pid or not

ok here is my situation running plc 5/40
1.i have a hydraulic cylinder that slowly oscillates in and out

2.i have analog feed back temposinic transducer that gives me relative position (not pulsing temposonic)

3. i have a time constant that changes according to machine speed being calculated in the plc time/stroke (450sec/stroke)this will not be constantly changing only with periodic machine adjustments

4.i am going to be controlling the cylinder speed with a proportional valve +/- 10v and a 1771-ofe1

now should i try to control this with a pid or do something like looking at the time value each stroke and adding a set amount to the gain or subtracting until i reach the time value necessary

If the cylinder position feedback signal is accurate, and if the cylinder moves relatively slowly, then I would try the PID first.

Or if it gets difficult, use FUZZY control.

Fuzzy logic isn't the answer. A PID by itself is not the answer either. cblarsen needs a target generator that moves the set point from one end of the stroke to the other at the desired rate. Then the PID can follow the slowly moving set point.

BTW, the analog temposonic rods use start and stop pulses and convert the difference between them to analog signals.

that is what i did im taking a sample of analog input every 20 seconds and compute travel per second and my setpoint is in travel per sec. so i can now use pid control . But i cant shut down process to implement . so i cant add pid file and dont have extra N: file words so i will just for now have to simply compair the actual speed to setpoint and adjust the channel data value acordingly ever 20 sec when i get new sample values
thanx cblarsen