RIDGID metal detector Podręcznik Użytkownika Pobierz pdf (Strona 46)

Installation

The alternative approach of permanently open circuiting the loop must be taken. This can be

done by electrically insulating one end of the roller shaft from the frame of the conveyor. In

practice it does not matter whether the eddy current path is open or short circuited, provided it

can guarantee to be constant throughout the life of the conveyor, since problems arise only

when the resistance of the path varies.

Be careful also when installing a conveyor, since large eddy current loops can be formed by

service conduits used for routing electrical and compressed air supplies. Only bring down one

electrical conduit since it has to be bonded to the conveyor frame for safety electrical earthing

purposes.

Ensure that the compressed air supply pipe, if metallic, is insulated where it touches the

detector or the conveyor frame at any point, or the electrical conduit in the region of the

conveyor. It is always better to bring the final air connection on a flexible nylon tube. To prove

the point one may like to try a simple experiment. Take a piece of wire and form it into a loop

a little smaller than the detectors aperture. Do not at this stage connect the two ends together.

It will be found that the open circuit loop can be brought quite close to the aperture without

causing the detector to trigger. If the ends of the loop are intermittently closed then open

circuited, it will be seen that the detector will trigger ate the instant of open or close circuiting,

even if is at some distance away from the head aperture.

Mounting Horizontal Heads for Use with Conductive Products

Loma heads up to 350mm in height are supplied with an adjustable height mounting kit. The purpose

of the height adjustment is to enable the centre line of the conductive product to pass through the

“centre line” of the head aperture.

Conductive Products and Mounting Heads Vertically

When mounting a metal detector head vertically, head the smallest dimension becomes the aperture

width. The same rules apply as for centring a conductive product for a horizontal head. However the

centre of the aperture now is in the vertical plane. For this set up, the product is centred using guides

mounted on the conveyor, these channel the product centre through the aperture centre.

■ Fixed metal

Since the detector is efficiently screened, large masses of metal near the top, bottom or sides

will not normally affect its performance. However metal that is nearer to the aperture than 1.5

times the smaller of the two aperture dimensions as measured from the centre of the case

depth, can frequently be a major cause of poor performance, requiring the detector sensitivity

to be reduced.

■

Moving Metal

Moving metal must be situated no nearer than 3 times the smaller aperture dimension from

the detector as measured from the centre of the case depth

Moving metal excludes concentric rotating rollers. If they are concentric and can be

guaranteed to stay that way, then they may be classed as fixed metal.

However it is important to reiterate that they must be insulated from the conveyor at one end

or it is possible that they will cause false triggering by creating an intermittent eddy current

path.

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