Analog Meter capability

[Clare Snyder]

Joe Boucher wrote:
> 
> Tom Cloud wrote:
> >
> > >I was thinking about setting up a GM MAP sensor on my Camaro, complete
> > >with a 5 volt signal, and trying to obtain some data relating manifold
> > >pressure to throttle position and RPM.
> >
> > what's wrong with a plain ole vacuum gauge ??  -- or are you wanting
> > a "real" electronic signal ??
> 
> I'm trying to get some data from the Camaro to start designing the op
> amp circuit.
> 
> 
> > >Would an analog meter with 10k internal resistance require more power
> > >than the sensor would put out?  I have a small 10 meg internal
> > >resistance voltmeter, but I don't think this would work well. The
> > >digital meter display wouldn't settle down enough to take readings.  The
> > >analog would tend to dampen out some fluctuations.
> >
> > first you say 10k and then 10M  --  I, personally, don't have a
> > clue as to the Zout (output impedance -- or ability to provide current)
> > of the MAP sensor.  I'd suspect that it was lower than that of the
> > EGO sensor though.
> 
> I have two meters, one is analog, one is digital.
> 
> >
> > typical DMM has 10M Zin.  typical VOM has 20k ohms/volt (unless you
> > get it from ratshack .... then maybe 5k or 10k ohms/volt.  If the
> > analog meter has an internal amp (does it need batteries for more
> > than the ohms scale ?), then it will likely also have 10M Zin.
> 
> It requires AA's and a 9 volt battery.  I haven't tried it without the
> batteries in it to see what does and doesn't work.
> 
> > The analog meter would definitely "smooth out" the reading so
> > you can more easily see trends, etc.
> >
> > Here's how to find out the answer to your question:  put a known
> > vacuum on the sensor and measure it with the DMM.  Then, measure
> > it with your analog meter and see if it's significantly different.
> > (Of course, if the Zin is 10M then there's no reason to do this,
> > it should work okay.)
> 
> I have one of those hand vacuum pumps.  I'll try it.
> 
> > Tom Cloud
> >
> >      Madness takes its toll   .....   please have exact change

If the multimeter uses both 3 volt and 9 volt bat power, it is LIKELY an
electronic meter with high impedence, and should work. (transistorized
version of VTVM) Do the comparison test detailed above to be sure, but
dollars to donuts you will be OK.
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