Earth to Dave Emery...you still with us? Pulse Devil updates...PLEASE!!!! n/t

[plumabob]

n/t

[NC-Dave]

Pulse Devil

Hi there, Sorry if I have not replied to anyones emails but I had a problem and I have just found out that many messages to me were lost.

I am currently getting the production version of the Pulse Devil ready. Some refinements I made to the design have increased the depth capability while making the detector lighter in weight. The downside to this is that you will need to carry a large shovel to dig the deep targets so there goes the weight advantage!

Today I have been making extra search coils for both the land and the water versions which will be tested around the world in the next few months.

The Pulse Devil will be suitable for coin hunting etc while the Surf Devil will be used as a fresh or salt water detector which can be submerged to about fifteen feet.

The main hold up has been on the mechanical end. Stupid little things like a vinyl grip I use on the handle suddenly became unavailable. There were no direct substitutions. This caused a major mechanical design change as there is a control mounted in the handle and everything was designed for the one type of grip.

This is but one of many of dozens of unexpected problems which I have encountered. It is one thing to make a detector and another thing altogether to make one ready for production. The good news is that everything is now falling into place. I will soon have the first production cases ready. As soon as they are ready I will post a picture or two of the detectors for you all to see. This will be followed by my website coming on line at www.hellfiredetectors.com My detector company, Hellfire Detectors will manufacture both the Pulse Devil, the Surf Devil as well as a prospecting version of the Pulse Devil.

I don't want to publish a full description of the detectors just yet as there will most likely be a few last minute changes made as final testing is being done. The test machines have extra controls on them just for this reason. I will however answer a few questions before anyone asks them. Here goes . . .

Question: Will the Pulse Devil work in bad ground? Answer: Yes. The Pulse Devil's have a ground control to help eliminate the most sever ground minerals. This includes the Australian gold fields. The prospecting version has a thumb operated ground fine tuning wheel built into the top of the handle.

Question: Does the Pulse Devil discriminate? The Pulse Devil sports a VLF type of discrimination control. You can adjust it from iron and nails through foil and pull tabs all the way to bottle cap reject if you wish. The audio tone varies for accept and reject targets. All non ferrous targets indicate as non ferrous and all ferrous targets indicate as ferrous.

Question: Can you change the coils? There will be a good choice of coils available. The coils are changeable on both the Pulse Devil and the Surf Devil as the connectors are waterproof to IP68 specifications.

Question: Can Minelab coils be used on the Pulse Devil's? No. The coils are of a special design. No other coils can be used.

Question: What type of battery does the Pulse Devil use. The Pulse Devil's use Lithium Ion or Li-Ion 14.8V battery packs. The packs are easily replaced or charged in situ. Charging takes about two hours. The charger works anywhere in the world accepting 100V to 240VAC. A 12 Volt car booster type charger will also be available. A freshly charged pack will provide about ten hours of continuous use.

Question: Does the Pulse Devil go deep on coins. Yes. The depth capability on coins is excellent. For those of you living in Europe the Pulse Devil loves medieval hammered silver and will detect it at great depths. It also ignores the mineralized pottery shards which are so common in England and France.

The Pulse Devil also does very well on small gold nuggets as well as the larger deeper nuggets. I will be at Ganes Creek in June looking for some!!! Last year I found my first detector found nugget at Ganes Creek with the Pulse Devil. The nugget weighed just under a half Troy ounce and was buried right below the middle of someones boot print next to an iron bolt!!!

Question: Does the Pulse Devil work the same way as Eric Foster's GS5? The ground balancing method as well as the discrimination method used by Pulse Devil is entirely different from the GS5. The number of pulses per second and their width are also quite different. Note that the GS5 is making a name for itself in Australia where it has been described as being able to go where no Minelab's will go. Congratulations to Eric on a fine job.

Question: Does the Pulse Devil have an ID meter - depth meter etc. This answer will ruffle some feathers but here goes. . . NO. I could add these features but to me they are mostly just marketing gimmicks. OK, some of you will tell me that they just have to have a TID meter. Believe me when I tell you that you will soon know what to dig and what to leave behind. The Pulse Devil is designed for thrills not frills.

OK, I will update you as soon as I get a better idea as to when the first Pulse Devil's and Surf Devil's are going to ship. They will be sold through mom and pop stores ONLY. You will never, ever find them being sold through Kellyco or any other warehouse operations. The mom and pop stores are vital to the industry. These people take the time to work with their customers and show them how to use their new detectors.

