Loma IQ2 Service Manual page 67

Figure 6 Shows how the cheese locus is "swung round" and made bigger by the 2mm
If we consider Figure 6, this shows the locus plot for a block of cheese with and
without the 2mm ferrous contamination. Clearly this produces a considerable R
signal, because of its large product effect, so it is no longer sufficient just to look
at the R signal to determine whether there is metal in the product or not - we
can't tell the difference any more between metal and product. It is now
necessary to look at the X signal as well, but again if we look at only the X signal
it will be difficult to see small pieces of metal as the cheese produces small X
signals, the same as a small ferrous contaminant will.
In order to see small pieces of metal it is necessary to combine the R and X
signals to attempt to eliminate the product effect, known as compensating out
the product. Applying the correct product compensation to the locus in figure 6,
the cheese plot, has the effect of "swinging" the locus around to produce Figure
7. The vertical axis is now referred to as the product signal axis (S). Now in
order to detect small pieces of metal the product signal is monitored, and when
it increases above a certain level, known as the threshold, the product is known
to be contaminated.
Module 7026
X
ferrous contamination
Configuration and Set up Information
Cheese + 2mm Fe
R
Cheese
5-45