National Instruments SCXI-1121 Manual

National Instruments™, NI™, ni.com™, NI-DAQ™, and SCXI™ are trademarks of National Instruments Corporation. Product and company names
mentioned herein are trademarks or trade names of their respective companies.
370258B-01 ©2000, 2001 National Instruments Corp. All rights reserved. September 2001
CALIBRATION PROCEDURE
SCXI -1121
Introduction
This document contains information and step-by-step instructions for
calibrating the National Instruments (NI) SCXI-1121 module.
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
constants. 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-1121 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-1121 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-1121 module.
Test Equipment
Calibration 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 120 and 800 Ω±10% precision resistors.
Instruments
NI recommends the following instruments for calibrating the SCXI-1121
module:
• 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-1121 front and rear connectors.
Software and Documentation
You do not need any special software or documentation to calibrate the
SCXI-1121 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-1121 User
Manual.

©National Instruments Corporation 3 SCXI-1121 Calibration Procedure
Test Conditions
Follow these guidelines to optimize the connections and environment
during calibration:
• Keep connections to the SCXI-1121 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-1121
module to ensure the measurement circuitry is at a stable operating
temperature.
Calibration
The calibration procedure for the SCXI-1121 module consists of the
following steps:
1. Setting up the module for testing.
2. Verifying the existing operation of the module to determine whether it
is operating within its specifications.
3. Adjusting the module with respect to a known voltage source.
4. Verifying that the module is operating within its specifications after
adjustments.

SCXI-1121 Calibration Procedure 4 ni.com
Setting Up the Module
Complete the following steps to set up the SCXI-1121 module for
verification:
1. Remove the grounding screw from the module.
2. Remove the cover on the module to access the potentiometers.
Refer to Figure 1 for an illustration of steps 1 and 2.
Figure 1. Grounding Screw and Cover Removal
3. Remove the side plate of the SCXI chassis.
4. Install the module into slot 4 of the SCXI chassis.
1 Grounding Screw 2 Module Cover
1
2

©National Instruments Corporation 5 SCXI-1121 Calibration Procedure
Refer to Figure 2 for an illustration of steps 3 and 4.
Figure 2. Side Plate Removal and Module Installation
The SCXI-1121 module does not need to be connected to a data acquisition
(DAQ) device. Leave the configuration of the digital jumpers W41–W45
and W46 unchanged because they do not affect this procedure.
Configuring the Half-Bridge Completion Jumpers
Verify that the half-bridge completion network is disabled prior to
calibrating the module. Refer to Figure 3 for the location of the jumpers and
Table 1 for the correct jumper settings to disable the network.
1 Thumbscrews 2Slot4 3 Side Plate
®
23
MAINFRAME
SCXI
NATIONAL
INSTRUMENTS
1

SCXI-1121 Calibration Procedure 6 ni.com
Figure 3. SCXI-1121 Parts Locator Diagram
1 Thumbscrews
2 Voltage and Current Adjust
3 Front Connector
4 Serial Number
5 Output Null Adjust Potentiometers
6 Second-Stage Filter Jumpers
7 Rear Signal Connector
8 Product Name, Assembly Number, Revision Letter
9 SCXIbus Connector
10 Terminal Block Mounting Hole
11 Excitation Level Jumpers
12 First-Stage Filter Jumpers
13 Second-Stage Gain Jumpers
14 First-Stage Gain Jumpers
15 Half-Bridge Completion Jumpers
16 Input Null Adjust Potentiometers
17 Excitation Mode Jumpers
18 Grounding Screw
Q2
U4
U7
R3
W33
R2
W32
R6
R7
R12
R13
R16
R17
R26
C2 C3
W1
W3
W14
W15
W16
W17
W18
W19
W27
W28
W29
W36
Q3
Q5
Q6
Q9
Q14
D1
D2
D3 D4
D11
D14
D15 D16
U18
U24
U28
U31
U39
W26
R33
U35
R10
U15
C14
C30
Q13
R277
C24
C25
D9
U6
C18
C424
U38
R275
R276
U2
Q1 U1
U19
U20
C125
W31
W30
Q4
W21
U3
C42
U22
L1 L2
C22
C21
J2
R274
R1 R15 R25
R8
R35
W20
U17
W4
W5
R21
C19
D6
U14
D5
C26
W38
C85
R5
R4
C70
R28
R27
W35
R30
D23
C29
D29
D38
R29
D22
D37
D28
U36
R32
R31
W34
Q20D34
W49
J1
R22
W24
R18
U25
W23
W22
Q7
R20
R19
D10
C36
W6
W8
W9
W10
W11
W12
W13
U40
D7
D21
D17
Q18
D39
C37
D30
Q16 Q17
C423
C15
C39
C38
R45
C33
D13
W25
C20
R46 C143
U51
D40
R281
W45
U61
R99
U27
U33
U9U8
R11
U21
C27
D41
U37
Q21
U48
U60
U50
C34
D19 D20
C425
U5
C16
D18
D26
D27
D36
D35
U47
U46
C32
R23
U11
C105
D12 Q8
U30
U42
D25 Q12
D24 Q11
U41
U34
U16
R9
U10
U23
U29
Q10
W2
W7
U44
U32
W37
U26
c
+
+
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S/N
AD705
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ISO122P
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1
HCT08 HCT00 HC05
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B
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LF347
GAINDIP
PRIMARY
PRIMARY
GAINDIP
RES
20K
RES
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RES
20K
DG409
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34072
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GAINDIP
34072 MC
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COPYRIGHT 1996
RES
20K
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LT-
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HCT03
HCT240
HCT273
ASSY181505F-01
SCXI-1121
HCT165
9
1
3
1
5
R42
R43
W41
Q19
R40
W42
W43
D32
D31
D33
R41
R38
R37
U43
W48W47
R39
U45
AD705
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R36
W39
W40
Q15
W46
R273
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W40
W41
W42
W43
BAEDCBADCBABA
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W46
R273
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16
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Front Rear
15
18

