Chapter 9 SCXI—Signal Conditioning

Note The SCXI-1125 does not have a user area in its EEPROM.

•The factory area has a set of factory calibration constants already stored in it when you receive your SCXI module. You cannot write into the factory area, but you can read from it, so you can always access and use these factory constants if they are appropriate for your application.

•The default load area is where LabVIEW automatically looks to load calibration constants the first time you access the module. When the module is shipped, the default load area contains a copy of the factory calibration constants.

Note You can overwrite the constants stored in the default load area of EEPROM with a new set of constants using the SCXI Cal Constants VI.

•The user area is an area for you to store your own calibration constants that you calculate using the SCXI Cal Constants VI. You also can put a copy of your own constants in the default load area if you want LabVIEW to automatically load your constants for subsequent operations. You can read and write to the user area.

Note Use the user area in EEPROM to store any calibration constants that you may need to use later. This prevents you from accidentally overwriting your constants in the default load area, because you will have two copies of your new constants. You can revert to the factory constants by copying the factory area to the default load area without wiping out your new constants entirely.

Calibrating SCXI Modules

The SCXI Cal Constants VI in LabVIEW automatically calculates the calibration constants for your module with the precision you need for your particular application. You can find this VI on the Functions»Data Acquisition»Calibration and Configuration palette.

For the SCXI-1112, SCXI-1125, and SCXI-1520 modules, you can use the SCXI Calibrate VI for easy one-point calibration (SCXI-1125) or two-point calibration (SCXI-1112) without the separate function calls necessary with the SCXI Cal Constants VI. Oneand two-point calibration are described in the SCXI Calibration Methods for Signal Acquisition section later in this chapter. You also can find the SCXI Calibrate VI on the

Functions»Data Acquisition»Calibration and Configuration palette.

Chapter 9 SCXI—Signal Conditioning

By default, calibration constants for the SCXI-1102, SCXI-1102B, SCXI-1102C, SCXI-1104, SCXI-1104C, SCXI-1112, SCXI-1122, SCXI-1125, SCXI-1141, SCXI-1142, SCXI-1143, and SCXI-1520 are loaded from the module EEPROM. The SCXI-1141, SCXI-1142, and SCXI-1143 have only gain adjust constants in the EEPROM. They do not have the binary zero offset. All other analog input modules do not have calibration constants by default and do not assume any binary offset and ideal gain settings. This means you must use one of the procedures described in the SCXI Calibration Methods for Signal Acquisition section to store calibration constants for your module if it is not an SCXI-1102, SCXI-1112, SCXI-1122, SCXI-1125, SCXI-1141, SCXI-1142, or SCXI-1143.

You can determine calibration constants based on your application setup, which includes your type of DAQ device, DAQ device settings, and cable assembly—combined with your SCXI module and its configuration settings.

Note If your SCXI module has independent gains on each channel, the calibration constants for each channel are stored at each gain setting.

SCXI Calibration Methods for Signal Acquisition

There are two ways you can calibrate your SCXI module—through one-point calibration or two-point calibration. Figure 9-15 illustrates why you may need to calibrate your SCXI module.