Safety

Fire-safety is a major design issue. An evolutionary machine needs to run unattended, 24 hours a day. In the Evolvatron, there are three lines of defence:

1.

A temperature sensor on each heatsink causes the controller to shut down the pump completely and immediately if thermal runaway is detected.

2.

What if the computer running the PD controllers (and the evolutionary algorithm) crashes, due to a programming error, hardware failure, or operating-system freeze? To detect this condition, a re-triggerable monostable circuit is used as a watchdog. Every time the PD controllers' state is updated, the software causes a digital output signal from the PC to toggle. If the watchdog circuit has not detected a toggle within the last 100s (this time-constant is adjustable), then it trips-out a relay which cuts the power to all heat-pumps.

3.

As a final resort, there is a thermal fuse electrically in series with each heat-pump, and attached to its heatsink. The fuses blow at $98^{\circ}$C.