Thermocouple Arrangement

The two thermocouples measure a temperature inside the oven. One of them is bent to the front. It is also not really fixed, so its tip can be rotated to be higher or lower. I use this as a feature so I can lower it to an object on the grate:

The straight thermocouple is called 'A', the bent one is called 'B'. This picture also shows the two heaters which are protected by some metal part with holes in it. Pretty bad for convection. The diameter of the heaters is $d_H \approx 12~\mathrm{mm}$, the length (also the width of the oven) is $L_H \approx 260~\mathrm{mm}$.

The Oven

I bought a simple "infrared oven" on the internet for about 20 euros. The main criterion for this model was that it is small and has a power per volume ratio of more than $100~\mathrm{W/liter}$ (Power $P=800~\mathrm{W}$, volume $V=6~\mathrm{liter}$). My impression is that they call it an infrared oven just because there are no parts that may increase heat transfer from the heaters to the air in the oven, so a great share is radiated to the walls and whatever else is inside. Measurements show that this is indeed the case (more on that later). Here is a foto:

The modifications I made:

• removed all plastic parts (some were holding the glass, so I replaced them with aluminium strips),
• removed all electronics: Timer, heater selector (off/top/bottom/both) and a temperature switch which was supposed to cut power to the heaters when the oven wall was above $180~\mathrm{^\circ C}$,
• added two type K thermocouples (I had no specific reason to choose type K, just had them lying around)
• connected both heaters to a cable for external connection,
• added thermal insulation (ceramic wool; glass or rock would have worked just as well) inside where there was room, and on the bottom (see below).

This is a picture of the bottom where I had to add "external" thermal insulation:

And here are thermocouple and heater cables: