Coolant Temp Sensor Calibration

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littlestevie
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Coolant Temp Sensor Calibration

Post by littlestevie » Tue Jul 27, 2010 5:23 pm

Hi Guys,

I am in the mist of calibrating the Coolant Temp Sensor. Following the instructions in the EM36 manual (Page 25-26), I am only able to calibrate a small range (30 to 100 degrees). A few questions:

1. I notice the manual mentioning the usage of "extrapolation" to derive unobtainable termperatures. Can you advice on this process? Do I use the "Fill" function?

2. What is the "Depth" and "Smoothness" of the "Smooth" function?

3. One way to calibrate for the lower range of temperatures (down to 0 degrees), is to use some ice. However, is it possible to use the "Resistance Vs Temperature" graph for calibration? I assume that the Coolant and Air Temp pins of the EM36 uses the typical "voltage divider" setup to obtained the necessary readings. In this case, some simple calculation would be able to yield the corresponding temp voltages. Is there some way or using this approach?

Appreciate your time on this.

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RickS
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Re: Coolant Temp Sensor Calibration

Post by RickS » Wed Jul 28, 2010 1:23 pm

Hello,

1) This depends on the temperature sensor you have but you can see if you look at the table in graph form whether the points are tending towards linear or not. Usually in the low and high temperature ranges of the sensor it does become more linear. If this is the case the easiest way is to look at the sensor in graph form and draw the rest of the table. Don't worry that this is not an accurate method because you have calibrated the important sites of the coolant temperature sensor and as long as you calibrate the cold start and warm up tables with a consistent temperature reading then it could be 10 degrees out but your engine would still run correctly because you have calibrated it there. A more accurate way to do it is to work out the degrees C per raw value between all of the calibrated sites in pairs. Write down the differences between them. The value you need to add or subtract from the next site should become obvious.

2) Smooth applies a linear phase low pass filter to the map or table.
Depth corresponds to the window size of the filter kernel (each site being a sample). A Higher value will allow lower cutoff frequencies. Smoothess corresponds to the cutoff frequency of the low pass filter. Higher values represent a
lower cutoff. I would not reccomend the smooth function for the coolant sensor table as you are probably aware.

3) Using the voltage/bit divider will give you the correct temp readings from the resistance temperature graph avoiding the steps in 1).


Hope this helps
Ed

littlestevie
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Re: Coolant Temp Sensor Calibration

Post by littlestevie » Wed Jul 28, 2010 3:45 pm

Hi Ed,

Thanks for the information. Can I also know the value of the pull up resistor for the Coolant and Air Temp pins? Is it ~4.5K?

Thanks!

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RickS
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Re: Coolant Temp Sensor Calibration

Post by RickS » Thu Jul 29, 2010 8:54 am

Hello,

It's a 4K7 pull up on both.

Hope this helps
Ed

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