How to adjust oil pressure sender to gauge (potentiometer)?

Just added the pot in parallel and it works great. Adjusted the pressure to what Trip Tek says and all is good.

Dan

Fairgrove,

As stated, you need to put a resistance in parallel with the sending unit to lower the resistance.

HOWEVER, I would advise against doing this as this will result in a non-linear pressure vs. resistance relationship. So if you get it to read the "normal" value, it will be off as the sending unit resistance changes. How much it will be off is difficult to tell without knowing the exact resistances and the pressure vs. resistance curve of the sending unit.

Will the difference matter? Hard to tell. It's your engine. If it were mine, I'd want to know. I'd probably opt to keep it the way it is knowing that it's reading "high".

Actually, I'd probably continue my quest for the proper sending unit. It must be out there someplace.

Good Luck,

~Rick

I think you need to adjust the potentiometer to about 50 ohms. If the sender resistance is 180 that will give you an overall resistance of 100 ohms.

Correction: you will need about 225 ohms on the pot.

Thanks Sloop I will try that.

Dan

You need to put the potentiometer in parralel (not series) with the pressure sender. Tap into the wire that goes from the sender to the gauge with one wire to the potentiometer and the other to ground. You should then be able to adjust the overall resistance close to the needed range.

Total resistance = (R1 x R2)/(R1 + R2)
R1 = Sender resistance
R2 = Potentiometer resistance

The main problem is all the senders I find that are the correct span and pipe size they are the wrong resistance. I need a 100 ohm VDO sender and almost all are 180 ohm.

Dan

You need to determine the signal range and buy the appropriate sending unit. My pickup was a 1 to 5 VDC.

It would be a lot easier to get the right resistance sender and use pipe adapters if size is a problem. Some gauges are set up so high resistance is a low reading, some the opposite.

Dan,

You should have looked up what the sensor was before you bought a replacement. I believe that the engine is a Cummins and there is a very good chance that someone at a Cummins shop could either tell you what it should be or even sell you a correct part.

Baring that, you need to do an experiment with you current instruments powered up and a couple of alligator clips and about a 300? wire wound pot. You can use that to determine what is low and what is full scale. Then, if you can't actually find a match (very unlikely) you can do weirdness with little resistors to make what you can get be what you want. (I have to do this sometimes for strange foreign boat engines that come my way.)

All the senders come in all kinds of ways. I won't even go into how many there are, just suffice it to say a few. The calibration and working range also vary all over the place.

Matt

You could experiment with various resistance in parallel with the sender. This would serve to lower the overall resistance. You could get the gauge to read zero without the engine running. I would be concerned with inaccuracy over the total range depending on whether the sender is linear or not. Best keep looking for a correct replacement.

Carl