I have a pressure sensor (100 psi out of a ashcroft 25D1005PS02 gauge) that purportedly is a 4 active element wheatstone bridge. I'm used to load cells with one active element, but how is 4 active elements different? What is the best way to read this sensor? The ashcroft also has a 4 pin com port internally but no data on accessing it.
You will need a Wheatstone bridge amplifier to read the [u]sensor element[/u] properly.
It would be best to use the gauge as it was intended to be used.
I've used whetstone bridge amplifiers before, but not with all four elements unknown. I was asking what the difference is. The controls no longer work, but the sensor is perfectly fine.
You need to identify the power and ground connections to the sensing element, then the other two leads will go to the inputs of a suitable differential amplifier.
If there are wire leads, the colors might help identify them (red and black are often power and ground), or you can carefully examine the connections to the rest of the circuitry. It should be obvious from the circuit board which leads are which.
Post clear photos if you can.
I would [u]guess[/u] that orange = Vcc, blue = ground and the others +/- signal.
If correct, try applying 5V between orange and blue, and measuring the green/white voltages to ground. They should be about 2.5V each, and change by a few mV relative to one another if pressure is applied.
It would help if you measured the resistance between all wire pairs and post those values.
Again, inspection of the connections to the PCB would make this clear.
[quote author=Steve Spence - KK4HFJ link=msg=3023093 date=1480523936] I've used whetstone bridge amplifiers before, but not with all four elements unknown. I was asking what the difference is. The controls no longer work, but the sensor is perfectly fine. [/quote]
The difference is all four elements are active, simple as that. Just like a strain-guage, becuase it is a strain-guage. You get temperature compensation for free and higher gain/sensitivity if you use all the elements.
I posted the picture of the connection to the PCB. Resistance between leads are as follows:
White - Orange 3.266 k White - Green 2.434 k White - Blue 2.403 k Blue - Green 3.265 k Blue - Orange 2.466 k Green - Orange 2.495 k
The picture of the PCB is unfortunately not informative, because all leads of the sensor go to a mystery IC. Try powering up the gauge and measuring the voltages on the sensor wires, with respect to the black power lead.
In any case these are the connections. Not obvious which would be the signal leads. It is safe to experiment.
Since they are all active, I guess it doesn't matter, as long as I use opposing pairs.