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Offline hod_shaerTopic starter
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« on: May 11, 2009, 02:26:38 am »
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Hello
What is the differences between TR,IB and VLF detectors. At the part "Metal Detecting Resources" on this site, I didn't see any articles about VLF detectors. Is there any difference? or they're all the same as VLF, but in other names...! Huh?
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Offline homefire
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« Reply #1 on: May 11, 2009, 08:12:22 am »
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TR:   Detection is determined by the amount of Transmitted signal induced into the Receive Coil by a Target!


IB:    Detection is determined by the Offset of Inductive Balance of two coils used in a Oscillator.


VLF:   Detection is determined by Phase relationship of Transmit Coil and Receive Coil.  The target will cause the Receive   signal to be advanced or retarded in relationship to the transmit signal depending on target type.  Mineral or Metal.

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Offline moonshadow
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« Reply #2 on: May 15, 2009, 10:59:51 am »
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Yes I agree with Homefire  In addition, all three work on the principle of of achieving a voltage null in the receive coil. This can either be by overlapping the coils or by achieving the voltage null by placing one coil at 90 degrees to the other. TR and IB worked because a coin disturbs this null and can be detected by amplitude changes in the received signal. VLF is very similar except we measure the phase signal at the null between the transmitted signal and the received signal. The idea is that if we can eliminate unwanted changes in the amplitude of received signal, the effect of ground effect can be much less. Many of the earlier designs had the transmit coil as a part of an oscillator circuit and when the coil was lowered to the ground it actually introduced an unwanted change in frequency as well as amplitude and phase. The answer was to make the transmitter side xtal controlled which prevented unwanted oscillator frequency and phase change, allowing greater sensitivity to be used.

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Offline ivan salis
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« Reply #3 on: May 15, 2009, 12:17:50 pm »
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as far as useage goes

-- vlf units can discrimate but does not get as much depth and often have issues in high mineral areas / beaches --- and aredesigned to be used on land

PI type machines are "all metal" only mode type machines without discrimation and are used a lot as ""water machines" --- they tend to be a bit too heavy for most folks to want carry about on dry land *--but do not tend to have issues at the beach and other high mineral areas. ---   

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