How to read frequency and adjust voltage output

I have a bs2 reading 3 shaft rpms. Presently the hydraulic pumps are controlled by pwm controls with ramping. Problem is variance in output because of heat in hydraulics.
Wanting the bs2 that is already reading the rpms to output a variable .75 -1.25 vdc to keep the shaft speed consistant regardless of any load or temp changes.

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  • tomcrawfordtomcrawford Posts: 920
    edited September 1 Vote Up0Vote Down
    You really haven't posted enough information to be able to help. A block diagram and current BS2 program would be good.

    That said, I guess the short answer would be to use a DAC or filtered pwm.
    Re-inventing the wheel is not a waste of time if, when you are done, you understand why it is round.
  • I'm guessing you want to make a closed loop system PID. That you want the BS2 to maintain a constant RPM. So you need a count sensor and a DAC to output the DC volts.
  • Already using Lm2907 freq to voltage on the alarms but didnt know of any way to tailer it be a control loop
  • This is new and from scratch.
    Currently the bs2 is just reading 3 mag sensors and displaying the rpm on a lcd screen. With rpm on top line and alarm point displayed beneath each output. If rpm falls below setpoint a led lights up and buzzer goes off. I am trying to include the control part to overcome the change in speed due to temperature change. The present control circuit is actually a proportional brake control circuit that i wired to just output a pwm output relative to a 20 turn pot input and included a rc circuit inline to accomplish ramping up to speed. But the fluctuations from temp are enough to change the rpm as much as 100rpm. So was hoping to just let the bs2 take the place of the pot input for the pwm brake control circuit
  • You should add a temp. senor so you can input that signal into the Bs2. This way you can program the temp. error into the code.
  • So you are currently basic open loop? The motor(s) are hard-wired to power and the ten-turn pot just controls a brake?

    I think you ought to be able to replace the pot with a DAC controlled by the BS-2. If the rpm is too high, you add more brake; if it is too low, you back off on the brake. Small steps and some hysteresis so it doesn't oscillate.

    Be sure the accuracy and precision of the sensors is adequate. Likewise the DAC.
    Re-inventing the wheel is not a waste of time if, when you are done, you understand why it is round.
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