A
Anonymous
Guest
Hi everybody,
I've found a document that describes the timings and internal block diagrams of the us army standard landmine detector AKA nato an/pss-12 , actually a schiebel (from austria) model of pulse induction metal detector. The document available from ieee :
http://ieeexplore.ieee.org/iel5/ 36/19440/00898665.pdf?arnumber=898665
Well...if you check the timing diagrams you can see that the pss-12 uses the same reverse pulsing as in the corbyn with actually about 120 us for each pulse, so first a 120 us pulse (positive) then a second (negative) pulse of 120 us, with some little delay between the first and the second (about 20 us). I think that the reason for using this pulsing scheme is to improve the S/N ratio, as in Corbyn's PI article, and to definitely cancel ground and target magnetization.
The receiver uses another coil , as in corbyn's but mono-coil (smaller, concentric, coplanar than the tx coil) and is completely different from any traditional pi, I mean there is not an analog integrator, either single or double (differential), the way I know. What you can see is a 'threshold' detector that inits the receiver front end sampling ,when it detecteds that the received signal reach 1.5 volts starting from 0 volts after the last tx switch-off; then after a delay of 10us a 10us window sample is taken (this is the signal sample) and passed to a sample-hold; then after about 15us of delay another sampling is done till the next tx switch-on and it's used to take an 'average' no-target level...then passed to another sample-hold. The two sample hold drive a difference amplifier that controls the audio generator for output. The rx part is, at the end, a different kind of difference 'integrator' but with sampling capabilities.
I think that pss-12 uses a mosfet h-bridge to switch the tx coil back and forward, but I'm not sure of that.
So I think that it will be interesting to study the document above...also to try to figure out some ne wer schematic or project about PI.
Best regards,
jetstream
I've found a document that describes the timings and internal block diagrams of the us army standard landmine detector AKA nato an/pss-12 , actually a schiebel (from austria) model of pulse induction metal detector. The document available from ieee :
http://ieeexplore.ieee.org/iel5/ 36/19440/00898665.pdf?arnumber=898665
Well...if you check the timing diagrams you can see that the pss-12 uses the same reverse pulsing as in the corbyn with actually about 120 us for each pulse, so first a 120 us pulse (positive) then a second (negative) pulse of 120 us, with some little delay between the first and the second (about 20 us). I think that the reason for using this pulsing scheme is to improve the S/N ratio, as in Corbyn's PI article, and to definitely cancel ground and target magnetization.
The receiver uses another coil , as in corbyn's but mono-coil (smaller, concentric, coplanar than the tx coil) and is completely different from any traditional pi, I mean there is not an analog integrator, either single or double (differential), the way I know. What you can see is a 'threshold' detector that inits the receiver front end sampling ,when it detecteds that the received signal reach 1.5 volts starting from 0 volts after the last tx switch-off; then after a delay of 10us a 10us window sample is taken (this is the signal sample) and passed to a sample-hold; then after about 15us of delay another sampling is done till the next tx switch-on and it's used to take an 'average' no-target level...then passed to another sample-hold. The two sample hold drive a difference amplifier that controls the audio generator for output. The rx part is, at the end, a different kind of difference 'integrator' but with sampling capabilities.
I think that pss-12 uses a mosfet h-bridge to switch the tx coil back and forward, but I'm not sure of that.
So I think that it will be interesting to study the document above...also to try to figure out some ne wer schematic or project about PI.
Best regards,
jetstream