Ship’s oil pressure gauge failure mode

[M016576]

On the panel in my M20J Missile, I installed an EI CGR-30P about 5 years ago, but I left all the original ships gauges (and consequently senders) installed and operating.  On my last flight, the ships gauge oil pressure (the one up in the strip gauges), pegged full to the right (full high)- the needle is obviously not reading a pressure- it’s just fully deflected right.  The oil pressure on the EI CGR-30P still reads normal.

my question is this- does anyone know the failure mode on the ships gauge?  If it has open voltage- is it full deflection high or full deflection low?  I tried spraying the ground with contact cleaner, and adjusted the ground post.  I haven’t messed with the sender input, nor have I stripped the cowling to inspect the sender itself. The oil pressure sender is installed on a T-Fitting with the EI oil pressure sender- so they should technically both read the same thing.  I’m trying to figure out if it’s the sender that’s busted, or the gauge itself.  

I’m kicking myself for this- but I just realized that I Have Not checked the strip oil pressure gauge when the power is on, but the motor is not running... that would at least answer on of my questions!

thanks in advance

[Yetti]

You have a direct short on the wire to the sensor.   Grounding out the sensor wire will give you a high full deflection reading.

[carusoam]

OilP is most likely a strain gauge... the higher the P, the higher the Vout will be...

Our gauges are typically built to protect themselves from a bunch of simple problems... like shorts, and open circuits...

A few things you can try...

• read the spec for the sensor... that will give some interesting explanations for the behavior....
• disconnect the sensor to see what the gauge reads, open circuit...

Expect that the open circuit results in a fully deflected indication...

If this logic is true... you might simply have a broken or disconnected wire... start at the sensor, trace back to the gauge...

PP thoughts only, not an instrument tech...

Best regards,

-a-

 

[M016576]

On 4/24/2019 at 5:15 PM, Yetti said:

You have a direct short on the wire to the sensor.   Grounding out the sensor wire will give you a high full deflection reading.

Thanks Yetti!  This is exactly what I was looking for- I’ll shoot the sensor wire.

[Yetti]

7 hours ago, M016576 said:

Thanks Yetti!  This is exactly what I was looking for- I’ll shoot the sensor wire.

CHT would be the same I think.