PSL and PSH are often abbreviations for Pressure switch high or low. These are often simply on /off devices that are set or adjusted locally independently of the SCADA or PLC. Very often these are used as a back up or secondary control to an analogue device such as a pressure transducer. Usually the set points are established at a point outside the min/max working range and will therefore activate if the process overshoots the normal range or there is some type of failure.They should be set at a point that still protects the system from destruction but should not activate in the normal operational range controlled by the analogue device.
Regards
Ashtree
"Any water can be made potable if you filter it through enough money"
You should use other methods to protect the system from destruction. PSH and PSL sensors often do not function properly and are only suitable for process control of flow, tank levels, etc. Leave protection (esp. from overpressure) to other more assurable methods.
Richard Feynman's Problem Solving Algorithm
1. Write down the problem.
2. Think very hard.
3. Write down the answer.
I agree with those comments.
Its more typical to use such set ups in tanks etc as LSH/LSL but there probably are some pressure switches out there suitable for back up type applications.
The OP was requesting guidance on the establishment of setpoints more so than the hardware being used i guess.
Regards
Ashtree
"Any water can be made potable if you filter it through enough money"
Most projects / companies now have an alarm and trip philosophy which specifies or gives guidance on the margins required between alarms, trips and low and high control set points.
This varies between companies and project but is often a set percent (say 5%) or minimum value (say 2 bar), with the larger one being used.
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