Loma IQ2 Service Manual page 59

You should check that the detector will detect the minimum contaminant sizes for your
company QA specification, under all production conditions, when the detector is
working with this threshold value.
Lower thrsh
This menu entry allows the lower threshold limit to be set. This value should be set as
low as possible, so that when product is running with low product signals no false
rejects occur.
NOTES
This menu is only accessible if the tracker facility has been enabled in the User
options menu.
For this facility to be operative, a photo eye (PEC) must be fitted for product
registration purposes.
This menu is product relative, i.e. there are on/off, upper limit and lower limit values
for each of the 100 products.
Tracking is initialised to the upper limit on a product change, a power up, if the reject
is enabled or the tracker limits are changed.
On completion of a calibration the threshold derived by the automatic calibration will
be used until tracking takes place, at which point either the upper or lower limit will
be used.
Product Signal Tracking (V1.5 & above)
When product is hard frozen (-18ºC) the product effect is very small when the product
has just come out of the freezer, allowing a low working threshold level to be used
giving a high sensitivity to metal contaminants. However, if the line stops for any
reason then the product could thaw slightly, or if the product were not fully frozen, a
significant product signal increase would result. In this event the working threshold will
have to be raised to allow the product to be passed, without false rejection. Raising the
working threshold to allow softer product to pass without false rejection will reduce the
sensitivity to metal contamination, i.e. larger pieces of metal will now be detected. If the
product becomes hard frozen whilst the raised working threshold is still set the
sensitivity to metal contamination will remain reduced because the working threshold is
higher than it now needs to be.
Tracking works by recording the product signal for each pack. From the values read
the working threshold continuously trends upward or downward between an upper and
a lower limit. The rate and amount by which the working threshold changes together
with limits between which it operates are controlled by user entered parameters.
It must be understood that this type of system may allow metal contamination that
would otherwise be detected when the product is fully frozen, to be accepted if product
softening has forced the working threshold to rise.
Module 7026
Configuration and Set up Information
5-37