Input Image – Data Words And Status Words - Allen-Bradley B Series User Manual

Input Channel Characteristics
Allen-Bradley
Publication 1746-6.16 – January 1999
Input Image – Data Words and Status Words
Eight words of the SLC processor's input image table are reserved
for the module. Input image words 0-3 (data words) hold the the
temperature values of thermocouple analog inputs for channels 0-3.
The data is valid only when the channel is enabled, no errors are
detected, and not during calibration.
Input words 4-7 (status words) contain the status of channels 0-3.
Status bits for a particular channel reflect the configuration settings
that you entered into the configuration (output image) word for that
channel. To receive valid status, the channel must be enabled and
the module must have stored a valid configuration word for that
channel. During calibration, these words return calibration status.
Each input image word has a unique address based on the slot
number assigned to the module.
Example Address – To obtain the status of channel 2 (input word 6)
of the module located in slot 4 in the SLC chassis, use address I:4.6.
Slot
File Type
Word
I : 4 . 6
Word
Element
Delimiter
Delimiter
Chapter 6, Channel Configuration, Data, and Status, gives you
detailed bit information about the content of the data word and the
status word.
Each channel has an 8 Hz digital filter for input noise rejection, a
multiplexer for processing cold-junction-compensation (CJC) values,
and an analog-to- digital (A/D) converter to provide digital values for
SLC processing.
Channel Cut-off Frequency, Update Time, and Step Response
The channel cut-off frequency is defined as the point on the frequency
response curve where frequency components of the input signal are
passed with 3 dB of attenuation by the input filter. All frequency
components above cut-off frequency are increasingly attenuated, as
show in the graph (next page). Cut-off frequency is also defined as the
Normal Mode Rejection (NMR) in dB of attenuation at 50 Hz
(European) or at 60 Hz (American).
We define module update time as the time required for the module to
sample and convert channel input signals, multiplex them with the
CJC reference value, and make the resulting values available to the
SLC processor. It is typically 200 ms for multiplexing and 200 ms for
sampling and converting.
Chapter 4
Preliminary Operating Considerations
4–3