Rockwell Automation 1769-IR6 Compact I/O 1769-IR6 RTD/Resistance Input Module - Manual (Page 73)

Rockwell Automation Publication 1769-UM005B-EN-P - March 2012 73
Module Data, Status, and Channel Configuration Chapter 4
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 lets it correct for accuracy errors caused
by component temperature drift over the module operating temperature range
(0…60 °C). Autocalibration occurs automatically on a system mode change
from Program-to-Run for all configured channels. It also occurs if any
online
(1)
configuration change is made to a channel. In addition, the module
lets you 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.
(1)
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 6-step cycle, unless any enabled
channel to be scanned (see Module Update Sequence on page 72) uses an
Input Type of the same Input Class (see Table 20 -) as any previously calibrated
channel. In that case, the calibration values from the previous channel are used,
and no additional calibration cycle time is required. The module current source
(0.5 mA and 1.0 mA) is also calibrated
(2)
during an autocalibration cycle to
ensure its accuracy. This uses a single module scan cycle for all enabled
channels. The following table defines these calibration steps, and the time
added to the normal module update time per step for each channel. The
calibration times are independent of the channel filter frequency selected.
EXAMPLE
1. Module Update Time with all channels enabled and
configured with 10Hz filter = 6 x 303 ms = 1818 ms
2. Module Update Time with all channels enabled and using
the 1 kHz filter = 6 x 6 ms = 36 ms
(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 that channel is not updated by the module.
(2) “Current source zero” and “current source gain” calibration times from Table 19 - are not needed if Class 3
input type is selected.