Is this Digital pyrometer any good??

C Craft

Well-Known Member
I am looking for a good digital pyrometer for reading temp. Something I can move around to double check temp readings I am getting! Is this any good!! Or should I be looking for something else! Yes, I realize this one is supposed to be for use with a kiln. Finding one that will read high temps is not easy!! I can rework the thermocouple if I need to, to make it hand held!!
https://www.amazon.com/gp/product/B00R32JKQI?tag=mc8239334-20

What are you using??
 

Sean Jones

Well-Known Member
Atlas Forge has one that goes to 1999 F for $40.00

I have the same setup that Ed Caffrey shows on his web page. It's a bit more money and you need to source the PID controller and thermocouple separately. Currently the PID Controller runs 28.95 and the thermocouple I have is from Omega. The link goes to a different model than the one I have. It looks like the one I have is discontinued. However that one goes to 2440 degrees F. I think mine goes to 1999 F
 

Doug Lester

Well-Known Member
Making it hand held might be a problem for that thermocouple. I've seen some that were in a long stainless steel tube but finding one that will go up to 2300° might be difficult and pricey. The problem, as I see it, with the thermocouple that comes with it would be protecting the contacts on the back around high temperatures. They can be inserted through holes in the sides of a forge, though.

Doug
 

C. Killgore

Well-Known Member
I had been looking at a few from omega. Was thinking about getting a handheld unit. Here's their cheapest one. Obviously you'd then still need to buy a type k thermocouple from them. Might want to look around on omegas site a bit. They've got some good stuff. I'm using one of their omegaclad XL probes in my forge. Seems to be holding up really well.

https://www.omega.com/pptst/HH-25U.html
 

Chris Railey

KNIFE MAKER
I so need one of these. I accidentally sold two knives Friday so now is the time I guess. I know nothing about them though. Cliff if mounted the one you are looking at in my forge would it work? Mostly for HT.
 

KenH

Well-Known Member
The one you linked to will work nicely, but for forge work you do NEED a ceramic sheath to protect that TC tip. Even with #8 wire it's not going to last very long inside the forge, especially if you get up to welding temps. Something like this I just ordered from Auber ($5 shipping):
https://www.auberins.com/index.php?main_page=product_info&cPath=20_3&products_id=40

Here's another choice you might consider, a tad less expensive and will do the same thing and even allows you to read from two different TCs at the same time: https://www.ebay.com/itm/292291928513?, but you will need to order this high temp TC for $9.23 (free shipping):
https://www.amazon.com/dp/B07KPFW79K/?

You'll have the same as the item you linked to for <$30, but will still need the ceramic sheath for $25 shipped from Auber.

With the ceramic sheath mounted in the forge (and can be slid out), the TC can easy be moved around to other places. Using the lower temp TC for Tempering oven, etc. Ooops, just realized, the high temp probe I linked to doesn't have the TC wire required to connect to the meter. I have used this probe: https://www.amazon.com/dp/B00XJ0VUBG/ which goes to 1300°C but doesn't last too long when inside the forge. Putting inside the ceramic sheath would work fine. You'll still need the plug to install on the TC wires. I can mail you a spare plug if you decide to go this route.

Ken H>
 
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Volkert Forge

KNIFE MAKER
I use the 1 that Sean mentioned from Ed's site. It works well for 3 months now I only use it for quick temp checks or I stick in my baffle when heat treating
 

C Craft

Well-Known Member
What I am trying to do is check a couple of installed thermocouples and PID units for true readings, so to speak!! That way if they are reading off I can re-calibrate the reading. That is why I want to build an accurate portable unit!!!

Come to think of it I have a thermocouple very similar to this one, https://www.omega.com/pptst/KQXL_NQXL.html somewhere out there in the shop!! I pulled it out of my toaster oven set-up cause it was in the way!!!

So now all I need is a unit to read the temp! Funny how seeing something can jog your memory!!
 

timgunn

Well-Known Member
I used to use TM902C handheld digital thermometers (pyrometers) from Ebay. They read DegC only and only work with a typeK thermocouple. One disadvantage is that you need to convert if you think in degF. An advantage is that there is no way of having it set on the wrong range. Another advantage is that it costs under 5 bucks delivered.

