[Gmecm] CTS and MAT lookup differences

[Robin Handley]

To add to this, I've just carried out a test of input MAT resistance (to
GND) vs. the Sunbird ALDL MAT value (Mode 1 data byte 23). Low values of
resistance gave low values of this MAT value, which makes me think this
value can't be straight A/D value, as resistance and A/D value should be
inversely proportional, instead of directly.

Can anyone help? Unfortunately I don't have a GM MAT sensor to test to shed
further light. I have a Bosch one
(http://apps.bosch.com.au/motorsport/downloads/sensors_temperature.pdf) but
don't know if its compatible w/o changing the lookup tables.

R

----- Original Message -----
From: "Robin Handley" <Robin at FuryWorld.fsnet.co.uk>
To: <gmecm at diy-efi.org>
Sent: 17 June 2006 13:49
Subject: [Gmecm] CTS and MAT lookup differences


> Comparing the CTS and MAT lookup arrays and comments in ANHT/$8D and
> Sunbird/$58 hacks that I have, I'm a bit confused:
>
> o The ANHT 4k array shows A/D values increasing (from the top down): 1, 6,
> 22, and up by 16 (note: first step not 16)
> o The ANHT 348R array shows A/D values increasing (from the top down): 0,
> 16, 32, and up by 16
>
> Is the hack right? If so, why the difference in A/D values? Is it to cope
> with high CTS non-linearity at high temperatures? Is it unreasonable of me
> to assume that all 17 element A/D lookup arrays map to A/D values of equal
> steps (i.e. 16)? :-)
>
> If I understand A/Ds correctly (that they measure the voltage across the
> sensor), then I can understand why the A/D value decreases when the
> resistance of the sensor decreases - which is when the temperature of a
> thyrister increases. So, I expect to see high temperatures for low A/D
> values and low temperatures for high A/D values. This is how the ANHT CTS
> arrays are set up in the hack that I have, and I'm happy that their
> behaviour is consistent with this.
>
> However, in the ANHT hack that I have, the ANHT MAT array shows low
> temperatures at the top and shows low A/D values there too. Can this be
> right? The Sunbird hack that I have shows high values at the top.
>
> Also, the Turbo P4 doc says that MAT in deg C comes straight from the A/D
> value. Is this right?
>
> Robin
>
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