[Diy_efi] Question relating to old posts.....cheap datalogger?

[Perry Harrington]

IAT sensors are thermistors.  Their resistance is a negative logarithic function.
At low temps they are high resistance, at high temps they are low resistance.

To sample an IAT you need a bias resistor to provide a pullup to +5v,  ECUs have
these internally. If you want to use an IAT by itself, you'll need to wire it up
with a bias resistor.

Basically, you'll need a regulated 5v power supply, an LM7805 is sufficient.  You'll
need an appropriate bias resistor.

There are only 3 *major* values of thermistor out there.  GM, Ford, and Bosch/Nippon
Denso.  For GM, use a 2.49k bias resistor, for Ford, use a 27k bias resistor, and for
Bosch/Nippon Denso, use a 2.2k resistor.  At 81 degrees fahrenheit the thermistor's
resistance will equal the bias resistor's value.  You can use a voltage vs temp curve
for a GM sensor if you use the above bias values.

The sensor is tied between ground and the bias resistor, you read the output from this.
The bias resistor's other leg is tied to +5v.

That's the short and sweet of how you read an IAT sensor without an ECU.

--Perry

On Sat, Jun 07, 2003 at 07:35:01PM -0500, Tim Drinkwater wrote:
> I wouldn't be the one to ask I'm more or less just a lurker.  I only 
> more or less know the general principles of EFI.  Hopefully someone else 
> can help you out.
> 
> Tim Drinkwater
> Mr Motor wrote:
> > Yup, that is what i was looking for thanks. :)
> > 
> > one thing i'm not sure about is if this is going to work for
> > what i want it to do. Do you know how IAT sensors actually work?
> > electrically? 
> > 
> > it says in this link that "Examples of low level signals that
> > are not suitable are directly connected thermocouples,
> > thermistors, RTDs, strain gages or strain gage-based
> > transducers." 
> > 
> > Do you know if i can datalog IAT temps using this software
> > setup? Thanks

-- 
Perry Harrington			Data Acquisition & Instrumentation, Inc	
perry at dainst dot com					 http://www.dainst.com/

Those who would give up essential liberty to purchase a little temporary safety
deserve neither liberty or safety. Nor, are they likely to end up with either.
                             -- Benjamin Franklin

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