This brief video clarifies how the Control Output affects the actual drive output frequency and shows why it is important to understand that when switching between auto and manual modes.
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We tend to draw the PID sub-system like this because it’s easy to understand. But it also causes some confusion because it’s easy to interpret this as the output of the drive. It isn’t. The control output is always in percent and can be viewed in parameter 917. And that gets converted to the ultimate drive frequency which is in hertz and can be viewed in parameter 2. The important thing to understand is that the control output percent is relative to whatever you enter for the min and max drive frequency in parameters 133 and 134. So, if you enter a 3 for the min frequency and 66 for the max drive frequency, a control output of 0 percent means 3 hertz and a control output of 100% means 66 hertz. And that’s really important to understand when switching between manual and automatic modes. When you are in manual mode, you are actually entering the drive frequency directly in hertz – not percent – and it does directly control the drive output frequency and therefore motor speed. Even the PID Wizard in the version of the WEG programming software I use shows it like this which adds to the confusion. This diagram would cause less confusion if these two were swapped, right? Hopefully this short video helps clarify in your mind where the PID control output fits in the overall scheme of things. Click here to see all of the videos in this series. Click here to subscribe to our YouTube channel and click here to learn about all of AutomationDirect’s free award-winning support options.
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