National Instruments SCXI-1120/D Manual
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.
370268B-01 ©2000, 2001 National Instruments Corp. All rights reserved. September 2001
CALIBRATION PROCEDURE
SCXI -1120/D
Introduction
This document contains information and step-by-step instructions for
calibrating the National Instruments (NI) SCXI-1120 and SCXI-1120D
modules.
What Is Calibration?
Calibration consists of verifying the measurement accuracy of a module
and adjusting for any measurement error. Verification is measuring the
performance of the module and comparing these measurements to the
factory specifications. During calibration, you supply and read voltage
levels using external standards, then you adjust the module calibration
circuitry. This circuitry compensates for any inaccuracies in the module,
and returns the accuracy of the module to the factory specifications.
Why Should You Calibrate?
The accuracy of electronic components drifts with time and temperature,
which can affect measurement accuracy as a module ages. Calibration
restores these components to their specified accuracy and ensures that the
module still meets NI standards.
How Often Should You Calibrate?
The measurement requirements of your application determine how often
the SCXI-1120/D module needs to be calibrated to maintain accuracy.
NI recommends that you perform a complete calibration at least once every
year. You can shorten this interval to 90 days or six months based on the
demands of your application.
™
SCXI-1120/D Calibration Procedure 2 ni.com
Equipment and Other Test Requirements
This section describes the test equipment, software, documentation, and
test conditions required for calibrating the SCXI-1120/D modules.
Test Equipment
Calibration 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.
Instruments
NI recommends the following instruments for calibrating SCXI-1120/D
modules:
• Calibrator—Fluke 5700A
• DMM—NI 4060 or HP 34401A
If these instruments are not available, use the accuracy requirements listed
previously to select substitute calibration instruments.
Connectors
If you do not have custom connection hardware, you need the following
connectors:
• Terminal block, such as the SCXI-1320
• Shielded 68-pin connector cable
• 50-pin ribbon cable
• 50-pin breakout box
• SCXI-1349 adapter
These components give easy access to the individual pins on the
SCXI-1120/D module front and rear connectors.
Software and Documentation
No special software or documentation is necessary to calibrate the
SCXI-1120/D module. This calibration document contains all the
information you need to complete the verification and adjustment
procedures. If you would like more information on the module, refer
to the SCXI-1120/D User Manual.
©National Instruments Corporation 3 SCXI-1120/D Calibration Procedure
Test Conditions
Follow these guidelines to optimize the connections and environment
during calibration:
•Keep connections to the SCXI-1120/D module short. Long cables and
wires act as antennae, picking up extra noise and thermal offsets 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.
•Maintain the temperature between 18–28 °C.
•Keep relative humidity below 80%.
•Allow a warm-up time of at least 15 minutes for the SCXI-1120/D
module to ensure the measurement circuitry is at a stable operating
temperature.
Calibration
The calibration procedure for the SCXI-1120/D module consists of the
following steps:
1. Set up the module for testing.
2. Verify the existing operation of the module to determine whether it is
operating within its specifications.
3. Adjust the module with respect to a known voltage source.
4. Verify that the module is operating within its specifications after
adjustments.
SCXI-1120/D Calibration Procedure 4 ni.com
Setting Up the Module
Refer to Figures 1 and 2 while performing the following steps to set up the
SCXI-1120/D module for verification:
1. Remove the grounding screw from the module.
2. Remove the cover on the module to access the potentiometers.
Figure 1. Grounding Screw and Module Cover Removal
3. Remove the side plate of the SCXI chassis.
4. Install the SCXI-1120/D into slot 4 of the SCXI chassis.
1 Grounding screw 2 Module cover
1
2
©National Instruments Corporation 5 SCXI-1120/D Calibration Procedure
Figure 2. Side Plate Removal and Module Installation
The SCXI-1120/D module does not need to be connected to a data
acquisition (DAQ) device. Leave the configuration of the digital jumpers
W41–W43 and W46 unchanged because they do not affect this procedure.
Configuring the Gain Jumpers
Each input channel has two user-configurable gain stages. The first-stage
gain provides gains of 1, 10, 50, and 100. The second-stage gain provides
gains of 1, 2, 5, 10, and 20. Table 1 shows the jumper reference designators
for gain selection associated with each channel. Table 2 shows how to
position each jumper to select the desired gain for each channel.
1 Thumbscrews 2Slot4 3Sideplate
Table 1. Gain Jumper Reference Designators
Input Channel
Number
First-Stage
Gain Jumper
Second-Stage
Gain Jumper
0W1 W9
1W2 W10
2W3 W11
®
23
MAINFRAME
SCXI
NATIONAL
INSTRUMENTS
1
SCXI-1120/D Calibration Procedure 6 ni.com
To change the gain setting of a specified channel on the module, move
the appropriate jumper on the module to the position indicated in Table 2.
Refer to Table 1 for jumper reference designators, and Figure 3 for the
location of the jumpers.
3W4 W12
4W5 W13
5W6 W14
6W7 W15
7W8 W16
Table 2. Gain Jumper Positions
Gain Setting Jumper Position
First Stage 1
10
50
100
D
C
B
A (factory setting)
Second Stage 1
2
5
10
20
A
B
C
D (factory setting)
E
Table 1. Gain Jumper Reference Designators (Continued)
Input Channel
Number
First-Stage
Gain Jumper
Second-Stage
Gain Jumper
©National Instruments Corporation 7 SCXI-1120/D Calibration Procedure
Figure 3. SCXI-1120/D Parts Locator Diagram
Note The SCXI-1120D module has an additional fixed pre-stage gain of 0.5.
