Special Operating Mode "Comparator"; Definition Of A Comparator; Two Comparators - Siemens SIMATIC S7-300 Manual

5.2

Special operating mode "Comparator"

Introduction
In certain scenarios it may be necessary to read an analog value more than once to allow for
high-speed response to a specific limit situation. The speed of standard procedure of control
systems is unsatisfactory, i.e. the time it takes to read the signal, processing it in the CPU
and to output the response is too long. SM 335 provides a special operating mode that
resolves this problem, namely the special operating mode "Comparator".

Definition of a comparator

Comparator compares values. That is, it compares the measured analog values with the
default analog value (reference value). The comparator triggers a specific reaction if the
measured analog value reaches the reference value.
You can define a reference value for each one of the two comparators.

Two comparators

In the special operating mode "Comparator" you can use two comparators which have
different properties.
Comparator
1
2
For more information about the parameterization for the "Comparator" mode, refer to chapter
SM 335 parameters for the special mode "Comparator" (Page 53).
SM 335 - High-speed analog mixed module for SIMATIC S7-300
Manual, 02/2009, A5E02409063-01
Measures End of cycle
interrupts
Analog input are
generated
Comparator 1
continuously
Analog input are
Comparator 2 suppressed
Special operating modes of SM 335
5.2 Special operating mode "Comparator"
On reaching the reference value
the SM 335 outputs the default analog values
•
to three analog outputs
generates a hardware interrupt
•
SM 335 switches to the "conditional cycle" or
•
"free cycle" mode
or
changes over to comparator 2
•
the SM 335 outputs the default analog values
•
to three analog outputs
generates a hardware interrupt
•
writes the number of suppressed end of cycle
•
interrupts
returns to the "conditional cycle" or "free cycle"
•
mode
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