Oil pressure indication high or low when sensor wire is shorted?

[Gedis]

When oil pressure gauge sensor wire is shorted to ground, would the indication be high oil pressure or low? Trying to figure out what to debug first.

[thinwing]

The sensor is a pressure activated poteniameter...higher the pressure the higher the resistance..the gauge  measures this resistance to ground.Grounding the sensor to gauge line means 0 resistance and thus zero pressure.

[thinwing]

You need a multimeter

[Gedis]

Thanks! The whole system works well when tested using shop air but when flying, needle starts twitching quite a bit and frequently redlines (engine is ok). From what you said I wonder if cable is broken and causes open circuit thus redlining the gauge. Vibrations could be causing intermittent connection problems.

[carusoam]

Start at the sensor at the engine and start cleaning every connection you can find.  There is probably a plug on the sensor that has some dirt or corrosion on it...

PP thoughts only.

Best regards,

-a-

Edited June 1, 2017 by carusoam

[RLCarter]

7 hours ago, thinwing said:

The sensor is a pressure activated poteniameter...higher the pressure the higher the resistance..the gauge  measures this resistance to ground.Grounding the sensor to gauge line means 0 resistance and thus zero pressure.

Isn't this backwards? Not wanting to start anything but grounding the wire at the sensor pegs the gauge or at least on mine

[carusoam]

The Oil temperature sensor is a thermistor.  Which means it is a variable resistor that is sensitive to temperature.

Somebody posted a chart for temperature vs. resistance for the sensor around here within the last month or so.

Either way, a voltage is applied to one end of the sensor and another voltage comes out of it.  The gauge on the instrument panel shows the voltage translated into temperature... or something similar to that...

does that help?

PP thoughts only...

Best regards,

-a-

Edited June 1, 2017 by carusoam

[Yetti]

My oil temp will max the gauge when shorted.   Not sure about pressure.   many time the ring terminal is the issue. It is easy to get corrosion in crimp connector.  There are proper tools for crimping ring terminals.

[carusoam]

I completely misspoke....  

I mixed up OilP and OilT sensor descriptions...

OilT is a thermistor.

Not sure how the oilP sensor works.  In industrial applications they use a piezo electric device... the modern equivalent of a thermocouple for pressure...

Best regards,

-a-

 

Edited June 1, 2017 by carusoam

[Yetti]

Takes a community to keep a mooney running. 

[Andy95W]

Everything old is new again!

[Gedis]

Thanks everyone!! Here is my debug plan. Hook up a multimeter to the gauge, reproduce the problem, and check what I see. If signal is not twitching when gauge is twitching - I know I have a bad gauge. If signal is twitching, I'll clean all the terminals and even better, replace the cable. If that doesn't help - need new oil pressure probe.

Now the question, how to access the signal wire from cockpit? Is it easy to remove the glareshield? Or is there a way to pull out the gauge?

[Dream to fly]

pretty sure if the circuit is open the gauge is max pressure shorting to ground it reads 0psi.  The same way the older trucks worked.  nothing like a resistor to make an engine look good

[Yetti]

On the F there is a cannon plug on the top copilots firewall outside.   I think that is where the gauge is going to come through the firewall (Also has the switched ground for the magnetos)  might want to wiggle and spray some contact cleaner there.  Cannon plugs need to be taken apart and put back together several times to fix things.   You could also check wiring and stuff to the gauge

[DAVIDN]

oil pressure would be low to trigger oil pump to fill day tank.