more thermocouple ?

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Installed my autometer, ultralite pyro and boost gauges - turned out great. Have a few questions though.

I made the mistake of cutting the end of the wires on my thermocouple about 8". After the fact, I remembered that it is a resistance wire of sorts and requires the exact length. Although I did this, I seem to get what would appear to be accurate readings. Cruises down the highway at around 600-650, cools down before shutting off to about 300, and on a WOT run in 6th gear, so far I have gotten it to about 1000. The probe is mounted pre turbo as you may have guessed. The boost readings appear to be normal as well. 5-7 psi cruising down highway on level ground, just over 19 max load. With this info, does anyone think I need to worry about the shortened wires.

And finally, I was wondering if anyone with the autometer setup knows of a shorter thermocouple. Doesn't seem to create a problem, just longer than necessary. The part number of my current probe is auto meter #5249. Is it possible to interchange different probes with the same gauge?
Thanks in advance

 

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cjohnson,

Everything sounds normal.

I work with thermocouples in the machinery the company I work for builds. At least in our applications, the length of the lead wires has no effect on the reading. We have them with wires as long as 100 feet and as short as two feet.

The millivolt signal that the thermocouple generates is right where the two wires connect. So little current flows through the wires that the resistance of the wires is neglegible.

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98. 5 2500 QC LB 4x4 5spd, white. BFG 285x75x16
Cummins 24v w/ TST PowerMAX w/EGT and Boost gauges on A-Pillar.
VanAaken CPC. K&N In the factory air box. Stock Injectors, Stock Exhaust (complete with rattling baffles in muffler).
SnugTop, JJ Stainless Running boards, Tow Hooks, Bushwacker Street Flares, and a Cup Smoothie.
57,000 miles (3/20/00)

 

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Sounds good to me Sean. Thanks for the info. One thing that concerns me is that the TST website has an install instr. It warns against shortening the wires. What do you make of this. Thanks again,
Craig

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2000, 2500,QC,4x4,white,tow,leather,6 spd,4. 10, 4" exhaust - turbo back, K&N, Balls of steel hitch, line-x bedliner...

 

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There is no reason not to cut your thermocouple leads to length, we're talking short leads here. Don't splice them to make them longer!

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Glen Eaton
2001 2500QC SLT LB 5sp 4x4 Garnet Line-X Steel GemTop

 

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Well guys, here's a possible reason for differing opinions about thermocouple leads.

Some pyro gauges, like the Auto-Meter, use a small module that requires 12V power. With these type of setups, it makes no difference if the leads are 2" or 50 feet. The other type of gauge, like the ISSPRO, does not use a power supply at all. The only connection is to the thermocouple probe. With this type, I do believe it makes a difference how long the wires are.

What do y'all think?

BOMBED


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Evan A. Beck
Prez, NW BOMBers

2001 4x2 QC, 139" WB, 6-speed, ETH, SLT... yadda yadda yadda... 1,350 miles and counting!

Check out NW Punk for more info!

 

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I wacked out 3ft of lead wire from my Isspro gauges,didn't make a difference. Am I lucky or just stupid? Don't answer that! #ad


-Mike

 

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Here is a little EE101. The thermocouple junction is made with two dissimilar materials. This junction, when heated, produces a small voltage that increases as the junction is heated. This voltage creates a current in the gauge to move the needle. For long runs there is a loss in the leads but for 5 or 15 feet the loss is so small that it can be neglected.

Use the lead wire supplied with the thermocouple and do not make splices in the wire. Each splice creates another junction which will add error to the system.

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Glen Eaton
2001 2500QC SLT LB 5sp 4x4 Garnet Line-X Steel GemTop

 

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Moved to products forum.