National Instruments SCXI-1121 Manual

CALIBRATION PROCEDURE
SCXI -1121
This document contains information and instructions for calibrating the
National Instruments SCXI-1121 signal conditioning module.
Contents
Introduction............................................................................................. 2
What Is Calibration? ........................................................................ 2
Why Should You Calibrate? ............................................................ 2
How Often Should You Calibrate? .................................................. 2
Software and Documentation.................................................................. 2
Test Equipment ....................................................................................... 3
Test Conditions ....................................................................................... 3
Calibration Process ................................................................................. 4
Initial Setup...................................................................................... 4
Configuring the Half-Bridge Completion Jumpers .................. 5
Configuring the Gain Jumpers.................................................. 7
Configuring the Filter Jumpers................................................. 8
Configuring the Excitation Jumpers ......................................... 9
Verification Procedure..................................................................... 10
Verifying Analog Input Offsets ................................................ 10
Verifying Voltage Excitation Limits ........................................ 11
Verifying Current Excitation Limits......................................... 12
Adjustment Procedure...................................................................... 13
Adjusting Analog Input Offsets................................................ 13
Adjusting Voltage Excitation ................................................... 14
Adjusting Current Excitation.................................................... 15
Verifying Adjusted Values .............................................................. 15
Test Limits .............................................................................................. 16
SCXI-1121 Front and Rear Panel Diagrams........................................... 19
™

SCXI-1121 Calibration Procedure 2 ni.com
Introduction
What Is Calibration?
Calibration consists of verifying the measurement accuracy of a device
and adjusting for any measurement error. Verification is measuring the
performance of the device and comparing these measurements to the
factory specifications. During calibration, you supply and read voltage
levels using external standards, then you adjust the device calibration
constants. The measurement circuitry compensates for any inaccuracies
in the device, and returns the accuracy of the device to the factory
specifications.
Why Should You Calibrate?
The accuracy of electronic components drifts with time and temperature,
which can affect measurement accuracy. Calibration restores these
components to their specified accuracy and ensures that the device still
meets NI standards.
How Often Should You Calibrate?
Calibrate the SCXI-1121 at a regular interval as defined by the
measurement accuracy requirements of your application. NI recommends
that you perform a complete calibration at least once every year. You
can shorten this interval based on the accuracy requirements of your
application.
Software and Documentation
You do not need any special software or documentation to calibrate the
SCXI-1121. This calibration document contains all the information you
need to complete the calibration procedure. Refer to the SCXI-1121 User
Manual for more information about the SCXI-1121.

©National Instruments Corporation 3 SCXI-1121 Calibration Procedure
Test Equipment
NI recommends that you use the equipment in Table 1 to calibrate the
SCXI-1121. If these instruments are not available, use the requirements
listed in Table 1 to select a suitable substitute.
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.
Test Conditions
Follow these guidelines to optimize the connections and environment
during calibration:
• Keep connections to the SCXI-1121 short. Long cables and wires can
act as antennas, picking up extra noise and thermal offsets that affect
measurements.
• Use shielded copper wire for all cable connections to the SCXI-1121.
Use twisted-pair wire to eliminate noise and thermal offsets.
• Maintain the ambient temperature between 18 °C and 28 °C.
• Keep relative humidity below 80%.
• Allow a warm-up time of at least 15 minutes for the SCXI-1121 to
ensure that the measurement circuitry is at a stable operating
temperature.
Table 1. Test Equipment
Equipment
Recommended
Model Requirements
Calibrator Fluke 5700A 50 ppm
DMM NI 4070 5 1/2-digit, 15 ppm
Resistors — 120 Ωand 800 Ω, ±10%

