electro-hydraulic valve driver / amplifier

V0N_hydro

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Join Date
Sep 2010
Location
lower mainland
Posts
560
Hi

I have an electro hydraulic valve with coil resistance 22 ohms that takes as +/-12V DC input with 40Hz dither superimposed. The valve controls oil flow to either side of the piston of a pilot servomotor.

There are centering springs on the valve spool so it requires +12V for opening at maximum rate and -12V for closing at maximum rate. There is only one coil on this valve.

The existing amplifier that drives this valve is all analog electronics designed in the 70s and manufactured in the 90s. The fellow who designed it and has previously done repairs is retired a long time ago.

Does anybody know of a product that can drive this valve? I have not found any yet that can handle the polarity requirements.

I suppose this valve is currently driven 'linearly' as opposed to with a PWM signal. I don't see why it wouldn't work with PWM.

Thanks for any pointers
 
Hi Peter,

I am going off a block diagram for the amplifier module that shows +/-12V at the output of an op-amp, which then has a 33 ohm resistor before the terminal where the field wiring connects. The valve coil is 22-25 ohms stamped on the valve. It probably will work on 250 mA (12V/(33+22 ohms)) and not require 545 mA.

I think any device that takes a PLC analog output as input, and outputs +/-300 mA with a 40 Hz triangle wave superimposed should produce the same signal as the device I have. If nobody makes one we will probably figure out a new block on the HPU so we can use an available proportional valve.

Thanks for your input
 
I think I've found a few:

https://www.selec.ch/wp-content/uploads/Datenblatt-E-AE-1D-1.pdf

http://www.axiomatic.com/valve-controller.pdf

http://www.vickers.sh.cn/pdfs/gb2093a.pdf
only does 200 mA but might be enough. looks like it is probably hard to get


https://www.w-e-st.de/files/pdf/SV-200-EN.pdf
They make an SV300 that can do 300 mA as well

All of these look like they will be a pain to procure new ones in 10-15 years again I am probably better off getting a new block machined and using some valve that is readily available. Although the last proportional valve we ordered took months to arrive.
 
Hi Peter,
I am going off a block diagram for the amplifier module that shows +/-12V at the output of an op-amp, which then has a 33 ohm resistor before the terminal where the field wiring connects. The valve coil is 22-25 ohms stamped on the valve.
The 33 ohms output resistance seems high, way too high. Think of all the power that is being wasted across that resistor as opposed to the coil. Maybe the 33 ohm resistor is just there to limit current.


In any case there isn't +/- 12 volts after the 33 ohm resistor and the peak current is 218 ma.


We sell voltage to current amplifiers that will take +/- 10 volts from a PLC or similar. There are two channels, each that output 100ma but they can be paralleled to give +/- 200 ma which is just short of 218 ma you are getting now. Our voltage to current amplifiers don't have dither. You would need to at this to the PLC.
http://deltamotion.com/products/acc/vc21xx.php
We sell a lot of these because they are relatively cheap and simple. No dither, not ramps, just converts voltage to current. The dither and ramps need to be a function of the controller.



If you need more than 200 ma then you can parallel two to get up to 400ma.


Note the current output for each channel is selectable in 10 ma increments.


Just remember, no dither and no ramps.
 
I've seen these in use. I haven't connected to them to mess with them yet, but it looks pretty solid.

Wandfluh-SD7-digital-amplifier-modules.jpg


USB connection, free software. very visual.
 

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