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'[OT] Maxim Pressure Sensors'
1999\08\31@111959 by Wagner Lipnharski

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Mike DeMetz wrote:
> Got an invite letter to a session at the Sensor Expo Show (Cleveland,OH
> 9/15) by Maxim on their 'next-generation pressure sensors'. First units to be
> 100-3500 kPa in PCB mount package featuring;
> On-sensor-chip fluid media compatibility
> On-sensor-chip vacum reference
> Plug and Play operation eliminating need for external compensation and
> amplification.
> +-1.5% total error band over temperature range.
> To be followed by higher pressure models(to 350Mpa) and threaded port
> packages.

Hi Mike, 1.5% of error is somehow high for certain applications, and
fair enough for other.
For example, I built a device using a 24bits ADC to keep the 0.1% of
some (Lucas Novasensor) pressure transducer to be used in a
calibrator/indiator. Software temperature and range calibration was a
must, so the actual instrument error spec is just caused by the
transducer drift against the calibration itself (repeatability error).

This is one area of measurements that was not evoluted enough.  We can't
ensure 0.01% of accuracy in a pressure transducer, except if you pay
more than $300 for it... someday somebody will find out a different way
to measure pressure.  It is a nasty physical variable, you *can not*
easily add, subtract, multiply or divide it. The transducers should be
able to cover all the range at once, so the accuracy problems.  If you
could use a 0-30PSI (0.1%)  transducer to measure the range between 500
and 530PSI, you would have a nice instrument, but not for a while.


1999\08\31@143409 by John Griessen

What if:

A sensor has silicon machined micro valve(s) that could
       divert to reading two pressure pathways.
One path is the pressure to be measured over long times >>10 msec.
The other path has a miniature dead weight tester and a small
       one atmosphere fluid reservoir of silicone oil at the end of it.
You arrange so that the pressure on the "to be measured"
       path can be released
       to a serpentine path that is effectively one
       way and keeps cleanliness inside.
Some dead weights are cylinder shaped and their smooth ends
       rest on micromachined silicon ports of a few
       diameters such that pushing on them until flow
       happens tells you when you move through
       a calibrated pressure.
You have silicon micro machined micro motor driven fluid pump
       for small volumes capable of the pressures
       you want to calibrate.
All the above fluid switching is arranged to switch on
       tiny amounts of power
       and could maybe yield a chopper stabilized
       amplifier for fluid pressure...

Remember the HP chopper stabilized millivolt meter?
It had a literal chopper wheel.

John Griessen
Austin TX

> -----Original Message-----
If you
> could use a 0-30PSI (0.1%)  transducer to measure the range between 500
> and 530PSI, you would have a nice instrument, but not for a while.
> Wagner

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