The aim was to cook “Sous Vide” (see recent post) and to do this I needed to build a proportional–integral–derivative controller (PID controller). It is a generic control loop feedback mechanism (controller) widely used in industrial control systems – a PID is the most commonly used feedback controller. A PID controller calculates an “error” value as the difference between a measured process variable and a desired setpoint. The controller attempts to minimize the error by adjusting the process control inputs.
While it sounds complex, in this case it is a box that turns the power on and off to a heater in response to the temperature measured and the desired set temperature. Pretty basic, but the control algorithm is complex because it tries to account for thermal mass and lag and minimise over and under shoot of the temperature. The image below shows the controller components. The features of the controller include, RTD temperature probe, PID module, Solid State 40Amp relay, Logic relays, timer module which can be linked or independent of the PID module.
The unit was completed and has been used successfully for Sous Vide cooking of steak, roasts, ribs, heart which was surprisingly good and shin (stewing) beef for a curry. We have also used it for Cheese Making where control of the temperature of the curd is critical and Distilling of beverages. We hope to use the controller in Tempering of steel knives we sometimes make here for our blacksmith projects.