—NI 4060 or HP34401A
If the exact instrument is not available, use the accuracy requirements listed
above to select a substitute calibration standard.
Software and Documentation
No software is required to verify the operation of the SCXI-1327. All
required documentation is found in this calibration procedure. However,
if you would like more information on the product, refer to the SCXI-1327
Terminal Block Installation Guide.
Test Conditions
Follow these guidelines to optimize the connections and the environment
during verification:
•
Keep connections to the SCXI terminal block short. Long cables and
wires act as antennae, picking 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.
•
Keep relative humidity below 80%.
•
Maintain temperature between 15 °C and 35 °C.
SCXI-1327 Terminal Block Calibration Procedure
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Verification Procedures
The following procedures allow you to verify the performance of two key
components of your SCXI-1327: the temperature sensor and the voltage
attenuator.
Temperature Sensor Verification Procedure
1.
Connect a +5 VDC power source to the terminal block.
a.
Hold the terminal block vertically and view it from the rear. The
terminals on the 96-pin DIN connector are designated as follows
for the purposes of this procedure:
–
Column A is on the right, Column B is in the middle, and
Column C is on the left.
–
Row 1 is at the bottom and Row 32 is at the top.
–
Individual pins are identified by their column and row. For
example, “A3” denotes the terminal located in Column A and
Row 3.
This conforms to the labeling of pins on the front connector of a
matching SCXI module. It does not necessarily correspond to the
labeling of pins on the rear of the terminal block connector itself,
which you can only view by opening the terminal block enclosure.
2.
© National Instruments Corporation
b.
Strip 0.5 in. of insulation from one end of a 22 AWG solid wire.
Insert the stripped end of the wire into terminal A4 on the 96-pin
female DIN connector on the rear of the terminal block. Attach the
other end of this wire to the positive terminal of the +5 VDC
power supply.
c.
Strip 0.5 in. of insulation from one end of a 22 AWG solid wire.
Insert the stripped end of the wire into terminal A2 on the 96-pin
female DIN connector on the rear of the terminal block. Attach the
other end of this wire to the negative terminal of the +5 VDC
power supply.
Connect a calibrated DMM to the temperature sensor output of the
terminal block.
a.
Strip 0.5 in. of insulation from one end of a 22 AWG solid wire.
Insert the stripped end of the wire into terminal C4 on the 96-pin
female DIN connector on the rear of the terminal block. Attach the
other end of this wire to the positive input terminal of the
calibrated DMM.
b.
Connect the negative input terminal of the calibrated DMM to the
negative terminal of the +5 VDC power supply.
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SCXI-1327 Terminal Block Calibration Procedure
3.
Place the terminal block in a temperature-controlled environment
where the temperature is between 15 °C and 35 °C.
4.
When the terminal block temperature equilibrates with it surroundings,
measure the temperature sensor output Vmeas using a calibrated DMM.
5.
Measure the actual temperature Tact in the temperature-controlled
environment using a calibrated temperature-measurement instrument.
6.
Convert Vmeas (in volts) to measured temperature Tmeas (in degrees
Celsius) by performing the following calculation.
a.
Calculate.
x=
b.
2.5 − Vmeas
5000
Calculate.
 Vmeas 
y = ln

 x 
c.
Calculate.


1
− 273.15
Tmeas = 
2 
 a + y b + cy 
(
)
where Tmeas is in °C.
7.
a = 1.295361 × 10
–3
b = 2.343159 × 10
–4
c = 1.018703 × 10
–7
Compare Tact to Tmeas.
–
If (Tmeas − 0.5 °C) ≤ Tact ≤ (Tmeas + 0.5 °C), then the operation of
the terminal block temperature-sensor has been verified.
–
If Tact < (Tmeas − 0.5 °C), the terminal block temperature sensor is
nonfunctional. Return the terminal block to National Instruments
for repair or replacement.
–
If Tact > (Tmeas + 0.5 °C), the terminal block temperature sensor is
nonfunctional. Return the terminal block to National Instruments
for repair or replacement.
SCXI-1327 Terminal Block Calibration Procedure
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Voltage Attenuator Verification Procedure
1.
Open the terminal block enclosure by removing the side cover.
2.
Place slide switches S1 through S16 in the “100:1” position.
3.
Locate RP1 (resistor package 1) on the printed circuit board. Note that
one end of RP1 is marked with a dot. This dot identifies pin 1. RP1 has
a total of five pins, numbered in order starting from pin 1. The voltage
divider in RP1 is associated with channel 0 on the terminal block.
4.
Using a calibrated DMM, measure the resistance Rmeas1 between
pins 1 and 3.
5.
Using a calibrated DMM, measure the resistance Rmeas2 between
pins 3 and 5.
6.
Calculate.
Atten =
Rmeas 2
Rmeas1 + Rmeas 2
7.
Using a calibrated instrument, measure the ambient temperature Tamb
of the terminal block.
8.
Determine if attenuation performance is meeting the specification.
9.
–
If 0.01 − [0.01 × {0.0006 + (Tamb − 25× 0.000015)}] ≤ Atten
≤ 0.01 + [0.01 × {0.0006 + (Tamb − 25× 0.000015)}], then the
attenuation performance of the terminal block has been verified.
–
If Atten < 0.01 − [0.01 × {0.0006 + (Tamb − 25× 0.000015)}],
then the terminal block is non-functional. Repair or replace it.
–
If Atten > 0.01 + [0.01 × {0.0006 + (Tamb − 25× 0.000015)}],
then the terminal block is non-functional. Repair or replace it.
Repeat steps 2 through 8 using the remaining resistor packages:
–
RP5 (channel 1)
–
RP3 (channel 2)
–
RP6 (channel 3)
–
RP8 (channel 4)
–
RP7 (channel 5)
–
RP4 (channel 6)
–
RP2 (channel 7)
You have completed the calibration verification procedure for your
SCXI-1327.
© National Instruments Corporation
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SCXI-1327 Terminal Block Calibration Procedure