Solidstate Relay for hydraulic prop valve

plc_user1973

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Join Date
Aug 2006
Location
Pennslyvania
Posts
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Hello, I was wondering if someone here could direct me to a company that makes a SS relay that is capable of driving a prop valve. My plc has a PWM output, but isn't capable of driving a proportional valve without a driver. I was hoping someone made a relay that could be used in a PWM scheme around 2kHz. I see Omron has the "hockey puck" type G3NA series, but their data sheet doesn't refer to a max on-off frequency.

Thanks in advance.
 
In my experience, proportional valves are ANALOG. Not digital. There are usually electronic circuits that allow for a digital enable signal, other setpoints, but the output is ALWAYS ANALOG! (Hydraulic/pneumatic)
How else would you proportion a signal to a device? It needs to be analog.
 
I am not sure about the G3NA but the G3R plug in type has a "High Speed" version rated for 1KHz.

Andybr
 
I am not entirely familiar with PWM, but if you are driving the relay with the PWM signal from the PLC won't the voltage that the relay sees be PWM also? An in that case will the relay switch if it is not seeing the voltage required? Or does the relay, since it is SS, open the channel to the valve slowly?
Sorry to jump in with a bunch of questions and no answers.
 
The actual, physical coils on the valves are current driven. All old prop valves had driver boards which took the process analog signal (0-10V or 4-20mA) and did the driving of the coils. The easiest way for the cards to provide a changing current is through a pulse width modulation scheme.


Newer valves with "On Board electronics" take a direct analog signal (0-10V, 4-20mA). They still have to drive the coils with a current but they have that circuitry on the valve instead of on a card in the panel.
 
Because my analog output is limited to 8bits and the I have a PWM output that is several kHz. The prop valve that I have is simple in design it accepts a signal from 0-24VDC and adjusts the spool accordingly. Look at commandcontrols.com about the valve if you wish. Yes they have additional circuitry that converts a analog signal to PWM, but like I mentioned above I am limited with that res. I am sure this will be just fine with a HS SS relay. The valve will look at the voltage/duty cycle and get an average voltage.

Thanks for the replies. Keep them coming.
 
Okay so looking at the relay link the relay will switch at 4V (should have looked at the link first). Will your duty cycle every cause the control signal to the relay to drop below 4V?
 
The PWM output would be switching between ON and OFF at a rate of 2KHz according to the original poster. The amount of the time spent ON is the variable. He wants a solid state relay which can switch at least the same rate.

But the final driven inductive coil being turned on and off in this manner will generate a large turnoff voltage. Make sure that the intervening solid state relay can take the turnoff voltage or that any needed protection is added.
 
Its working with the same PLC with a MosFet transistor in another project, but if the owner needs to replace it, there is soldering involved so this is the reason for the relay. Much simpler for novice replacement. I know you guys understand how this works, I don't understand the dilema. Its just a PWM output on a PLC that doesn't have the drive current to handle the coil without a driver. The PWM is changing duty cycle so its applying full 24VDC on/off depending on duty cycle. The coil sees this as an average voltage. Simple. Average voltage is then adjusting the coil proportionally.

The necessary protection is accross the coil. (DIODE)
 

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