Oil pressure gauge / transducer

[acronut]

Ok my airplane comes out of annual and the oil pressure gauge pegs when I tun on the master switch.  I'm guessing something is shorted out.  It has one wire that goes to the transducer.  When I pulled the wire off the transducer I get the same result.  Next I plan on puling the wire off the back of the gauge and seeing what it does.  If it does the same thing I'm guesing it's the gauge itself.  Is this correct thinking or does it need a "good" transducer hooked up to read zero?  Its a 68 M20F but it has a 201 style panel and gauges.  It's the horizontal gauges across the top of the glare shield.  Any help is much appreciated.

Merry Christmas everyone!

Kendal

[Ron McBride]

Check to make sure the gauge is grounded well. You may need to clean all of the grounds up.

Let us know what you find.

Ron

[DonMuncy]

My experience is that the gauge is seldom bad. Clean off the posts of the gauge really well, both the hot and the transducer side, before you do anything else. In aviation terms, the transducers are very cheap ($30 something), so you can probably get it going without undue expense.

[acronut]

I guess the short question is can anyone tell me what the gauge should do if the transducer wire is disconnected, it's properly grounded, and power is applied.

Thanks

Kendal

[DonMuncy]

I think my memory is correct, that with the wire to the transducer removed, it is supposed to read "full pressure". The transducer is a variable ground which translates into the proper pressure reading. Thus, if you ground the wire which goes to the tranducer, it should read zero. Your indications are an "open" transducer. But I would still clean both posts and terminals to the gauge. If it still doesn't function, then replace the transducer. 

[acronut]

Quote: DonMuncy

I think my memory is correct, that with the wire to the transducer removed, it is supposed to read "full pressure". The transducer is a variable ground which translates into the proper pressure reading. Thus, if you ground the wire which goes to the tranducer, it should read zero. Your indications are an "open" transducer. But I would still clean both posts and terminals to the gauge. If it still doesn't function, then replace the transducer. 

[DonMuncy]

I got mine from Aircraft Spruce. Mine is a K model, but I would assume they are the same. If you have a problem, I think I can dig through my invoices and find the part number

[acronut]

Yea I'm guessing the K  model must be different Don.  I can't find anything close to that part number or anything that looks like it might be it on Spruces site.  Thanks again for the help.  Wish it wasn't Saturday Christmas Eve!!!  Guess I'll have to cancel my trip to my sisters on the 26th. 

Merry Christmas Everyone

Kendal

[DonMuncy]

Kendal,

I can't seem to find it in my Spruce catalog at the moment, but they call mine a Mitchell 150 psi sender, part number 10-25055, for $37.50 plus freight. I would have to look at my hangar, but I think they buy it from Mitchell, but the actual unit has someone else's name on it; maybe VDO. If my memory is working right, it has a 1/8 inch pipe thread and only one electrical terminal on it.

[acronut]

Quote: DonMuncy

Kendal,

I can't seem to find it in my Spruce catalog at the moment, but they call mine a Mitchell 150 psi sender, part number 10-25055, for $37.50 plus freight. I would have to look at my hangar, but I think they buy it from Mitchell, but the actual unit has someone else's name on it; maybe VDO. If my memory is working right, it has a 1/8 inch pipe thread and only one electrical terminal on it.

[acronut]

Hmmm that pic didn't attach for some reason I'll try again...

 

Ok it's not working I can't seem to upload any photos.  Even tried to upload it to my gallery and it uploads then says error.  It's just a 500KB JPEG so I'm not sure what the deal is but it's not working. 

 

Ok got a different one to post to my profile I'll try here too...

[DonMuncy]

I can't be certain, but I think they look the same. I believe my gauges are Rochesters, but I think you have to take them out to find the name on them. If you are willing to go to the trouble, you can go buy a dozen or so resistors at Radio Shack, in 25, 50 and 100 Ohm range. By hooking them in series and using them in place of the transducer, you can figure out what range your gauge reads. On mine, the following is the ohm range for various pressures:

10 psi= 26 ohms    15=35      20=40     25=48    30=54   35=62     40=67    45=73    50=84  

Rather than burdening the forum with our chatter, feel free to PM or call me; or if the group is interested, we can do it here.

Don 214 207-6744     d.muncy@sbcglobal.net