VTB vs. FTB for PID
- Thread starter Frogdude
- Start date
Help Support Homebrew Talk:
What parameters are to be used to determine how the time interval is varied? I've never heard of variable intervals in control loops (and I do this for a living)..... but that doesn't mean they're not out there.
When tuning a loop, the time interval is usually the first thing to get set.... it stays constant and is linked to the system's hardware. As long as the system doesn't change dramatically (in this case: volume of water being heated, heater element wattage, etc), the time interval should stay constant.
The general rule of thumb we use is (initial) interval=(time from ambient to 80% of target)/10, which usually gets us in the ballpark.
Unless.... someone else has heard of this?
When tuning a loop, the time interval is usually the first thing to get set.... it stays constant and is linked to the system's hardware. As long as the system doesn't change dramatically (in this case: volume of water being heated, heater element wattage, etc), the time interval should stay constant.
The general rule of thumb we use is (initial) interval=(time from ambient to 80% of target)/10, which usually gets us in the ballpark.
Unless.... someone else has heard of this?
I have not heard about this in control systems. The only application I can remember using something like this is circuit simulation (Spice). I don't understand what the benefit would be in a control system. In a classic continuous PID (op amp based) it does not even make sense.
Yeah, after checking into it a little more, I realized that it is specific to the Watlow PID that I am using. With the FTB, it turns the output on and off every three seconds, but with the VTB it turns it on and off every three electrical cycles (I even have to tell it if my service is 50 or 60 Hz).
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