Rockwell Automation 1769-IR6 Compact I/O 1769-IR6 RTD/Resistance Input Module User Manual
Page 77
Rockwell Automation Publication 1769-UM005B-EN-P - March 2012
77
Module Data, Status, and Channel Configuration Chapter 4
Calculating Module Update Time with Cyclic Lead Wire
Compensation Enabled
The following example illustrates how to determine module update time with
cyclic lead wire compensation enabled.
EXAMPLE
Two Channels Configured with Cyclic Lead Wire Compensation Enabled
Channel 0 Input: 100
Ω Platinum 385 with 60 Hz filter (use 60 Hz filter for lead wire)
Channel 1 Input: 100
Ω Platinum 385 with 250 Hz filter (use 250 Hz filter for lead wire)
From Table 18, Channel Update Time versus Filter Frequency, on page 4-72:
1. Calculate Module Update Time without a Lead Wire Compensation Cycle
= Ch 0 Update Time + Ch 1 Update Time = 53 ms + 15 ms = 68 ms
2. Calculate Module Update Time during a Lead Wire Compensation Cycle
Channel 0 Scan 1 (Module Scan 1)
Ch 0 Update Time + Ch 0 Lead Wire Compensation Time + Ch 1 Update Time
= 53 ms + 53 ms + 15 ms = 121 ms
The above module update time impact lasts for two more module scans, before the lead-wire compensation
cycle is complete for Channel 0:
Channel 0 Lead Wire Compensation Cycle Time
= (3 x 121 ms) = 363 ms.
After that, a 3-scan lead wire cycle begins for Channel 1:
Channel 1 Scan 1 (Module Scan 4)
= Ch 0 Update Time + Ch 1 Update Time + Ch 1 Lead Wire Compensation Time
= 53 ms + 15 ms + 15 ms = 83 ms
The above module update time impact lasts for two more module scans, before the lead-wire compensation
cycle is complete for Channel 1:
Channel 1 Lead Wire Compensation Cycle Time
= (3 x 83 ms) = 249 ms.
3. Calculate Total Time to Complete Lead Wire Compensation Cycle
= (Ch 0 Lead Wire Compensation Cycle Time) + (Ch 1 Lead Wire Compensation Cycle Time)
= (363 ms) + (249 ms)
= 612 ms = 0.612 seconds
After the above cycles are complete, the module returns to scans without lead wire compensation for
approximately 5 minutes. At that time, the lead wire compensation cycle repeats.
If both cyclic autocalibration (see page 4-73) and lead wire compensation are enabled, the two functions run
concurrent to one another.