Subminiature pressure sensor

Does anyone know about a source for very small pressure sensors, diameter about 3mm (0.01 inch)? I've found www.entran.com, but are they really
the only ones?
--Lars
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Dear Lars Johansson:

0.1 inch, actually.

The others are larger, because they are packaged so they can be mounted and plumbed. Some of them look like ICs with hose barbs. Pressure measurements are usually differential pressure measurements. Unless you have a known-pressure reference...
What are you trying to measure the pressure of, and how will you connect to it?
David A. Smith
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On Tue, 1 Feb 2005, it was written:

Yes, thanks, writing this was the last thing I did before leaving work yesterday, I must have been sleepy!

It's intracellular fluid in the body; hence the need for as small as possible equipment.

Thanks for your interest
--Lars
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Dear Lars Johansson:

You will not find what you seek in a transducer, since "known pressure references" automatically make this device as large as you have seen.
Let me suggest some alternatives... to get your noodle running. - Sperry Flight Systems (now Honeywell) used to have a vibrating diaphragm that had vacuum on one side, and air of unknown pressure on the other. The vibration was pumped, but the frequency was a function of pressure. Perhaps ultrasound or one of its close cousins... - Speed of sound is a function of pressure also. So time of flight in a sound pulse directed through the area of interest... - Diffusion is a function of pressure (and more). If you can find an innocuous substance to inject, you can track its arrival (or departure). - Put the transducer in a syringe, and insert a needle filled with fluid to the point of interest. With no flow, the pressure at the tip will be the same as measured (except for altitude changes from tip-to-transducer).
Others might have some bright ideas.
David A. Smith
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On Wed, 2 Feb 2005 07:00:26 -0700, "N:dlzc D:aol T:com \(dlzc\)" <N: dlzc1 D:cox T: snipped-for-privacy@nospam.com> wrote: ///

///
c is a function of temperature not pressure in a given gas.
Brian W
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Dear Brian Whatcott:
wrote:

I will meet you halfway. c_medium is a function of specific volume (or density), which is a function of both temperature *and* pressure (and the specific gas/mixture). The OP is interested in intercellular pressure, so I don't think gas speed is of importance.
David A. Smith
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On Wed, 2 Feb 2005 18:46:56 -0700, "N:dlzc D:aol T:com \(dlzc\)" <N: dlzc1 D:cox T: snipped-for-privacy@nospam.com> wrote:
...

You read the equation and you certainly won't be the first to suppose that c is a function of pressure. That's what it seems to say, after all. But it isn't. Take my word for it.
Brian W
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On Thu, 03 Feb 2005 04:00:57 GMT, in sci.engr.mech Brian Whatcott

You're talking about a gas. In liquids the effect of compressibility would appear to be on the order of 10-20%. ---------- Ed Ruf Lifetime AMA# 344007 ( snipped-for-privacy@EdwardG.Ruf.com) http://EdwardGRuf.com
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wrote:

True. I should know better than continue after making a correction - but I will this time. Not only was I talking about gases, Ed, so were *you*. Take a look at this quote of yours:
"I will meet you halfway. c_medium is a function of specific volume (or density), which is a function of both temperature *and* pressure (and the specific gas/mixture)."
Brian W Altus
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Dear Brian Whatcott:

Dude, that was "David A. Smith" that said that.
David A. Smith
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On Thu, 3 Feb 2005 07:02:33 -0700, "N:dlzc D:aol T:com \(dlzc\)" <N: dlzc1 D:cox T: snipped-for-privacy@nospam.com> wrote:

Yep, sounds like I was trying to pick an argument with someone who was agreeing with me. Ah well....
Brian W
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On Fri, 04 Feb 2005 01:08:38 GMT, in sci.engr.mech Brian Whatcott

FWIW, this came up recently in sci.mech.fluids. I wasn't aware of the magnitude of the correction in real systems and was informed of the 10-20% range. ---------- Ed Ruf Lifetime AMA# 344007 ( snipped-for-privacy@EdwardG.Ruf.com) http://EdwardGRuf.com
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On Thu, 03 Feb 2005 12:38:59 GMT, in sci.engr.mech Brian Whatcott

Go back and re-read my post again. That's NOT my reply, it's David's. ---------- Ed Ruf Lifetime AMA# 344007 ( snipped-for-privacy@EdwardG.Ruf.com) http://EdwardGRuf.com
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Lars Johansson wrote:

Does the sensor have to be in the body for a prolonged period? If it's just for sampling, perhaps you can just place a very narrow duct to the area in question and measure the pressure in the duct at the other side. This method is used with a needle to determine swelling-induced pressure in various parts of the body (ex. snakebite victims). In essence, you're transporting the pressure outside the tissue to make it easier to measure.
Hope that helps, Dave
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Thanks to all who replied, I have picked up a few leads that I will pursue.
--Lars
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Lars Johansson wrote:

I have some pressure transducers from Endevco the size of 10-32 screws. In fact it screws into a 10-32 threaded hole. The "other end" of the device is a little larger- it is turned with a 5/16" wrench. Look at http://www.endevco.com/ they may have even smaller ones by now.
Richard
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Lars,
Try msi sensors: http://www.msiusa.com/icsensors/products.asp Look at the model 1620 listed at the bottom of the page. (You'll have to register with them to look at the datasheets). This sensor is a disposable pressure sensor, very small, typically used for disposable blood pressure measurements. The only down side to this particular sensor is that it does have a shelf-life due to the gel that is used in the package. But, it is very small. I think I was given a quote of about $1US in 10k quanities.
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