PID Controller for Hydraulic Proportional Relief Valves

My line is Oil Hydraulic design.

Frequently I require a method to precisely set pressure from remote using a amplifier that is driving a proportional relief valve. All or most general amplifiers are open loop. Meaning they take in a 0-10V command and convert that to a 0-600mA current output to drive a proportional relief valve. But in this case we can only get about 5% repeatability on set value.

So recently I bought a Redlion process PID controller to generate the command in closed loop. The loop is closed by signal feedback from a Pressure Sensor.

Problem : Unable to get this working either with Manual Tuning or Auto Tune ( in AutoTune the controller does nothing ) . With lot of struggle got it going but the control was not smooth not precise. Most part it was hunting.

One reason I can think of is the response time of the proportional valve - it is less than 50mS from zero to full pressure. Whereas the Redlion controller ( Model : PXU41DE0) output cycle time can only be set for a minimum of 100mS.

So is there any general purpose PID controller that has an output update of around 5mS ( 1/10 of my process response ) [ or ] is it a matter of setting with the Redlion ??
 
There are dozens, if not hundreds, of brands and models of commercial, relatively inexpensive, stand-alone single loop PID controllers.

In my experience they are better named temperature controllers because they're designed primarily for temperature control because that is the biggest market for stand-alone PID controllers. Hence the response times are no where near what you are looking for in a hydraulic loop controller.

I doubt you're going to find any generic PID controller that does what you need.

If Peter Nachtway replies, he might have other insights or advice given his experience in hydraulic control.
 
@David_2 Very true. The PID controllers out there are primarily targeted towards the temperature control applications.

It is not that we don't have dedicated PID controllers for hydraulic proportional or servo valves. There are many but the price bracket way beyond normal applications. So I was looking at generic controllers which are low cost to see if they can be made to work.

But as you rightly said most of these have a rather low bandwidth. Shall wait for more inputs to see if a solution does exist .
Thanks
 
Much depends on what is being controlled. Controlling the pressure of small volume of oil is much harder than controlling the pressure of a large volume of oil because the same amount of oil change will affect the pressure much more in a small volume.

There are many PLCs that can close the loop every 5ms or even down to 2ms. A simple PID should be good enough. The potential problems I see is what if the supply pressure is fluctuating, what if the valve has a lot of hysteresis, what if the output of the digital to analogue board is slow, what if the volume of oil is small so that a 5ms scan is not fast enough. There are too many what ifs without more information.
 
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