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CPLC vs Script PLCs
#1
We're going to use the Power PMAC to control the antenna of a weather radar. The antenna has azimuth and elevation drive motors. A typical motion control program would start the antenna at 0.5 degrees elevation, and scan between 40 and 120 degrees in azimuth at 5 degrees per second. When the antenna reaches one of the azimuth scan limits, it slows down, increases elevation by 1.0 degree, and scans at 5 degrees/sec in the opposite direction. This sequence repeats until some maximum elevation is reached.

[Image: PPI.png]

The path to the next elevation angle doesn't need to be a semi-circle, we simply want to change elevation quickly once the antenna passes one of the azimuth limits, and have the antenna accelerate smoothly so it reaches the desired velocity as it reaches the left or ride side of the scan.

Any advice on how to write a motion control program to do this?

What are the tradeoffs of using C language PLCs vs Script PLCs for controlling the drive motors? Are people writing new motion control programs using Script PLCs, or are script PLCs mostly used for compatibility with earlier PMAC products?
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#2
We have two major program types in the PowerPMAC, Motion programs, and PLC programs. There is overlap in their ablities but the general idea is that motion programs are like the workers in a factory, they are given a job to do and they do it. PLCs are like supervisors, they look at inputs and then tell the workers what jobs to do and what jobs to stop. So PLCs usually monitor IO and decide which motion programs to start and stop.

From the description it seems like a motion program would be a better approach than a PLC for commanding the antenna motion. I would use Linear mode and then controlling the path is straight forward since all sequencing is automatically performed by the motion program.

Using a PLC to control motion adds significant overhead since a PLC does not scan in sequence with the motion. Once you command motion from a PLC you must fall into some logical condition to determine when the motion has started and then another to determine when the motion has stopped or when some specific criteria has been reached and you want to send another command.

your specific questions about script PLC vs CPLC is harder to answer since it is really a matter of opinion. In my opinion script plcs are a little easier to use when commanding motion. Script PLCs have more direct access to some status information you might need and script plcs can be enabled and disabled more directly from other Power PMAC programs. All of this is rather minor it is just a matter of setup, once the setup has been done and the program structure has been determined both will work.
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