©National Instruments Corporation 7 SCXI-1121 Calibration 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. The device ships with the first-stage gain set to
100 (position A) and the second-stage gain set to 10 (position D).
To change the gain setting of a specified channel on the module, refer to
Table 2 for the jumper reference designator of the channel gain stage you
want to change, and Figure 3 for the location of this jumper. Move the
jumper to the position indicated in Table 3.
Table 1. Completion Network Jumpers
Channel Jumpers
Enable
Completion
Disable Network
(Factory Setting)
0W1 and W2
1W17 and
W18
2W27 and
W28
3W39 and
W40
A B
W2
W1
1 2 3
A B
W2
W1
1 2 3
W18
A B
W17
1 2 3
W18
A B
W17
1 2 3
W28
A B
W27
1 2 3
W28
A B
W27
1 2 3
W40
A B
W39
1 2 3
W40
A B
W39
1 2 3

SCXI-1121 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 equals the
desired final gain value.
Configuring the Filter Jumpers
Each input channel also has two user-configurable filter stages.
The SCXI-1121 module ships in the 4 Hz position. Refer to Table 4 to find
the correct jumper setting for the desired cutoff frequency. Figure 3 shows
the locations of the jumper blocks on the SCXI-1121 module. Verify that
both filter stages are set to the same filter setting to ensure that you achieve
the desired bandwidth.
Table 2. Gain Jumper Reference Designators
Input Channel
Number
First-Stage
Gain Jumper
Second-Stage
Gain Jumper
0W3 W4
1W19 W20
2W29 W30
3W41 W42
Table 3. Gain Jumper Positions
Gain Setting Jumper Position
First-Stage 1 D
10 C
50 B
100 A (factory setting)
Second-Stage 1 A
2 B
5 C
10 D (factory setting)
20 E

©National Instruments Corporation 9 SCXI-1121 Calibration Procedure
Configuring the Excitation Jumpers
You can configure each excitation channel of the SCXI-1121 module to
either a voltage or current excitation mode. Each channel has two jumpers
for this purpose. Set both jumpers in the same mode for correct operation
of the excitation channel. Refer to Table 5 to determine how to set up the
module in the mode you want. The SCXI-1121 module ships to you in the
voltage mode.
Table 4. Filter Jumper Settings
Input
Channel
Number
First Filter Jumper Second Filter Jumper
4 Hz
(Factory
Setting) 4 kHz
4 Hz
(Factory
Setting) 4 kHz
0W5-A W5-B W6 W7
1W21-A W21-B W8 W9
2W31-A W31-B W10 W11
3W43-A W43-B W12 W13
Table 5. Voltage and Current Mode Excitation Jumper Settings
Excitation
Channel Jumpers
Voltage Mode
(Factory Setting) Current Mode
0W14 and
W15
1W22 and
W23
2W34 and
W35
3W46 and
W47
W14
1 2 3
W15
1 2 3
W14
1 2 3
W15
1 2 3
W22
1 2 3
W23
1 2 3
W22
1 2 3
W23
1 2 3
W34
1 2 3
W35
1 2 3
W34
1 2 3
W35
1 2 3
W46
1 2 3
W47
1 2 3
W46
1 2 3
W47
1 2 3

SCXI-1121 Calibration Procedure 10 ni.com
Configuring the Excitation Level
Each excitation channel of the SCXI-1121 module has two different current
or voltage levels. You can set a given channel to one of the following level
modes:
• In the current mode—0.150 or 0.450 mA
• In the voltage mode—3.333 or 10 V
After selecting the excitation mode of operation desired—voltage or
current—as described in the previous section, refer to Table 6 to set the
SCXI-1121 module for the level of operation. The SCXI-1121 module
ships with the voltage mode set to 3.333 V.
Table 6. Excitation Level Jumper Settings
Excitation
Channel Jumpers
3.333 V or
0.150 mA
(Factory Setting) 10 V or 0.450 mA
0W16 and
W26
1W24 and
W25
2W36 and
W37
3W48 and
W49
W16
1 2 3
1
2
3
W26 W16
1 2 3
1
2
3
W26
W24
1 2 3
W25
1 2 3
W24
1 2 3
W25
1 2 3
W36
1 2 3
W37
1 2 3
W36
1 2 3
W37
1 2 3
W48
1 2 3
W49
1 2 3
W48
1 2 3
W49
1 2 3