3

Apologies in advance, my electronics knowledge is very poor.

I've got myself a resistor that I believe is appropriate for the job I want to do on my vehicle. I'm replacing the factory sensor; there are two wires going to the sensor from the car's management system.

The way I understand how it's working is that one of the wires is providing 5v to the sensor which reads a value and returns the voltage back to the ECU. I need the resistor because the curve is different to the original. The resistor required has already been calculated.

Does it matter which wire I put the resistor on?

This is the sensor: -

http://www.bmotorsports.com/shop/product_info.php/products_id/400

Improve this question
11
  • When you say "the curve is different to the original"; are you talking about the unloaded resistance vs temperature chart? If so, if you bought that sensor, how do you know the curve is different?
    – Nick Williams
    Commented Mar 13, 2015 at 12:29
  • My semantics are, more than likely, off; please forgive that. There is information available on the car forum I use that has stated that a 14.2k resistor is what I need to ensure the resistance vs temperature curves match. I'm asking here because I'd like to learn more myself.
    – chrisw69
    Commented Mar 13, 2015 at 12:35
  • I'll just assume the forum is right for simplicity. You ask: "which wire to put the resistor on?" which suggests the resistor is intended to be wired in series with the sensor (is this right?). In which case, it doesn't matter which wire or position from the sensor. The resistance of the resistor and the resistance of the sensor will add up the same amount.
    – Nick Williams
    Commented Mar 13, 2015 at 12:44
  • 1
    I love sparkfun, this entire page will keep you busy for a month probably: learn.sparkfun.com/tutorials/analog-vs-digital/res The "Resistors" link is a pretty thorough breakdown.
    – Nick Williams
    Commented Mar 13, 2015 at 13:02
  • 4
    @Passerby The content of the question is electrical based; why does it matter if it is for an automotive application?
    – Nick Williams
    Commented Mar 13, 2015 at 13:52

1 Answer 1

Reset to default
5

By our discussion we assume that:

  • An external 14.2kOhm resistor is needed
  • The resistor must be wired in series

From this, it will not matter the wire, nor position that the resistor is applied. The resistance will add the same.

schematic

The wires (ideally) have no resistance, so POS is arbitrary, the resistance across A and B will be the same. The fact that R1 is attached to node A is arbitrary as well.

Improve this answer
2
  • That CircuitLab tool is very useful too! Nice one. I guess my concern was that if I placed the resistor before the sensor, with the sensor requiring 5v, it could lower the voltage that the sensor receives.
    – chrisw69
    Commented Mar 13, 2015 at 13:04
  • 3
    @chrisw69 If you placed the resistor after the sensor, there would still be a voltage drop across the resistor. The voltage drop across the sensor would be the exact same; regardless of the resistor being before or after sensor.
    – Nick Williams
    Commented Mar 13, 2015 at 13:49

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .