pyro calibration

[jkern]

my pyrometer always reads anywhere from 75* to 150* when the truck is cold. the ambient air temp has been anywhere from 0* to 40*, i i would expect the pyro to read accordingly on a cold engine (without the block heater). is there any way to calibrate this, or is that the inherant error in a 0-1500 degree gauge. maybe my EGT are lower than i thought!!

any input... thoughts?


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Jeremy Kern
1999 2500HD 4x4 QC,SB, ISB, 5spd, 3. 54LSD, 33x12. 50 cooper STT's Denver off-road bumper with Ramsey RE12k, PIAA series 520 lights, Rancho RS9000's, heavy ft. springs, JVD Torque Enhancer, DiPricol boost and pyro gauges, and a bunch of other little things! www.geocities.com/phrn30 for pics!

 

[Guest00]

I asked Isspro the same thing. #ad

They said that at ambient temp the meter will read 75 to 150*, It is normal. The Isspro pyro accruacy is at 1200*. #ad


[This message has been edited by JNutter (edited 03-08-2001). ]

 

[Vaman]

The thermocouple can't be calibrated (the physical charactistics of the two metals can't be changed) but the indicator can and should be calibrated.

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98. 5 2500, 24v, QC, 4x4, 4. 10 LSD, short bed, Line-X liner, tow package, camper suspension, Westin nerfs, camper shell, TST PowerMax3, 275 RVs, EGT/Boost pillar gauges... Love my Cummins, no love for Dodge

 

[illflem]

There is no way to calibrate a pyro that I know of,but not to worry they are most accurate in the middle of the gauge's range which for you is 750°.

 

[TowPro]

I have the same problem. But was told they are calabrated at 1200 deg. It you want to test it, get something called a Temple stick from a welder supply. This is like a crayon that melts (actualy changes color) at a preset temp. Get a 1000 deg one. Remove the probe, mark the end with the temple stick, and heat the end until the color changes. (don't put the flame to the spot you just colored, the temple stick would burn off, you have to heat the other side of the end of the probe) At that point see what the gauge reads (you will have to have somebody reading the gauge for you, the probe would cool off by the time you could run around and look at the gauge. We used a standard Propane Torch, it took about a minute or two to get a reading that high.

This is not the "recomended" way to test them, but the only way I could figure with the stuff I got.

Now the Factory has Mili Volt readings for testing the probe (with a digital VOM) I think I posted them before, maybe a search would turn them up.

 

[dodgedieselguy]

Here's why your gauges read 75-150 degrees when cold:

Thermocouples don't read absolute temperatures. They produce a voltage which is proportional to the temperature *difference* between a hot junction (in the turbo elbow, etc) and a cold junction. The cold junction is actually formed by the connection of the wires at the meter. Now comes the tricky part: Simple analog meters don't know what the cold junction temperature is, so they just assume you're going to try to be a comfortable human and set your heater or A/C to around 75 degrees in the truck. So they assume 75 degrees for the cold junction temp. Now when you get in your truck first thing in the morning, both junctions would be at the same temperature. The voltage roduced is zero. So the meter reads the 75 degree offset it *assumes* for the inside cab temperature. A good way to calibrate your meter is to stick the hot junction end into a pan of boiling water, which boils at 212 degrees at sea level. If the cab temperature is 75 and the gauge reads 212, you're right on.

-HotVP44
Blue Chip R&D