Need someone to look over a proportional control circuit that is unstable .

I have a proportional control circuit that i have been using for several years and the mfg of the equipment using them changed from 12vdc solenoids to 10vdc solenoids and my controls are very unstable now. Just not able to get them to stop moving up/down continuously. Have tweaked the circuits in several places with each having visably noticeable results but not being able to make it stable. Think i need a way to just slow down the change coming from the input sensor. Mabye a cap with resister to slow the change and possibly different resistance for voltage going higher vs dishcharge since. Or possibly a way to cap the output voltage so it cannot move the unit so quickly.
Here is the control context.
Agricultural unit floating across the ground.
Has skis that move across the ground connected to 3wire 0-5v sensor.
Control has reference 0-5v pot.
Output is a variable duty cycle with adjustable dither frequency to overcome valve stinction.
Hydraulic valve is a bypass valve with one port to pressure and other to return tank.
And center to hydraulic cylinder to raise/lower unit. Constant 12vdc on one side of solenoid. We output lowside with around 3.3vdc and lower drops unit. And 3.9vdc raises unit. And approx 3.6vdc holds unit steady...
I have played with the circuit and can change the response output at several different places in the span. So i think i just need to slow the change inth sensor rise time or possible cap the output so it cannot jump so quickly as to over correct and then immediately have to drop in an oscillating pattern.


  • edited 2018-10-29 - 22:09:24
    Would a series resistor to drop the voltage across the valve to 10 volts work? Change to a 10V power supply for the solenoid?
    Infantryman's Axiom; Always cheat, always win.
  • Sounds like you just need to drop the gain.
    Failure is not an's bundled with the software.
  • Checkout my comment in general discussion. Under How would you power this solenoid posted by Tchap. I posted a schematic of a hydraulic proportional solenoid control.
  • kwinnkwinn Posts: 8,327
    edited 2018-10-30 - 14:23:44
    Mickster wrote: »
    Sounds like you just need to drop the gain.

    In science there is no authority. There is only experiment.
    Life is unpredictable. Eat dessert first.
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