Switching distance of inductive proximity switches?
Good morning,
I'm currently working with inductive sensors. For this, I need to know how the different switching distances are created. Because the switching distance depends on the material. And I need to explain why certain materials are detected earlier or later.
At first, I thought I understood. My thought was: The more conductive an object is, the sooner it is detected, and therefore the greater the switching distance. Conductive objects generate eddy currents that become stronger the more conductive the object is. These eddy currents lead to energy loss, which the sensor then detects through a damped amplitude. Based on this, I thought copper was one of the materials with the longest switching distance.
Now, however, I've discovered that the exact opposite is true. Copper is detected last, and materials like steel, which aren't nearly as conductive, have the greatest switching distance. And my question is, why is that? Steel should have much smaller eddy currents, which should lead to a small energy loss, which should lead to a delayed detection. I've obviously made some kind of error in my reasoning or misunderstood something.
I look forward to your answers,
LG
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You forget that steel is mostly iron and therefore ferromagnetic. The iron atoms always try to align themselves according to the magnetic field, with significantly more energy being converted.
For example, induction heaters can heat iron significantly better than copper. Only above the curie temperature, i.e. the temperature at which the iron loses its ferromagnetic properties, does not seem to go much further at once (at least if the workcoil of the IH is part of a parallel oscillating circuit if I remember correctly).
Thanks for the answer, that was helpful. But what I still don’t understand is when now ferromagnetic materials are taking on the outside that the conductivity somehow has a completely different effect than I thought. Because it seems like this: the sensor apparently recognizes a material so poorly as conductive it is. The smallest switching distance has copper, then comes aluminum, brass and finally steel. I can’t get that in my head.
That’s a mystery to me, too. In my opinion, everything says that a higher conductivity should mean more absorbed energy…
Do your test objects all have the same dimensions? This is of course also crucial.
Yeah, well, thank you for trying to help.
LG
Interesting. Maybe you could put another question on it so that someone can tell us.
Yes the experimental objects had the same dimensions, but regardless of the experiment, this is also in the teaching documents:
“If a different material is used for the measuring plate instead of the material (St 37) determined by the standard, the switching distance must also be corrected. In inductive proximity switches, this correction factor is directly dependent on the electrical conductivity of the material, since it determines the level of the eddy current losses (exception: ferromagnetic materials, see below).
Thus, it can be seen in the following illustration that, in the case of a very good electrically conductive material such as copper or aluminum, a correction battery gate results which results in a lower switching distance. In contrast, the electrical conductivity of graphite and ferromagnetism in the iron cause the losses in the oscillating circuit to be greater here, so that the switching distances to be achieved are also correspondingly greater. This results in the surprising consequence that material is detected to a greater extent, the better its conductivity.‘
I think conductivity doesn’t matter. Rather, it is the size and shape of the object. The surface may also play a role.
Well, something nonconductive and non-ferromagnetic can hardly interact with a magnetic field.
Nee with wood becomes the nix when it is dry. But whether there is such a difference between steel or copper?
All right, yeah. In steel anyway, this is ferromagnetic. But even between copper and aluminum there is a noticeable difference, although both metals conduct quite well. Can you read my answer and the comments below.