Rockwell Automation 1762-IR4 RTD/Resistance Input Module - Manual (Page 64)

Publication 1762-UM003A-EN-P - February 2003
3-30 Module Data, Status, and Channel Configuration
Effects of Cyclic Lead Wire Compensation on Module Update
Time
The 1762-IR4 module provides the option to enable lead wire
compensation for each channel. This feature improves measurement
accuracy for 3- and 4-wire RTDs by compensating for the resistance of
the RTD lead wire. Lead wire compensation occurs automatically on a
mode change from Program-to-Run for all configured channels
regardless of the type of RTD being used. In addition, you can either
configure the module to perform a lead wire compensation cycle
every 5 minutes during normal operation or disable this feature using
the Enable/Disable Cyclic Lead Wire function (default: Enable). You
can also implement a lead wire compensation cycle anytime, using
your control program to enable and then disable this function.
If you enable the cyclic lead wire compensation function, the module
update time will increase when the lead wire compensation cycle
occurs. To limit its impact on module update time, the lead wire
compensation function is divided over 2 module scans. The amount of
time added for lead wire compensation per module scan depends on
the filter frequency (channel update time) selected for that channel.
The amount of time added to each module scan during a Lead
Compensation Cycle depends on the filter frequency selected for that
channel and can be found in Table 3.15 on page 3-27.