Hydraulic Generators

[HydraulicGen]

I am trying to come up with a solution to control a hydraulic proportional valve using either the output frequency of an ac generator or a pulse signal, basically I need the proportional valve to provide a constant flow to a hydraulic motor such that the driven speed of the hydraulic motor remains constant. So far all I have managed is to adapt the machine to provide a 600 pulse per second signal, what I need to do is to convert this to a dc voltage or current which signals the proportional valve to open and close responding to fluctuations in flow. Anyone out there know how to do this or can come up with a solution. At the moment I use a mechanical flow control valve, problem with this is that if you set the flow rate when the oil is cold the viscosity is x but when the oil is hot it is y so the driven speed of the ac alternator changes significantly.

 

[kellys_eye]

A frequency-to-voltage IC is readily available although this can be done using discrete parts too.

http://pdf1.alldatasheet.com/datasheet-pdf/view/462646/TI1/LM2907-N.html

Study the data sheet (which is VERY comprehensive) and in particular page 9 onwards where practical examples are shown.

 

[Alec_t]

Sounds as though you need to provide a signal proportional to motor speed, for use in a control loop to vary the valve position. Is the 600Hz signal a PWM one, with pulse width related to motor speed?

 

[HydraulicGen]

This signal is produced by a 12 tooth rotating plate fixed to the alternator / hydraulic motor drive shaft, the AC alternator is 50hz, 3000rpm, therefore generating a pulse signal of 600 pulses per second, I effectively need to maintain this irrespective of external factors, so therefore need to send a control signal to the proportional valve to adjust the valve accordingly. So yes the signal is directly proportionate to motor speed, motor runs slow pulse signal decreases and vica versa.

 

[kellys_eye]

As per my first post, the LM2907 performs all the necessary functions to deliver a proportional control voltage that you require. The scaling of the voltage can be achived partly by correct components associated with the LM2907 but also via simple level shifting using op-amps if necessary.

The resultant control voltage can also be used to control a range of other signal sources according to the needs of the hydraulic modulation vlave.

 

[Alec_t]

So yes the signal is directly proportionate to motor speed

This would seem to be one approach :-
If you use the pulse signal to trigger a fixed-width pulse monostable you'd get a FM signal with a speed-proportional duty cycle. The partly-smoothed inverse of that could drive the valve directly. Pulsing of the valve is advantageous (as a well-known anti-stiction technique). Adjustment of the monostable pulse width would enable the desired speed to be set.