Moto Pressure Sensors

[Chris Conlon]

Hi all,

I've been using some of the signal-conditioned pressure transducers,
the MPX4xxx series, and I've been very happy with them.

> But to be honest, I'd think that still the 3-5% accuracy of these
> present devices is adequate for my needs, so I'll settle for 3-5% if I
> can't get 1% at the moment. Just wait a year or so, and they'll be at 1%
> accuracy anyway! B)

They're pretty close to that now. The spec on the MPX4200A is +/- 1.5%
of full scale, over 0c to 85c. If you control the temperature, the
accuracy is a bit better. Also a lot of this error comes from the
slight nonlinearity of the sensor itself, it reads high in the middle
of it's range and low on the ends. You can compensate for this
somewhat without even having to calibrate each specific unit (see
App Note 935, in the sensor data book DL200/D rev 3), and perhaps
do even a bit better if you have a reference to calibrate against.

Someone else commented about long hoses from manifold to pressure
sensor. Personally I haven't seen any problems with this, but
you can get into a lot of trouble if your signal isn't filtered
properly. These sensors are more than fast enough to see a lot of
the extreme pressure swings from valves opening and closing, and
that signal will be affected by the length/shape of your hose.
Thus the use of equalization tubes or cans that Orin mentioned.
Personally I like to do that filtering in software (cos I think
it's easier for me to tune) but either way should be workable.
All I really want is the average over a couple engine rotations,
not the detailed ups-and-downs. (Plus I feel having the sensor in
a milder, more stable temperature environment will pay back in
better accuracy/repeatability).

Anyway I've been having a blast with them and think they're great.
I'll try Newark next time I need more. Most places I tried it was
a long-lead/high-minimum part, but I'm one of those obnoxious types
who feels Moto ought to sample me a few in such cases.

   Chris C.