3 ms·
On-off or "bang-bang" control actually makes a lot of sense for home thermostats. For example consider: - With a home thermostat you probably want it to reach
by shawnz 5y ago
On-off or "bang-bang" control actually makes a lot of sense for home thermostats. For example consider:
- With a home thermostat you probably want it to reach the desired temperature as quickly as possible. PID will never reach the setpoint as fast as bang-bang control since bang-bang control will always use the maximum possible power.
- PID might help you avoid overshooting the desired temperature but that's not really an important issue for a home furnace. In fact it might be better if it overshoots the desired temperature a bit on very cold days.
- The air in the home acts like a big thermal battery that helps negate the need for a sophisticated controller.
PID works very good for a wide variety of situations but it's important to remember it is not always the best tool for every job. In that way it is kind of like "quicksort".
- kevinsundar 5y agoWell.. that and your heater / ac state is binary. The heater is either on or off, and the ac is either on or off. PID loops require a continuous variable to set. If the only thing you can do is turn something on and off, a bang-bang controller is the only thing that works.
- jbay808 5y agoAlthough overkill for a heater, you can often pulse-modulate a binary output to simulate a continuous output variable. This can be used together with a PID controller.
- bumby 5y agoYou can often run into equipment reliability issues with this approach because you are constantly short-cycling your systems. I know on HN we’re generally focused on the software aspect but in the real world it’s important to consider the overall system
- jbay808 5y agoMy point is about how "binary" signals are controlled via modulation to emulate an analog variable for use with a continuous controller, not a recommendation to run your gas furnace this way. (That might have been lost because of the line the conversation followed). In a real system this is exactly how MOSFETS are used to control a voltage; you would almost never use an analog amplifier for high power because of the losses, so voltage control is binary on/off, but that doesn't restrict you to just bang-bang control despite the GP's statement. In fact, an electric heater can and often will be controlled via a PWM method with a continuous controller rather than via hysteresis.
- deleted 5y ago[deleted]
- thrdbndndn 5y agoProbably will literally kill the heater, haha
- pillefitz 5y agoThat's how AC motors are controlled, but generally wouldn't recommend it for mechatronic systems (EM emittance, wear and tear etc.)