I don't visit this section of the forum very often but with little to do, I took a peek. I noticed some guys having a problem with this little formula question. For "Rich57" there is some good news and bad news...
The GOOD...
R1 x R2 90 x 45 4050
Rt= over Rt= over Rt=over Rt=30ohms
R1 + R2 90 + 45 135
so:Rt is the valve you need the sensor to be.
:R1 is the value the sensor is now.
:R2 is the value (45 ohm)you need to put in PARALLEL with the sensor.
The BAD...
"Waldo53" is right, A new sensor is the right way to go if you want it to read correctly all the time.
Your gauge linearity is out the window. It will only be correct for two readings, empty and full. For an example...1/2 a tank would be 45 ohms on your 90 ohm sensor. If you plug that number in above you get 22.5 ohms or about 1/3 tank showing.
A couple of other things...45 ohms is not a standard resistor but 47 ohms is and that will be ok. On temp. sensors the game is a little different in my option. The only linear portion of the temp. curve I worry about is 180 to 220 degrees. So you can "pad" an electric sensor to be linear in this portion of it temp. curve. I don't worry if the water temp. is a 125 degrees and the gauge is showing 140. I only worry about the range noted above.
Hope this helps.
The UGLY...
