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'[OT:] How do you measure hysterisis'
2005\03\10@210253 by John Pearson

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I need to measure the amount of hysterisis there is with a pressure sensor and circuit. I have the measuring and pressure applying equipment, I just don't know the procedure and math and stuff. Please assume I am either younger than 9 or older than 40.

Thank you
John

2005\03\10@212845 by Bill McDonald

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> older than 40.
>  
>

Thems fitin words ya yung whipersnapper.

Grin

2005\03\10@234023 by Russell McMahon

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> I need to measure the amount of hysterisis there is with a pressure
> sensor and circuit. I have the measuring and pressure applying
> equipment, I just don't know the procedure and math and stuff.
> Please assume I am either younger than 9 or older than 40 **.
/>

Presumably you have either an on /off sensor and wish to measure
"stickiness" around trip point OR an analog sensor with electronic
output.

1.    Digital

- Increase pressure slowly
- Record pressure where switch activates.
- Decrease pressure slowly.
- Record pressure where switch deactivates.

Hysteresis % is (Pon-Poff) * 200 / (Pon + Poff) %


2.    Analog

Start at 0 pressure and slowly increase pressure to max and then
decrease to zero again.
Plot Pressure versus voltage curve.
Hysteresis causes the area between the ascending and descending
curves.

% hysteresis depends on what use you want to make of the data.
At any given pressure its (arguably) as above but substitute analog
output variable for pressure.

eg        (Vup - Vdown) * 200 / (Vup + Vdown) %


       Russell McMahon
       Aged 42* (base 13) ***

       * The answer to life, the universe and everything.


       ** To what base?

       *** Where the 13 is to base ten.

2005\03\11@025315 by Robert Rolf

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John Pearson wrote:

> I need to measure the amount of hysterisis there is
with a pressure sensor and circuit. I have the measuring
and pressure applying equipment, I just don't know the
procedure and math and stuff. Please assume I am either
younger than 9 or older than 40.

So that means you are either smart enough to find it on the
web in a second, or that you wouldn't remember the answer
even if we gave it to you? <G>

Step the pressure up to a calibration value, and take your reading.
Step the pressure down to the SAME calibration value,
and take your 2nd reading. If they are not the same,
you have hysterisis. With a dead weight tester this is
done by adding 1 then 2nd weight, then removing the 2nd weight.
You usually get different hysterisis values for different step sizes.

Robert

2005\03\11@063302 by Gerhard Fiedler
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Russell McMahon wrote:

> Hysteresis % is (Pon-Poff) * 200 / (Pon + Poff) %

I usually look at hysteresis in absolute values (would be Pon-Poff) rather
than in %.

In many cases, the difference Pon-Poff doesn't change substantially with
Pmean (at least not proportionally), which makes the % value not very
valuable.

And when giving % values, the question is always "percent of what?". Could
be % of the actual (or mean) value as you used, could be % of end of scale.
So you have to add this information anyway -- then it's easier (and more
informative) to say "hysteresis of x Pa at y Pa" than "x% of hysteresis,
relative to y Pa".

Gerhard

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