Thermo Scientific APEX 100, User Manual

Page: 65 / 442

Thermo Scientific APEX User’s Guide
Page 65
Setting Reject Parameters
This section tells you how to set reject parameters for a typical gravity-feed application.
Reject Totals
Understanding Reject-Delay and Reject-Duration Timing
In a gravity-feed application, the detector’s search head surrounds a duct where product
is falling vertically under the influence of gravity. When the search head detects metallic
contaminants in the product, the product continues down the duct, and is diverted into a
secondary duct by a gate that closes off the main duct. (Looking at the figure on
page 304 will help you understand this explanation for a typical gravity-feed
application.) The gate stays closed for a set period of time (usually about one second) to
divert the contaminated product, then opens again to allow uncontaminated product to
again flow freely. Thus, for the reject process to work properly, two critical time
parameters must be set.
• Reject-Delay Time
In most gravity-feed applications, where the gate is located close to the search
head, the reject-delay time is usually set to 0.00 seconds. Thus, when the search
head detects contaminants, the gate closes immediately.
However, in applications where the gate is located some way from the search
head, a time delay is needed, because the product takes a finite time to move
from the search head to the vicinity of the gate. Clearly, the reject-delay time
should be set to make sure that the gate closes completely before the
contaminated product actually reaches the gate. Reject-delay times, when
needed, are set in seconds and hundredths of a second.
• Reject-Duration Time
This is the time (in seconds and hundredths of a second) that the gate remains
closed to divert contaminated product into the reject bin. A typical time for a
normal gravity-feed application is one second.
Once you have set the reject-delay time and reject-duration time parameters, you must
test the reject process. Then, if needed, you may want to fine-tune the detector’s
response to vibration caused by the gate opening and closing by enabling the reject
suppression feature.