Rockwell Automation 1762-IT4 Thermocouple/mV Input Module - Manual (Page 30)

Publication 1762-UM002A-EN-P - July 2002
2-14 Installation and Wiring
Calibration The thermocouple module is initially calibrated at the factory. The
module also has an autocalibration function.
When an autocalibration cycle takes place, the module’s multiplexer is
set to system ground potential and an A/D reading is taken. The A/D
converter then sets its internal input to the module’s precision voltage
source, and another reading is taken. The A/D converter uses these
numbers to compensate for system offset (zero) and gain (span)
errors.
Autocalibration of a channel occurs whenever a channel is enabled.
You can also program your module to perform cyclic calibration
cycles, every five minutes. See Selecting Enable/Disable Cyclic
Calibration (Word 4, Bit 0) on page 3-14.
To maintain optimal system accuracy, periodically perform an
autocalibration cycle.
IMPORTANT
The module does not convert input data while the
calibration cycle is in progress following a change in
configuration. Module scan times are increased by up
to 112 ms during cyclic autocalibration.