Oven temps

[jdm61]

I have been a bit concerned about my Paragon, so I tried to check it. I have a thermocouple device that I got at a pottery supply hose years ago. I used it in my kiln before I got my oven. It has the long themrocouple probe with the braided wire. I haven't used it for years and just replaced the 9 volt battery. I put the probe entirely in my oven. At "idle" it was within 1 degree of what the oven's internal thermocouple said. like 84F. BUT, who I set the oven to 1500F, it read 1500F and the meter read as high as like 1530F. So what do I do/ I have no idea which one if either, is accurate. The other problem is that while the oven was heating up, the probe was indicating temps like 100 plus degrees lower than the oven thermocouple. ti didn't catch up for a while, but then shot past.

 

[Karl B. Andersen]

In my Evenheat there is as much as 20 degrees difference between the oven's read out - which is at the top/ceiling of the oven, and where my thermocouple is - lower toward the center/floor.
I just had to chalk it up to simple physics - heat rises.
The difference is greater the cooler the oven. At tempering temps it's about 15-20 degrees cooler in the center of the oven, and at higher temps it's with 2-3 degrees.
It will also depend on the distance from the coils.

 

[Stacy E. Apelt - Bladesmith]

The only way to check accurately is to place the test TC in the exact spot the oven TC is ( or very close to it).

TC will vary a bit depending on the TC grade, wiring used, and the readout quality. .3% is very good. 1% isn't uncommon. At 1% you ca have a +/- 15° variance. That would allow for two TC to show as much as 30° difference and still be within tolerance. If they read within 20°, I would consider the oven YTC accurate.

While we all like to see folks claiming a HT recipe using (eg) 1479°F. that is just the reading on the person's oven that works for him. Yours may vary a bit. After using his 1479°F, try a HT at 1470 and 1490 and see how the end results vary in testing. The truth is that 10° variance will not be detectable on most steels and most home HT setups. The reason most HT regimens are given in a range (1475-1500) is that they don't know your exact situation.

 

[Randy3000]

If you are still concerned, you may try melting something with a known melting point. They sell things specifically for this purpose, forget what they are called.

 

[Stacy E. Apelt - Bladesmith]

Problem with using temperature cones (firing cones) is you can't observe the cone slump. There is a time factor involved which is hard to pinpoint when the slum starts and when it ends (especially when the cone is in a closed oven).

Tempilstik crayons aren't as accurate as one would want for HT ranges because of so many variables. You can use them as a check if you are familiar with them, but I wouldn't calibrate with them (I used to recommend them for checking ovens, but have decided they are too hard to get accuracy in the range we need for HT). They are great for checking pre/post-heat in welding.

A reasonable quality PID and a TC that is the same as the one in the oven are all you need to check the temp. In many cases you can slide it in along the existing TC. The TC will also be an on-hand spare for when the existing one fails.

 

[jdm61]

Karl, the problem is that the PID is on the side of the oven closer to the coils, but the TC is on the floor in the middle of the oven and the TC is reading higher. With that said, the PID is close to the door and the tip of the TC 12-15 inches into the oven.

In my Evenheat there is as much as 20 degrees difference between the oven's read out - which is at the top/ceiling of the oven, and where my thermocouple is - lower toward the center/floor.
I just had to chalk it up to simple physics - heat rises.
The difference is greater the cooler the oven. At tempering temps it's about 15-20 degrees cooler in the center of the oven, and at higher temps it's with 2-3 degrees.
It will also depend on the distance from the coils.