# Scaling a 0-90 ohm range to 10-520

The fuel sending unit in my car operates within a range of 10-520 ohms. I want to replace this unit for one that runs in a range of 0-90 ohms. I'm assuming I will need something to compute the change, but I'm not sure where to begin as I'm not versed in electricity. Can someone help me out? Thanks in advance!

Where do you have these numbers from? Datasheet?

You could measure the resistance, calculate the corresponding value and pass it on to an Digital potentiometer. If you have some coding experience on Arduino or similar, this is a days work.

But I am quite certain, that there is a simpler way. But to figure out what works, you would have to find out how the resistance is measured. Is a constant current flowing through the sensor? Or is it part of a voltage divider?

Try to measure the following: How much current flows on "empty"? How much current flow on "full"?

• From the FSM for my model of car under diagnostics. I think it's just a constant 14v signal, but I'll need to ask the people in the car group if they have a solid answer to that. – Michael Lowry Oct 26 '20 at 13:49
• 14V is only the charging limit of the battery. It is nit very constant. Also if your R goes down to 0Ohm as you descibed, ti would blow the fuse . – Silvan Zuppiger Oct 26 '20 at 13:51
• So then adruino and digipot it is? – Michael Lowry Oct 26 '20 at 13:53
• That is one option. The other option is to figure out what exactly is beeing measured. There are so many ways to measure the resistant, that without knowing how it is done, one can not build a replacement model. Or even better: Get a fuelgauge with the right spec...... – Silvan Zuppiger Oct 26 '20 at 13:56
• It's an old car from the 80s with a digidash that I want to keep functional. There isn't a replacement made for my fuel level sender. I posted the question in the 300zx group, so I'm just waiting to see if someone knows. – Michael Lowry Oct 26 '20 at 14:01