A conventional Pulse Induction metal detector is based on the idea of pulsing the coil with a high voltage, a powerful electromagnetic field is burst into the soil, a target is excited and eddy current flow due to self inductance generate an electromagnetic field. The transmitter is turned off after the pulse so the self induced electromagnetic fled can be detected. We often see these detectors using a single coil in the search head. Since we have pulses the coil can double as the transmitter and receiver coils. There are problem with using a single coil in that we would be better off with a large transmitter coil for depth but a smaller receiver coil for sensitivity to smaller targets. There are other parameters involved but what the Explorer does is use an inductively balance coil to over the limitations of a single coil.
The Explorer is very unique in that the transmitter generates continuous pulses but they are of different durations. A specific series of pulses is a cycle of operation and has at least one long, one short and regular pulses in a continuous pulse train. The explorer uses a sampling technique to gate the receiver demodulators ON or OFF. This alloys the detector to operate as if the transmitter is ON and OFF. The receiver coil is first connected to preamplifiers that operate as a pair with one being an inverting amplifier. These are connected to demodulators that work in pairs to output three signals that are then filtered and averaged to be processed.
By using two coils with inductive balance in free space there is no need for the high voltage pulse to the transmitter coil. The receiver coil senses any conductive metal target in the target volume which consists of the soil and any conductive metal. The gating of the demodulators ON and OFF allows the continuous pulse train to accomplish the same thing as turning the transmitter ON and OFF since the receiver is decoupled from the receiver coil when the demodulators are gated off.
Why am I posting this? It is a good question to my way of thinking for a user to question if the Explorer is a PI detector. We might even conclude from the above that the Explorer is a hybrid between a VLF and PI but is in my opinion a giant step beyond the prior PI art and is patented as such. (There are still good applications of the conventional PI just as we see SF (Single Frequency) in the X-Terra.)
In general if a detector is pulse drive it is some type of a PI detector may be a good general statement. The Explorer is a pulse driven time domain metal detector so we might consider time domain vs. frequency domain.
Time domain is concerned with analyzing the temporal evolution of signals. Frequency domain is primarily concerned with analyzing the signals in terms of phase angles. That is normally based on negative and positive phase angles in that any signals with a plus such as +24 is a good target and one with a negative such as -45 is a trash target. It would be similar to the Iron Mask being the negative signals and the right half of the screen being positive. Negative phase angles are considered to be ferrous and positive signal nonferrous.
VLF is a term used when the first ground balanced detector was invented and operated at a little less than 3khz. This detector required no motion, was single frequency, but did not discriminate between ferrous and nonferrous targets. VLF is very low frequency and not imply multiple frequency. Multiple frequency can be accomplished in several ways. We could use several sine waves for multiple frequency CW type of operation. However, it is better to use a digital signal such as we see with rectangular or square wave driven coils. It is a little hard to see but a square wave or rectangular contains many frequencies depending on the shape of the pulse. Circuits can be designed to process any of the frequencies in contained in the square wave. As an example if we rotate a conductor in a magnetic field we get a sine wave. A square wave has to be generated and can be shows to contain multiple frequencies so engineers use a square wave instead of multiple frequencies sine waves.
The Explorer is very unique in that the transmitter generates continuous pulses but they are of different durations. A specific series of pulses is a cycle of operation and has at least one long, one short and regular pulses in a continuous pulse train. The explorer uses a sampling technique to gate the receiver demodulators ON or OFF. This alloys the detector to operate as if the transmitter is ON and OFF. The receiver coil is first connected to preamplifiers that operate as a pair with one being an inverting amplifier. These are connected to demodulators that work in pairs to output three signals that are then filtered and averaged to be processed.
By using two coils with inductive balance in free space there is no need for the high voltage pulse to the transmitter coil. The receiver coil senses any conductive metal target in the target volume which consists of the soil and any conductive metal. The gating of the demodulators ON and OFF allows the continuous pulse train to accomplish the same thing as turning the transmitter ON and OFF since the receiver is decoupled from the receiver coil when the demodulators are gated off.
Why am I posting this? It is a good question to my way of thinking for a user to question if the Explorer is a PI detector. We might even conclude from the above that the Explorer is a hybrid between a VLF and PI but is in my opinion a giant step beyond the prior PI art and is patented as such. (There are still good applications of the conventional PI just as we see SF (Single Frequency) in the X-Terra.)
In general if a detector is pulse drive it is some type of a PI detector may be a good general statement. The Explorer is a pulse driven time domain metal detector so we might consider time domain vs. frequency domain.
Time domain is concerned with analyzing the temporal evolution of signals. Frequency domain is primarily concerned with analyzing the signals in terms of phase angles. That is normally based on negative and positive phase angles in that any signals with a plus such as +24 is a good target and one with a negative such as -45 is a trash target. It would be similar to the Iron Mask being the negative signals and the right half of the screen being positive. Negative phase angles are considered to be ferrous and positive signal nonferrous.
VLF is a term used when the first ground balanced detector was invented and operated at a little less than 3khz. This detector required no motion, was single frequency, but did not discriminate between ferrous and nonferrous targets. VLF is very low frequency and not imply multiple frequency. Multiple frequency can be accomplished in several ways. We could use several sine waves for multiple frequency CW type of operation. However, it is better to use a digital signal such as we see with rectangular or square wave driven coils. It is a little hard to see but a square wave or rectangular contains many frequencies depending on the shape of the pulse. Circuits can be designed to process any of the frequencies in contained in the square wave. As an example if we rotate a conductor in a magnetic field we get a sine wave. A square wave has to be generated and can be shows to contain multiple frequencies so engineers use a square wave instead of multiple frequencies sine waves.
How have you been ?
Don't you love how I segway from one topic to the other ?