mcafone
Member
Hi,
I'm working on a hydraulic rupture disk testing system. I have a variable speed DC motor/gearbox driving a hydraulic generator (a big stainless steel syringe) which is then attached to a valving system, water reservior and a fixture to hold the rupture disk. A pressure sensor provides 0-10 volt feedback to an analog input on an AD DL06 PLC which then controls the DC motor/hydraulic generator speed.
The process starts off with the motor driving at a fixed speed until an initial pressure is reached (around 5000 psi). This pressure is held for a little while to check for leaks and then the pressure needs to ramp up again while controlling the rate of pressure increase at around 100psi/sec.
The question I'm getting around to asking is: what is the best method to control this ramp rate? I was thinking of using a timer to trigger a bit of logic to calculate the current rate of pressure increase and feed that to a PID loop to control the motor speed but, If I remember correctly these PLCs only have 100ms timers and I don't think this will give me the response time I need. Somebody mentioned that a cascaded PID loop might be applicable here but, I don't have any experience with that. The fastest update rate you can set on the PID loop is 50ms so any pressure rate calculation would have to take less time than this. Any suggestions?
I'm working on a hydraulic rupture disk testing system. I have a variable speed DC motor/gearbox driving a hydraulic generator (a big stainless steel syringe) which is then attached to a valving system, water reservior and a fixture to hold the rupture disk. A pressure sensor provides 0-10 volt feedback to an analog input on an AD DL06 PLC which then controls the DC motor/hydraulic generator speed.
The process starts off with the motor driving at a fixed speed until an initial pressure is reached (around 5000 psi). This pressure is held for a little while to check for leaks and then the pressure needs to ramp up again while controlling the rate of pressure increase at around 100psi/sec.
The question I'm getting around to asking is: what is the best method to control this ramp rate? I was thinking of using a timer to trigger a bit of logic to calculate the current rate of pressure increase and feed that to a PID loop to control the motor speed but, If I remember correctly these PLCs only have 100ms timers and I don't think this will give me the response time I need. Somebody mentioned that a cascaded PID loop might be applicable here but, I don't have any experience with that. The fastest update rate you can set on the PID loop is 50ms so any pressure rate calculation would have to take less time than this. Any suggestions?