How to Calibrate and Verify a Heating Oven

[Dongzkie]

Hello guys. Just want to do a verification with our heating oven range is up to 150?C. I have here a digital thermometer, but I want to know if what type of thermocouple should i use during the verification, I need some 3 meters long thermocouple. Although I do have 1 meter long of type J and K but I have doubts in using it because I dont know there application type, I am afraid that the thermocouple will bend or deformed when I close the door of the oven. please need some advise. thank you.

 

[dgriffith]

You don't say what kind of oven nor how large. Does the oven have a pass-thru access port? If not and you are going to run the TC where the edge of the door seal will crimp it, then depending on how soft the seal(s) are you may encounter errors. A crimped TC wire within a thermal transition zone is not good.
The TC sheath will need support inside the oven--clamps along the side-wall would do. You could even run it along the ceiling(roof) and let the end hang straight down at any location and whatever length you need. Otherwise, you could get support from an all-metal stand or two (or racks) placed inside during your test.

Don't forget to either calibrate the TC (calibrated accuracy) or use new TC wire (published limits of error). Also, your TC readout will add to the error of readings, so account for that.

 

[Dongzkie]

@dgriffith
yes thats what i mean, the TC might be crimped on edge of the ovens door during the verification. oven size was 824 X 1183 x 684mm. And i have checked that before the access ports but nothing, the TC will have to pass through the door.

 

[dgriffith]

Well, for soft seals, the thicker the probe sheath and wire, the less likely to crimp badly, but more likely to allow leakage around the seal. 33"x 47.5"x 27" isn't too large a volume. What oven controller type do you have and how does it control--analog, digital, PID, Dead Band, etc.? Type of temperature probe it uses and location (PT100, TC, near a inner wall, next to any internal work lamp, etc.)?

There are many factors to consider--these are just a very few: Stability (better with PID), gradients (vertical and horizontal), temp controller and probe error, and control probe location may add additional errors if not placed where the 'product' is. Internal work lamps when lit are notorious for screwing with the temperature measurements.

Also consider that some test engineers require the air temperature surrounding the test article to be known, and some require the test article temperature itself to be known.

If you know something about the walls in your oven, you might pick one, drill a hole carefully through the outer wall, find the inner wall if unobstructed, and drill it to get a small opening to the inside. Run a TC into the chamber and seal the hole with high-temp epoxy, rubber gasket, etc.