As to the cost. I honestly cannot answer this just yet as I don't know how much they will cost to build. This will change in the next month as the pricing comes in.

OK, if Carl agrees to it you can ask your questions right here. All the very best, Dave. * * *

[plumabob]

Thank you Dave for that update! I along with everyone else who are interested in you PD sure appreciate it!

[Unregistered]

Pulse Devil

Hi Dave,
I,m from Hastings,UK.
I corresponded with you via e-mail several years ago about the Pulse Devil you were then developing.
I hope you can answer some questions.
In the UK as you are aware there is so much iron that finding a small hammered coin amongst iron is very diificult,will the Pulse Devil be better at this than any VLF detector?
Is the iron discrimination tone only & is it a low tone for iron & a higher tone for non-ferrous?Can you also just set the disc to ignore iron only, as listening to every signal can be very tiring after a while.
Will it be sensitive enough to find the tiniest gold,silver hammered coins some only 4 or 5mm in diameter & will it find these deeper & easier than the best VLF's in iron?
Can you use it on wet sand like other PI's & is it as deep and sensitive as the best PI's on fine gold chains,rings etc?
Can it be swung fairly quickly with out losing sensitivity to small items.
Does it have a very fast recovery speed for finding coins close to discriminated iron?
Thanks,
Mark.

[NC-Dave]

Mark,

I know Hastings very well. My parents used to take my sister and myself there for a holiday when we were little kids. I remember that the top of the beach was covered with rocks. We used to watch the fishing boats being dragged out of the water. Back then they used to catch a lot of fish.

OK, The Pulse Devil can be set to null out a lot of iron in a similar way that the ground balance control nulls out the ground mineral signal. This allows for working in England's iron infested fields.The Pulse Devil loves hammered silver. I am not going to claim depths here but one could dig a deep hole for a hammered penny.

I can't go into the tone method just yet. More on that subject later. As to small hammered, I use a tiny quarter of a cut penny for testing and I can pick it up at a fair distance. My guess is that it will beat most detectors on such a target depth wise. For anything smaller I would suggest using something like a Fisher Gold Bug. High frequency VLF's such as the Gold Bug don't have a lot of depth but they can pick up tiny targets.

As to beach work, I would say that the Pulse Devil will stand it's own with any PI on the market. The swing speed can be pretty fast but I do not advise going too fast. The Pulse Devil has a fast response as it does not rely on integrator circuits as other PI's do. The fact is though that if you swing too fast you WILL miss deep targets.

OK, Hope this helps, Dave. * * *

[Unregistered]

Pulse Devil

Dave,
Can you please tell me can if the Pulse Devil will find small hammered coins etc very close to lots of various shape & sized iron whilst discriminating the iron?
Is it as good as the best VLF's at doing this?
Would a small coil be best at this & if yes which size & type of coil would you say is the best?How much depth loss is there using a smaller coil than a standard one?
Would a large coil still find small hammereds well in iron?
Which would be best for this DD or concentric?
Thanks,Mark.

[Sean Goddard]

Dave, PLEAse email me I need to talk to you URGENTLY please. Alternatively you have my phone number, PLEASE, PLEASE call me Weekends only ASAP. Thanks M8!!

[Unregistered]

Goldringer

Hi Dave,

If you need a Hawaii contact to test a Pulse Devil water machine over highly mineralized bottom let me know.

I have years of experience with water machines, (using, not building) I have had experience with Whites, Fisher, Garrett, Minelabs and others. dug thousands of rings.

Ken

[Unregistered]

Hi Dave, i live in the Uk on the south coast can you give me any ideas as to when this Pulse devil will be available to buy overhere?
Ive heard alot of good comments about this machine and would love to try one out.
Look forweard to your reply.
Andy...

[Unregistered]

Trip to England

Andy,

Send me your email address to [email protected] I will provide you with some info regarding your being able to see a Nemesis being tested on the south coast of England in early August. All the very best, Dave. * * *

[Unregistered]

PULSE DEVIL PATENT APP

Here is the patent app# with details on the pulse devil, interesting approach

http:\uspto.gov/patft/index.html

20090045813A1

[Unregistered]

United States Patent Application 20090045813
Kind Code A1
Emery; David February 19, 2009
Resonant pulse induction metal detector

Abstract

A metal detector transmitting high current pulses and employing the high voltage back EMF signals which occur at their termination. The method employed uses a resonant tuned receive coil which provides a major improvement in the depth of detection of metallic objects and interference rejection over current time and frequency domain metal detectors.
Inventors: Emery; David; (Charlotte, NC)
Correspondence Name and Address:

