Ground fault sensors

A customer has got rid of his leased machines and bought new/used ones. These machines pull steel wire through straighteners and then bend, cut and drop into bin. The old machines had a sensor system called TYCO Protek II that had bendable pieces of metal rod mounted on nylon isolation blocks near where the product was likely to jam and bend out of place.they could bend and shape the rod to whatever shape they wanted around the path of the incoming steel wire. The (grounded steel)product would touch one of these rods and open the stop circuit. The new machines did not come with this system and we would like to find something that can do the same job.

well there are isolation meters that will sound alarm when one of the fases is grounded (when there is current flowing thru the meer.
an easier one is to use an arduino with some input_PULLUP. that will detect when any of your sensors is touched, and that for a price of 50 cents/sensor.
obvious you could use any 24 V PLC and some resistors to pull up the input. easy and very reliable.

That doesn't sound like it would be difficult to make your own system if you can't locate one.
I made something similar using a small 12vdc power supply and a relay. The negative side of the power supply was grounded and the positive side connected to the relay coil. The other side of the relay coil was connected to the sensor. When the sensor was grounded it turned on the relay.

Would there be any sparking from that? on some of these machines there is oil in the area where they lube the moving parts.

We use this product for level control. Basically a resistance sensor with a relay. Max voltage/current of sensing circuit is 5V/1mA

http://uk.rs-online.com/web/p/monitoring-relays/6149347/

bdoutney said:

Would there be any sparking from that? on some of these machines there is oil in the area where they lube the moving parts.

Click to expand...

It would depend to some extent on what type of relay that you use, but generally the answer would be no as long as you stay at 12vdc. I used a 1 amp 12vdc power supply with the relay coil in series rated at 16ma. That would qualify it for a class 1, div 2 hazardous location if it had a reverse diode across the relay coil. If there were aerosol solvents involved you could use something like a GEMS Senors intrinsically safe relay.

AustralIan said:

We use this product for level control. Basically a resistance sensor with a relay. Max voltage/current of sensing circuit is 5V/1mA

http://uk.rs-online.com/web/p/monitoring-relays/6149347/

Click to expand...

+1

Also: http://www.littelfuse.com/products/.../pump-controls-and-liquid-level-controls.aspx

Do you WANT to roll your own, or are you looking to buy one? The Protek II is a viable product used to attach to drills that are drilling into non-conductive material (like wood or concrete) to detect and shut down the drill if it hits metal, like a pipe or wire. Used all the time in the construction trades. Sounds as though someone simply adapted one for your machine in a rather inventive way. I don't see why that would be hard to duplicate. In your scenario the wire feed becomes the "drill bit" and you simply create a wire loop that if it touches, triggers the relay to drop out power to your feed motor.

Your problem in searching for it may have been the use of "Tyco". I don't know where that came from but the company that sells them now is called Lorien.

I found them thank you. But I would like to make this work with a PLC because after looking into how these machines work I can see a need for an updated control. They have lube system that they plug in with an extension cord instead of running only when the machine is in motion which explains the oil all over the place, they have a mechanical limit switch being hit by a keyway on a shaft that spins all day for the product count. On some of them the motor starter has a 120 volt coil with the neutral side tied to a mounting bolt.

I have used the Omron D5C capacitive touch switches with good results. You probably want the 'free-attachment' version, so you can put your own actuator on it.

https://www.ia.omron.com/data_pdf/cat/d5c_ds_e_4_3_csm594.pdf?id=562



-Eric