SCXI-1322 Terminal Block Calibration Procedure

CALIBRATION PROCEDURE
SCXI -1322 Terminal Block
™
This document contains information and step-by-step instructions for
verifying the temperature sensor performance of the National Instruments
SCXI-1322 terminal block.
What Is Calibration?
For SCXI-1322 terminal blocks, calibration is simply determining the
measurement accuracy of the components on the SCXI-1322. 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-1322
terminal block is still meeting NI standards. If the results of the procedure
indicate that your terminal block is out of specification, return it to NI for
repair.
How Often Should You Calibrate?
The measurement accuracy requirements of your application determine
the calibration interval of your SCXI-1322 terminal block. NI 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.
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.
NI recommends you use the following instruments for verification of an
SCXI-1322:
•
Calibrator—Fluke 5700A
•
DMM—NI 4070 or HP 34401A
If these instruments are not available, use the accuracy requirements
previously listed to select a substitute calibration standard.
Software and Documentation
No software is required to verify the operation of the SCXI-1322. All
required documentation is found in this calibration procedure. However,
if you would like more information on the product, refer to the SCXI-1322
High-Voltage Terminal Block Installation Guide.
Test Conditions
Follow these guidelines to optimize the connections and the environment
during verification:
•
Keep connections to the SCXI-1322 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.
•
Allow a warm-up time of at least 15 minutes to ensure that the circuitry
is at a stable operating temperature.
SCXI-1322 Terminal Block Calibration Procedure
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Verification Procedure
1.
Connect a +5 VDC power source to the terminal block.
a.
Hold the SCXI-1322 vertically and view it from the rear. The
terminals on the 96-pin DIN connector are illustrated in Figure 1.
C
Column
B
A
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-1322 96-Pin DIN Connector
© National Instruments Corporation
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SCXI-1322 Terminal Block Calibration Procedure
This conforms to the labeling of the pins on the front connector
of a matching SCXI terminal block. It does not necessarily
correspond to 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.
b.
Strip 12.7 mm (0.5 in.) of insulation from one end of a 22 AWG
solid wire. Insert the stripped end of the wire into terminal A7 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 12.7 mm (0.5 in.) 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 negative terminal of the
+5 VDC power supply.
Connect a calibrated DMM to the temperature sensor output of the
terminal block.
a.
Strip 12.7 mm (0.5 in.) 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.
b.
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 °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 temperature-measurement instrument.
SCXI-1322 Terminal Block Calibration Procedure
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6.
Convert Vmeas (in volts) to measured temperature Tmeas (in °C) by
performing the following calculation.
a.
Calculate.
2.5 – V meas
x = -------------------------5000
b.
Calculate.
V meas
y = ln  -------------
 x 
c.
Calculate.
1
- – 273.15
T meas = --------------------------------2
a + y ( b + cy )
where
a = 1.295361 × 10–3
b = 2.343159 × 10–4
c = 1.018703 × 10–7
7.
Compare Tact to Tmeas.
•
If (Tmeas − 0.65 °C) ≤ Tact ≤ (Tmeas + 0.65 °C), you have verified
that the operation of the terminal block temperature sensor is
within its specifications.
•
If Tact < (Tmeas − 0.65 °C), the temperature sensor is nonfunctional.
Return the terminal block to NI for repair or replacement.
•
If Tact > (Tmeas + 0.65 °C), the temperature sensor is nonfunctional.
Return the terminal block to NI for repair or replacement.
You have completed the calibration verification procedure for the
SCXI-1322.
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