sensor type??

[clarke]

we have a machine for grinding product, when the machine grinds the finer product passes through a screen with the larger product passsing out of the end of the machine. If the screen gets a hole the larger product contaminates the finer. My question is does anyone know of a sensor that could sense the extra(larger) product so that we know we have a burst screen. I was thinking of some sort of pressure or force sensor in the low of product.

 

[buzzp]

How is the grinder driven, hydraulic? electric? If electric, the power used by the grinder would likely indicate when you have a clogged screen, if the load is semi continuous. Just an idea.

How large are the small and large particles? What material are they made of?

 

[clarke]

it is driven by an electric motor. The motor load does drop when a screen bursts but this also so happens when other things happen within the grinder so we are looking to isolate a screen burst some other way.
The material is maize.

 

[IRstuff]

One possibility is to use a thin, intermediate plate that the product impinges on that's connected to a microphone or other pressure sensor and look for the difference between the ground product, which should look like noise and the kernels, which should have a more distinctive pop when it hits the plate

TTFN

 

[automatic2]

Not sure of the screen area, but could you pass a small current through it and measure a change that might indicate a disruption. Another thought might be passing a fixed light value through the free falling fines. Denser coarse might be detectable with reduced passing of light value. Another option might be air deflection of the fines. Coarse could then be detected by its seperation.

 

[ICman]

Just throwin' out some ideas:

** There are some particle size analyzers on the market. They are expensive, but would probably work. They measure the particle sizes in a flowing "pipe" and provide an instaneous average. If the average suddenly goes up, you've got a large particle. I don't know who manufactures these, but you could probably find out with a search.

** Or, if you could measure the weight of the receiving "tray", you might watch for a sudden increase.

** I wonder if there is a visual detection method? A camera either on the screen or on the receiver perhaps?

** Could you use two screens, of the same size and orientation? Chances of both having holes might be less.

That's it for now. My brain is starting to hurt.

. . . ICMan

 

[logbook]

There seem to be two different approaches:
1) Measure the screen to see if it has a hole
2) measure the output to see if it has large particulate.

1) depends on the aspect ratio of the screen. If it is long and not wide then a hole would show a more significant change in resistance. Of course if it is the other way around then pass the current though it lengthways. But if it is square, and the hole is quite small relative to the overall size, then the change of resistance could be down in the few percent region and that would be hard to detect in a noisy environment.

Measuring the output in a flowing stream is going to take considerably more development effort. Presumably the machine has to be stopped and fixed immediately the screen breaks. If you let the stream flow through a funnel which is just small enough to stop a large particulate, then the funnel will fill rapidly when blocked and the increased weight could turn on a micro-switch. Simple, but the exact size and shape of the funnel will take some experimental work.

I would suggest vibrating the funnel to keep it clear of the normal particles.

 

[BrianR]

A first approach might be to have 2 screens one above the other however in the long term an optical approach might work.

An optical scanner scanning the surface of the load below would see a change in texture caused by a larger particle. Dealing with the amount of dust that must be there will be a challenge though.