I had maybe 20 of them over 4 or 5 years, bought in ones and twos. Every one went on the calibrator at work and they were all as accurate as western-built (US, UK, Germany, etc) units costing upwards of 20 times the price. I bought about a dozen of them in a single order a year or two back and they didn't look quite the same as the previous units when they arrived. This batch all checked out perfectly up to 800 degC (1472 degF), then started to show an error which increased with temperature. I can't remember which way round the error went at the maximum I could compare: I either had a reading of 1290 degC (2354 degF) at a simulated 1372 degC (2500 degF), or a reading of 1372 degC at a simulated 1290 degC. Either way, it was no use for measuring forge temperatures.

Although I would no longer trust one I had not personally checked at temperatures above 800 degC, they are fine at typical tempering temperatures. They come with a Glassfibre insulated bead thermocouple that is good to around 400 degC, 750 degF and is great for checking accuracy on tempering equipment, being thin and flexible enough to close in an oven door for those using domestic ovens. To me, a TM902C is worth having for that thermocouple alone.

I now use primarily DM6801A units, again off ebay. These are switchable degF/DegC, have proved boringly accurate on the calibrator and are about 10 bucks delivered. Again they are type K only. All mine have come with what seems to be a PVC-insulated bead-type thermocouple. PVC insulation is only good to around 105 degC/221 degF, limiting it's usefulness to us. One of these will work with your Omega thermocouple, assuming it is a type K, though it's worth checking the connector. The link shows a standard (round-pin) connector and you would need to adapt to a miniature (flat-pin) connector to plug into the instrument.

My preferred thermocouple is an Omega KHXL14GRSC24. It has a 24" long, 1/4" diameter super Omegaclad XL sheath, which is rigid enough to hold it in place wherever you want to measure within the forge. It has a handle and a curly cable ending in a miniature plug which fits most handheld type K pyrometers, including those mentioned above. The sheath material will tolerate short periods at most bladesmiths' idea of welding temperature and will respond fast enough to allow you to measure the temperature profile in your forge quickly enough that you might actually do it.

https://www.omega.com/pptst/KHXL_NHXL.html

The part number builder on the web page will not let you have 24" long, but if you put the part code into the search box at top right, it'll give you a price.

Personally, I have never really liked the idea of a permanently-mounted thermocouple in a general-purpose forge for a number of reasons. Type K thermocouples suffer from "drift": a progressive loss of accuracy caused by time spent at high temperatures. Most forge/burner systems can be set to a gas and air intake value and will hold pretty tightly to a temperature once set. This enables the thermocouple to be removed once the forge is stable at temperature. Having the thermocouple in there when it is not actually needed means that it will be less accurate when it is needed due to drift.

In order to be useful, the thermocouple usually needs to be reading the temperature at the workpiece location. This tends to mean it is in the way while the forge is in use.

However, if the forge has a large work volume at an even temperature, a reasonably out-of-the-way location might be found that is consistently the same temperature as the workpiece location, so that a permanent thermocouple can be installed there. Few forges seem to have such even heat distribution and on those that do, finding that permanent location is likely to require temperature-profiling the forge with a movable thermocouple. Once you have a movable thermocouple and can set the gas/air/temperature settings, there actually seems little advantage to a fixed thermocouple.

There are certainly some specific forge designs and uses for which permanent thermocouples are appropriate. To me they just don't seem to include a general-purpose forge for hobby-type use.

We use various different thermocouples at work. Several years ago, we were looking into thermocouples for a particular process when a change in emissions limits meant that we needed to reduce our process temperature from 1200 degC (2192 degF), initially to 1100 degC (2012 degF), then to 1000 degC (1832 degF). We had been using type S thermocouples with ceramic sheaths for the 1200 degC process, but wanted to change to base-metal thermocouples in metallic sheaths for reasons of cost and ruggedness. We were aware of the theoretical possibility that drift would be an issue, but could not find any information to indicate how significant it would be. To find out, we set up Type N and Type K thermocouples in the process next to the Type S, displaying the temperatures shown by all 3 on the operator panel. With the temperature at 1200 degC, the type K showed drift, relative to the type S, in excess of 10 degC (18 degF) over less than 70 hours (fitted on Friday, showing over 10 degC of drift on Monday), increasing to a 23 degC (41 degF) drift after a week, where it remained for the next two weeks. The Type N remained within a couple of degC of the type S for the full 3 weeks. We changed the Type K, but not the type N, and ran at 1100 degC. This time, it took over a week for the type K to drift 10 degC (18 degF) from the type S and it drifted to 14 degC from the type S over 3 weeks. The type N remained within a couple of degC of the type S for the entire 3 weeks (so 6 weeks in all). We again changed the the type K, left the type N in place, and ran the process at 1000 degC. All 3 thermocouples were still showing within a couple of degC of each other after 3 months of operation. We have since replaced type S thermocouples with type N whenever the type S have failed or whenever we have had an opportunity to do so at a plant shutdown.

