National Instruments SCXI-1121 Calibration Procedure
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National Instruments SCXI-1121 Calibration Procedure

National Instruments SCXI-1121 Calibration Procedure

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CALIBRATION PROCEDURE
™
SCXI -1121
Introduction
What Is Calibration?
Why Should You Calibrate?
How Often Should You Calibrate?
™
™
National Instruments
, ni.com
herein are trademarks or trade names of their respective companies.
370258A-01
This document contains information and step-by-step instructions for
verifying and calibrating the National Instruments SCXI-1121 signal
conditioning module.
Calibration is a procedure of reading offset and gain errors from a device
and updating special analog calibration circuitry that corrects these errors.
During the factory calibration process, the calibration constants are stored
in the non-volatile memory of the device. These values are loaded from
memory and used as needed by the device. SCXI-1121 modules have two
potentiometers per channel for amplifier offset nulling. One potentiometer
nulls the input offset, the other nulls the output offset. During calibration,
you adjust these onboard calibration potentiometers with respect to
external standards.
Offset and gain errors drift with time and temperature, which could
invalidate the factory-set calibration of a device. Calibration restores the
device to its specified accuracy.
The measurement accuracy requirements of your application
determine how often you should calibrate your SCXI-1121 module.
National Instruments 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.
™
™
, NI-DAQ
, and SCXI
are trademarks of National Instruments Corporation. Product and company names mentioned
© Copyright 2000 National Instruments Corp. All rights reserved.
July 2000

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Summary of Contents for National Instruments SCXI-1121

  • Page 1 During the factory calibration process, the calibration constants are stored in the non-volatile memory of the device. These values are loaded from memory and used as needed by the device. SCXI-1121 modules have two potentiometers per channel for amplifier offset nulling. One potentiometer nulls the input offset, the other nulls the output offset.

  • Page 2: Equipment And Other Test Requirements

    If you do not have custom connection hardware, you need a connector block such as Note the National Instruments SCXI-1320, a shielded 68-pin connector cable, a 50-pin ribbon cable, a 50-pin breakout box, and an SCXI adapter. These components give easy access to the individual pins on the SCXI-1121 front and rear connectors.
  • Page 3 Install the module into slot 1of a properly functioning SCXI chassis. Remove the side plate of the SCXI chassis and the cover on the module to access the potentiometers. The SCXI-1121 does not need to be connected to a data acquisition device during this procedure. Refer to...
  • Page 4 Table 3. Filter Jumper Allocation First Filter Jumper Second Filter Jumper Input 4 Hz 4 Hz Channel (Factory (Factory Number Setting) 4 kHz Setting) 4 kHz W5-A W5-B W21-A W21-B W31-A W31-B W43-A W43-B SCXI-1121 Calibration Procedure ni.com...
  • Page 5 Table 4. Voltage and Current Mode Excitation Jumper Setup Excitation Voltage Mode Channel Jumpers (Factory Setting) Current Mode W14 and W15 W22 and W23 W34 and W35 W46 and W47 © National Instruments Corporation SCXI-1121 Calibration Procedure...
  • Page 6 The verification procedure determines how well the SCXI-1121 module is meeting its specifications. You can use this information to select the appropriate calibration interval for your application. Refer to Table 8, Table 9, and Table 10 for the test specifications of the SCXI-1121. SCXI-1121 Calibration Procedure ni.com...
  • Page 7 Repeat steps 5 through 8 for the remaining analog input channels. 10. Repeat steps 3 through 9 for the remaining gain and filter values specified in the appropriate table. You have completed verifying the analog input offsets of your SCXI-1121. © National Instruments Corporation SCXI-1121 Calibration Procedure...
  • Page 8 800 Ω resistor, and repeat steps 3 and 4. Repeat steps 2 through 5 for all remaining channels. You have completed verifying the analog input offsets of your SCXI-1121. If any of your measurements fall outside the specifications listed in Table 9,...
  • Page 9 DMM is 0.0 ±6 mV. Refer to Table 6 for potentiometer locations and functions. Repeat steps 1 through 7 for the remaining analog inputs. You have finished adjusting the analog input offsets of your SCXI-1121. © National Instruments Corporation SCXI-1121 Calibration Procedure...
  • Page 10 Adjust the excitation voltage potentiometer until the voltage reading falls between 10.040 V and 9.960 V. Repeat steps 1 through 7 for all remaining channels. You have now completed adjusting the voltage excitation channels of your SCXI-1121 module. SCXI-1121 Calibration Procedure ni.com...
  • Page 11 Verifying the Operation of Your Module. Verifying the adjusted values ensures that your SCXI-1121 module is now operating within its specifications. © National Instruments Corporation...

  • Page 12: Front And Rear Panel Diagrams

    Front and Rear Panel Diagrams Figure 1 shows the pin assignments for the SCXI-1121 module front panel connector. Figure 2 shows the pin assignments for the SCXI-1121 rear panel connector Signal Column Signal Number Name Name CH0– CGND CH0+ CH1–...
  • Page 13 SLOT0SEL* 31 32 33 34 DIG GND 35 36 SCANCLK 37 38 SERCLK 39 40 41 42 43 44 RSVD 45 46 47 48 49 50 Figure 2. SCXI-1121 Rear Connector Pin Assignments © National Instruments Corporation SCXI-1121 Calibration Procedure...

  • Page 14: Specifications

    Specifications The following tables contain test specifications for the SCXI-1121 signal conditioning module. If the device has been calibrated within the last year, the Test Point value should fall between the Upper Limit and Lower Limit values. Table 8. SCXI-1121 Specifications...
  • Page 15 Table 8. SCXI-1121 Specifications 4 Hz 10 kHz Gain Test Point (V) Upper Limit (V) Lower Limit (V) Upper Limit (V) Lower Limit (V) 2.250000 4.534803 4.465197 4.534834 4.465166 0.000000 0.005652 –0.005652 0.005683 –0.005683 –2.250000 –4.465197 –4.534803 –4.465166 –4.534834 0.900000 4.535454...
  • Page 16 4.052257 0.000000 0.418052 –0.418052 0.418592 –0.418592 –0.002250 –4.052797 –4.947203 –4.052257 –4.947743 Figure 3. SCXI-1121 Voltage Excitation Limits Test Point (V) Upper Limit (V) Lower Limit (V) 3.333 3.334333 3.331667 10.040000 9.960000 Table 9. SCXI-1121 Current Excitation Limits Test Point (mA)

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