pulldown value on temp inputs

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GrocMax
MegaSquirt Newbie
Posts: 17
Joined: Thu Nov 14, 2013 4:46 pm

pulldown value on temp inputs

Post by GrocMax »

There appears to be a pulldown on the temp inputs, what is its value?

Important for calculating accurate thermistor tables as the pulldown adds parallel resistance and skews the reading the closer to the pulldown value the thermistor is at.
GrocMax
MegaSquirt Newbie
Posts: 17
Joined: Thu Nov 14, 2013 4:46 pm

Re: pulldown value on temp inputs

Post by GrocMax »

If there isn't a pulldown I need a way to do a better thermistor calibration, the 3 pt curve is missing the hump on the high resistance end of the scale.
Matt Cramer
Super Squirter
Posts: 910
Joined: Sat Jul 03, 2004 11:35 am

Re: pulldown value on temp inputs

Post by Matt Cramer »

There isn't a pulldown, at least not one that's there intentionally. What resistance values are you using?
Matt Cramer at DIY Autotune
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GrocMax
MegaSquirt Newbie
Posts: 17
Joined: Thu Nov 14, 2013 4:46 pm

Re: pulldown value on temp inputs

Post by GrocMax »

OK, I think what I am seeing is not due to a pulldown, but a really bad curve fit in the 3 point curve generator, it acts the same as having an input pulldown and not calculating the parallel resistance on an NTC, bad offset in the high voltage area. NTC curves are usually a double curve and the curve generator is more than likely 1st order so its missing the upper voltage curve back. As long as you're never in a really cold climate it won't matter, but if you are it will at some point.

Been making custom NTC sensors for years and providing +/- 1c calibration info for ECU's, as long as the pullup voltage, pullup resistance, and pulldown resistance are known, accurate cals can be done.
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