Following this, I only ever fit type N thermocouples to my homebuilt HT ovens.

I use type K thermocouples for "normal" short-term use in forges because the extra range is useful. If I am tuning burners, I use type S thermocouples (the ones removed before they failed at work).
 

EdCaffreyMS

Forum Owner - Moderator
What I am trying to do is check a couple of installed thermocouples and PID units for true readings
Don't get yourself too deep into that one! It'll drive you nuts! Normally, the level of temp measuring devices used in most home/one man shops is going to be +/- a given percentange...... remember when I posted about heat treat ovens? Same thing applies to pyrometers.....whether homemade or commercially purchased. What I'm saying that in order to aquire a pyrometer that will read "dead nuts"...... you'd pay THOUSANDS of dollars for what is referred to as "Labratory Grade". ;)

The thermocouple you reference in your post above, is the one I use. The one I list on my site for building a pyrometer is a cheaper version, that's only rated for 2000F...... I did that because people where whining and crying about the thermocouple being "too pricey!" :) We all know that those are the one's who are NOT serious about any of this...... so I list the cheaper one so I don't have to read all the whiny emails. :)
 
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EdCaffreyMS

Forum Owner - Moderator
I was referring to the one in his most recent post above.......

BUT.... just for clarity sake.... either of the following are ones I either use, or would use in my welding forge....
https://www.omega.com/pptst/KMQXL_NMQXL.html

https://www.omega.com/pptst/KQXL_NQXL.html

Also, just my thoughts on specs....
-Type K
-1/4" diameter (I've found the 1/4" will far outlast anything of smaller diameter)
-UNGROUNDED
-12" length
The PID I recommend is here: http://www.caffreyknives.net/forge_pyrometer.html (click on the pic and it will take you where you can purchase)

AND, likely the thing that most take for granted, but likely the most important part...actual, real, THERMOCOUPLE WIRE. You would not believe how many people have built this pyrometer, then called me screaming that it won't work.......and when we go through things step by step and get to the "wire"....... many tried to use household thermostat wire.....and a couple even tried using an old lamp cord!!! (for attaching the thermocouple to the PID) If you want it to work, it's gotta be honest to goodness, actual, thermocouple wire.
NO MATTER HOW HARD YA TRY..... YA JUST CAN'T FIX STUPID!!! :)
 
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timgunn

Well-Known Member
As Ed says, the wire is absolutely critical. I’ll try to explain why.

A thermocouple is just 2 different metals in intimate contact with one another. When the junction is heated or cooled, a (very small) Voltage is produced which varies with the temperature. There are an infinite number of possible metal combinations and a very small number of them have been identified as giving “useful” temperature:Voltage relationships over different “useful” ranges. These have been given identifying letters and the temperature/Voltage relationship for each has been tabulated.

A thermocouple measuring circuit consists of the two different wires joined at the measuring junction and at the instrument displaying the temperature. The instrument looks at the Voltage it is getting from the measuring junction and looks up the temperature to which this corresponds in its internal look-up table. This tells the instrument how much hotter or cooler the measuring junction is than the other junction at the instrument. By convention, this junction at the instrument is referred to as the “cold” junction, even though it may be at a lower temperature than the measuring junction (aka the “hot” junction). Confused yet?

A separate precision measuring circuit within the instrument tells the instrument the temperature at the instrument (“cold”) junction. The instrument adds the relative temperature of the hot junction to the cold junction temperature as measured at the instrument and displays the resulting measuring junction temperature.

For all this to work properly, the legs of the thermocouple need to be the same material all the way back to the instrument.

If you introduce a different metal for the wiring, you will have a new junction where the different metals join and this will produce a Voltage of its own which depends on the composition of the metals and their temperature. In most cases, the material combination will not be one of the standard combinations and the temperature will not be known. The Voltage generated at this rogue junction will add to the Voltage generated at the hot junction and the instrument will look up the resulting Voltage, add it to the instrument temperature and display the result. It will, of course, be wrong.

Interestingly, one of the worst things you can do is to use the correct wire but use it the wrong way round. In this case, you will have 2 new junctions, each generating a Voltage, at the connection location. The resulting error will be twice the difference in temperature between the instrument and the terminal block where the wires are joined.

