Thermo Scientific APEX 100 User Manual page 306

frequently. As a guide it must be decided how much product would have to be put on
hold for re-inspection, if a detector fails the test. Typically the minimum frequency is
once per shift, while other applications require hourly tests be performed.
Rejected Product Examination
If possible, product, which has been rejected by the detector during production, should
be examined to establish the source and type of contamination. This may lead to an
improvement in the process equipment upstream from the detector. It is also useful to
display these contaminants so that all employees can see the benefit of the metal
detector.
Tube Size
Use the following formula to calculate the approximate duct/chute dimensions for the
system.
2
In = Flow Rate (lbs/hr)
Bulk Density (lbs/ft
Choose the duct/chute size so the product fills no more than 80% of the product tube.
Here is an example. If the product to be inspected has a bulk density of 30 lbs/cubic ft,
and a flow rate of 15,000 lbs/hr, the result would be 12 square inches. With 80% fill, the
chute should be sized to 15 square inches. The dimensions of the metal detector should
be kept to the smallest size possible for the best sensitivity. It is then a matter of
choosing a product tube with the same square inches that is best suited for the
application. In the above example you could use a chute dimension as follows.
•
127 mm (5") x 76 mm (3").
•
203 mm (8") x 51 mm (2"), or 129 mm (4.75") diameter.
By choosing the 203 mm (8") x 51 mm (2") chute there will be a smaller stroke on the
reject valve and a faster reaction time. The metal detector will be approximately 25 mm
(1") larger on both the length and width (rounded up to the next available size), giving
an aperture of 250 mm (9.8") x 75 mm (3"). If the product is prone to bridging, the 127
mm (5") x 76 mm (3") or 120 mm (4.75") diameter units would be preferable. Contact
Thermo Fisher Scientific—as described in the "Contacting Thermo Fisher Scientific"
section at the end of the manual—for further assistance.
The Next Step
Now that you have completed the electrical and mechanical set up for your gravity-feed
application, please go to the "Getting Started" section on page 11 to learn how to
operate your newly installed APEX detector.
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Thermo Scientific APEX User's Guide