Thermo Scientific APEX 100 User Manual page 308

of the aperture. When a complete system with frame and throughput tube has been
supplied by Thermo Fisher Scientific, these considerations have already been factored in
to the design of the system.
Factors That Can Influence the Operation of the Detector
It has been proven that causes external to the APEX, are the main reasons for faulty
operation or random false triggering. When installing the APEX on an existing or custom-
built pipeline system, the instructions below should be carefully studied. Only when
correctly installed will the equipment perform optimally. The APEX may have been
installed correctly initially, but conditions change that may cause intermittent problems
with the metal detector. If the APEX develops fault symptoms such as intermittent
triggering, the factors in this section should be carefully studied before any electronic
servicing is contemplated.
Throughput Tubes
Any tube material passing through the APEX must be totally metal free. Sometimes
metal particles or grease that has become loaded with metallic dust, becomes embedded
in the tube.
Aperture Clearances
The plastic throughput must not touch the aperture in any way at any time. Touching
the inside of the aperture can cause nuisance rejects.
Mounting
The support structure used for mounting the APEX, should be constructed in a way that
minimizes the amount of vibration transmitted to the APEX. This structure must be flat
and parallel. This minimizes possible twisting torques to the case of the detector, which
will distort the electromagnetic field and cause false triggering.
Vibration and Mechanical Shocks
Some level of vibration is present in most industrial environments and the APEX is
designed to operate satisfactorily under these conditions. However, false triggering may
be caused by sudden bumps or dumping of heavy loads nearby, particularly when
working at very high detection sensitivities. The APEX should not be fixed directly to a
vibrating packaging or processing machine.
Electrical Loops
Intermittent electrical loops are the largest single cause of faulty metal detector
operation. The search field in the metal detector sets up a high-frequency electrical field
in the aperture. The metal case of the detector head acts as a screen to prevent metal
outside the detector head affecting the search field. Some of the high-frequency
electrical field from the search coils does escape from the aperture through which the
product passes. This field can cause very small electrical currents to flow in nearby
metal structures. This causes no problem if the loops are completely closed, but, if the
electrical path is intermittent, then false triggering of the detector is likely.
Typical causes of intermittent electrical loops include loose bolts on the framework or on
the detector's mounting, corrosion of metal work, broken welds, open hinged doors, and
broken or rubbing contacts.
Page 308 Thermo Scientific APEX User's Guide