Cause of Continuous Alarm of the Metal Detector Unit?

Hi guys,

We are in a sugar manufacturing plant and we have installed a flow through metal detector unit last Nov. 2012 and it was working well but as of this week the unit kept sounding off even though we found no metal inside the sugar bags except for caramelized sugar less that 1.5 mm black specs (non-magnetic). But we noticed some encrustasion around the flow trough tube before the MD. Is this the cause of the continuous alarm of the unit? Can anyone suggest what are the possible cause of the continuous sounding of the unit.

Hope to hear from everybody.

Thank you in advance.

Hi guys,

We are in a sugar manufacturing plant and we have installed a flow through metal detector unit last Nov. 2012 and it was working well but as of this week the unit kept sounding off even though we found no metal inside the sugar bags except for caramelized sugar less that 1.5 mm black specs (non-magnetic). But we noticed some encrustasion around the flow trough tube before the MD. Is this the cause of the continuous alarm of the unit? Can anyone suggest what are the possible cause of the continuous sounding of the unit.

Hope to hear from everybody.

Thank you in advance.

2nd, 3rd hand ??

it's probably faulty or wrongly set up. sometimes it's related to the matrix of the sample, eg ice in frozen items.

My advice > local supplier for tech support.

If it does not trigger for the metal test pieces, it's definitely faulty,but in a more dangerous way.

Rgds / Charles.C

Does the metal detector pass your operational tests? What size test pieces is it calbrated/certified for?

These "black flecks" you discuss: they don't have to be magnetic to trip a metal detector. Our flow through md detects down to 1mm fe and non-fe, and depending on the mass of a piece it can see items that are smaller. Metal detectors are weird like that.

In my experience, "encrustination" hasn't affected our flow through md. We perform operational tests every two hours with the certified test pieces and even with product buildup it still detects our test pieces in a stream of product.

Our brainaic cleaning crew constantly sprays the detector with water. This will set off the detector until you wipe all the excess water off. They're very sensitive in that case. not only for metals, but for minerals in general. We deal with olive brine and are forced to set it at a lower frequency or else it rejects everything from the high salt content.

Should they be unplugging the detector prior to cleaining? No reason to have it on and going berzerk with water all over it.

You might need to re-calibrate it for the sugar you are running. The black flecks still make me wonder, but if they don't concern you then...

Might be time to consider a tech visit too.

Sometimes they unplug them. Like I said, they're "brainaics". I swear half of them live in La-La Land all day long. They feel spraying sanitizer in every direction is the solution to all problems. Then they let it sit and I have to wipe it down in the morning.

Does the metal detector pass your operational tests? What size test pieces is it calbrated/certified for?

These "black flecks" you discuss: they don't have to be magnetic to trip a metal detector. Our flow through md detects down to 1mm fe and non-fe, and depending on the mass of a piece it can see items that are smaller. Metal detectors are weird like that.

In my experience, "encrustination" hasn't affected our flow through md. We perform operational tests every two hours with the certified test pieces and even with product buildup it still detects our test pieces in a stream of product.

Hi John123

Our test piece is 1.5 mm Fe and nFe including 2.5mm SS. All these test pieces are detected by the MD unit but lately as I've said the unit keeps on ringing but when we stop bagging the alarm will also stopped ringing.

We are waiting for the supplier tech guy.

Thanks everyone for the help.

There could be a few things causing the problem you describe;

1) Is it near a metal wall or other large piece of equipment made of metal? - or has it been recently moved? this can be a reason
2) Another reason could be the sensitivity of the machine - they detect via density, if the sensitivity is to high then it will trigger off
3) The rollers of the conveyor can create a feedback loop and set it off - your eng would be the best bet for exploring this


General tip - if your metal detector goes off on a product then dissemble it piecemeal at a time - f.x - you have a 2kg bag of sugar that gets rejected, get two plastic containers and pour half of the sugar into one and put the rest of the pack into the other, keep doing this until you find the source. Your test pieces are very small which means your machine is calibrated to detect swarfs of metal which can be easily missed. Also magnets are your friends (in some cases)

take care,
Pry

Chebar,

I too work in a sugar refinery, and we are had similar issues with false "hits" on our metal detectors when we first started. After EXTENSIVE investigation, it was determined that vibration of the detector itself when fast-moving railroad locomotives passed nearby was the cause of the false "hits". Once we stabilized the detectors a little better, the problem went away.


Also, just a note on the encrustation of sugar before the detectors...we use a product called "Sugar-EEZ" on all equipment surfaces to remove sugar buildup/prevent it from being able to build up in the future. This product is composed of a food-grade lubricant that works wonders where sugar buildup is a problem. Just let me know if you are interested in this product and I can email you the order info.

Chebar,

I suggest that the two most likely causes of the false alarm are (in order):

1. The black specs. I'd be prepared to put some money on this. The black specs are probably burnt sugar. If you burn sugar (or any other organic matter) you are left with carbon. Carbon is what metal (steel) is made from i.e. carbon steel. The metal detector will detect carbon.

2. Vibration. If the false alarm stops when the system stops, then either the black specs have stopped falling through the MD, or the vibration that was casing the rejecting has stopped.



So...
To resolve:
Step 1. Get as many of the black specs as you can and squash / stick / hold them all together in some way and make a ball or bag of them and drop them through the MD with the system stopped. Does it reject / alarm? If so then it would appear that this is the problem.


Step 2. Stop all product flow through the machine and start the system. Does the MD reject / alarm? If so then it would appear that vibration is causing the problem.




Given that the system worked ok for a while then it is unlikely to be vibration (unless something has worked itself lose).


You could also look at the reject chute (assuming that you have one). Is product building up in there? This can sometimes be an issue.