National Instruments SCXI-1303 Use and care manual

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370253B-01 ©Copyright 2000 National Instruments Corp. Allrights reserved. November 2000
CALIBRATION PROCEDURE
SCXI -1303 TERMINAL BLOCK
Introduction
This document contains information and step-by-step instructions for
verifying the performance of the temperature sensor on the
National Instruments SCXI-1303 terminal block. This temperature sensor
is for cold-junction compensation of thermocouples on the terminal block.
What Is Calibration?
Calibration consists ofverifyingthe measurement accuracy ofa device and
correcting for any measurement error. For SCXI-1303 terminal blocks,
calibration is simply verifying the measurement accuracy of the
components on the terminal block. Because these components are not
user-adjustable, calibrationconsistsof verificationonly,withoutcorrecting
for any error. Verification is measuring the performance of a device and
comparing the results to the factory specifications of the device.
Why Should You Verify?
The accuracy of electronic components drifts with time and temperature,
which can affect measurement accuracy as the device ages. Verification
ensures that your SCXI-1303 terminal block still meets
National Instruments standards. If the results of the procedure indicate that
the temperature sensor onyour terminal block isout of specification, return
the sensor to National Instruments for repair or replacement.
How Often Should You Verify?
The measurement accuracy requirements of your application determine
how often you should verify the performance of your SCXI-1303 terminal
block. National Instruments recommends you verify your terminal block
at least once every year. You can shorten this interval to six months or
90 days, based on the demands of your application.
™

SCXI-1303 Terminal Block Calibration Procedure 2 ni.com
Equipment and Other Test Requirements
This section describes the equipment, software, documentation, and test
conditions required for verifying the performance of your SCXI-1303
terminal block.
Test Equipment Verification 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 thermometer that is accurate to within 0.1 °C.
National Instruments recommends you use the following instruments for
verifying the performance of your SCXI-1303 terminal block:
• Calibrator—Fluke 5700A
• DMM—NI 4060 or HP 34401A
If these instruments are not available, use the accuracy requirements listed
above to select a substitute calibration standard.
Software and Documentation
You can find all the necessary information to verify the performance
of the SCXI-1303 in this verification procedure. No other software or
documentation is required. If you would like more information on the
SCXI-1303, refer to the SCXI-1303 Terminal Block Installation Guide,
which you can download from the National Instruments Web site at
ni.com/manuals
Test Conditions Follow these guidelines to optimize the connections and the environment
during verification:
• Keepconnections to the SCXI-1303 terminal block short. Longcables
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 a temperature between 15 and 35 °C.

©NationalInstruments Corporation 3 SCXI-1303 Terminal Block Calibration Procedure
Verification Procedure
This section contains step-by-step instructions for verifying the
performance of the temperature sensor on your SCXI-1303 terminal block.
Verifying Temperature Sensor Performance
Complete the following steps to verify the performance of the temperature
sensor on your 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:
– 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.
Figure 1 illustrates the connector pin assignments. Individual pins
are identified by their column and row. For example, A3 denotes
theterminal locatedinColumnA andRow 3.Thisconformstothe
labeling of the pins on the front connector of a mating 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.
b. Strip 0.5 inches of insulation from one end of a 22 AWG solid
wire. Insert the stripped end of the wire into terminal A1 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 inches 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.

SCXI-1303 Terminal Block Calibration Procedure 4 ni.com
2. Connect a calibrated DMM to the temperature-sensor output of the
terminal block.
a. Refer to Figure 2 to locate jumper W1 on your terminal block and
verify that MTEMP is jumpered.
b. Strip 0.5 inches of insulation from one end of a 22 AWG solid
wire. Insert the stripped end of the wire into terminal A3 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.
c. Connect the negative input terminal of the calibrated DMM to the
negative terminal of the +5 VDC power supply.
3. Place the terminal block in a temperature-controlled environment
where the temperature is between 15 and 35 °C.
4. When the terminal block temperature equilibrates 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 thermometer.
6. Convert Vmeas (in volts) to measured temperature Tmeas (in degrees
Celsius) by performing the following calculations:
a. Calculate
b. Calculate
c. Calculate
where Tmeas is in °C
a= 1.295361 × 10–3
b= 2.343159 × 10–4
c= 1.018703 × 10–7
x2.5 Vmeas
–
5000
---------------------------=
yVmeas
x
-------------


ln=
Tmeas 1
aybcy
2
+()+
---------------------------------- 273.15–=

©NationalInstruments Corporation 5 SCXI-1303 Terminal Block Calibration Procedure
7. Compare Tact to Tmeas.
• If (Tmeas −0.5 °C) ≤Tact ≤(Tmeas +0.5 °C), the performance of
the terminal block temperature sensor has been verified.
• If Tact <(Tmeas −0.5 °C),the terminal block temperature sensor is
nonfunctional. Do not substitute parts or modify equipment.
Return the terminal block to National Instruments to ensure that
the safety features are not compromised.
• If Tact >(Tmeas +0.5 °C), the terminal block temperature sensor is
nonfunctional. Do not substitute parts or modify equipment.
Return the terminal block to National Instruments to ensure that
the safety features are not compromised.
8. Return jumper W1 to its original position.
You have completed verifying the performance of the temperature sensor
of your SCXI-1303 terminal block.

SCXI-1303 Terminal Block Calibration Procedure 6 ni.com
Figure 1. SCXI-1303 Front Connector Pin Assignments
B1
C1 A1 (+5 VDC)
C32
B32
A32
A3 (Temp Sensor)
A2 (GND)

©NationalInstruments Corporation 7 SCXI-1303 Terminal Block Calibration Procedure
Figure 2. Location of Jumper W1 on the SCXI-1303 Terminal Block
Jumper W1