Thermo Scientific APEX 100 User Manual page 297

Note: A loop effect becomes greater in detectors having an aperture height greater than
five inches (125 mm) and a width greater than 12 inches (300 mm), as shown in the
figure below.
Loops as far as 3 ft (1 m) away may affect the operation of the detector, depending on
roller, bearing, frame materials, and on the quality of the contact. To avoid loop effects
due to these causes, the following steps are recommended.
• All cross members and transfer plates should be welded or securely fastened.
• Rollers cannot be secured, but should be isolated from making electrical contact.
Note: Only one side of each roller assembly needs to be isolated. Do not isolate both
ends.
Roller Isolation Methods
The materials generally used to isolate rollers are plastic and phenolic. Care should be
taken to ensure raw products do not come into direct contact with phenolic materials.
Listed below are several methods for isolating rollers to prevent loop effects.
Stub Shaft Method
With this design, the roller shaft does not continue through the roller. This separation
removes the electrical loop within the roller, as shown below.
Note: The roller must be non-metallic.
Thermo Scientific APEX User's Guide Page 297