Rockwell Automation 1769-IT6 Compact I/O 1769-IT6 Thermocouple/mV Input Module - Manual (Page 71)

Rockwell Automation Publication 1769-UM004B-EN-P - March 2010 71
Module Data, Status, and Channel Configuration Chapter 4
If you enable the cyclic autocalibration function, the module update time
increases when the autocalibration occurs. To limit its impact on the module
update time, the autocalibration function is divided over two module scans. The
first part (offset/0) of a channel calibration adds 71 ms and the second part
(gain/span) adds 112 ms to the module update. This takes place over two
consecutive module scans. Each enabled channel requires a separate offset/0 and
gain/span cycle, unless any channel to be scanned uses an Input Type of the same
Input Class as any previously calibrated channel. See the figure on
page 69 and
the Input Class table below. In that case, offset and gain calibration values from
the previous channel are used, and no additional time is required.
Calculating Module Update Time
To determine the module update time, add the individual channel update times
for each enabled channel and the CJC update time if any of the channels are
enabled as thermocouple inputs.
Table 8 - Input Class
Input Type Input Class
Thermocouples B, C, R, S, and T 1
Thermocouples E, J, K, and N 2
50 mV 2
100 mV 3
CJC Sensors 4
EXAMPLE 1. Two Channels Enabled for Millivolt Inputs
Channel 0: ±50 mV with 60 Hz filter
Channel 1 Input: ±50 mV with 500 Hz filter
From Channel Update Time, on
page 42 .
Module Update Time
= Ch 0 Update Time + Ch 1 Update Time
= 53 ms + 9 ms
= 62 ms
EXAMPLE 2. Three Channels Enabled for Different Inputs
Channel 0 Input: Type J Thermocouple with 10 Hz filter
Channel 1 Input: Type J Thermocouple with 60 Hz filter
Channel 2 Input: ±100 mV with 250 Hz filter
From Channel Update Time, on
page 42 .
Module Update Time
= Ch 0 Update Time + Ch 1 Update Time
+ Ch 2 Update Time + CJC Update Time (uses lowest
thermocouple filter selected)
= 303 ms + 53 ms + 15 ms + 303 ms
= 674 ms