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Date:         Mon, 29 Dec 2003 11:02:50 -0800
Reply-To:     David Marshall <vanagon@VOLKSWAGEN.ORG>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         David Marshall <vanagon@VOLKSWAGEN.ORG>
Subject:      Re: What makes a pyrometer's cable so special? - conclusion
Comments: To: Carl Hansen <carl_hansen@IEEE.ORG>
In-Reply-To:  <v0401170abc158b413069@[192.168.0.101]>
Content-Type: text/plain; charset="us-ascii"

Carl, There are a few things that bother me here...

1 The back of the VDO gauge has four connectors, not three. 1, 2, +, - 1 - signal wire (red) 2 + signal wire (yellow) + 12V - GND

2 If the connections are so important, why did they not give me any crimpable female spade connectors for the back of the gauge?

3 There are four connections between the inside of the gauge and the thermocouple. A pair at the gauge and a pair at the thermocouple.

Of course, VDO technical service isn't available for some reason today.... sigh...

David Marshall

Fast Forward Automotive Inc. 4356 Quesnel-Hixon Road Quesnel BC Canada V2J 6Z3

http://www.fastforward.ca mailto:sales@fastforward.ca Phone: (250) 992 7775 FAX: (250) 992 1160

- Vanagon Accessories and Engine Conversions - Vanagon, Transporter and Iltis Sales and Importation - European Lighting for most Volkswagen models

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-----Original Message----- From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com]On Behalf Of Carl Hansen Sent: December 29, 2003 12:12 AM To: vanagon@GERRY.VANAGON.COM Subject: Re: What makes a pyrometer's cable so special? - conclusion

David,

Well everyone is bouncing around the right answer here, but in technical terms that might not be easily understood so here's a laymans explanation. I learned the answer 30 years ago when I added a VDO Head Temp Gauge to one of a string of modified Beetles and/or Loafs. I'm also an electrical engineer so I guess I'm supposed to know this stuff.

The system is calibrated to work properly with a length of wire AND 3 connections:

The wires ARE two individually different wire TYPES so that a small potential (or voltage) is generated when the end connection is heated. Actual length is not so important as is the number of connections. There are 3 terminals, one terminal at the end that senses the heat (as was noted by others, typically a soldered joint) and 2 other connections, one + and one - at the gauge.

If additional connections are added, they also can generate a small potential (or voltage). The additional potential can throw the calibration of the gauge off. The potential generated can be millivots at best, hence the sensitivity to ADDING an additional length of wire..

p.s., if memory serves me correctly, I was able to run the ?14 foot length? of wire provided by VDO back to the engine compartment of my vans without having to add lengths of wire, or was it the beetle?? umm, that was a long time ago..... so I put on a jacket and went out to measure SyncroBeast and note that 14 foot might be a challange to run to the back.

Ch carl_hansen@ieee.org

'96 GLX Passat Wagon - they were all green - weren't they? '87 944 na - RED! needs head gasket & tires (but what a sweet ride) '89 SyncroBeast Vanagon - parked for the winter - boo hoo '87 16V GTI - dead, needs rings '80 850 Yamaha Special - burns oil '89 16V GTI w/ toasted motor - needs tranny '99 Beetle - red, red, red (SO's)

New Jursey (Gawd Forsaken State of) (our hearts remain in MinneSnowta)

In a perfect world without walls or fences........ .....................why would we need Windows or Gates?

........... Only a True Jedi Master can touch the dark side ............ and remain untainted!

We will return... when we get back... from where we are going! Ed


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