Much of my work lately has been building new things in the lab, we are adding some tests to our arsenal, one of my projects has been to wire a temperature controlling system for a heater. This required using a solid state relay to control the heater. The reason the relay had to be solid state, is that mechanical relays are very limited in speed, and they wear our faster over time. The SSR is controled by a DC current provided by the temperature controlling computer, but this entire system had to be wired together for others to use. This included fuses, switches and a safe box to keep the wires protected. The included photo is of a mostly-complete controller. I still need to add a master switch for the AC circuit.
