willpower100
Member
I was called in yesterday by a customer to look at a hydraulic proportional valve driven system. They have 2 non-feedback single stage proportional valves driving several cylinders. The input signal for the prop amplifiers comes from several analog adjustments on the console.
What is happening is this, when they shut off power to the system, ie, turn off the electric motor for the pump and associated input power to the 24Vdc power supply and proportional amps, the proportional valves are shifting slightly, the pump continues to produce flow for several revolutions and with the valves open slightly the hydraulic cylinders are jumping several inches.
When you remove the DIN plugs from the valves and repeat the shutdown, the valves do not shift, this then eliminates solely the hydraulics as the problem.
The valves and amps are basic older Parker models, output to the valve is PWM with a small AC dither signal, (Thats what I think anyways, as the product info on the Parker website is somewhat sketchy about exact output stage, they say something about pulsed so I assumed that is standard PWM). The amp gain is set correctly.
There does not appear to be any induced offset at the amp, the valves are A and B closed in the center envelope anyways and there is no creeping of the cylinders which would indicate that the valves are open a bit. The valves are overlapped spools, nothing very fancy.
What I am thinking is that there may be a line surge when the electric motor is shut down causing interference on the output stage of the amps or in the cables connected to the valve DIN plugs. I know that the caps in the 24Vdc power supply provide momentary power to the amps after the input is shut down until they decay. But without a input signal, nothing should move for that 1.5 sec.
A quick low tech solution would be to add solid state relays on the amp outputs to the valves, when the stop button is pressed it cuts out the contacts quickly on the relays therby isloating the proportional valve solenoids.
Any thoughts or suggestions.
What is happening is this, when they shut off power to the system, ie, turn off the electric motor for the pump and associated input power to the 24Vdc power supply and proportional amps, the proportional valves are shifting slightly, the pump continues to produce flow for several revolutions and with the valves open slightly the hydraulic cylinders are jumping several inches.
When you remove the DIN plugs from the valves and repeat the shutdown, the valves do not shift, this then eliminates solely the hydraulics as the problem.
The valves and amps are basic older Parker models, output to the valve is PWM with a small AC dither signal, (Thats what I think anyways, as the product info on the Parker website is somewhat sketchy about exact output stage, they say something about pulsed so I assumed that is standard PWM). The amp gain is set correctly.
There does not appear to be any induced offset at the amp, the valves are A and B closed in the center envelope anyways and there is no creeping of the cylinders which would indicate that the valves are open a bit. The valves are overlapped spools, nothing very fancy.
What I am thinking is that there may be a line surge when the electric motor is shut down causing interference on the output stage of the amps or in the cables connected to the valve DIN plugs. I know that the caps in the 24Vdc power supply provide momentary power to the amps after the input is shut down until they decay. But without a input signal, nothing should move for that 1.5 sec.
A quick low tech solution would be to add solid state relays on the amp outputs to the valves, when the stop button is pressed it cuts out the contacts quickly on the relays therby isloating the proportional valve solenoids.
Any thoughts or suggestions.