How do I tell if my pyrometer is a resistance type or an electric type? If it needs power only for the light I would tend to think that it's an electric type one.

Which one is better?

 

My Stewart Warner would probably be resistance type as is has just 2 wires. No outside source needed to make it work. My bro has a Autometer that requires 12v to work. That would be, to me, a electric one. I think

 

can anyone verify that?
I had heard that the autometer ones were resistance type. Were you told not to cut the wires?
I thought a resistance type would need power to operate because it is resistance and creates no voltage.....hmmmmm

Other opinions???

 

I thought all thermocouples created a voltage?

My Isspro uses two wires from the thermocouple (it did warn not to shorten/lengthen the wires) then a box that I assume is an amplifier, then wires to the gauge. The box requires 12v.

 

I believe it is resistenace, not voltage. Resistance across the thernocouple drops as heat rises. That's why they warn you not to shorten the wires. They're very sensitive and calibrated to account for resistance of the wire itself.

 

I have always been told DO NOT MESS WITH THE WIRE LENGTH .

 

Thermocouples produce a very small voltage. There are direct (2 wire) and amplified (Isspro, AutoMeter) style pyrometers out there. Direct pyros are more fragile because they are so sensitive.

 

To avoid someone getting confused, ISSPRO makes both, mine being two-wire direct.

 

my auto meter is 2 wire direct, and i have a problem with the gauge sticking on the low side untill you tap it with you finger

 

Right you are Dave. Theres no such thing an a resistance pyrometer. All thermocouples produce a varying millivoltage that changes directly with the change in exhaust gas temperatures. This difference in millivoltage is simply displayed by the incab guage.

With ISSPRO guages, The EV series pyros (the ones with the amplifier boxes) are much better and offer much better lighting than the old HD style Isspro pyros.

 

So then the reason for the wire length is due to voltage drop caused by resistance?

 

Kind of.

The resistance of the thermocouple extension wire is negligable. The reason you dont want to cut the extension wire on the two wire guages is because the whole thing is calibrated at the factory - cutting the wire will change the mV reading.

 

The autometer guage has like 5 wires in it that need 12v and it's one that you can't touch the lead length. So I'm a bit confused...

I have a stewart warner one with 2 wires that needs 12v only for the light.

If I get a generic thermocouple with 2 wires will it work?????

 

I have an old Isspro 2 wire pyro in my truck. I have a new Isspro EV pyro in my VW. IMO I like the 2 wire pyro better. It has slightly better response time than the EV pyro. The EV does look better though.

Dean

 

...because what causes a change in voltage when you shorten the wire?