Preasure Measurement
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Posts: 46,084
I need to measure the fluid preasure in a small (~3mm) elastic tube
at as high a temporal resolution as possible. This tube is in a
harsh environment. I can cut the tube open and put something inside
it, or even seal it up with wires running out of the side if
necessary.
Any ideas?
-selket
at as high a temporal resolution as possible. This tube is in a
harsh environment. I can cut the tube open and put something inside
it, or even seal it up with wires running out of the side if
necessary.
Any ideas?
-selket
Comments
you just need to select the pressure range of the motorola sensor and the
number of bits from the a/d converter.
the a/d converter is really the heart.
an 8 bit a/d = 256 bits resolution or 5 / 256 = 0.01953125 volts per data
bit.
an 10 bit a/d = 2048 bits resolution or 5 / 2048 = 0.00244140625 volts per
data bit.
as you can see a 10 bit converter has 4 times the resolution of the 8 bit.
norm
>From: "selket_10027 <selket_10027@y...>" <selket_10027@y...>
>Reply-To: basicstamps@yahoogroups.com
>To: basicstamps@yahoogroups.com
>Subject: [noparse][[/noparse]basicstamps] Preasure Measurement
>Date: Tue, 28 Jan 2003 17:31:54 -0000
>
>I need to measure the fluid preasure in a small (~3mm) elastic tube
>at as high a temporal resolution as possible. This tube is in a
>harsh environment. I can cut the tube open and put something inside
>it, or even seal it up with wires running out of the side if
>necessary.
>
>Any ideas?
>
>-selket
>
>
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>at as high a temporal resolution as possible. This tube is in a
>harsh environment. I can cut the tube open and put something inside
>it, or even seal it up with wires running out of the side if
>necessary.
>
>Any ideas?
>
>-selket
By harsh environment, what do you mean? What pressure range? What
temperature range? What resolution, accuracy? What time scale?
What fluid? So many questions!
You have to respect the maximum pressure ratings silicon strain gage
sensors, because they _will_ break if you exceed the maximum
overpressure rating.
Pressure sensors have strong temperature dependence, so they need
temperature compensation. Some sensors have that compensation built
in, but you still have to evaluate it to see if it's specs are good
enough in that respect. If it is going to see extremes of
temperature or rapidly fluctuating temperature, the compensation has
to be very good and it has to be done by using the pressure bridge to
sense its own temperature (i.e., not an external temperature sensor).
Does the pressure sensor have to fit inside the 3mm tube (A tall
order!), or can the tube be attached to a nipple?
There are clever solutions to pressure measurement that have been
invented in the biomedical field. For example, they can be passive
(no battery), and small enough even to be implanted or swallowed and
read remotely. A self-resonant circuit with an inductance or
capacitance dependent on pressure can be detected with a loop antenna
held outside. I have seen those small enough to be implanted in the
eye.
-- best regards
Tracy Allen
electronically monitored ecosystems
http://www.emesystems.com
mailto:tracy@e...
--- In basicstamps@yahoogroups.com, "norman doty" <normdoty@h...>
wrote:
> use a motorola sensor, and an a/d converter.
> you just need to select the pressure range of the motorola sensor
and the
> number of bits from the a/d converter.
> the a/d converter is really the heart.
>
> an 8 bit a/d = 256 bits resolution or 5 / 256 = 0.01953125 volts
per data
> bit.
>
> an 10 bit a/d = 2048 bits resolution or 5 / 2048 = 0.00244140625
volts per
> data bit.
>
> as you can see a 10 bit converter has 4 times the resolution of the
8 bit.
>
> norm
>
>
>
>
>
>
>
> >From: "selket_10027 <selket_10027@y...>" <selket_10027@y...>
> >Reply-To: basicstamps@yahoogroups.com
> >To: basicstamps@yahoogroups.com
> >Subject: [noparse][[/noparse]basicstamps] Preasure Measurement
> >Date: Tue, 28 Jan 2003 17:31:54 -0000
> >
> >I need to measure the fluid preasure in a small (~3mm) elastic tube
> >at as high a temporal resolution as possible. This tube is in a
> >harsh environment. I can cut the tube open and put something
inside
> >it, or even seal it up with wires running out of the side if
> >necessary.
> >
> >Any ideas?
> >
> >-selket
> >
> >
> >To UNSUBSCRIBE, just send mail to:
> > basicstamps-unsubscribe@yahoogroups.com
> >from the same email address that you subscribed. Text in the
Subject and
> >Body of the message will be ignored.
> >
> >
> >Your use of Yahoo! Groups is subject to
http://docs.yahoo.com/info/terms/
>
>
> _________________________________________________________________
> The new MSN 8: advanced junk mail protection and 2 months FREE*
> http://join.msn.com/?page=features/junkmail
pressure range is the first place to start. most pressure sensors
have a 1% error as the standard. (often called 1% accuracy, but then
that would really mean it is useless)
Also, most pressure ranges start at around 5 psi and go up to
millions of psi. Higher is easier and low is not.
ultra low pressure sensors, 0.1" full span ( that is 1/277 of a psi
full span) get pretty expensive.
amplifying an incorrect span just doesn't work well. if you want to
measure 1 psi, and use a 10 psi span with 1% error, you amplify the
error so your ADC will see a reading but the reading will have a 10%
error.
Physical size is also important. a 2" x 4" x 1" pressure sensor may
be small for a car, but as big as a small robot.
wetted surface is also improtant. most units are detailed as to the
external enclosure but not the actual surface of the sensor. I was
involved with some Hydrogen Sulfide monitoring. I think the unit
disolved in a little over 2 weeks as that is when the readings
stopped, but when the unit was opened after 6 weeks there was
litteraly nothing inside.
That should get you started.
Dave
--- In basicstamps@yahoogroups.com, "selket_10027
<selket_10027@y...>" <selket_10027@y...> wrote:
> I need to measure the fluid preasure in a small (~3mm) elastic tube
> at as high a temporal resolution as possible. This tube is in a
> harsh environment. I can cut the tube open and put something
inside
> it, or even seal it up with wires running out of the side if
> necessary.
>
> Any ideas?
>
> -selket