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Description
An electrical substitution radiometer (ESR) is an instrument used to measure radiation by comparing the incident optical power with the equivalent electrical power. It works by comparing the electrical power used for the Joule heating of the receiving cone with the absorbed solar radiation required to reach the same temperature. An example of use is the Total Irradiance Monitor (TIM), an instrument designed to measure total solar irradiance, which has four cavities operating in pairs, with one cavity absorbing the optical power from the Sun, and the other to be heated by the electric circuit until their temperatures match. Accurate optical radiation measurements require highly stable thermal control systems, so developing a reliable electronic control for ESRs remains essential, and it has to be thoroughly made. Here we show the development and assembly of the electronic circuit for an ESR using low-cost and readily available components. First of all, the electronic components to simulate an ESR were acquired to assemble the test circuit, such as a heating resistor, a MOSFET and an ESP32 microcontroller to implement a proportional–integral–derivative (PID) control for the heating process. Tests and necessary adaptations were made so we could apply a simpler control code on the circuit first, and then move on to the PID code. The adjustments of the PID parameters are being made until the output signal behaves accordingly, i.e. without overshoot or steady state error. So, after all the tuning needed, we expect to set up a lookup table to consult the electrical power needed to reach closer to the target temperature for some initial values. This will accelerate the heating process, so the PID control only needs to work very close to the reference temperature.