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Quick question on what industry uses proportional pwm speed control — Parallax Forums

Quick question on what industry uses proportional pwm speed control

sport270sport270 Posts: 82
in BASIC Stamp
I used a pwm control from a proportional brake control and just used a pot to dial it in to the voltage i needed to make a suar danfos h1 hydrostat pump output the flow needed to achieve a given rpm.... works but operator is having to adjust it when first started up and cold hydraulic fluid, then again when heated up.... was wondering easiest way to add proportional control to keep rpm constant. Or even better ... a off the shelf pwm control to do this... as volume needed is only around 10 needed. And this is on 12dc mobile equipment

Comments

  • evanhevanh Posts: 15,187
    It would pay to confirm, by carefully monitoring the analogue and PWM levels, to see if your analogue demand is drifting over time.

    If instead it's the hydraulics that isn't consistent then you're probably looking at needing feedback to form a servo loop from.
  • rabaggettrabaggett Posts: 96
    You will need to somehow measure the RPM. the easiest is perhaps with the Hall-effect sensor available on this site, and a magnet. Most hydraulic equipment operates at a slow enough RPM that gluing a magnet to the side of a shaft (or get one that will fit in an empty keyway) somewhere convenient to the sensor is practical.

    A simple PI controller can increment the PWM time when below the desired RPM and decrement the time when too fast. Put it in a timer loop, and tune the response using the timer value.

    Retain the pot to vary the target setpoint as needed.

    Many commercial PID controllers will accept pulses like this for an input.

    These sensors will work for sensing gear or sprocket teeth, or even a keyway: http://www.motionsensors.com/speed-sensors/variable-reluctance-speed-sensors.shtml
    Many of the small PLCs in the 'Smart Relay' category have frequency counter capable inputs and PWM capable outputs. Check TriPlc.
  • sport270sport270 Posts: 82
    Thanks for the advice.. sorry took so long to reply
  • DigitalBobDigitalBob Posts: 1,486
    A danfoss H1 is a pretty good size hydraulic pump. I would use a servo flow control and keep the pump RPM constant. You could take a flow signal from a turbine flow meter and feed it to a servo amplifier that would govern the electric servo flow control valve. Then set it to a constant 10 GPM. Closed loop PID.
  • MicksterMickster Posts: 2,610
    In cases where closed-loop is not an option, some choose to maintain the oil temperature, during shut-down, to minimize the viscosity fluctuations.
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