SCXI-1121 Calibration Procedure 4 ni.com
Calibration Process
The calibration process has the following steps:
1. Initial Setup—Configure the SCXI-1121 for calibration.
2. Verification Procedure—Verify the existing operation of the
SCXI-1121. This step determines whether the SCXI-1121 is operating
within its test limits.
3. Adjustment Procedure—Perform an external calibration that adjusts
the SCXI-1121 calibration constants with respect to a known voltage
source.
4. Verifying Adjusted Values—Perform another verification to ensure
that the SCXI-1121 is operating within its test limits after adjustments.
Initial Setup
Complete the following steps to configure the SCXI-1121 for calibration.
Refer to Figure 1 for steps 1 and 2 and Figure 2 for steps 3 and 4.
1. Remove the grounding screw from the SCXI-1121.
2. Remove the cover on the SCXI-1121 so that you have access to the
potentiometers.
Figure 1. Grounding Screw and Module Cover Removal
1 Grounding Screw 2 Module Cover
1
2

©National Instruments Corporation 5 SCXI-1121 Calibration Procedure
3. Remove the side plate of the SCXI chassis.
4. Install the SCXI-1121 into the right-most slot of the SCXI chassis.
Figure 2. Side Plate Removal and Module Installation
You do not need to cable the SCXI-1121 to a DAQ device. Leave the
configuration of the digital jumpers W32, W38, and W45 unchanged
because they do not affect this calibration procedure.
Configuring the Half-Bridge Completion Jumpers
Verify that the half-bridge completion network is disabled prior to
calibrating the SCXI-1121. Refer to Figure 3 for the location of the
half-bridge completion jumpers. Refer to Table 2 for the correct jumper
settings to disable the completion network.
1 Thumbscrews 2 Right-Most Slot 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
ISO122P
ISO122P
AD705
ISO122P
ISO122P
1
1
HCT08 HCT00 HC05
11
11 11
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1111
1
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B
A
LF347
GAINDIP
PRIMARY
PRIMARY
GAINDIP
RES
20K
RES
20K
RES
20K
DG409
34182
MC
34182
MC
34072
MC
GAINDIP
34072 MC
AD705
34072
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34072 MC
RES
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AD705
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BAABCDABCDEAB
AEDBADCABAB
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COPYRIGHT 1996
RES
20K
MC
34080
CD4047
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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
GAINDIP
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34072
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AD705
BAEDCBADCBA
R36
W39
W40
Q15
W46
R273
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8
7
10
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W40 W41
W42
W43
BAEDCBADCBABA
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R36
Q15
W46
R273
W48W47
W39
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 SCXI-1121 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 SCXI-1121, refer
to Table 3 for the gain jumper reference designators. Refer to Figure 3 for
the location of the gain jumpers. Move the jumper to the position indicated
in Table 4.
Table 2. Completion Network Jumpers
Channel Jumpers
Enable
Completion
Disable Network
(Factory Setting)
0W1 and W2
1W17 and
W18
l
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 ships in the 4 Hz position. Refer to Table 5 for the correct
jumper setting for the desired cutoff frequency. Refer to Figure 3 for the
locations of the jumper blocks on the SCXI-1121. Verify that both filter
stages are set to the same filter setting to ensure that you achieve the desired
bandwidth.
Table 3. Gain Jumper Reference Designators
Input Channel
Number
First-Stage
Gain Jumper
Second-Stage
Gain Jumper
0W3 W4
1W19 W20
2W29 W30
3W41 W42
Table 4. 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 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 6 to determine how to set up the
SCXI-1121 in the desired mode. The SCXI-1121 ships to you in the voltage
mode.
Table 5. 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 6. Voltage and Current Mode Excitation Jumper Settings
Excitation
Channel Jumpers
Volta g e M o de
(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 has two different current or
voltage levels. You can set a given channel to one of the following levels:
• In the current mode—0.150 mA or 0.450 mA
• In the voltage mode—3.333 V or 10 V
After selecting the excitation mode of the desired operation—voltage or
current, refer to Table 7 to set the SCXI-1121 for the level of operation. The
SCXI-1121 ships with the voltage mode set to 3.333 V.
Verification Procedure
The verification procedure determines how well the SCXI-1121 is meeting
its test limits. You can use this information to select the appropriate
calibration interval for your application.
Verifying Analog Input Offsets
Complete the following steps to verify the analog input offsets:
1. Refer to Table 12 in the Test Limits section for all acceptable settings
for the SCXI-1121. NI recommends verifying all ranges and gains, but
you can save time by checking only those ranges used in your
application.
Table 7. 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