ISSPRO Pyrometer not at zero

[Booyah45828]

I've got an isspro pyrometer #604. I've had it in a box of spare gauges and went to pull it out today to order a thermocouple for it. Anyways, the gauge without a thermocouple on it sits at 200*F. Touching the terminals together makes the needle wiggle a bit, but it never returns to zero.

I don't remember what it was sitting at when I bought it and put it in the box, but I don't think what it's doing now is normal. Is there any way to recalibrate these things or reset them to zero?

 

[Isaac Ristow]

theres a isspro in a old semi out back that hasn't run in 10 years it also sits at around 200-300 degrees I think if I remember right the thermocouple is shot and maybe not hooked up. If you can still get thermocouples I might use it one day

 

[DrCharles]

Any K-type thermocouple will work. They range in price from $6.99 (don't waste the money) to $100 (probably overpaying for the name on the box). Just remember you need special leads to extend the cable if it's not long enough (can't just splice in some copper wire).

 

[YJMike92]

I have Hewitt Pyrometers in two of my trucks which read around 100 degrees regardless of ambient temperature.
I called tech support they said it was normal. Maybe yours is as well? Call their tech line and ask.

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[DrCharles]

It may be "normal" for them, but tells me their cold-junction compensation is fixed (so only correct at one ambient temp) or nonexistent!

The cold junction is where the chromel/alumel thermocouple leads meet the terminals on the back of the gauge. A good pyrometer will have a temp sensor thermally coupled to ( or at least physically near) the cold junction, so its reading should track the hot junction (the tip of the probe where the chromel & alumel wires are welded together), regardless of ambient temp.

I'd be interested to know what your Hewitt (or any other pyro) gauge says if you put the probe in slushy ice, which is very close to 32F, or boiling water (212F at sea level, about 1F lower for every 500' elevation)... and how much the reading changes if the gauge itself is at winter temps or 120F heat-soaked-cab summer temps.

I guess it's only important to have an accurate pyro if you're pushing the 1200F limit of our engines. If it's 100F off that could be important...

 

[ttman4]

I have Isspro pyro & boost gauges put in back in '90. About a yr ago I noticed my pyro sits at 100* when I start up. About the same time the boost gauge never goes below 1#. Think I'll call Isspro & find out things.

When I put this thing under one of my big loads I'd kind'a like to know where I'm at for sure.

I have a new Isspro pyro & Isspro boost gauges still in box & other day I cked them, they both on 0.

 

[YJMike92]

It may be "normal" for them, but tells me their cold-junction compensation is fixed (so only correct at one ambient temp) or nonexistent!

The cold junction is where the chromel/alumel thermocouple leads meet the terminals on the back of the gauge. A good pyrometer will have a temp sensor thermally coupled to ( or at least physically near) the cold junction, so its reading should track the hot junction (the tip of the probe where the chromel & alumel wires are welded together), regardless of ambient temp.

I'd be interested to know what your Hewitt (or any other pyro) gauge says if you put the probe in slushy ice, which is very close to 32F, or boiling water (212F at sea level, about 1F lower for every 500' elevation)... and how much the reading changes if the gauge itself is at winter temps or 120F heat-soaked-cab summer temps.

I guess it's only important to have an accurate pyro if you're pushing the 1200F limit of our engines. If it's 100F off that could be important...

You kind of lost me there. I think the answer to that in the case of these gauges is even when it is 6 degrees outside these gauges sit at about 100 degrees (both gauges the same). I have the same concern about the accuracy of the gauges that is why I called Hewitt. The picture I posted of the single gauge is from the Amazon sales information.

 

[YJMike92]

I have Isspro pyro & boost gauges put in back in '90. About a yr ago I noticed my pyro sits at 100* when I start up. About the same time the boost gauge never goes below 1#. Think I'll call Isspro & find out things.

When I put this thing under one of my big loads I'd kind'a like to know where I'm at for sure.

I have a new Isspro pyro & Isspro boost gauges still in box & other day I cked them, they both on 0.

I hope you do call. Keep us posted. A pyrometer isn't much good if you can't trust it.

 

[The_Josh_Bear]

FWIW my autometer phantom sits very close to ambient with the power on but engine cold. So on 90* summer day it reads about 100*, and at almost freezing like this morning the needle is buried inside a box without numbers but corresponds to the mid-30's.

So it may be be common for your brand but I'm with the above thinking that if you can't trust it at lower temps...can you trust it at higher ones?

I know that typical gauge accuracy is better in the middle of the swing, but that's more for mechanical gauges rather than electric. Maybe someone knows more about how perfect an electric gauge should be at the very beginning of its scale.

 

[ttman4]

I hope you do call. Keep us posted. A pyrometer isn't much good if you can't trust it.

I'm going to try in next couple days, got lot happening right now.

Originally my pyro was in my inlet side of my 088 turbo on this '90 since '90. I was used to driving it with some really nasty heavy loads, & could run it by "feel" to a point. Now I have this factory '94 IDIT engine in here with my pyro in the upper part of my down pipe. Like I say, I haven't really worked it yet under a heavy load & need to get a "feel" for the new mt location.

Working it hard I used to run 1200*-1250* with my 088 kit. Several have told me that mted now in my down pipe I probably should run around 900* or so working it hard & heavy.

If all goes to plans I'll probably be giving Bessie a work out in next couple months. Need to make a run to Texas & probably be grossing 25K-30K. About 2000 mi should be a fair work-out????

I've also had an Isspro TTM (Turbo Temp Monitor) switch wired into my pyro set at about 300* that lets the rig run & cool down, then shuts engine off. Had this since truck was new. I suspect that has helped extend the life of my 088 turbo kit (approx 800K mi), that & decent oil changes intervals.

Incidentally, I've had some fun a few times thru the yrs with that kill switch. Pull up, get out, lock her up, start walking off & somebody will say "your truck still running." I stop, look at them, look at Bessie a few times, & then about the time she should die I'll give her a magic hex sign with both hands like I got supernatural powers. She dies & I walk off like a big-shot.

 

[Thewespaul]

Isspro has fantastic customer support along with autometer, if you have an issue with the gauge they typically replace it regardless of how old it is or what the story is. You get what you pay for with gauges, and customer service is apart of the cost.

 

[ttman4]

Isspro has fantastic customer support along with autometer, if you have an issue with the gauge they typically replace it regardless of how old it is or what the story is. You get what you pay for with gauges, and customer service is apart of the cost.

Yes I've always had a good feel for Isspro gauges etc. Never been round autometer much but hear good things about them.

 

[DrCharles]

FWIW my autometer phantom sits very close to ambient with the power on but engine cold. So on 90* summer day it reads about 100*, and at almost freezing like this morning the needle is buried inside a box without numbers but corresponds to the mid-30's.

This is exactly how a properly designed (e.g. temperature compensated) pyrometer should work. I wouldn't trust any gauge that doesn't read ambient when the exhaust pipe/manifold is dead "cold".

 

[YJMike92]

This is exactly how a properly designed (e.g. temperature compensated) pyrometer should work. I wouldn't trust any gauge that doesn't read ambient when the exhaust pipe/manifold is dead "cold".

Kind of what I was thnking myself. I may call Hewitt again for a little more clarification. I have my pyrometer sensor mounted in the drivers side exhaust pipe about six inches below the manifold. I can get to 1000 degrees there pretty easy. Does anyone have thoughts as to what maximum temp at that location should be?

 

[The_Josh_Bear]

Max sustained EGTs right there is generally thought to be about 1150*. Or anywhere towards the exhaust valves for that matter. Mine is between #6 and #8 in the exhaust manifold and I use 1150*.