Reflow Toaster Oven - Part 5 - Crispy Thermocouples

I like my thermocouples well done...

So that little blue piece of shrink tubing(?) doesn't seem to cope well with 200+ degrees C. Oh well.
Did a bit of testing tonight. I placed the four thermocouples in and around the oven:
- one attached to the heater
- one just floating in the middle of the oven
- one stuck through one of the vent holes on the side
- one attached to the top of the oven
And then I turned the oven on :) I recorded the whole thing and manually put all temperatures at 5 second intervals into a spreadsheet. Here's the result:

At one point the thermocouple on the heater fell off, that's when I turned the oven off. The interior was about 270 degrees C by then and kept rising for a short period. Then I opened the oven's door and the air temperature plummeted.The reason these readings differ so much from earlier profiling is because of the thermocouple I used. There small ones have very little mass, so they heat up much faster than the one I used earlier.
What worries me a bit are the green and purple lines. They reach about 80 degrees C, that means the oven is way too hot to put any electronic controls inside. I hope this is reduced significantly after I insulate everything.

I also played a bit with RaceRender, it can overlay various types of data on video images.

Nice :)

To Measure Is To Know

Mailbag time!

I got this HT-9815 4 channel K-type digital thermometer from eBay seller PerfectPrimeUSA (which of course is located in Hong Kong). Got it for a mere $26 (including free shipping) and four (cheap) thermocouples included. And it actually seems to work fairly well! Refresh rate is about once per second, it remembers lowest and highest temperatures measured as well as average temp. It can switch between degrees Celsius, degrees Fahrenheit and Kelvin and it actually appears to be reasonable accurate. The backlight is piss-poor (one LED located on the left side) but for this kind of money I can't complain really. Just shipping it back to Hong Kong would probably cost me more than what I've paid for it :)

I'll crack it open tomorrow, see what makes this thing tick, and I'll do some measurements with the oven.