pressure regulators

[Brian Dessent]

Steve.Flanagan at VerizonWireless.com wrote:

> looking to making a control for the waste gate that is solid state, just
> tossing around some ideas and seeing what devices are already available.

Oh.  So you want to measure pressure and actuate a solenoid at a certain
point.  I would start with Motorola's line of pressure sensors, have a
look at:

http://e-www.motorola.com/brdata/PDFDB/docs/SG162.pdf

I recommend the "integrated" type because their output signal is much
more robust and this is much easier to deal with in the extremely noisy 
(in the electrical sense) automotive environment.

The mpx4250a reads absolute pressure from 20 to 250kPa, which
corresponds to about 24" Hg vacuum to 21.6psi of pressure.  Yes, I think
this is the same sensor Megasquirt uses.  I'm using it to make a
solid-state vacuum/boost gague.  Anyway, you could use this or a similar
one (in your case you could use a differential/gage type since you only
care about pressure and not vacuum) and use set up a comparator to fire
the solenoid at a certain pressure.  Or you could get more advanced and
use PWM to slowly turn on the wastegate as opposed to an on-off deal.

The only company I could find that carries the above part in stock with
no minimum order quantity or 6-week lead time was Newark
(www.newark.com) and I paid $22.58 for mine.  I got the ported version
(ends in -ap) which means it has a nipple to which you can attach a
vacuum line.

If you want a look at some other options, you can try Digikey.  Have a
look at their current catalog, pp795-797 for comparison: 

http://info.digikey.com/T013/V5/795.pdf

While they have some that are comparable in price, they are either not
signal conditioned (in which case you're dealing with a 110mV FULL SCALE
output signal which requires an instrumentation op-amp even in the best
case) or they can't be hooked up to a vacuum hose easily.

Brian

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