Rockwell Automation 1769-IT6 Compact I/O 1769-IT6 Thermocouple/mV Input Module - Manual (Page 70)

70 Rockwell Automation Publication 1769-UM004B-EN-P - March 2010
Chapter 4 Module Data, Status, and Channel Configuration
The CJC input is sampled only if one or more channels are enabled for any
thermocouple type. The CJC update time is equal to the largest channel update
time of any of the enabled thermocouple inputs types. In that case, a single CJC
update is done per scan. See the scan diagram on the previous page. The cyclic
calibration time applies only when cyclic calibration is enabled and active. If
enabled, the cyclic calibration is staggered over several scan cycles once every five
minutes to limit the overall impact to module update time.
Effects of Autocalibration on Module Update Time
The module’s autocalibration feature allows it to correct for accuracy errors
caused by temperature drift over the module operating temperature range
(0…60 °C (32…140 °F)). Autocalibration occurs automatically on a system mode
change from Program-to-Run for all configured channels or if any online
(1)
configuration change is made to a channel. In addition, you can configure the
module to perform autocalibration every 5 minutes during normal operation, or
you can disable this feature by using the Enable/Disable Cyclic Calibration
function (default is enabled). This feature allows you to implement a calibration
cycle anytime, at your command, by enabling and then disabling this bit.
(1)
(1) Not all controllers allow online configuration changes. Refer to your controller’s user manual for details.
During an online configuration change, input data for the affected channel is not updated by the module.