1 Thumbscrews
2 Front Connector
3 Product Name, Assembly Number,
and Serial Number
4 Output Null Adjust Potentiometers
5 Second-Stage Filter Jumpers
6 Rear Signal Connector
7 SCXIbus Connector
8 Input Null Adjust Potentiometers
9 First-Stage Gain Jumpers
10 Second-Stage Gain Jumpers
11 First-Stage Filter Jumpers
12 Terminal Block Mounting Hole
13 Grounding Screw
3
6
7
1
2
1
4 5
89 10 11
12
12
Front Rear
V25 V26 W27 W28 W29W30 W31V32V33 W34 W35 W36V37 V38 V39 V40
W45
W43
W42
R18
AA ABB BCCDDE
Q12
AD705
GAINDIP
U14
W6
22 W14
AD
13
SCXI-1120/D Calibration Procedure 8 ni.com
The order of the settings for the first- and second-stage gain does not
matter as long as the first-stage gain multiplied by the second-stage
gain—multiplied by 0.5 when using the SCXI-1120D—equals the desired
final gain value.
•SCXI-1120—To determine the overall gain of a given channel on the
SCXI-1120 module:
•SCXI-1120D—To determine the overall gain of a given channel on the
SCXI-1120D module:
Configuring the Filter Jumpers
Each input channel also has two user-configurable filter stages.
The SCXI-1120 module ships in the 4 Hz position and the SCXI-1120/D
module ships in the 4.5 kHz position. Refer to Table 3 or 4 to find the
correct jumper setting for the desired cutoff frequency. Figure 3 shows the
locations of the jumper blocks on the SCXI-1120/D modules. Verify that
both filter stages are set to the same filter setting to ensure that you achieve
the required bandwidth.
Table 3. SCXI-1120 Filter Jumper Settings
Input
Channel
Number
First Filter Jumper Second Filter Jumper
4Hz
(Factory
Setting) 10 kHz
4Hz
(Factory
Setting) 10 kHz
0W17-A W17-B W25 W26
1W18-A W18-B W27 W28
2W19-A W19-B W29 W30
3W20-A W20-B W31 W32
4W21-A W21-B W33 W34
5W22-A W22-B W35 W36
6W23-A W23-B W37 W38
7W24-A W24-B W39 W40
F
irst-Stage Gain Second-Stage Gain×Overall Gain=
First-Stage Gain Second-Stage Gain×()0.5×Overall Gain=
©National Instruments Corporation 9 SCXI-1120/D Calibration Procedure
Verifying the Operation of the Module
The verification procedure determines how well the SCXI-1120/D module
is meeting its specifications. You can use this information to select the
appropriatecalibrationintervalforyour application. Refer totheSetting Up
the Module section for information onhowtoconfigure thechannel filter
and channel gain.
Complete the following steps to verify the operation of the SCXI-1120/D
module:
1. Read the Test Conditions section inthisdocument.
2. Refer to Table 7 for the SCXI-1120 module or Table 8 for the
SCXI-1120D module for all acceptable settings for the module.
Although NI recommends verifying all ranges and gains, you can
save time by checking only those ranges used in your application.
3. Set the channel filter for all channels on the module to 4 Hz for
the SCXI-1120 module or 4.5 kHz for the SCXI-1120D module.
4. Set the channel gain on all channels to the gain you want to test,
starting with the smallest gain available for the module. Available
gainsareshowninTables7and8.
5. Connect the calibrator to the analog input channel you are testing,
starting with channel 0.
If you do not have an SCXI terminal block such as the SCXI-1320,
refer to Table 5 to determine the pins on the 96-pin front connector that
correspond to the positive and negative inputs of the specified channel.
Table 4. SCXI-1120D Filter Jumper Allocation
Input
Channel
Number
First Filter Jumper Second Filter Jumper
4.5 kHz
(Factory
Setting) 22.5 kHz
4.5 kHz
(Factory
Setting) 22.5 kHz
0W17-A W17-B W26 W25
1W18-A W18-B W28 W27
2W19-A W19-B W30 W29
3W20-A W20-B W32 W31
4W21-A W21-B W34 W33
5W22-A W22-B W36 W35
6W23-A W23-B W38 W37
7W24-A W24-B W40 W39
SCXI-1120/D Calibration Procedure 10 ni.com
For example, the positive input for channel 0 is pin A32, which is
labeled CH0+. The negative input for channel 0 is pin C32, which is
labeled CH0–.
Table 5. SCXI-1120/D Front Connector Pin Assignments
Pin Number Column A Column B Column C
32 CH0+ NP CH0–
31 NP NP NP
30 CH1+ NP CH1–
29 NP NP NP
28 NC NP NC
27 NP NP NP
26 CH2+ NP CH2–
25 NP NP NP
24 CH3+ NP CH3–
23 NP NP NP
22 NC NP NC
21 NP NP NP
20 CH4+ NP CH4–
19 NP NP NP
18 CH5+ NP CH5–
17 NP NP NP
16 NC NP NC
15 NP NP NP
14 CH6+ NP CH6–
13 NP NP NP
12 CH7+ NP CH7–
11 NP NP NP
10 NC NP NC
9NP NP NP
8NC NP RSVD
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