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We need to build or buy economical submersible pressure transducers
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viper:

--- Quote from: IanB on January 05, 2022, 10:57:46 pm ---It might be interesting to think about the physics of this.

A pressure transducer is going to measure the difference in pressure between the sensed pressure and a reference pressure, probably by deforming some kind of material and looking at its changing electrical properties.

If the sensor is in the open, then the reference pressure is easy, it can be atmospheric pressure.

If the sensor is submerged and down a hole, then what is the reference pressure? The sensor has to somehow be hermitically sealed, and presumably has to contain some kind of internal known pressure to compare against, which is stable over a long working life, and relatively insensitive to temperature and so on.

This might illustrate the difference in cost of such sensors. I wouldn't say you could just pot an open environment sensor, because you might stop it working if you did that.

--- End quote ---

You bring up a very good point sir!  I am not yet sure, and will now find out, how these 'gauge' sensors are referenced.  That could spoil a few things for us. 
Marco:

--- Quote from: IanB on January 05, 2022, 10:57:46 pm ---If the sensor is submerged and down a hole, then what is the reference pressure? The sensor has to somehow be hermitically sealed, and presumably has to contain some kind of internal known pressure to compare against, which is stable over a long working life, and relatively insensitive to temperature and so on.

--- End quote ---
Buy an absolute pressure sensor and let the manufacturer worry about it? Then you can just pot the electronics?
IanB:

--- Quote from: Marco on January 06, 2022, 12:37:27 am ---Buy an absolute pressure sensor and let the manufacturer worry about it? Then you can just pot the electronics?

--- End quote ---

Well, sure. But I think the question was about why do pressure transducers suddenly get vastly more expensive when you give this requirement? If there is an inexpensive absolute pressure sensor that satisfies the environmental requirements, then that is presumably what the OP is looking for.
viper:
bam!  I am on the trail!  It seems there is competition in the type of sensor pictured above. Have now found an affordable one with pigtails, which is perfect for us.  They are absolute sensing, and I now need to figure out how I can get them in for testing.  The one vendor is showing end of the month delivery.  Surely someone in the states has these.....  I'd like to be a "buy American" fanboy, but we all know none of this is made here, just marked up to line pockets here. 

SmallCog:

--- Quote from: Gregg on January 05, 2022, 11:32:16 pm ---If you are going to have wires exiting the pressure vessel, why not use a thin tube with some sort of bladder or bellows on the end?  It shouldn’t be too hard to attach an external pressure sensor, fill the system with a compatible liquid and have atmospheric pressure as the reference pressure.

--- End quote ---

I’ve actually got an off cut of that sort of cable on my bench!



Also has Kevlar in it for weight bearing
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