Serial No.: 891718
Series Code: 11
Filed: August 13, 2007

U.S. Current Class: 324/329
U.S. Class at Publication: 324/329
Intern'l Class: G01V 3/11 20060101 G01V003/11
Claims


1. A detector comprising:a metal detector which transmits energy from high voltage flyback pulses which occur at the termination of each of a continuous train of high current pulses;a transmit coil energized by the continuous train of high current pulses;a receive coil connected to a parallel capacitor forming a parallel tuned circuit;signal samplers and processor for sampling and processing signals intercepted by the receive coil; andindicators to alert the operator of the equipment when the signal processing yields results that meet predetermined criteria.

2. The detector of claim 1, wherein the transmit and receive coils are balanced for a minimum output from the receive coil when no metallic objects are in the transmitted magnetic field.

3. The detector of claim 1, wherein a reference burst or decaying sinusoidal oscillation is generated by a voltage pulsed directly into the receive coil at a time when signals from metallic objects are substantially zero.

4. The detector of claim 3, further comprising accurately measuring a cycle of the reference burst to produce accurate timing and sample demodulator clock pulse generation.

5. The detector of claim 3, further comprising deriving sampling pulses for the processing so that the signals intercepted by the receive coil are separated into resistive and reactive signal components.

6. The detector of claim 1, further comprising high pass filtering resistive and reactive signal components by using two differentiator circuits in each signal channel and causing an output indication only when both signals are of the same polarity thus indicating the presence of a non ferrous metallic object in the field produced by the transmit coil.

7. The detector of claim 7, further comprising tuning the differentiator circuits by a ganged potentiometers or electronic chip resistors.

8. The detector of claim 6, further comprising a display to display said ratio of the resistive and the reactive components of the metallic object as an indication as to the nature of the metallic object in the field of the searchcoil.

9. The method of metal detecting comprising:exciting a transmit coil of a metal detector with high current pulses;producing high voltage flyback pulses;using the high voltage flyback pulses as a primary source of transmit energy;intercepting signals from metallic objects in the transmitted magnetic field using a receive coil; andtuning the receive coil to a resonant frequency with a parallel capacitor.
Description


FIELD OF THE INVENTION

[0001]The invention relates generally to a metal detector.

BACKGROUND OF THE INVENTION

[0002]There are two main types of hand held metal detectors in common use. A first type of metal detector is referred to as an Induction Balance detector or more commonly a very low frequency "VLF" metal detector, as they operate using very low frequencies. That type of metal detector operates in the frequency domain and uses a sinusoidal transmit signal to transmit a varying magnetic field.

[0003]A second type of metal detector called a Pulse Induction or "PI" detector operates in the time domain. The PI metal detector transmits a magnetic field due to a transmit coil being energized by high current pulses.

[0004]Most VLF metal detectors use a searchcoil assembly which contains a transmit and a receive coil and a feedback or bucking coil. The coils are physically arranged in such a way as to cause a null in the receive coil to the signal from the transmit coil. Metallic objects entering the searchcoil's field upset the balance, causing a signal in the receive coil. The received signal has a phase and amplitude which is dependent on the type of metal as well as the size and shape of the metallic object.

[0005]As the transmit signal is sinusoidal, many metal detectors incorporate the transmit coil into an oscillator circuit, with the transmit coil becoming the oscillator's tank circuit. The continuous sinusoidal signal provides a phase reference for one or more synchronous demodulators or synchronous sampling circuits which output a DC signal containing information regarding the phase and amplitude of the receive signal.

[0006]By adjusting the clock phase of the synchronous demodulators or sampling circuits relative to the sinusoidal transmit reference, it is possible to obtain a DC signal which has essentially no component due to mineral ground. The synchronous demodulators or synchronous sampling circuits output a DC signal which is, for example, positive for non ferrous targets and negative for ferrous targets.

[0007]Only positive signals are chopped at an audio frequency and amplified to a speaker or headphones to indicate the presence of a metallic object which falls within a predetermined range.

[0008]The positive or negative DC signal may also be applied to a meter.

[0009]Pulse Induction metal detectors operate by switching high current pulses through a transmit coil. The current causes a magnetic field to surround the transmit coil. The field causes eddy currents to flow on the surface of metallic objects. Either the same coil used for transmit or a separate receive coil picks up signals from the metallic targets after the transmit pulses terminate. The received signal is sampled one or more times and processed so as to provide a DC signal to cause a voltage controlled oscillator to output an audio amplitude and/or a frequency change of the audio output stage to indicate the presence of a metallic object.

