quote:

---

> I have a metal detector which is beeping for no reason when people pass
> it by with the talkie-walkies. The talkie-walkies use UHF radio waves,
> and so I know that I have to somehow block the radio waves. I have
> tried chicken wire grids as small as 1cm by 1cm meshes, making a
> faraday Cage around the machine, but the small opening in the cage is
> enough for the Radio waves to get through now and then.
>
> I also read that broken fluorescent lights can attenuate the RF waves,
> but I have no idea how and why that should work...
>
> I was hoping for suggestions about metal detectors and RF interference,
> May be a way to fully shield the metal detector from the waves without
> having to completely seal it in a grid.
>
> P.S. I can supply more information if required.
>
> Thank you in advance
> Josh
>

quote:

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> it's actually a LOMA IQ2 metal detector for food industry. The
> walkie-talkies use 450 Mhz signal.
> The metal detecotor itself works pretty much like an AM radio. It has 3
> coils along the convoyer belt line. The central coil transmits a signal
> similar to that of AM broadcasting ( 530-1,710 kHz). Spaced equally
> from the centre transmitter coil, are the two recieving coils which act
> as aerials to pick up the radio signal. The metal detector measures the
> difference in voltage between 2 recieving coils. If a metalic object
> passes by, this difference voltage (obviously becomes more than a
> certain amount) and that triggers the alarm.
> But where does the RF interfere?
>

quote:

---

> it's actually a LOMA IQ2 metal detector for food industry. The
> walkie-talkies use 450 Mhz signal.
> The metal detecotor itself works pretty much like an AM radio. It has 3
> coils along the convoyer belt line. The central coil transmits a signal
> similar to that of AM broadcasting ( 530-1,710 kHz). Spaced equally
> from the centre transmitter coil, are the two recieving coils which act
> as aerials to pick up the radio signal. The metal detector measures the
> difference in voltage between 2 recieving coils. If a metalic object
> passes by, this difference voltage (obviously becomes more than a
> certain amount) and that triggers the alarm.
> But where does the RF interfere?
>

quote:

---

>I have a metal detector which is beeping for no reason when people pass
>it by with the talkie-walkies. The talkie-walkies use UHF radio waves,
>and so I know that I have to somehow block the radio waves. I have
>tried chicken wire grids as small as 1cm by 1cm meshes, making a
>faraday Cage around the machine, but the small opening in the cage is
>enough for the Radio waves to get through now and then.
>
>I also read that broken fluorescent lights can attenuate the RF waves,
>but I have no idea how and why that should work...
>
>I was hoping for suggestions about metal detectors and RF interference,
>May be a way to fully shield the metal detector from the waves without
>having to completely seal it in a grid.
>
>P.S. I can supply more information if required.
>
>Thank you in advance
>Josh

quote:

---

>I personally have experience with Gorring Kerr metal detectors, the
> principle is similar to the Loma that you describe. Although I assume
> you are using O frame detectors, as opposed to single sided units.
>
> This application is in paper processing, so the product is not as wet
> as food, but it is on the borderline of what a metal detector
> considers wet. I have 3 units in similar installations, on 3 separate
> lines. Two behave flawlessly, the other is possessed. My problem is
> not equipment, but location, because I can physically move the entire
> installation, and it will work.
>
> This problem unit is a single sided detector. I use very fine copper
> screen like is used in aircraft skins. There is a 4'x8' piece above
> the detector to shield and a similar size 12" below the detector face
> which acts as ballast, which allows us to raise the sensitivity, while
> still ignoring external interferance. A transmitting two-way radio
> still causes problems, but only within a few feet.
>
> If your problem unit is an O frame, your problem may have been
> identified by a previous poster. The mutliple coils can shift their
> alignment over time, which requires a "Balance" adjustment which is
> typically on the detector head. It may also require a "phase"
> adjusctment to compensate for product moisture. Also as previously
> mentioned, these units are not impevious to water. small amounts of
> water change the magnetic field as viewed by the sensing coils.
>

quote:

---

> I have a metal detector which is beeping for no reason when people pass
> it by with the talkie-walkies. The talkie-walkies use UHF radio waves,
> and so I know that I have to somehow block the radio waves. I have
> tried chicken wire grids as small as 1cm by 1cm meshes, making a
> faraday Cage around the machine, but the small opening in the cage is
> enough for the Radio waves to get through now and then.
>
> I also read that broken fluorescent lights can attenuate the RF waves,
> but I have no idea how and why that should work...
>
> I was hoping for suggestions about metal detectors and RF interference,
> May be a way to fully shield the metal detector from the waves without
> having to completely seal it in a grid.
>
> P.S. I can supply more information if required.
>
> Thank you in advance
> Josh

quote:

---

>
><me@home.com> wrote in message
>news:5lhbd1t355c380h99or830v66ed7qqo1o2@4ax.com...
>
>I, too, have had experience with Goring-Kerr's single sider model. We used
>them in food processing and they were constructed in stainless steel frames
>with a food-grade epoxy on the sensing face. Goring-Kerr did what they could
>to water-proof them, but we only got about 4 or 5 years of service out of
>them.
>
>In our application, we needed an unobstructed field of view of the product
>(meat) as it passed over the detector. We were looking for large metal
>objects (meat hooks, knives, bolts) lodged within piles of meat as they were
>conveyed to a grinder. The requirement for a clear line of sight of the
>product and the rather relaxed contaminant specs eliminated the need for the
>more conventional closed aperture style.
>
>In your case, you describe a biasing screen added above the single sided
>detector that, I imagine, blocks the view of product. Why not use a closed
>aperture detector for that application? They are considerably more sensitive
>to contaminants and there is less fringing of the electric field (and hence,
>require a smaller metal-free zone).
>
>Also, you mention the anomalous behaviour of one of your detectors seems to
>be "location sensitive". We experienced something similar to this. It turned
>out one of our detector conveyors, when positioned, had two legs resting on
>a pair of the many floor drain grates. As these legs were on opposite sides
>of the conveyor's eddy current break, the drains (cast iron) bridged the
>eddy current break, resulting in weird operation. We ended up insulated all
>our metal detector conveyors' feet from the floor. Probably not the same
>conditions you have, but maybe floor surface variations between one location
>and another cause vibrations in your conveyor that's affecting the detector.
>

quote:

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>
> "Josh" <ASiavashJ@gmail.com> wrote in message
> news:1121264161.187496.11110@f14g2000cwb.googlegroups.com...
>
> its is time to read the operator manual or consult the manufacturer.
>
> the unit is either functioning normally or needs repair or adjustment.
>
>
>
>