pyrometer vs IR thermometer

oldanvilyoungsmith

oldanvilyoungsmith

Joined
Feb 7, 2011
Messages
427
Okay, here's the deal. Right now I do most of my heat treating in a propane forge, I've gotten good results thus far with judging by eye, magnet, and testing.

But...

I'd like to do better. There's no way I'm getting a kiln anytime soon, but I'd like to have a way to know my temps pretty accurately. Thus, either a pyrometer or a IR thermometer.

I know a lot of people use a pyrometer, and I'm looking at one kinda like this - link of course I'd also need a probe to go with it, they've got high temp ones for it.

But while in most cases I use my propane forge to HT sometimes I need to use my coal forge, or even make a new coal ground forge for HTing large stuff, so it makes me wonder if I'd rather go with a high temp IR thermometer so that I can just read the temp of the blade itself, whether I'm using my propane forge, or a coal forge.




What do ya'll think? Any reccomendations? I've done a handful of searching, but havent found much on the benefits of one over the other.



Thanks guys, Stephen.
 
Last edited:
Unfortunately the IR thermometers accuracy will vary too greatly. There's factors like emissivity of the objects being tested changes the readings. I've no experience with solid fuel forges to help you with that. I'd say a magnet is your friend there still.

I have the Auber PID with Type K thermocouple on my forge and it works great.
 
As Brian points out, the emissivity of the thing you are measuring is pretty variable and quite a lot of the variation is down to the process itself, making it virtually impossible to eliminate the variables: things like the thickness of the Oxide layer.

Having flames present doesn't help either. Heat reflected from the surface or flames between the surface and the instrument tend to cause false readings.

I have an expensive IR thermometer that is good to 1600 degC (2912 degF) and just don't find it useful in the real world.

A hand-held type K readout and a good Mineral Insulated, handled type K thermocouple provide much more useful information in my, admittedly limited, experience.
 
Okay, thanks guys, I was leaning away from the IR already, but I thought I'd see what experience others have had with these things.
 
Brian - can you give us a little more detail on what your setup is? I'm interested in a PID and thermocouple, but no idea how it all works. Does the PID control the flow of gas to regulate the temperature? What's the interface between the PID and the fuel flow (or whatever the PID controls). This is probably a really stupid question, but it's completely new technology to me.

Brian Ayres said:
Unfortunately the IR thermometers accuracy will vary too greatly. There's factors like emissivity of the objects being tested changes the readings. I've no experience with solid fuel forges to help you with that. I'd say a magnet is your friend there still.

I have the Auber PID with Type K thermocouple on my forge and it works great.
Click to expand...
 
PID means Proportional Integral Derivative, or more simply 'feedback control'. The three terms represent the three values one enters into the controller to be near the setpoint and manage oscillation around the setpoint.

In laymans terms, the oven temp is used to regulate the amount of heat (gas flow). Higher temp, lower flow, or lower temp, higher flow.

It is better than simply on/off control, gives tighter control. The trick is placement of the probe in a spot that is truly representative of the chamber - which requires thermal mapping.

part of what I do at work is the mapping piece....
 
The pyrometer you link to is for cooking. It won't work in the ranges we need for HT. 99% of IR and "laser" hand held units won't work for HT either. As you saw in the list of pyrometer reviews, only one operated in that range, and it was very expensive. Unless it is a lab unit with good emissivity adjustment, a hand help non-contact pyrometer will not give any readings accurate enough to use for HT. Above 1100F there is a problem with the steel giving off light as it glows. This messes up the IR reading and makes it not accurate ( super simplified explanation). Even the good units are not all that accurate in the 1500F range. For anything that will read HT temps accurately, plan on spending about the cost of two 24" Paragon HT ovens.

What the cheap pyrometers and IR guns do well is read the temperature of the quench tank and tempering oven. in the 100-500 range, =most all read close enough for our purposes.

A PID and a TC will work surprisingly well if the forge is built well enough to soak the refractory and hold an even temperature. A 2BF or paint can forge will not hold an even temperature reading with a reading device, but a full size forge with a good refractory lining will hold as close as +/- two degrees. The stickies has a section in PID control and such. You don't need PID control to use the PID as a reading device, but one great thing about installing a PID as the reading device is that you can add the control function later on easily. The use of a TC sheath is a very good idea. The TC will work without one, but will not last long.

Ebay has lots of PID, TC, and sheath packages. Auberins and other companies sell them, too. The stickies has some parts numbers and info on suppliers.


Summation:
Forget any cheap reading device.
Build a full size robust forge with a heavy duty lining and a good coating of satanite or other refractory. Use ITC 100 as a final coating.
Install a PID, a 1/8" or 10 gauge TC, and a ceramic sheath. Install the TC sheath close to where the blade will be if possible.
Seriously consider having the PID control the forge to make it run at a pre-set temperature.
 
I used a pyrometer and k type thermocouple from auberins for most of the past year. I have had good results as my forge had good thermal mass. Even without pid control, just adjusting the propane flow, I was able to hold pretty accurate temps. I could get + - 5f and hold it long enough for over 10 minutes for a soak.
 
You must log in or register to reply here.
Back
Top