Instrument interlock setpoint issue
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This post was last edited by Really on 2021-1-8 08:40. Is it reasonable to set the instrument interlock value at the upper limit of the range? Why? Are there any relevant specifications? A reward will be given to those who give good answers.
Firstly, it’s certainly unreasonable. Secondly, the interlock values need to be specified by the process team; the instrumentation should not create problems on its own and take responsibility for that
When selecting the gauge range, it should be around 120% of the possible maximum value. The alarm values and interlock values should be included within this range. Therefore, it is clearly unreasonable to set the upper range limit at the interlock value.
Generally, interlock actions occur at around 95% of the process parameters (such as liquid level)
The delay in sequential execution time needs to be considered. Therefore, a margin needs to be set when determining the chain value.
Are there any corresponding specifications or standards?
Is there a standard upon which this 95% figure is based?
It is related to the specific processes and actuators. The liquid level rises quickly, so there is a bit more headroom.
This situation also needs to be regulated; it makes no sense at all. With interlocking at the maximum value, the actual value during interlocking becomes uncertain, as it’s possible to exceed the range. If your process says that this value isn’t important, then let them decide.