SCXI-1313 High-Voltage Attenuator Terminal Block Calibration

SCXI-1313 High-Voltage Attenuator Terminal Block Calibration
CALIBRATION PROCEDURE
SCXI™-1313 HIGH-VOLTAGE ATTENUATOR
TERMINAL BLOCK
Introduction
This document contains information and step-by-step instructions for
verifying the performance of the resistor divider networks and the
temperature sensor on the National Instruments SCXI-1313 high-voltage
attenuator terminal block. The resistor divider networks provide the
attenuation that allows the SCXI-1125 module to read large signals of
up to 300 Vmeas.
What Is Calibration?
Calibration consists of verifying the measurement accuracy of a device
and correcting for any measurement error. For SCXI-1313 terminal blocks,
calibration is simply verifying the measurement accuracy of the
components on the terminal block. Because these components are not
user-adjustable, calibration consists of verification only, without correcting
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-1313 terminal block still meets its specifications.
If the results of the procedure indicate that the resistor networks or the
temperature sensor on your terminal block are out of specification, return
the terminal block to NI 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-1313 terminal
block. NI recommends that you verify your terminal block at least once
National Instruments™, NI™, 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.
370316A-01
© Copyright 2001 National Instruments Corp. All rights reserved.
April 2001
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 required for verifying the performance of your SCXI-1313
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.
NI recommends you use the following instruments for verifying the
performance of your SCXI-1313 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-1313 in this verification procedure. No other software or
documentation is required. If you would like more information on the
SCXI-1313, refer to the SCXI-1313 Terminal Block Installation Guide,
which you can download from the NI Web site at ni.com/manuals.
Test Conditions
Follow these guidelines to optimize the connections and the environment
during verification:
•
Keep connections to the SCXI-1313 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 a temperature between 15 and 35 °C.
SCXI-1313 Terminal Block Calibration Procedure
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Verification Procedures
This section contains step-by-step instructions for verifying the
performance of the resistor divider networks and the temperature sensor on
your SCXI-1313 terminal block.
Verifying Resistor Divider Networks
Complete the following steps to verify the performance of each of the eight
divider networks, RP1 through RP8. Figure 1 shows the pin designations
on the resistor network.
177 EBG
177 EB6G-A15
6-A 00 8T6
1 2
-E
00258T624
24 -E
Pin 1
Pin 3
Pin 5
Figure 1. SCXI-1313 Resistor Network Pin Designations
1.
© National Instruments Corporation
Set your DMM for resistance measurement. To access the pins of the
resistor networks, you need to remove the device from its casing. Refer
to Figure 1 to locate the parts and do the following:
a.
Removing the two screws located on the outside of the casing.
Figure shows the location of these screws.
b.
Remove the two screws holding the strain relief bar and remove
the bar.
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SCXI-1313 Terminal Block Calibration Procedure
c.
Remove the two screws that attach the device to the casing.
d.
Take the board out of the casing and turn it over to the back side.
The pins of the resistor networks should be protruding slightly
from the back of the board.
6
1
2
7
5
4
3
Front View
Back View
1
2
Top Cover Screws
Top Cover
3
4
Thumbscrew
Mating Connector
5
6
Strain-Relief Bar
Strain-Relief Screws
7
Safety-Ground Lug
Figure 2. SCXI-1313 Parts Locator Diagram
2.
3.
Measure the resistance of each of the eight resistor networks on your
device:
a.
Measure and record R1-5, which is the resistance value from pin 1
to pin 5 on the resistor network you are testing.
b.
Measure and record R3-5, which is the resistance value from pin 3
to pin 5 on the resistor network you are testing.
Calculate the following:
Ratio n = R 3 – 5 ⁄ R 1 – 5
where n is the designation of the resistor divider network. Carry the
calculation out the nearest 10-7 decimal place.
SCXI-1313 Terminal Block Calibration Procedure
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4.
Compare the Ration value to the nominal value of 1/100 (0.01):
a.
If 0.0099940 ≤ Ration ≤ 0.0100060, you have verified the
performance of the resistor network RPn.
b.
If Ration < 0.0099940, the performance of the resistor divider
network is out of specification.
c.
If Ration > 0.0100060, the performance of the resistor divider
network is out of specification. After you have verified all eight
resistor networks, you have completed the verification procedure
for the resistor networks. If this procedure determined that any of
the components are out of specification, do not attempt any
adjustments. Return your device to NI to ensure that the safety
features of your device are not compromised.
You have completed verifying the performance of the resistor divider
networks on your SCXI-1313 terminal block. Continue to the next section
to verify the performance of the temperature sensor.
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.
Refer to Figure 3 for the pin assignments on the SCXI-1313.
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 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.
Note
Not all pins are populated for this connector.
b.
© National Instruments Corporation
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
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SCXI-1313 Terminal Block Calibration Procedure
other end of this wire to the positive terminal of the +5 VDC
power supply.
c.
2.
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.
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 stabilizes 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
x=
b.
2.5 − Vmeas
5000
Calculate
 Vmeas 
y = ln

 x 
c.
Calculate


1
Tmeas = 
− 273.15
2 
 a + y b + cy 
(
SCXI-1313 Terminal Block Calibration Procedure
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)
ni.com
where Tmeas is in degrees Celsius.
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), 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 NI for repair 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 NI for repair to ensure that the safety
features are not compromised.
You have completed verifying the performance of the temperature sensor
of your SCXI-1313 terminal block.
© National Instruments Corporation
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SCXI-1313 Terminal Block Calibration Procedure
B32
C32
(Temp Sensor) C4
A32
A4 (+5 VDC)
A2 (GND)
C1
Figure 3. SCXI-1313 Connector Pin Assignments
SCXI-1313 Terminal Block Calibration Procedure
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