Rockwell Automation 1746-INT4 Thermocouple/MV Isolated/ User Manual - Manual (Page 39)

Publication 1746-UM614B-EN-P - September 2007
Preliminary Operating Considerations 39
Cut-off Frequencies
The following table summarizes the input channel characteristics:
Effective Resolution of a Channel and Input Device
The effective resolution of an input channel depends upon the type of
input device connected to it.
For thermocouples, we define resolution as the smallest increment of
temperature that can be sampled after A/D conversion. It varies with
temperature and with the type of thermocouple.
We present a resolution graph for each type of thermocouple in
Appendix A, Module Specifications.
Millivolt devices are generally considered linear, and the effective
resolution is that of the channel itself.
00 db
-75db
-25db
-50db
-100db
1 100 10
6
6
6
50 5
80%
70%
60%
50%
40%
30%
20%
10%
0 240 180 60
100%
90%
120 300 360 420 480 540 600
Frequency — Hz
Attenuation % of Final Value
Frequency Response of the 8 Hz Filter Converter Step Response (worst case) for Filter, Multiplexer, and A/D
Time (ms)
Multiplex CJC Values
(200 ms) A/D Conversion
(200 ms)
Input Channel Characteristics
Corner
Frequency 50/60 Hz NMR Filter
Time Update
Time Step Response
(worst)
8 Hz 50 … 60 dB 180 ms 400 ms 600 ms
Millivolt Devices
Type of Device Resolution
Thermocouple 0.05…0.75 °C @ 300 °C
(32.1…33.4 °F @ 572 °F)
depending on the thermocouple
Millivolt Sensor 3.4 µV/bit