[0010]A further detailed description of the above metal detector technologies is not provided, as both methods are well known in the art.

[0011]Both Induction balance--VLF and Pulse Induction "PI" metal detectors have a number of drawbacks.

[0012]One drawback with VLF metal detectors is that they are very difficult to build using a resonant tuned receive coil. Small temperature changes in the searchcoil can translate into a phase shift of the receive signal, which in turn causes errors in the ability of the metal detector to cancel signals due to mineral ground and to discriminate against unwanted metallic objects. The effect however of using a non-resonant tuned coil is a major reduction in the metal detector's sensitivity and poor interference rejection capabilities.

[0013]Another drawback of most VLF metal detectors is that their detection depth is limited due to the low power of the transmitted signal.

[0014]Pulse Induction or PI metal detectors generally have greater depth capabilities than VLF metal detectors. PI metal detectors, however, have, at best, only a very limited discrimination ability.

[0015]Minerals such as iron oxides in the ground also adversely effect a metal detector's discrimination ability often to the point where discrimination between different metallic objects is not possible.

[0016]Accordingly, there is a need for a metal detector which has the ability to work with a tuned searchcoil, has a major depth capability, superior noise rejection and the ability to discriminate against a range of unwanted metallic objects which are buried in highly mineralized soil.

SUMMARY OF THE INVENTION

[0017]In a PI detector, high voltage back electromotive force, back EMF, commonly referred to as a flyback pulse, follows the termination of each transmit pulse. The energy in this pulse is not used by pulse induction metal detectors and is thus wasted.

[0018]The present invention employs the use of high voltage back EMF signals caused by pulsing high currents through a transmit coil and providing discrimination of ferrous and non ferrous objects which are buried in mineralized ground.

[0019]Unlike a Pulse Induction or PI metal detector which wastes the flyback pulse energy in the transmit coil, it is this energy which is used by the Resonant Pulse Induction or RPI metal detector of the present invention to interrogate metallic objects in the field of the searchcoil.

[0020]The invention described and claimed herein is closely related to both PI and VLF type metal detectors. It is an easy matter to convert the RPI detector to a conventional PI detector. Indeed, a hybrid of the two types of metal detector can be made by making only minor modifications to the invention being claimed.

[0021]The RPI detector uses a tuned receive coil. The transmit and receive coil form a balanced searchcoil arrangement.

[0022]A decaying sinusoidal oscillation occurs in the tuned receive coil after the termination of each high voltage flyback pulse in the transmit coil if the balance of the searchcoil is disturbed by the presence of a metallic object.

[0023]The high voltage back EMF or flyback pulse in the transmit coil can be measured in hundreds or even thousands of volts. The RPI method provides a metal detector with extreme depth capabilities.

[0024]As the receive coil is part of a parallel tuned circuit, the resonant frequency of the decaying oscillation is due solely to its inductance and the value of the resonating capacitor.

[0025]Circuitry provides accurate timing for two or more sampling circuits regardless of changes in the tuned receive coil's resonant frequency which are either intentional or due to temperature drift.

[0026]One object of the present invention is to provide new and useful metal detector apparatus which has greater sensitivity and vastly improved depth capabilities.

[0027]Another object of the present invention is to provide a means which may substantially eliminate interference such as radio transmissions and electrical noise by using a tuned receive coil.

[0028]Still another object of the invention is to provide a new and useful metal detector apparatus which discriminates between different kinds of metals while not being affected by ground mineralization.

[0029]Still another object of the invention is to provide new and useful metal detector apparatus which has the capability of controlling the timing of a number of synchronous sampling circuits even when the resonant frequency of the receive coil is changed or changes due to temperature variations.

[0030]These and further and other objects and features of the invention are apparent in the disclosure, which includes the above and ongoing written specification, with the claims and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031]FIG. 1 is an overall block diagram of the invention

[0032]FIG. 2 is an overall block diagram of the timing circuit of the invention.

[0033]FIG. 3 is a drawing of the waveforms associated with the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034]Referring to FIG. 1, a timing generator 1 provides pulses with a typical duration of 50 .mu.s as shown in FIG. 3a at a frequency of between approximately 200 Hz to 1 KHz. The pulses drive a high power field effect transistor or FET 2, which switches transmit coil 3 and bucking coil 4 to the negative power supply, thus energizing them.

