Drive by wire and the wish to survice the experience.

[Bruce Plecan]

-----Original Message-----
From: Ronald T. Webb <rwebb at ptialaska.net>
To: diy_efi at efi332.eng.ohio-state.edu <diy_efi at efi332.eng.ohio-state.edu>
Date: Thursday, December 31, 1998 2:12 PM
Subject: Re: Drive by wire and the wish to survice the experience.

Maybe that is the most common failure of a pot, but, in a auto application
there
are lots of other things to go wrong, and it would provide some redundancy
in
other failures than the pot, so for the min of effort to do that I think
it's worth while.
Bruce


>Very inventive - but bogus (IMHO).
>
>The most common thing that goes wrong with a POT is the wiper connection.
That'd
>kill both sides, and you're right back to no redundancy.
>
>Keep thinking though...one time in ten "almost a good idea" turns into a
GOOD
>idea!
>
>>
>> One comment:
>>
>> If the TPS is *just* a normal pot, and you're building all the
>> circutry yourself, you can easily get one level of failsafe by
>> doing things a little differently. Normally you put +5 (or
>> whatever) to the top of the pot, ground the bottom, and read Vs
>> from the wiper. Instead, put +5 to the wiper, and use both the
>> other terminals of the pot as the "top halves" of 2 separate
>> voltage dividers. (i.e. put a resistor from the top of the pot
>> to ground, and measure the voltage at that connection. Do
>> likewise with the bottom of the pot.) Now you have 2 separate
>> signals coming from one TPS, and thus a way to check A against
>> B. The drawback is the signals have the funky curve of that
>> type of voltage divider (you may need more bits in your A/D)
>> and the relationship between A and B is a little weird. But
>> almost any common pot failure mode (open, dead spot, short)
>> will give A/B signals that are obviously inconsistent, and
>> there's your extra safety margin.
>>
>> > Any recommendations of A/D sampling freq. for the TPS?
>>
>> And one question: Bruce (I think) mentioned an OE app using 180Hz
>> sample rate on the TPS. Does anyone have an idea of the sample
>> rates used for other sensors, in any other application? Mainly
>> I'm thinking about MAP, but any trivia would be interesting.
>>
>>    Chris C.
>
>