AT calibration curve help

[M800]

Hi all,

On the M800, I'm wanting to use the stock engine temperature sensor as it has 3 pins and serves the in-dash temp gauge.

So I have developed a calibration curve (resistance vs temp C) for the sensor.

However in the custom sensor setup, for the AT, the fields are volts and Temp. I can use V=IR to establish V but I need to know the current ..... or am I going about setting up the calibration table incorrectly?

Also can we use another AT for the Air temp apart from AT1 ?

Thanks for the help

Bazz

[RossB]

Hi Bazz,
To work out your voltage from resistance you need to take in to account the pull up resistor (1000 ohms on M800) supply voltage (5V) and the sensor resistance at a particular temperature. The calculation is:
V=Supply V x (R/(Pull-up+R)).
I have attached a spread sheet which I use for this to make it easier, just fill in the pink cells and you will have your calibration in volts.

[M800]

Cheers Ross,

We are back on the dyno again on Wednesday and this is one less thing that Lee has to worry about

It was the pull up value I was needing, so it's all good now, thanks

Hopefully the timing belt will stay on this time

[John Reed]

Ross's answer surpassed mine over on EFI101 with that spreadsheet, that will come in handy for sure!

[RossB]

Forgot to say, you can use any AT Input for Air Temp. We normally use AT1 and AT2 for Air Temp and Engine Temp and if you were to upgrade a file from an M4 or M48 this is where they would be asigned. I would say that it is probably a good idea to stick to this convention but it is up to you.

[M800]

Thanks John and Ross, you both had the answer

John, I had actually used your hint successfully, but as you say the spreadsheet is a handy item to have available for future use.

Cheers Guys