Frequency of Solenoid

Hey Guys,

New to forums, work with PLC's on a daily basis but I myself don't know how to program them (however I would like to learn). Currently working on a system that doesn't use a traditional PLC. Somehow this machine is able to apply a voltage to a solenoid all the time and able to open and close it without changing the voltage. My only theory is that it's able to change the frequency. Has anyone heard of this or able to confirm that solenoids are able to work that way? Any help is appreciated.

Never seen anything like that in the food and pharma industry. Could it be a changing DC signal with just a bunch of noise on it?

The coil uses 24VAC. This machine probably has 100 water/air/chemical valves that all operate like this.

jedman said:

The coil uses 24VAC. This machine probably has 100 water/air/chemical valves that all operate like this.

Click to expand...

Probably a proportional control valve, not a traditional "solenoid" valve. It might look the same on the outside. You power it with 24VDC, then there would be another control signal going to it, like 0-10VDC or 4-20mA that tells it how far open or closed it needs to be. Might even be a wireless signal going to it now.

Can you provide the complete catalog/model/brand number if this "solenoid"
valve?

There are 'proportional' solenoid valves that provide proportional operation via pulse width modulation (200Hz for water) of a 24Vdc DC control signal.

Look up Asco 8202.

If you put a DVM on a PWM control signal it could 'look' like AC.

It could be connected to a sinking g output. If you measured from positive on solenoid to gnd, voltage would be present.

If you're measuring 24VAC to ground at the solenoid, the non-PLC could be switching the neutral to turn it on and off.

If there's 24VAC to ground on both sides of the solenoid coil, then the solenoid will be off, and I'll bet (pocket change only, as Ron would say) that the neutral is open circuit. When the solenoid comes on, you'll likely find 24VAC to ground on one side of the coil, and 0V to ground on the other side.

Or, you could measure voltage across the coil, rather than to ground - if it's 24VAC across the coil, the valve should be open, and if it's zero, then evenn if there is 24VAC to ground, the neutral will be open circuit and the valve will be closed.

Of course, it could be a proportional valve as well, like the others have suggested - if so, there will be more than two wires on it. Worth investigating further.

They could be on a bus system ("unconventional PLC")something like ASI bus, interbus or any number of propriaty bus systems where the signal to switch or the feedback signals open/closed etc. are modulated across the supply cables and decoded at the valves themselves which are all individually addressed.

Steve

Maybe you're overlooking the obvious? Could it just be a solenoid driven by a triac? If you measure voltage at the solenoid, it appears to be ON all the time due to leakage current.

Sorry it took me a bit to get back to this thread but I tested the voltage across the coil and not to ground. A proportional control valve isn't useful in this type of application, it's either the valve is open or closed, no in between.

can you give us the numbers from the valve - as Mickey requested in Post #5? ... that would probably take a lot of the quesswork out of this problem ...

You indicate that the coils are driven from a PLC, but a not traditional PLC.

Can you give us the brand and model of that PLC and the output cards.