Rockwell Automation 1762-IR4 RTD/Resistance Input Module - Manual (Page 62)

Publication 1762-UM003A-EN-P - February 2003
3-28 Module Data, Status, and Channel Configuration
Module update time can be calculated by obtaining the sum of all
enabled channel update times. Channel update times include channel
scan time, channel switching time, and reconfiguration time.
Effects of Autocalibration on Module Update Time
The module’s autocalibration feature allows it to correct for accuracy
errors caused by component temperature drift over the module
operating temperature range (0 to 55°C). Autocalibration occurs
automatically on a system mode change from Program-to-Run for all
configured channels. In addition, the module allows you to configure
it to perform an autocalibration cycle every 5 minutes during normal
operation or to disable this feature using the Enable/Disable Cyclic
Calibration function (default: Enable). With this feature, you can
implement a calibration cycle anytime, using your control program to
enable and then disable this bit.
If you enable the autocalibration function, the module update time
increases when the autocalibration cycle occurs. To limit its impact on
module update time, the autocalibration function is divided over
several module scans.
Each enabled channel requires a separate 4-step cycle. If cyclic lead
compensation is disabled, each enabled channel requires only a
separate 3-step autocalibration cycle. The time added to the module
update time depends on the filter selected for that channel as shown
in Table 3.16 below.
EXAMPLE
1. Module Update Time with all channels enabled
and configured with 10 Hz filter = 4 x 303 ms =
1212 ms
2. Module Update Time with all channels enabled
and using the 1 kHz filter = 4 x 6 ms = 24 ms
Table 3.16 Calibration Times by Input Filter Selection
10 Hz 50 Hz 60 Hz 250 Hz 500 Hz 1 KHz
RTD ADC Self-calibration 603 ms 123 ms 103 ms 27 ms 15 ms 9 ms
Current ADC Self-calibration 603 ms 123 ms 103 ms 27 ms 15 ms 9 ms
Current Source Calibration 303 ms 63 ms 53 ms 15 ms 9 ms 6 ms
Lead Wire ADC
Self-calibration (if cyclic lead
compensation enabled) 630 ms 150 ms 130 ms 42 ms 30 ms 24 ms