A
Anonymous
Guest
I tested the principle I posted earlier for iron discrimination with a PI. I divided a master oscillator with two different dividers to obtain two frequencies f1 and f2. I used one frequency to generate positive going pulses and the other to generate negative going pulses. The setup was crude. The transmit coil was center tapped with the center tap at ground. I switched the power supply first through one side of coil for f1 and the other for F2. The transmit coil was half of a dual D configuration. the receiver used the other coil. The non linearity of the iron produced a beat note or difference frequency between f1 and f2. this was filtered before being displayed on an oscilloscope. A standard PI sampling method was used for the signal at f1. The above provided a standard PI detector and a seperate beat note detector. As predicted and computer modelled, the beat note was only present for iron targets. The targets ranged from large pieces of iron to small steel nails. ALL made a beat note! The beat note and the PI seemed to be about as sensitive as each other.If anything the beat note had more range. Conductive targets did not give a beat note except for a small signal which was received from a nickel coin. The signal was much smaller than the PI slope output, so my guess is for a ratio measurement to ID such a target. In short, the thing seems to work just fine. There where some interesting correlations between the signals produced Vs the power levels for the positive and negative pulses along with some other things. I need to investigate these more fully. Still, it all looks very hopeful. I will be busy next week but will try to do some more testing. I will post the results for all to see, Dave. * * *