Overview Measured value monitoring

This block monitors a measured value against up to four limits: a warning and an alarm limit each for the lower and the upper direction. Every limit is activated separately. Hysteresis, delay and acknowledgement avoid false messages caused by short outliers.

Distinction: the block Limit switch switches immediately according to two limit values. This block adds warning and alarm levels, delay and acknowledgement.


Inputs

WT Value Measured value to be monitored.
FR Enable 0 switches the monitoring off, all outputs become 0. If the input is not assigned, monitoring is enabled. “Generate variables” deliberately does not create an address for this input, because a new address starts at 0 and would therefore block the monitoring.
QU Acknowledge A rising edge clears a latched state. Only effective if “Acknowledgement required” is active.



Outputs
UG Lower limit Becomes 1 if a lower limit (warning or alarm) is reached.
OG Upper limit Becomes 1 if an upper limit (warning or alarm) is reached.
AL Alarm Becomes 1 if an alarm limit is reached.
ST State
  • 0 = in order
  • 1 = warning low
  • 2 = alarm low
  • 3 = warning high
  • 4 = alarm high



Parameters
Use lower warning limit Switches the lower warning limit on. If it is switched off it is not evaluated.
Lower warning limit The state becomes warning low as soon as the value reaches or falls below this limit.
Use lower alarm limit Switches the lower alarm limit on.
Lower alarm limit The state becomes alarm low as soon as the value reaches or falls below this limit.
Use upper warning limit Switches the upper warning limit on.
Upper warning limit The state becomes warning high as soon as the value reaches or exceeds this limit.
Use upper alarm limit Switches the upper alarm limit on.
Upper alarm limit The state becomes alarm high as soon as the value reaches or exceeds this limit.
Hysteresis A detected state is only left when the value has returned into the permissible range by this amount. This prevents the outputs from chattering right at the limit.
Delay fault on (s) Time in seconds that a limit violation has to be present continuously before it is reported.
Delay fault off (s) Time in seconds that the value has to be in order again before the message is withdrawn.
Acknowledgement required The reported state remains even after the value is in order again, until it is acknowledged via input QU.

See also: Limit switch, Change per time, Measured value plausibility

See also common parameters of all function blocks.