Paul Andrulis
New Member
First, I know that it is next to impossible to provide a solution, without first knowing what is being attempted. Therefore, I will give a heads up of my project.
I do not know how many here are familiar with metal detection circuits, but a common problem with these circuits is discrimination of "trash" signals produced by undesirable objects, such as common iron nails, pop tabs, etc. On many vlf machines, this is easily accomplished. However, I am trying to rig up a unit that can discriminate for a pulsed induction metal detector, not an easy task. A pulsed induction unit sends DC pulses through the coil, waits a period of time for the back emf to decay, and then "listens" for inductive replies from metal buried within the ground. Not much information is sent back by the buried object, and the entire section which distinguishes one metal from another tends to be in the short decay section of the received signal. Some metals have a very short decay time, and others, like iron, have a long decay. However, the decay is an oscillation, and according to what I have tested on my B&K O-scope, it oscillates slightly differently from one metal to the next.
What I need to do is isolate this oscillation from the decay section, spread it out to give a PIC controller time to analyze the signal, and from there it is a matter of programming the PIC.
Could I do this using frequency division, and still save the information from the signal? Would there be a better way? The decay signal is a very short oscillating ramp signal, which has changes in both voltage and frequency as it dies out.
Any ideas, thoughts, or comments on the matter would be welcome.
Paul
I do not know how many here are familiar with metal detection circuits, but a common problem with these circuits is discrimination of "trash" signals produced by undesirable objects, such as common iron nails, pop tabs, etc. On many vlf machines, this is easily accomplished. However, I am trying to rig up a unit that can discriminate for a pulsed induction metal detector, not an easy task. A pulsed induction unit sends DC pulses through the coil, waits a period of time for the back emf to decay, and then "listens" for inductive replies from metal buried within the ground. Not much information is sent back by the buried object, and the entire section which distinguishes one metal from another tends to be in the short decay section of the received signal. Some metals have a very short decay time, and others, like iron, have a long decay. However, the decay is an oscillation, and according to what I have tested on my B&K O-scope, it oscillates slightly differently from one metal to the next.
What I need to do is isolate this oscillation from the decay section, spread it out to give a PIC controller time to analyze the signal, and from there it is a matter of programming the PIC.
Could I do this using frequency division, and still save the information from the signal? Would there be a better way? The decay signal is a very short oscillating ramp signal, which has changes in both voltage and frequency as it dies out.
Any ideas, thoughts, or comments on the matter would be welcome.
Paul