Sum of Null Discrimination (Long and dull)

[Cody]

I have lost my place in all this so started another post instead of replying to a one in specific. Let me define a couple of statements I made and then explain them a little.

When I talk about capacitor on the input to the receiver I am not talking about blocking DC but a low or high pass filter. Most detectors have filters for this purpose directly at the input which is why we call detector two, three, and four filter machines. The coil and the capacitor is a mechanical filter and now we also see digital filters. An interesting feature of the Explorer is the coil is directly connected to the preamplifiers. Power that would be consumed by the filter is eliminated and the receiver coil is more sensitive to weaker signals. The filters in the Explorer are after the signals have been preamplified and demodulated.

Serial and parallel in reference to targets is defined by how the targets enter the electromagnetic field of the search head. An example of serial could be if we place a dime and quarter in a straight line and sweep the coil over the two coins then they are in series. If we place the dime and quarter side by side and sweep the coil over the two coins they are parallel. Since the detection field is oval we have targets entering the detector

 

[Cody]

n/t

 

[Cody]

With the detector set to discriminate iron.

Give this a try and see what you think. Turn the Explorer on and lay it on a wooden bench with no metal near enough to be detected. Take a piece of iron say half the size of a horseshoe and hold it in your hand and move it towards the coil. The threshold will null. While the threshold is in null take a quarter in the other hand and sweep it past the coil and notice the detector detects the quarter. So, we detect a quarter when the threshold is in null......right?

Now put the quarter and iron in the same hand and sweep it past the coil and the threshold will go into null.

Why? There has to be relative motion between the coil and targets for discrimination to function properly. This is one reason why sweep speed is important. What we see are the basic principles behind rejecting iron minerals and that we can discriminate between metals but need motion.

See what happens if we go to IM-16 and do the same test.