Date:         Sat, 28 Sep 2013 09:15:45 -0400
Reply-To:     Dennis Haynes <d23haynes57@HOTMAIL.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Dennis Haynes <d23haynes57@HOTMAIL.COM>
Subject:      Re: Temp II (for ECU) Sensor: Voltage Range?
Comments: To: neil n <musomuso@GMAIL.COM>
In-Reply-To:  <CAB2RwfiVWQpk3cE7jNm=FFJD_gwz2qy0_iR8wQfTPwfKwZ7CNw@mail.gmail.com>
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If you want to be "electrically obsessed, learn Ohm's and Kirchhoff's laws. Add the formulae for power and the will be no DC circuits you can’t figure out. 
Then for working on programmable logic controllers, (PLC's) and most other ECU controlled stuff you need to understand the difference between sinking and sourcing circuits. This can get confusing as outside a battery current is actually flowing form - to +. 
Most work done on semi-conductor based controllers works off 5 volts. The VW ECUs are no exception. The sensors except for O2 are sinking.  In other words, there is a 5 volt supply that feeds all the sensing circuits. The temp sensors sinks that circuit to the chassis. As the sensor warms up the resistance goes down, current increases and voltage drops. 

Even the gauges operate at some voltage below battery. This is done so system voltage does not affect gauge readings.

So those numbers in the real world are possibly meaningless. 

Dennis


-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of neil n
Sent: Friday, September 27, 2013 1:49 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Temp II (for ECU) Sensor: Voltage Range?

Hi all.

With a "Luxemburg" Motronic 2.9 and Vanagon WBX Digifant coolant temp (for ECU) sensor in hand, I noticed each had a different voltage range stamped on them:

Motronic sensor: rated up to14.x Volts
WBX sensor: rated up to 12.x

My guess is that this is due to the WBX Digifant and Motronic engine management (ECU) systems having different voltage demands and control parameters. True? But ....

Since some (all?) aftermarket sensors may not have a voltage rating stamped on them....

Do aftermarket unmarked sensors possibly fail early due to a limited voltage range?

Just some Friday Fodder from the Electrically Obsessed,

Neil.

--
Neil n

Blog: tubaneil.blogspot.ca

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http://tinyurl.com/d7gd5ej