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Programming
5.7 Blocks for analog value functions
Parameters
Output parameters
Output
Error
5.7.3
Difference limit switch
Function
An analog input is monitored for two values and a digital output signal is set that depends on
the function of the block.
Functions of the block:
● Limit value with hysteresis
● Window (range monitoring)
The function results from the position of the threshold value decided by the programming of
the "Function" parameter.
The functions of this block correspond to those of the block "Limit value switch". With
Difference limit switch the position of the monitored values relative to each other is specified,
while with Limit value switch the position is absolute.
Calculation of the threshold value
The threshold value is calculated with the three function parameters:
● "Limit value"
– Is the first of the values of the input signal to be monitored.
– Is the basis for calculating the threshold value.
● "Function"
Decides the position of the threshold value compared with the limit value:
– Positive: Threshold value > Limit value
– Negative: Threshold value < Limit value
The position of the threshold value decides the function of the block, see below.
● "Amount of difference"
Decides the amount of the threshold value compared with the limit value.
222
Tag type / range of
Description
values
Digital output / bit
Tag in which the value calculated by the block is output.
memory
Digital output / bit
Error display:
memory
•
•
For the meaning, see Often used parameters
(Page 198).
0: Block processing completed without errors
1: Block processing aborted with an error
Operating Instructions, 09/2017, C79000-G8976-C382-04
RTU3030C
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