2/18/2023 0 Comments On off switch symbolIn that case, I'd use the LSL for the low level switch and the LSH for the first high level switch, with both lines from each bubble feeding into a diamond with an I (for interlock) in it, and the output of the diamond feeding to the pump. If you want to use letter suffixes, you could use LSL-01A, LSH-01A, LSHH-01A, and LSHH-01B to tag your devices. In the 2009 version of ISA 5.1, there is no example to show differential pump control. The older version of the standard says you should use no more than four letters for the description in the tag, but doesn't say you can't use more. That leaves you free to use LSH and LSHH for the other two switches. This is how differential control of a pump is shown as an example in the superseded version of ISA 5.1 (1984-R1992). You can use an LC with a line labeled START for the low level switch, another LC with a line labeled STOP for the first high level switch, with both lines feeding into a diamond with an I (for interlock) in it, and the output of the diamond feeding to the pump. "As iron sharpens iron, so one person sharpens another." RE: Pump ON/OFF Control P&ID symbols jkate (Mechanical) I no longer have access to our control elementary diagrams, and can't confirm what we do in fact use, but since Start and Stop both begin with the same letters, and a hand-written S can be misinterpreted as the number 5, and since On and Off both begin with the letter O, easily misread as the numeral zero, LSN and LSF could be used as Level Switch ON and Level Switch OFF.but this is only a suggestion if there's a prevailing standard out there that addresses all of this, I'd certainly like to know what it is. For instance: since the first letters of In and Out can easily be confused with the numbers 1 and 0, we instead use their last letters, such in the case of power flows from a generator where the real power output is denoted, by way of example, as 250 MW T and 20 MX N. The approach we use in such situations is to choose words that have different last letters, and use the last letter of those words. My company generally takes the view that it would be confusing to have a switch labelled as LSHH - meaning with two aitches - deliver a 'high level' alarm with only one aitch similarly a three-aitch device delivering a two-aitch alarm.which seems to agree with your manager's viewpoint. Within my discipline an LSH typically delivers a 'high level' alarm of some description, and an LSHH delivers a 'high high level' alarm similarly for LSLs and LSLLs. I'm not a controls engineer either, and I have no intimate knowledge of P&IDs.but I still hope to contribute something of value notwithstanding.
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