I have to develop the electronics and control software for a Compression testing machine - with some modifications from a conventional setup.
I have a PID loop in place using dsPIC to control and acheive the required(target) load (pressure). That part is Ok.
But I have to increment the load in a specified pace rate. for example, load should increment 1kn/Sec or 2kn/Sec etc. For 2kn/Sec - once started load should be 2kn in the first sec, 4kn in the 2nd second etc, till a specified value.
What could be a suitable algorithm/strategy/method to implement this purpose in software, so that a optimum linearity can be achieved in the increment process?

TU

 

Use timer overflow to the max delay and increment a variable till you obtain two seconds delay . Within the timer ISR you will increment the load by a fixed quantity till your PID will require it.

Cheers

Alberto

 

Thanks Alberto for the response. I believe such a attempt will make the load response in a step by step manner. If we simply wait for one second and apply the new target value, the response may not be smooth. I feel we somehow reduce the steps into small chunks and split increments. This is a pressure system with very low displacement for the hydraulic piston. So PID will reach target very fast.