CALIBRATION PROCEDURE
SCXI™-1321 TERMINAL BLOCK
Introduction
This document contains information and step-by-step instructions for
verifying the temperature sensor performance and the value of shunt
calibration resistors of the National Instruments SCXI-1321 terminal
block.
What Is Calibration?
For SCXI-1321 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-1321
terminal block still meets 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-1321 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™, ni.com™, and SCXI ™ are trademarks of National Instruments Corporation. Product and company names mentioned herein are
trademarks or trade names of their respective companies.
370254A-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 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 your SCXI-1321:
•
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-1321. You can
find all the necessary information in this calibration procedure. However,
if you would like more information on the product, refer to the SCXI-1321
Terminal Block Installation Guide.
Test Conditions
Follow these guidelines to optimize the connections and the environment
during verification:
•
Keep connections to the SCXI-1321 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-1321 Terminal Block Calibration Procedure
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Verification Procedures
This section contains step-by-step instructions for verifying the
performance of the temperature sensor and the value of the
shunt-calibration resistors of your SCXI-1321 terminal block.
Verifying Temperature Sensor Performance
Complete the following steps to verify the performance of the temperature
sensor on your SCXI-1321 terminal block:
1.
Connect a +5 VDC power source to the terminal block.
a.
Hold the terminal block vertically upright 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 corresponds to the labeling of the pins on the
front connector of a matching SCXI module. It does not
necessarily correspond to the labeling of the 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-1321 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 has equilibrated with its
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 instrument.
6.
Convert Vmeas (in volts) to measured temperature Tmeas (in degrees
Celsius) by multiplying Vmeas by 100.
7.
Compare Tact to Tmeas.
a.
If (Tmeas − 0.9 °C) ≤ Tact ≤ (Tmeas + 0.9 °C), the operation of the
temperature sensor has been verified.
b.
If Tact < (Tmeas − 0.9 °C), the temperature sensor is nonfunctional.
Repair or replace the terminal block.
c.
If Tact > (Tmeas + 0.9 °C), the temperature sensor is nonfunctional.
Repair or replace the terminal block.
You have completed the procedure for verifying the operation of the
temperature sensor on the SCXI-1321 terminal block.
Verifying the Value of the Shunt-Calibration Resistors
Complete the following steps to verify the value of the shunt-calibration
resistors on your SCXI-1321 terminal block:
1.
Open the terminal block enclosure by removing the side cover.
2.
Place nulling-circuit jumpers W1 through W4 in the “D” (disabled)
position.
3.
Locate R4 on the printed circuit board. R4 is a socketed resistor used
for shunt calibration of channel 0. National Instruments provides the
SCXI-1321 terminal block to users with a 301 kΩ, 1% tolerance
resistor installed. However, users are free to replace this resistor with
another one having different resistance or tolerance values. If R4 is not
a 301 kΩ, 1% tolerance resistor, modify step 5 accordingly.
4.
Using a calibrated DMM, measure the resistance of R4.
5.
Determine if the value of the shunt-calibration resistor meets the
specification.
a.
If 301 kΩ− {0.01 × 301 kΩ} ≤ R4 ≤ 301 kΩ + {0.01 × 301 kΩ},
the value of the shunt-calibration resistor has been verified.
b.
If R4 < 301 kΩ− {0.01 × 301 kΩ}, the shunt-calibration resistor
is out of specification. Return it to National Instruments for repair
or replacement.
SCXI-1321 Terminal Block Calibration Procedure
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c.
6.
7.
If R4 > 301 kΩ + {0.01 × 301 kΩ}, the shunt-calibration resistor
is out of specification. Return it to National Instruments for repair
or replacement.
Repeat steps 3 through 5 for the remaining shunt-calibration resistors:
a.
R6 (channel 1)
b.
R8 (channel 2)
c.
R10 (channel 3)
Close the terminal block enclosure by attaching the side cover.
You have completed the procedure for verifying the value of the
shunt-calibration resistors on your SCXI-1321.
© National Instruments Corporation
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SCXI-1321 Terminal Block Calibration Procedure