timgunn1962
Member
- Messages
- 318
- Location
- Lancashire UK
As alluded to above, emissivity (the shininess or otherwise) of the target makes a massive difference to the reading. At work, everything we need to check the temperature of on a regular basis has a little square of Matt Black Paint to aim at (we have sites all over the country and use Electrolube MBP for consistency: I don't know whether it has a higher or lower emissivity than other brands).
If we are checking anything different, we tend to use an IR thermometer with adjustable emissivity, measure the target temperature with a type K thermocouple and adjust the emissivity until the IR and thermocouple readings agree.
If all you want to do is compare similar surfaces, a fixed-emissivity IR thermometer removes the biggest variable from the equation, but only tells you where the hotter and cooler bits are: it won't necessarily give you meaningful temperatures.
If you need actual numbers, an adjustable-emissivity IR thermometer and a contact thermometer are probably the best combination.
I have access to a calibrator at work, which is quite useful. I used to recommend TM902C type K pyrometers off ebay to knifemakers, as I'd had dozens of them on the calibrator and they were as accurate as big-name instruments at 20+ times the price over the full range of the type K thermocouples (-200 to 1372 degC). They come with a Glass-Fibre-Insulated bead probe that is good to around 400 degC and is flexible enough to close in an oven door to check tempering temperatures (the forge temperatures need a probe that's built for the temperature). I received an order of ten, perhaps 5 years ago, that were accurate up to 800 degC, then started to deviate as the temperature rose. I can't remember whether they read 1290 degC at 1372 degC, or read 1372 degC at 1290 degC. Either way, they were no good for checking/setting forge temperatures.
If you don't need to measure over 800 degC, a TM902C is around six quid delivered (slowly) off ebay.
If we are checking anything different, we tend to use an IR thermometer with adjustable emissivity, measure the target temperature with a type K thermocouple and adjust the emissivity until the IR and thermocouple readings agree.
If all you want to do is compare similar surfaces, a fixed-emissivity IR thermometer removes the biggest variable from the equation, but only tells you where the hotter and cooler bits are: it won't necessarily give you meaningful temperatures.
If you need actual numbers, an adjustable-emissivity IR thermometer and a contact thermometer are probably the best combination.
I have access to a calibrator at work, which is quite useful. I used to recommend TM902C type K pyrometers off ebay to knifemakers, as I'd had dozens of them on the calibrator and they were as accurate as big-name instruments at 20+ times the price over the full range of the type K thermocouples (-200 to 1372 degC). They come with a Glass-Fibre-Insulated bead probe that is good to around 400 degC and is flexible enough to close in an oven door to check tempering temperatures (the forge temperatures need a probe that's built for the temperature). I received an order of ten, perhaps 5 years ago, that were accurate up to 800 degC, then started to deviate as the temperature rose. I can't remember whether they read 1290 degC at 1372 degC, or read 1372 degC at 1290 degC. Either way, they were no good for checking/setting forge temperatures.
If you don't need to measure over 800 degC, a TM902C is around six quid delivered (slowly) off ebay.
