Pressure Transducer and connections to BS?
Genesis
Posts: 42
Hi folks;
Been browsing around the net and various search engines looking for a 0-200 psia precision (0.25%) pressure transducer.· Has to be able to handle potentially-condensing atmospheres (breathable), and under "ugly" conditions (faults) might be exposed to sea or freshwater (surviving that if it happens is a plus!)
Application is a pressure transducer for a hyperbaric environment being monitored by a stamp....
I'm having trouble finding something that isn't (1) huge in physical size and (2) outrageously expensive (found one suitable unit but it was $500 Q1!· Yikes!)
Anyway, if anyone has had use for such a device and has any pointers, that would be great.·Sensors that can be excited with +5VDC are the best option since that happens to be running around [noparse]:)[/noparse]
Thanks in advance.....
Been browsing around the net and various search engines looking for a 0-200 psia precision (0.25%) pressure transducer.· Has to be able to handle potentially-condensing atmospheres (breathable), and under "ugly" conditions (faults) might be exposed to sea or freshwater (surviving that if it happens is a plus!)
Application is a pressure transducer for a hyperbaric environment being monitored by a stamp....
I'm having trouble finding something that isn't (1) huge in physical size and (2) outrageously expensive (found one suitable unit but it was $500 Q1!· Yikes!)
Anyway, if anyone has had use for such a device and has any pointers, that would be great.·Sensors that can be excited with +5VDC are the best option since that happens to be running around [noparse]:)[/noparse]
Thanks in advance.....
Comments
http://www.gp50.com/
·
http://www.gp50.com/pdf/1000.pdf
http://www.kele.com/olcat/P4/209.PDF
http://www.kele.com/olcat/P4/209-V.PDF
These seem to be psig and I don't see an option for psia
but that was a quick look and they should have a line using psia
edit Can't you convert by +14.7 from the psig reading?
Post Edited (Orion) : 12/13/2005 2:09:33 AM GMT
I have used pigtails and pressure transducers on steam boilers you can keep your hand on the transducer when using a pigtail but not without. over long periods of time hours there may not be much differance though.
I sure as heck don't want a $300 sensor being toasted if I can avoid it. This one sensor looks to·exceed the cost of the entire rest of the controller!· That bites.....
The sensor cannot be referenced to the atmosphere because the entire unit will be inside the hyperbaric environment.· Building a 1ATA reference chamber into which the transducer goes and then dealing with sealing the fitting on that is certainly possible but unless I need to I'd prefer not - plus, with an absolute gauge I can detect altitude (in air)·above sea level which is potentially useful for other reasons.
The reason for the 200psi range is that this entire thing is planned to have an operating depth approaching 300fsw; if that operating range is violated I'd like to have a record of it in the data log (otherwise a 150psia sensor would be adequate.)
Honeywell has a fairly inexpensive 0-100psia DIP sensor but nothing with a higher range.
I'll keep looking..... (yeah, I know its a kinda odd requirement [noparse]:)[/noparse] )
Post Edited (Genesis) : 12/13/2005 2:21:55 AM GMT
I do not know if this will help absolute gauge· these transducers are at
·http://www.setra.com/tra/pro/p_in_546.htm
· Options Gauge
Sealed Gauge*
Absolute**
*Available on ranges 300 psi up to 10,000 psi
**Available on ranges 15 psi up to 10,000 psi
I hope this help we use setra for some of our transducer where i work
sam·····
Post Edited (sam_sam_sam) : 12/13/2005 3:27:33 AM GMT
[noparse][[/noparse]quote]Interesting! Just out of curiosity...any good stories of testing electronics at this pressure?? Do electrolytic caps hold up in 150psi? Any thing need to be adapted for this?
The trick is to pot the entire thing - that way there is no pressure gradient (no "airspace") and the external structure of the potting takes the pressure. I've done this before with "ordinary" components without trouble. The only problem of course is that you can't rework anything - if any part of the controller fails then you toss the whole thing and install a new one, because you can't get to it once you pot it. Any connections you need must be brought out on wireleads. You can use either commercial potting compounds or epoxy - the latter has the benefit of being (mostly) clear so you can see any voids or problems in the pour, but has the downside of getting rather hot during the cure if you're not careful. You need to choose your resin/hardener combinations wisely.
If you try to avoid potting by putting the electronics in a 1 ATA enclosure inside the unit then ANY violation of the seal is usually instantly fatal to the electronics, and sometimes with extremely bad results, because frequently the surrounding atmosphere has oxygen partial pressures that support elevated rates of combustion (that is, sparks or "letting the smoke out" of components could be REALLY REALLY REALLY BAD!)
The way you test this beast is to put it in a pressure pot and crank it down to the expected depth (330' = ~300psi). The bad news is that safety requires you do it with the pot full of WATER rather than air (water doesn't compress - if you use air which does and the lid lets go you have a bomb instead of a mess) - you get to find out real quick if your potting (or 1 ATA housing) methodology is worth anything or not. If not when you pull it back out it doesn't work anymore.... [noparse]:)[/noparse]
Fun stuff......
(Code's working on the bench already - I REALLY like the BS series for this kind of thing - especially the integrated I/O support in the language - it saves you a shizload of time over handcoding assembler or something similar!)
The nice thing about wax, you can melt it slowly and then rework/repair the board.
Bob N9LVU
It has to be a solid once cured - that's the point of potting it in this case, as that is what creates the rigid shell that prevents the pressure outside from affecting the circuitry inside.
THIS looks real promising on the sensors.... can't find pricing though..... will have to call them tomorrow.....
http://www.meas-spec.com/myMSI/sensors/pdf/pressure/entran/EPB.pdf
Post Edited (Genesis) : 12/13/2005 4:56:46 AM GMT
www.jpl.nasa.gov/releases/99/monterey.html
One concern was that crystals packaged in hermetic ceramic to metal packages might be crushed at those pressures, and that epoxy packaged crystals would be better in that respect. I have reason to believe that some aspects of that instrumentation are Stamp controlled. I don't know what they are using for a pressure sensors, but probably cost is not a big concern.
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Tracy Allen
www.emesystems.com
PSIA -30 to 200 psi
PSIG 0 to 200 psi
http://www.meas-spec.com/myMSI/download/pdf/english/icsensors/pressure/pressure_sensor/model_86_ultrastable.pdf
$70.00
That works....
If you look at the mechanical drawings in the second link it shows a vent tube.· It·may need to be vented to normal atmosphere pressure, but looks like an option?
Post Edited (Orion) : 12/13/2005 11:09:09 PM GMT
If you order "A" version (absolute) the vent tube is not there as the entire unit is hermetically sealed and has an internal reference.
(I spent about an hour on the phone with one of their engineers today [noparse]:)[/noparse] )
Got one coming - we'll see how it works... I can live with $70/unit - that's pretty reasonable, all things considered.