Rockwell Automation Publication 1756-UM540E-EN-P - December 2017 63
Temperature-sensing Analog Modules Chapter 4
1756-IRT8I Notch Filter Setting
The following tables lists the available Notch Filter settings for the 1756-IRT8I
module.
If your application requires a Notch Filter setting of 50 Hz, the module’s
minimum RPI rate is 20.7 ms. In this case, sampling speed is more important
than noise rejection. The module automatically uses a SINC^1 filter.
If your application requires a Notch Filter setting of 50 Hz and the greater level of
noise rejection provided by a SINC^3 filter, the minimum RPI rate is 62.1 ms.
The module automatically uses a SINC^3 filter.
The RPI must be > 1/Notch Filter plus some small scan time for the ADC to
sample properly. The SINC^3 filter takes three times as long and thus requires
RPI > 3/Notch plus some small scan time. The module rejects combinations
which violate that relationship.
To see where to set the Notch Filter, see page 132
.
Table 12 - 1756-IRT8I Notch Filter Settings
Notch Setting 5 Hz 10 Hz 15 Hz 20 Hz 50 Hz 60 Hz
(Default)
100 Hz 500 Hz 1000 Hz 5000 Hz
Minimum Sample Time
(RPI) - SINC^1 Filter
(1)
207.0 ms 103.5 ms 69.1 ms 51.8 ms 20.7 ms 17.3 ms 10.4 ms 2.1 ms 1.1 ms 1.0 ms
Minimum Sample Time
(RPI) - SINC^3 Filter
(1)
621.0 ms 310.5 ms 207.1 ms 153.4 ms 62.1 ms 51.9 ms 31.2 ms 6.1 ms 3.1 ms 1.0 ms
0…100% Step Response
Time
(2)(3)
600 ms +
1RPI
300 ms +
1RPI
200 ms +
1RPI
150 ms +
1RPI
60 ms +
1RPI
50 ms +
1RPI
30 ms +
1RPI
6 ms + 1 RPI 3 ms + 1RPI 1 ms + 1RPI
-3 dB Frequency
(2)
1.3 Hz 2.7 Hz 4.3 Hz 5.1 Hz 13 Hz 15 Hz 26 Hz 128 Hz 258 Hz 1296 Hz
Typical Effective
Resolution
(2)
(4)
19 bits 18 bits 18 bits 18 bits 17 bits 17 bits 17 bits 16 bits 15 bits 14 bits
(1) The minimum RPI value for the module depends on the channel with the lowest Notch Filter setting. For example, if three of the channels on a module use a Notch Filter setting of 20 Hz and one channel
uses a Notch Filter setting of 60 Hz, you cannot set the module RPI lower than 50.1 ms.
(2) Using the SINC^3 filter.
(3) Worst case settling time to 100% of step change includes 0…100% step response time plus one RPI sample time.
(4) Measured in ±100 mV range.
Table 13 - 1756-IRT8I Notch Filter Settings and the RPI Values
Notch Filter Fastest Available RPI Fastest RPI for a SINC^3 Filter
5 Hz 207.0 ms 621.0 ms
10 Hz 103.5 ms 310.5 ms
15 Hz 69.1 ms 207.1 ms
20 Hz 51.8 ms 153.4 ms
50 Hz 20.7 ms 62.1 ms
60 Hz (default) 17.3 ms 51.9 ms
100 Hz 10.4 ms 31.2 ms
500 Hz 2.1 ms 6.1 ms
1000 Hz 1.1 ms 3.1 ms
5000 Hz 1.0 ms 1.0 ms
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