PID timer

Discuss tuning PID coefficients to maximize system efficiency.
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PID timer

Post by gustavf » Mon Apr 06, 2009 9:01 am

I assume the PID functionality in BCS-460 regulates the manipulated value by turning on and off the output (23% is 23 seconds on and 77 seconds off). How long interval is used? Is there any plan to make this configurable?

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Re: PID timer

Post by ECC » Tue Apr 07, 2009 7:28 pm

When using the Duty Cycle control, the output is controlled over a 10s window, so 10% would be 1s on and 9s off. However, the PID operates in a different manner. The output is switched on whenever the algorithm is above 50, and off when its below 50. The PID sample period, or output period, limits how often the output is switched, which is adjustable. It is defaulted at 1sec, so the maximum that it could switch in this setting is once every 2 seconds (one second on, one second off). You can set it to a minimum of 0.1sec, or to a longer setting.

This is a somewhat unconventional way to use a PID, since 20% will be off (not on 20% of the time).. But in practice it works quite well, the PID output quickly climbs above 50 when heat is needed, and then quickly falls off when it approaches the setpoint, regulated by the PID coefficients. So if 20% power is needed to hold a setpoint, the algorithm will cross the 50 switch point on average 20% of the time.

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