I know all this stuff and can deal with it, but I do like an easy life. I tend to buy my thermocouples with the cable, and if required a plug, already fitted by someone who does it all day, every day. Hence my recommendation for a plug-and-play handheld thermocouple assembly.

Just for info: Thermocouple “extension” cable is made from exactly the same materials as the thermocouple legs. There is also thermocouple “compensating” cable. This is made from cheaper materials which, crucially, behave identically to the thermocouple legs over the much narrower range of temperatures to which the wiring between the thermocouple and instrument is likely to be subject (maybe 0-250 degF). The cost difference between extension cable and compensating cable is minimal if we are dealing with type K thermocouples, but can be pretty substantial if we are dealing with Platinum-based thermocouples.
 

Daniel Macina

Well-Known Member
Hey C Craft, I actually have a brand new, in box PID if you want it. If you haven’t picked one up yet. I started sourcing parts to build an oven last year, but decided against it ultimately. It’s a pretty nice one. You are welcome to it my friend.:) I have no use for it, and not going to waste time trying to sell it. Also have a couple 40a heat sinks and a spool of 16gauge event wire. Don’t have a TC though. Again, all unused in original packages.

Some good folks in here!:)
 

Jim Levite

Well-Known Member
The one you pictures from Amazon, I purchased from aubrins with ceramic Sheath. With a heavy duty 11" probe and ceramic Sheath think I paid about $85. Works well so far.
 

mpcoppin

Member
I have a question for timgunn and EdCaffreyMS.

It seems like Tim recommends the 24” Omegaclad and Ed suggested 12”.

How deep into the forge do you have to insert the probe?

I’ve been looking at the 1/4”, 24” long with the handle and the piggy tail wire because I worry about the handle and connections overheating if I get a 12”.

Thoughts?
 

timgunn

Well-Known Member
I go in through the work port of the forge and this lets the tip be put pretty much anywhere that the workpiece might reach. I tend to want to know how temperatures vary throughout the forge. Insertion depth depends on the forge and the reason I use 24” is to keep the handle, and my hand, from overheating. Occasionally, I’ll poke the thermocouple through an offcut of ceramic fibre blanket or board as a heat shield if I am checking a longer forge than about 15”.

The Omegaclad XL will not need a ceramic outer sheath. As with anything on the hot end of a forge setup though, it is important to recognise that thermocouples are consumables.

The part number I quoted above was for the grounded junction. It looks like Ed spotted it and I did not. The better one for general use is the KHXL14URSC24, with the 7th character denoting the Ungrounded junction. The grounded junction responds faster and does have advantages in specific applications (mine was trying to check the small temperature variations throughout a dedicated HT forge). The biggest disadvantage of the grounded junction is that it is much more susceptible to thermal shock: the junction is welded to the inside of the sheath at the tip. If you stick a cold thermocouple in a hot forge, the sheath gets hot and expands before the heat gets to the thermocouple “legs”.This can cause the legs to break.

Ungrounded thermocouples have the Magnesium Oxide insulating powder between the junction and the sheath and therefore do not put the legs under the same tension when inserted into a hot forge.

The most common failure mode for Mineral Insulated thermocouples that I see is loss of the sheath as a result of temperature cycling and Oxide layer shedding. When the sheath gets hot, it forms an Oxide coating which largely prevents further Oxidation. When it cools, the Oxide layer can detach. After a few cycles, there will be no sheath left in places and the thermocouple will fail. Different sheath materials can retain the Oxide through different temperature cycles. Types 304 and 316 stainless steels have about 18% Chromium and 8% Nickel and they will lose their Oxide layer when cycled to around 850 degC. Type 310 stainless has a higher Chromium content (25%) helping to form a stronger Oxide layer, and a higher Nickel content (20%) which brings the thermal expansion coefficient of the metal closer to that of the Oxide. As a result, it will retain its Oxide layer through cycles to around 1100 degC. Inconel sheaths will handle similar cycles to 310. The Omegaclad XL is claimed to be good to 1335 degC. Whilst I cannot say how many cycles to this temperature it will last, my limited experience with it certainly confirms that it outlasts type 310 at the higher temperatures.
 

Benjy

Active Member
Ok, I need to replace my thermocouple in my forge, I used Ed's design to build it a year ago. That thermocouple had wire that connected to the PID. It looks like the new one does not come with them... I am looking at the K QXL 14 U 12. I am not sure what I need....
 
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