MicroSquirt.com read only forum (Jan.15,2018)

Hello,
I custom made my own 10 Kohm NTC temperature sensors because of where they had to go in my application. I wanted a very small sensor tip for my air intake sensor so going with GM style sensors was not going to work. Here is my question:

If the actual thermister has only two leads because it is essentially a resistor, what is the third wire for? If the third wire is supposed to be connected to VRef, how does it get wired to the sensor?



Is this close? If so, what size resistor goes to the 5 volt line?

Hi mechyank,

If the actual thermister has only two leads because it is essentially a resistor, what is the third wire for? If the third wire is supposed to be connected to VRef, how does it get wired to the sensor?

Google is your friend...halfway down the page...How to Make a Thermistor Measurement
Also look at this, which is a simpler diagram, and the resistor inline with the Vref or 5V is a "bias" resistor, just like the coolant temperature sensors you can buy. You need to fit one of these, and then map the temperature resistance at a few key points...but as I've just seen your image in Google images, I think you know this already!

Mike

What I didn't mention, the MicroSquirt can read a 2 wire sensor no problem, and so one wire goes to the relevant sensor input, the other to the sensor ground input.

What size resistor goes in line with the Vref (Ohms and watts). I have taken my multi-meter and recorded resistance values for each of the sensors at ice-water (32 deg F), boiling water (212 deg F), and ambient air temp. Do I have to do this over again? If so, what is the setup?.... Connect to Vref with a resistor and measure across the two leads?

Hi again, that diagram you posted is old hat....all you need to do is connect one wire to the MicroSquirt, and another to the sensor ground if you have a two wire sensor. All your doing is finding the resistance value (using a multimeter) for different known temperatures, and plotting a decreasing resistance with temperature increase for your sensor. However you should get this of the manufacturers spec sheet.

Have you read this?

I should mention that I am using a Microsquirt V2 module. Can the V2 use the two wire setup as you described with out connecting to Vref?

The link you supplied that explains the setup does not give a suggested value for the resistor that limits the current to the module (R sub p).

It doesn't but then does say very little current will flow to the pin, because of the bias resistor & thermistor interplay, so it's high impedance anyway.
No idea what the actual current limits are though on the IAT or CLT processor pins though.

PS Yes the V2 is a two wire set up too, so one wire to sensor ground, the other to the relevant processor pin. The GM sensor has a bias resistance of around 2490 Ω

Thank you so much for the information so far! OK so I will get a 1/8th watt 2 or 3 K ohm resistor to use in line with the Vref. Then, I suppose because I am using a bias resistor I will have to redo the temperature measurements again measuring between ground and the line going to the ECU pin.