Dr. P.
The last one I installed used one of these for air velocity measurements: https://www.dwyer-inst.com/Product/AirQuality/AirVelocityTransmitter/Series641#specs the shutdown was part of a PLC based system, The deal is, you have to be able to see the display when cleaning/commissioning/installing, so the local readout makes a LOT of sense. The model this one replaced was much larger and didn't average. These are pretty nice.
They also had a DIN readout/power supply/alarm unit. As I said, you have to pull out, clean the dust and re-install/reposition. Our frequency was like every 4-6 months.
Fire alarm testing generally caused the cleaning to occur. these systems used Hydride gases like Silane, Diborane, Arsine, phosphine etc. Definitely, not good stuff. the stupid one was for a Hydrogen Selenide reactor. If everything worked, the effluent should have been scrubbed. Those labs had 100% make-up air.
The other ones used were a Dwyer Magneheilic differential pressure gauge (inches of water) with a pointer. I'm not sure exactly how it was plumbed. e.g. https://www.dwyer-inst.com/Product/Pressure/DifferentialPressure/Gages/Series2000-SP There's a whole bunch of other choices: https://www.dwyer-inst.com/Products/CatalogSearch.cfm the most nasty stuff was Bromine Methanol and some cyanide compounds. Most hoods were equipped with an acid neutralizer and the nasty-est was concentrated Hydrofluoric Acid. Only one hood was designated for use with HF and it wasn't a daily thing. When I was working with HF, safety was a bit more lax and I may have used the stuff once every two weeks or so. That's a training video you really need to see. Very nasty stuff. I have some stuff at home that contains about 1% HF and 1% Hydrochloric.
In some cases, you may need to use a room differential pressure sensor.
FWIW: Dwyer also makes some differential pressure switches that seem to be pretty reliable. One was used in a 1000 W tube RF transmitter. Replaced it once in maybe 30+ years.
Never sent any of Dwyer's stuff back for repair except the 30 YO broken sensor.
FWIW: These **broken link removed** are very nice flow switches. We only used it on a Scanning Electron Microscope. the cost is pretty high. GemsSensors makes some inexpensive water flow switches. In one case, we just used a visual rotary water flow sensor. Our water had a lot of iron in it. The lab should have had a central chiller for 50 deg F water. One was actually engineered and shown to have a decent payback, but not directly. We had no incentive to reduce our water use and it was a lot just for cooling,
The last one I installed used one of these for air velocity measurements: https://www.dwyer-inst.com/Product/AirQuality/AirVelocityTransmitter/Series641#specs the shutdown was part of a PLC based system, The deal is, you have to be able to see the display when cleaning/commissioning/installing, so the local readout makes a LOT of sense. The model this one replaced was much larger and didn't average. These are pretty nice.
They also had a DIN readout/power supply/alarm unit. As I said, you have to pull out, clean the dust and re-install/reposition. Our frequency was like every 4-6 months.
Fire alarm testing generally caused the cleaning to occur. these systems used Hydride gases like Silane, Diborane, Arsine, phosphine etc. Definitely, not good stuff. the stupid one was for a Hydrogen Selenide reactor. If everything worked, the effluent should have been scrubbed. Those labs had 100% make-up air.
The other ones used were a Dwyer Magneheilic differential pressure gauge (inches of water) with a pointer. I'm not sure exactly how it was plumbed. e.g. https://www.dwyer-inst.com/Product/Pressure/DifferentialPressure/Gages/Series2000-SP There's a whole bunch of other choices: https://www.dwyer-inst.com/Products/CatalogSearch.cfm the most nasty stuff was Bromine Methanol and some cyanide compounds. Most hoods were equipped with an acid neutralizer and the nasty-est was concentrated Hydrofluoric Acid. Only one hood was designated for use with HF and it wasn't a daily thing. When I was working with HF, safety was a bit more lax and I may have used the stuff once every two weeks or so. That's a training video you really need to see. Very nasty stuff. I have some stuff at home that contains about 1% HF and 1% Hydrochloric.
In some cases, you may need to use a room differential pressure sensor.
FWIW: Dwyer also makes some differential pressure switches that seem to be pretty reliable. One was used in a 1000 W tube RF transmitter. Replaced it once in maybe 30+ years.
Never sent any of Dwyer's stuff back for repair except the 30 YO broken sensor.
FWIW: These **broken link removed** are very nice flow switches. We only used it on a Scanning Electron Microscope. the cost is pretty high. GemsSensors makes some inexpensive water flow switches. In one case, we just used a visual rotary water flow sensor. Our water had a lot of iron in it. The lab should have had a central chiller for 50 deg F water. One was actually engineered and shown to have a decent payback, but not directly. We had no incentive to reduce our water use and it was a lot just for cooling,