pressure PID control issue
pressure PID control issue
(OP)
Hello,
I am newbie to hydraulic system and working on a project which is pressure control.
the hydraulic system has a motor driven pump which gives a constant pressure (~3,000psi). I have attached a schematic to show the control schematic. the output pressure of the intensifier is the controlled variable and the pressure is controlled through a proportional valve.
The issue I am encountering is that there is undershoot when the pressure setpoint changing from high to low and the undershoot seems happens randomly. Please see the attachment. Green line is setpoint and red line is actually pressure output. I am guessing that the undershoot is caused by the intensifier since I can hear click sound anytime when there is undershoot. I understand that the intensifier automatically correct itself when it runs out of stroke.
Anyone has experience in how to control intensifier pressure?
Any tips are very appreciated.
Best regards,
I am newbie to hydraulic system and working on a project which is pressure control.
the hydraulic system has a motor driven pump which gives a constant pressure (~3,000psi). I have attached a schematic to show the control schematic. the output pressure of the intensifier is the controlled variable and the pressure is controlled through a proportional valve.
The issue I am encountering is that there is undershoot when the pressure setpoint changing from high to low and the undershoot seems happens randomly. Please see the attachment. Green line is setpoint and red line is actually pressure output. I am guessing that the undershoot is caused by the intensifier since I can hear click sound anytime when there is undershoot. I understand that the intensifier automatically correct itself when it runs out of stroke.
Anyone has experience in how to control intensifier pressure?
Any tips are very appreciated.
Best regards,





RE: pressure PID control issue
Ted
RE: pressure PID control issue
Thank you very much for your reply.
Regarding the intensifier, it is minibooster and ratio is 1:5, the max pressure we use in our application is 12,000psi. Do you think PID control is the suitable controller in the application?
Please let me know if you need more information.
Your help is greatly appreciated.
Best regards,
RE: pressure PID control issue
RE: pressure PID control issue
Do you mean the intensifier should be put before the proportional valve and after the pump, as well as an accumulator? The system has been built and I am developing control software. I can ask vendor to change it if that is the only solution.
Thank you very much.
RE: pressure PID control issue
Are you using this G-model of HC2?
Ted
RE: pressure PID control issue
Peter Nachtwey
Delta Computer Systems
http://www.deltamotion.com
RE: pressure PID control issue
It does not seem to be any problem with the pressure source because the problem occurs when you send the oil to the tank.
I am convinced that your phenomenon does not occur randomly, but it depends on the volume of oil or elasticity in the part of the circuit where you measure the pressure. The gain to adjust the PID depends on the elasticity of the system. A you to vary the gain with info taken on your machine.
RE: pressure PID control issue
The response to decreasing pressure steps appears to be characteristic of the intensifier. The check valves in the intensifier prevent flow backwards when the output pressure is higher than the lower desired output pressure. There must be some means other to reduce output pressure other than back through the intensifier.
Ted
RE: pressure PID control issue
RE: pressure PID control issue
I am sure I joined to the right forum, a lot helpful info.
I don't know the hydraulic system much and try my best to understand and explain it to you guys.
@Ted, the intensifier is HC2-5.0-G
the system doesn't have flow or very little, at least no flow in the UUT.
Best Regards,
RE: pressure PID control issue
Several ideas:
We delivered a HC2-5.0-B model and you have connected you A proportional valve to the IN and B to R: in this case it does not work well and your DV controlled valve opens abruptly and falling pressure too fast.
It has given you the right model, namely HC2 -5.0 - G and you have made the same connection as described above. Not good because the pressure in R when you want to lower the pressure disrupts the operation of the pressure intensifier.
You have the right model and the R is permanently connected to the tank. This should work. The first thing to check is the absence of abnormal internal leakage by maintaining a constant pressure to the IN port, and measuring with a bucket to drain the hole R. Ask the manufacturer if this value is correct. The solution to the electronics and check that the DV valve works well: Vary the pressure on the IN port on the rise and the descent. Record the pressure at the IN port and port H. You will see that we have an offset between ascending and descending pressure. For example the rise to 1000psi in IN at the rise was 5000psi H and for these to 5000psi descent found in 900PSI IN. So after he would get to set your electronique to account for this offset.
A test that could be done (if the mechanical elasticity to the cylinder and the volume of oil in the pipe is very low) is to add a larger dead volume of oil: for example a long flexible purged well.
You can also try putting a needle valve with check valve on the outlet H for limiting the flow of the actuator to the multiplier.
If you've always random phenomenon there must be pollution which disturbs the operation of the RV valve: remove and clean or put a new component