Pyrometer Probe Installation Question

[patty]

so iv got everything all wired up and ready to go...asides the from the part the supplied wires aren't long enough, but thats an easy fix. anyways, my current step is drilling the exhaust manifold post turbo. iv been calling exhaust shops up because i dont have a drill or a tap (or know really what the tap does) to see if they can do it, leading me to my main question.

when putting the probe in post turbo, does it need to be welded in place, or is there enough meat in that part of the manifold to keep the probe from moving? most local exhaust shops say it will need a quick weld, thus they can't do it.

Thanks

[patty]

slowly piecing things together and am leaning towards i wont need a weld

[tonydca]

so iv got everything all wired up and ready to go...asides the from the part the supplied wires aren't long enough, but thats an easy fix.

My apologies in advance if you already know this, but I believe EGT pyrometers are calibrated to the resistance of the probe wire, so if that is the too-short wire to which you refer, I don't think it is as easy as just soldering/crimping on an extension.

Disclaimer: I have not installed an EGT before, so I may not know what the heck I am talking about , but you might want to double-check...

Tony.

[lrp374]

This is the location I installed my probe. It was an easy place to drill and had lots of thickness to tap. Your Probe should have instructions on the size of drill and tap required. You can buy the tap for a few bucks@ CT or any tool store.

[patty]

-yeah i drilled the manifold pretty close to where yours is located, but the i got a little sloppy in the end with the drill and now im having trouble threading in the bung. im sure i will get it to fit!

-thats the first iv heard of pyrometers wiring being pre calibrated tonydca? does any one else know if this is the case?

[EnviroImports.com]

why not just take off your egr valve and put the pyro probe in the new plate, then you get a great double duty, get rid of the black smoke monster and put in a pyrometer.

[Green1]

so iv got everything all wired up and ready to go...asides the from the part the supplied wires aren't long enough, but thats an easy fix.

My apologies in advance if you already know this, but I believe EGT pyrometers are calibrated to the resistance of the probe wire, so if that is the too-short wire to which you refer, I don't think it is as easy as just soldering/crimping on an extension.

I would say that the resistance of the wires should be negligible in comparison to the resistance of the probe itself, as such, adding a few feet to it shouldn't really make a noticeable difference in your reading (you will be affecting the total resistance by less than a couple of ohms), and definitely less of a difference than moving the probe a few inches would (also as stated in several other posts, the actual reading on the gauge is not as important as the relative readings (your own personal max/min/normal readings))

[mararmeisto]

It is unlikely the pyrometer is calibrated to the resistance of the wiring (there simply isn't the requirement for that kind of resolution with the resistance of a conductor), but the meter will definitely be calibrated to the resistance of the pyro probe.

The probe will be a thermistor, which is a special kind of resistor that changes resistance inverse-proportionally to temperature (as the temperature goes up, resistance goes down and vice versa). The meter will be calibrated to the range of the probe, so if you change the probe you'll have to re-calibrate the meter or replace the meter. The wire (a conductor) will present a change in resistance due to increased length (and due to change in temperature), but this is generally considered to be too insignificant to be taken into account by the meter. Select the same gage of wire, but I wouldn't worry too much about the length (other than providing enough to reach from your install point to the gauge).

[tonydca]

It is unlikely the pyrometer is calibrated to the resistance of the wiring (there simply isn't the requirement for that kind of resolution with the resistance of a conductor), but the meter will definitely be calibrated to the resistance of the pyro probe.

Not 100% sure on that point there, Kemo-sabe.

As I said, I have not installed a pyro gauge before, but each one I've read about has something like the following in the installation instructions:

(Source example: http://www.autometer.com/download_instruction/0593A.pdf )

"With the probe installed, the wire harness can now be routed to the gauge. The wire harness is an integral part of the pyrometer calibration. It may not be shortened or lengthened without affecting the gauge calibration. You will need to determine a suitable location to coil the excess wire, and tie it loosely with a wire tie."

And adding crimps in series along the conductors will also affect resistance, and hence meter reading.

Just a heads up, s'all...

[Green1]

I have a feeling that's more the manufacturer covering themselves than something that would be an actual problem, I just can't picture a length of wire (with a total resistance of 0.012 ohms per foot (for 20awg)) having that much effect, even if you add 6 feet to it (likely WAY more than you need) you'll only be affecting the resistance by less than 0.15 ohms. Sure, technically your reading will be wrong, but by what, a couple degrees when you're measuring for hundreds of degrees?

[patty]

in the end i shifted things around abit and it was just long enough the way it came

[tonydca]

I have a feeling that's more the manufacturer covering themselves than something that would be an actual problem, I just can't picture a length of wire (with a total resistance of 0.012 ohms per foot (for 20awg)) having that much effect, even if you add 6 feet to it (likely WAY more than you need) you'll only be affecting the resistance by less than 0.15 ohms. Sure, technically your reading will be wrong, but by what, a couple degrees when you're measuring for hundreds of degrees?

Thing is, I believe the wires from the probe back to the gauge are the same composition as the probe itself (Chromel/Alumel for type K thermocouples). If you just solder/crimp on an extension of standard copper or aluminum wire, you introduce another electrical/voltage-potential junction into the probe, which screws up the calibration - you're measuring the tiny voltage changes from the probe as the temperature changes.

I think just cutting and re-crimping it is sorta OK if done carefully, but adding an extension is not, unless you use the correct type of wire.

http://www.picotech.com/applications/thermocouple.html

Quote:

"Most measurement problems and errors with thermocouples are due to a lack of understanding of how thermocouples work. Listed below are some of the more common problems and pitfalls to be aware of.

Connection problems. Many measurement errors are caused by unintentional thermocouple junctions. Remember that any junction of two different metals will cause a junction. If you need to increase the length of the leads from your thermocouple, you must use the correct type of thermocouple extension wire (eg type K for type K thermocouples). Using any other type of wire will introduce a thermocouple junction. Any connectors used must be made of the correct thermocouple material and correct polarity must be observed. "

Patty, glad to hear that it all worked out anyways.

[Green1]

Are you sure these are thermocouples? I always thought they were thermisters... (which wouldn't have the problem you list)

[mararmeisto]

A bit further reading, and I concur: if it's a thermocouple the wiring will matter. Because the temperatures are over 100 degrees C, it's probably a thermocouple rather than a thermistor.

Good to hear that you were able to route the wiring so it fit with the provided length.

[Green1]

Because the temperatures are over 100 degrees C, it's probably a thermocouple rather than a thermistor.

What makes you say that? the engine temperature sensors are thermisters.
Also when searching for information on pyrometers, all the stuff I found talked about thermisters, not thermocouples.