# Pressure Transmitter Failures



## ScooterMcGavin (Jan 24, 2011)

All of our 4-20 loops are fused to blow at 80ma. Our newer Rosemount transmitters have a varisistor which goes to ground at 80V. We recently got 120VAC into our loop power supply. It melted all the resistors and blew the fuses, but all of the transmitters survived the incident. I have never heard of a sumpmersible transmitter. What application is it being used in?


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## Jlarson (Jun 28, 2009)

I don't see too many failures. Most submersibles seem to be pretty resilient little buggers. 

What brand?


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## Big John (May 23, 2010)

These are Mercoid SBLT2, 5 and 10PSI. It's odd because most of our transmitters have been in reliable service for a million years.

I know in at least one case it wasn't grounded and I have my suspicions about the other two. Has anyone seen these operate long-term without surge suppression?

-John


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## Jlarson (Jun 28, 2009)

The T2's have built in protection, was the shield not grounded?

I've seen some improperly protected ones do ok, some don't last long, luck of the draw I guess.


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## Big John (May 23, 2010)

Jlarson said:


> The T2's have built in protection, was the shield not grounded?


 On one I found I know it wasn't. The other two cases I don't know for sure because I didn't disconnect 'em.

I might be looking at the wrong root cause, but I can't think of anything else that might kill them. Reverse voltage shouldn't do it. Low voltage shouldn't have any affect. And they're just in river water.

-John


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## Jlarson (Jun 28, 2009)

Surges, mostly lightning seems to be the popular reason for them failing. I guess the piezoelectric sensor in them doesn't like lightning.


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## tommu56 (Nov 19, 2010)

We have trouble at our WWTP with transmitters i think it has to do with the lightning and the 69,000 v wires almost over head and the steel tanks in the ground.

I eliminated most of the problems by putting phoenix 4-20 ma isolators on the lines these are end up in SLC 504's analog input card.

tom


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## erics37 (May 7, 2009)

I've had one I've replaced a couple times at a clean water storage tank on top of a hill out in BFE. There's no electrical service up there. They've got only the pressure transducer and they're leasing a phone line to transmit the signal like 2 miles away to the pump station :blink:

It gets nailed by lightning a lot.

Had another one fail at a wastewater lift station a couple months ago. It started fritzing out and giving random weird level readings (so sometimes the PLC was telling the pumps to suck the well almost dry; other times it was almost overflowing). The city guys pulled it up and cleaned all the grease and tampons and crap off of it, dropped it back in, and then it just wouldn't read anything.

That's when they called us in a panic because they have NO BACKUP system whatsoever and NO REPLACEMENT transmitters at their shop and they had to have a rotating shift of dudes standing around all day manually pumping the level down while I rigged up a ghetto float backup system (just high and low) to the VFD jog contact.

I don't know what made that one fail though. Utility power is usually pretty stable out there.


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## Jlarson (Jun 28, 2009)

erics37 said:


> I've had one I've replaced a couple times at a clean water storage tank on top of a hill out in BFE. There's no electrical service up there. They've got only the pressure transducer and they're leasing a phone line to transmit the signal like 2 miles away to the pump station :blink:


I hate that. Those leased lines are surge magnets, I try to sell a solar powered RTU with a radio, usually using the lack of a phone bill and not having to deal with the phone company as big selling points.


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## erics37 (May 7, 2009)

Jlarson said:


> I hate that. Those leased lines are surge magnets, I try to sell a solar powered RTU with a radio, usually using the lack of a phone bill and not having to deal with the phone company as big selling points.


That's a great idea, but this tank is surrounded by 100+ year-old second growth Doug Fir forest. It gets about 10 minutes of sun a day :laughing:


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## Jlarson (Jun 28, 2009)

erics37 said:


> That's a great idea, but this tank is surrounded by 100+ year-old second growth Doug Fir forest. It gets about 10 minutes of sun a day :laughing:


Yeah I have that problem with our northern clients. Real pain, I usually end up with a pressure switch at the bottom of the fill line then use math to figure the fill height, obviously when I get a top fill tank its a real pain to retrofit.


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