Hi Jerry,
Reverse discrimination is the term used to explain how the discrimination operates on a PI.
Basically, the way to discriminate on most PI's is to increase the delay when the sample pulse is taken. As you increase the delay, objects having low conductivity, such as gold, will be ignored. Objects having a higher conductivity will still provide a strong signal.
Actually VLF discrimination circuits do about the same thing. If you turn the disc control up, gold falls out or is ignored first.
However, the big difference between PI's and VLF's lies in how PI's and VLF's "see" iron. PI's "see" iron as a highly conductive object, while VLF's "see" iron as a very low conductive object. So, when in the disc mode of a VLF, iron is ignored. On a PI, when you turn the delay up, iron still gives a very strong signal.
Why this occurs is more complicated than just conductivity, but the basic concept fits. The average operator doesn't care why, he or she just wants an idea of what the object might be.
So, on a PI, if you increase the delay and the object disappears, there is a good possibility the object is gold. If the object still provides a very strong response, then the object most likely is NOT GOLD.
My interpretation of the term "reverse discrimination" is how it relates to gold objects and the response you get from them. So, if you turn the disc control up (delay control) and the "good" object disappears, then the good obect could very well be gold. Since the desireable object (gold rings, nuggets, etc) is now discriminated out, it can be thought of as reverse discrimination.
Reg
