PID for Proportional Valve

I want to use a proportional valve for controlling the pressure in a tank/cylinder. In our design we need to have two profiles for PC valve. The profiles have to be time based . One profile is to build the pressure from 0 bar to 50 bar and another to drop the pressure from 50 bar to 0 bar (see figure below). Profile is shown in attachment. The PC valve I am using is Reducing/Relieving valve. Does my design require a PID? . Any help is appreciated....

That's so fast that I don't think a PID would do anything.

What are you using to develop the command value (what is your controller). What accuracy do you require? What is the accuracy spec of you reducing valve? Do you have any reason to believe that the reducing valve will not be able to regulate to the pressure you command?

Generally speaking a pressure reducing valve will control to the pressure you command. Unless there are known losses in your system that will result in the pressure at the test point being different than the pressure at the reducing valve, a pressure PID probably won't do you any good unless your desired pressure accuracy is tighter than what the reducing valve can deliver on its own. Even then, you would be better off spending your money of a better pressure control valve.

Keith

Reducing/Relieving valve

Thanks Widelto and Mr Keith for the reply.

In the query I have attached two jpg files, which shows my requirement. I have 1.2 sec for building pressure from 0 to 50 bar and 1.2 Sec for releasing pressure from 50 to 0 bar.
The accuracy isn't that much stringent.

I am a newbie in the field of hydraulics.
The valve I have chosen is, pressure reducing/relieving. My doubt is, whether I can achieve the requirement as per in graph using an Open loop method. Or should I go for a closed loop method (using PID/similar) since over the period the spring constant of valve may get changed and thus the pressure values as per current rating.

Thanks and regards
Manu

Oil will compress about 0.5% for 70 bar. In your case the oil will compress a little less because you are only going up to 50 bar. If the volume of oil you are going to pressurize is small the valve will need to be able to meter in and out oil at very small rates.

Normally using a voltage control pressure regulating valve would be a good idea but I wonder if the pressure regulation will be good around 0 bar. Still I would try the voltage controlled pressure regulating valve first.

The next option is closed loop control.

Bosch Rexroth recently came out with a pressure control valve (DBETA) that has an internal pressure transducer and closed loop control onboard. With the closed loop controller, it eliminates errors due to viscosity changes in the oil which occur as the temperature varies.

The valve lets you get pretty low but as Peter mentioned, getting to zero is very hard with a pressure control valve. There is info on that valve here:
http://www.boschrexroth.com/en/us/p...to-hydraulics/proportional-valves/dbeta/index

We have only achieved zero bar using a zero Lapp 4 way valve with the B port blocked and the A port connect to the volume to be controlled. Also closed loop is required for that.

<disclaimer- I work for a Bosch Rexroth distributor >