Rockwell Automation Publication 1769-UM021G-EN-P - October 2015 199
Use I/O Modules with CompactLogix 5370 L2 Controllers Chapter 8
Channel Input Type and Filter Frequency Selection Update Time
When you enable an embedded analog input channel, you must select an input
type and a filter frequency for that input. The selections that are made determine
the value that is required when calculating channel update time.
Tab le 12
shows the channel update times for each channel input type and filter
frequency selection.
Cold Junction Compensation Update Times
When you use any of the thermocouple input types on your embedded analog
input, you must account for more voltage at the junction of the thermocouple
field wires and the input point. More voltage can alter the input signal on that
point and, therefore, affect the update time of that channel.
The process to account for increased voltage at an input point by using a
thermocouple type input is cold junction compensation (CJC). You enable CJC
for a given channel on the Input Configuration tab of the Module Configuration
dialog box, as shown in the following graphic.
Each channel input type has multiple ranges or types. For example, a voltage
input type can use one of six voltage ranges, as listed in Table 10 on page 187
.
Regardless of which voltage range the channel uses, the channel update time
remains the same. For more information, see Table 12
.
Table 12 - Channel Update Times
Filter Frequency
Selection
(1)
(1) Filter frequency selections are made on the Input Configuration tab of the Module Properties dialog box.
Channel Update Times Based on Input Type Selection
Voltage, Current or
Thermocouple Input Type
Resistance or RTD Input
Type
10 Hz 307 ms 614 ms
50 Hz 67 ms 134 ms
60 Hz 57 ms 114 ms
250 Hz 19 ms 38 ms
500 Hz 13 ms 26 ms
1 kHz 11 ms 22 ms
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