The model 402 system is supplied completely assembled and tested from the factory.  Four mounting holes are located at the top of the frame to support this system. The typical mounting method is to suspend the system with threaded rod. The threaded rod should support the complete load of the system. When securing the threaded rod to the 402 frame isolation bushings should be used on all four mounting holes. This will electrically isolate the frame from any support structure. The 402 system is not designed to support piping from any of the ports. Piping connected to any of the ports should be independently supported. Hanging piping from the reject value may distort the valve body and cause unreliable rejection.

When testing a gravity feed system, it is very important that the test sample travels at the same speed as the product.  In order to verify the response time of the reject gate, metal must be introduced at the same point where the product starts it’s vertical fall.

Allowances must be made to retrieve the test sample, even if it fails to be rejected.  Low air pressure or “sticky” solenoids are typical reasons for failing this test.  Short air lines, high speed solenoids with quick exhaust air fittings, or increased distance between the metal detector and the reject gate, will all improve response time.

The metal detectors “fault” system can be extended to monitor the operation of the reject gate. With this option, hall effect sensors mounted on the reject air cylinder, verify the response time for every detection signal.

Rejected product should be periodically examined to verify that metal contaminants are actually leaving the system.  This will build confidence in your metal detector while isolating possible false rejects.
 

Design Considerations

Free fall of product.

Three key factors are used to determine whether a system will react in time to reject the metal contamination.

1 ) Distance between search head and reject valve

Maximizie the distance between the search head and reject system within the overall system height

2 ) Response time of electronics and air operated components

Make sure the metal detector manufacturer is using the fastest acting electronics, relay, and solenoids.

3 ) Free fall of product

Reduce the freefall of the product as it enters the system to reduce its initial velocity. If this is not possible use bafuls to redirect and slow the product down.  Failing that you must increase the distance between the search head and reject device.