Reflow soldering - Part (3) Temperature controller

Controller unit with SSR and thermocouple wire connected

Internal view - MAX6675 on mini board alongside PIC

I have made another oven temperature controller in a convenient to use enclosure, which has a sloping surface for the back-lit liquid crystal display module. It looks quite professional. The circuit is the same as the earlier experimental version, ( posted on 11 November ), using a PIC microcontroller and MAX6675 temperature sensor chip. It is ready for integrating with the oven. The output of the 15 amp solid state relay ( SSR ) has to be connected in series with the mains lead to control the power. The thermocouple will be situated inside the oven eventually very close to, or actually touching, the circuit board which is being soldered.
I am thinking that it would be beneficial to add a programming interface to the controller so that I can re-program the embedded PIC in-situ.

Reflow soldering - Part (2) Measuring temperature

Thermocouple and serial data connections
MAX6675 on underside of top board

Temperature in my electronics lab

Since posting Part (1) on 8 October I can now measure temperature with 0.25C resolution using the MAX6675 temperature sensor chip and a thermocouple. I wrote some code for a PIC microcontroller's MSSPI to receive the 16 bits of serial temperature data from the MAX6675, display a value and update it every second. The display also shows the phase in progress during the reflow-soldering process, e.g., ramp to soak.

The next step of this project is to use the temperature measurement as the basis for controlling the rate of temperature change inside the oven. I have the plots made earlier of the temperature change at various power duty-cycles to the elements and I shall be using these at the starting point for each phase of the process