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Channel Filter Frequency
Selection
Input Image – Data Words and Status Words
The 8–word, RTD module input image (defined as the input from the RTD
module to the CPU) represents data words and status words.
Input words 0–3 (data words) hold the input data that represent the
temperature value of the RTD input or ohmic value of the resistance inputs
for channels 0–3. This data word is valid only when the channel is enabled
and there are no channel errors.
Input words 4–7 (status words) contain the status of channels 0–3
respectively. The status bits for a particular channel reflect the configuration
settings that you have entered into the output image configuration word for
that channel and provide information about the channel's operational state.
To receive valid status information, the channel must be enabled and the
channel must have processed any configuration changes that may have been
made to the configuration word.
Example – To obtain the status of channel 2 (input word 6) of the RTD
module located in slot 3 in the SLC chassis, use address I:3.6.
File Type
Element Delimiter
Chapter 5, Channel Configuration, Data, and Status, gives you detailed bit
information about the content of the data word and the status word.
The RTD module uses a digital filter that provides noise rejection for the
input signals. The digital filter is programmable, allowing you to select from
four filter frequencies for each channel. The digital filter provides the
highest noise rejection at the selected filter frequency.
Selecting a low value (for example, 10 Hz) for the channel filter frequency
provides greater noise rejection for a channel, but also increases the channel
update time. Selecting a high value for the channel filter frequency provides
lesser noise rejection, but decreases the channel update time.
Table 4.A on page 4–4 shows the available filter frequencies, as well as the
associated minimum normal mode rejection (NMR), cut–off frequency, and
step response for each filter frequency. The figures on pages 4–7 and 4–8
show the input channel frequency response for each filter frequency
selection.
Chapter 4
Preliminary Operating Considerations
Slot
Word
I : 3 . 6
Word Delimiter
4–3
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