Difference Limit Switch - Siemens Simatic RTU303xC Series Operating Instructions Manual

Program blocks
5.7 Blocks for analog value functions
5.7.4

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.
The absolute value of the threshold value is calculated as follows:
● "Limit value" + "Amount of difference" ("function" = positive)
or
● "Limit value" - "Amount of difference" ("function" = negative)
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Operating Instructions, 06/2019, C79000-G8976-C382-06
RTU303xC