Thermo Scientific DSP2 Installation And Operation Manual page 17

Roller Isolation
Loop effect is most prominent with detectors having an aperture height ( smaller dimension 'B' ) greater than five inches and a
width ( or 'A' dimension ) greater than twelve inches. Loops as far as three feet away may affect the operation of the metal
detector. This depends on roller, bearing and frame materials and on the quality of contact.
It is recommended that all cross members and transfer plates, etc., be welded or securely fastened. Rollers, of course, cannot be
secured and, therefore, should be isolated from making electrical contact. Only one side of each roller assembly needs to be
isolated. DO NOT isolate both ends. The materials generally used are plastic and phenolic.
Option 1) Stub Shaft
With this design the roller shaft does not continue through the roller. This
separation removes the electrical loop within the roller.
Note: The roller must be non-metallic
Option 2) End Cap
Placing a closed ended plastic cap on one end of the roller shaft will break
the electrical connection between the shaft and bearing assembly.
Option 3) Bearing Isolation
Isolating the bearing assembly requires both isolation of the housing, and the
mounting bolts. An insulating sleeve is used to electrically isolate the bearing
housing from the conveyor frame. Plastic inserts are used to isolate the
mounting bolts from the bearing assembly.
Option 4) Plastic Bearing
The plastic bearing assembly is one of the easiest designs to implement.
Most plastic bearings are available in standard mount designs. However,
some plastic bearings contain a metal sleeve in the mounting holes which is
internally connected to the bearing raceway. With this bearing plastic
inserts would have to be used to create the electrical isolation.
Standard Roller
Design
Figure 11
11
Stub Shaft
Design
Non-metalic roller
Shaft does not continue
through roller
End Cap
Design
Plastic Cap
Isolated Bearing
Design
Conveyor Frame
Bearing Assembly
Roller
Plastic Inserts
Insulating Sleeve
Plastic Bearing
Design
Plastic Bearing Housing
Roller