I need to detect Iron moving at a decent speed. This is going to be a safety device on an electric fence wire winder. The intent is that, if the operator fails to turn off the motor before the end of the wire wraps around the spool, then the flailing wire will be detected and the motor will be turned off. Normally, there is a heavy weight at the end of the wire to add tension; but I would like this to work even if the weight breaks off. That is, I would like this to be able to detect a 17 awg wire flailing at about 175 rpm. Will an inductive proximity sensor work?
Also, ideally the sensor would work like this out to about an 8-10 inch range. I'm not convinced that the precision needed to detect the 17 gauge wire is achievable without also being triggered by spool to shaft tolerances, etc. The machine itself has pretty loose tolerances! If it detects the weight the first time, every time, that should work pretty well. There will be a fair amount of iron in the vicinity. The only moving parts will be the spool/shaft and the wire/weight.
What would you suggest?
No.
No inductive proximity sensor will work in tbst scenario. You need to find another method that doesn't involve inductive sensors. Whoever thought of that has never used one.
If the flailing end of the wire is slapping any part of the winding frame, or if you can add such a frame member, then you can use a piezo disc to detect the hits.
You're right I've never used one. That's why I'm asking here.
"An inductive sensor is an electronic proximity sensor, which detects metallic objects without touching them" I read that statement from Wikipedia and thought an inductive sensor might work. Can you explain why it won't work?
The piezo disc would work with just wire hitting the frame, but the weight is about 10lbs of steel (an old window sash weight). I don't think I want that hitting anything. Any other options for non-contact detection of steel?
The wiki didn't mention it has to be no more than 2 mm away and this distance must not change and the distance can only change in that one axis and not the other three ?
Thanks for the explanation. The induction sensors work by detecting changes in the magnetic field created by the coil, right? The field is changed, if a magnetic object enters the field, and that results in a change in the current through the coil. That's the theory behind inductive sensors, right? Hopefully I'm not too far off in left field here!
Then, the distance would depend on the size of the coil and the sensitivity of the equipment used to measure the current. I don't quite understand why the distance would only be able to change in one axis.
Thanks for the link. That clears things up. I had a couple things backward in my mind!
Would an ultrasonic sensor work? Program it to activate when it measures a distance less than say 10". I kind of doubt it would read the thin wire but it might be able to pick up the weight its about 2" in diameter.
The best method by far is just get a small pulley and let the wire run over the pulley creating tension on the pulley mount. If the pulley is mounted with a plunger in a solid block with a spring, the tension of the wire on the pulley pulls downward pulling the plunger (or pin if you want to call it that) downward in the smooth sleeve in the block which has it's own solid mount via an L-shaped arm. The downward tension on the pulley , can be used to depress a microswitch until the wire runs out and the tension disappears and the switch opens. Alternately some other kind of sensor could be used to take advantage of the tension on the pulley. An inductive proximity switch would work to sense the pin position if the pin was steel and not aluminum. I don't think they respond to aluminum.If for example the pin could only move in front of the proximity sensor with downward tension or otherwise the spring would pull the pin up out of range of the proximity sensor. An inductive sensor will only work when the part to be sensed is totally captive and has no where to go other than up or down in a precision machined sleeve that guarantees the distance from the sensor to the pin is 1 to 2 mm and not more. (the sensor is 90 degree to the pin or perpendicular to the pin with the position adjusted with the threaded nuts on the sensor that allow you to move it forward (closer to the target object) or backward (further from the target object). It mounts in an 1/8" L bracket with a hole in it with nuts on both sides of the bracket.
Thanks for that suggestion. Unfortunately, I doubt it would work. This system bounces around quite a bit under normal operation. Imagine a weight on the end of a wire being dragged across a field or pasture. The weight gets caught on random twigs, mounds of dirt, tufts of grass etc. It jerks around quite a bit! This unit is mounted on the receiver hitch of a pickup and driven with a 5 hp gas engine. The weight tied to the end of the wire provides tension to keep it tight on the spool. I'm starting to think that there is not an easy/cheap solution to this issue. So at the moment, operator awareness will remain the main safety feature.
You can't build a pulley on a pivot with a spring or shock pushing it up under the wire close to the spool so the tight wire prevents the pulley from raising past a certain point. When the wire runs out there is to tension to keep the pulley down and it moves up further releasing pressure from the microswitch.
That would work for just a straight wire, but when the weight comes in: It's a straight piece of steel about a foot and a half long and 2" in diameter, i think it would knock that sensor out of place.
Looking at it, this is really unprecise machine that I'm trying to control with a precise controller!
Can you have the wire go through the loop of a coil?