[time-nuts] Environmental sensor recommendations

[Tisha Hayes]

I would suggest that if you are looking at taking temperature sensor data
and attempting to control some type of heating/cooling device that you
implement a PID loop for stability.

https://www.crossco.com/blog/basics-tuning-pid-loops

Many simplistic approaches use an ON-OFF controller to turn on cooling or
heaters. These can make your stability problems worse than if you just
wrapped things up in an insulating blanket. You end up cycling from one
extreme to the next.

PID loops when properly tuned will vary the speed, current or duty cycle as
the temperature approaches a set-point. This avoids overshoot and gives
much finer control over the temperature.

We used to use 4 wire platinum probes to measure temperature down to the
hundredth of a degree. Then for control of the heater element we had a PWM
(pulse width modulated) supply. Once the loop was tuned (to minimize
positive feedback that causes increasingly crazy oscillations in
temperature while at the same time settling in once the temperature soaked
through the mass) we could hold a set-point through some wild external
temperature extremes.

There are software implementations of PID (Proportional, Integral,
Derivative) that are pretty easy to understand. There are also surplus
temperature controllers on eBay that can accomplish the same thing.

*Ms. Tisha Hayes, AA4HA*