[0035]Resistor 6 provides a degree of damping to transmit coil 3 and bucking coil 4.

[0036]Capacitor 7 resonates the receive coil 5 to form a parallel tuned circuit.

[0037]The coil assembly A includes transmit coil 3, bucking coil 4 and receive coil 5. The coil assembly is configured as a balanced coaxial coplanar searchcoil which is well known in the art.

[0038]The coil assembly is balanced to provide little or no signal output from the receive coil during the transmit periods in the absence of a metallic target. Other types of balanced coil assemblies can be used, but a balanced coaxial coplanar assembly is preferred.

[0039]The termination of each transmit pulse shown in FIG. 3a causes a high voltage flyback voltage to be generated. The flyback pulse is used in the invention to provide the useful energy transmitted from the searchcoil.

[0040]A metallic target in proximity to the searchcoil will unbalance it and cause a decaying sinusoidal signal in receive coil 5 after the termination of the flyback pulse which occurs after each transmit pulse as shown in FIGS. 3c and 3d.

[0041]The phase and amplitude of this decaying sinusoidal signal as measured to the end of the flyback pulse is dependent on the type of metal and its size and shape.

[0042]FIG. 3b shows the receive signal when no metallic objects are present in the field of the searchcoil.

[0043]FIG. 3c shows a typical receive waveform when a ferrous metallic object is in the field of the searchcoil.

[0044]FIG. 3d shows a typical receive waveform when a non-ferrous metallic object is in the field of the searchcoil. Note the phase difference of the decaying sinusoidal signal compared to FIG. 3c.

[0045]Referring to FIG. 1, the decaying sinusoidal signal in receive coil 5 is amplified by a low noise amplifier 8 and is provided to sampling circuits 9 and 10. The outputs of the sampling circuits are low pass filtered by filters 11 and 13 and are buffered by buffer amplifiers 12 and 14.

[0046]Sampling demodulator circuits 9 and 10 are clocked by a fast sample clock of approximately 1-5 .mu.s duration once during each receive period to interrogate the decaying sinusoidal oscillation due to the searchcoil being unbalanced by a metallic object in its proximity. Sample circuit 10 is clocked at a time when the reactive signal component of the mineralized ground is at its zero crossing point.

[0047]The output of sampling demodulator 10 is primarily caused by the resistive component of a metallic target. This signal is the same polarity for both ferrous and non-ferrous metallic targets. It is used in the invention as an all metal type of indication or "all metal signal".

[0048]The output of sampling demodulator 9 is primarily caused by the reactive component of a metallic target. This signal has a 180 degree phase difference between ferrous and a non-ferrous metallic targets which causes either a positive or negative polarity output.

[0049]The ratio of the amplitude of the resistive to the reactive components and the exact phase of the receive signal is dependent on the type of metal as well as the size and shape of the metallic object and the frequency of the sinusoidal signal.

[0050]By adjusting the timing of the clock pulse to demodulator 10, it is possible to obtain a signal which is free of the mostly reactive signal caused by ground minerals. The sample clock is adjusted to occur at the zero crossing point of the signal caused by the ground mineralization at the location the metal detector is being used.

[0051]The resulting all metal signal is now free of the effects of the ground minerals and has the same polarity for ferrous and non-ferrous metallic targets.

[0052]By adjusting the timing of the clock pulse to demodulator 9, it is possible to obtain a positive going signal for non ferrous and a negative going signal for ferrous metallic objects.

[0053]This range can be expanded to provide a range of unwanted ferrous and non-ferrous metallic objects to cause a negative going signal while wanted non ferrous signals cause a positive going signal. Negative going signals cut off the audio output of the metal detector, thus providing a rejection of unwanted metallic objects such as iron, nails and thin aluminum foil.

[0054]The discrimination signal as provided becomes totally unreliable in the presence of mineralized ground. This problem can generally be overcome by taking advantage of the fact that the signal from mineralized ground is generally slowly changing and can be removed by high pass filtering both the all metal and the discrimination channels. This method is commonly used in VLF metal detectors.

[0055]The discrimination signal from sampling demodulator 9 is low pass filtered by low pass filter 11 and buffered by amplifier 12 before being applied to a first differentiator circuit comprising capacitor 15 and resistor 16. The signal is buffered and amplified by amplifier 20. The output of amplifier 20 is applied to a second differentiator comprised of capacitor 21 and resistor 22. The resulting signal is applied to the inverting input of voltage comparator 25.

[0056]The ground balanced, all metal signal from sampling demodulator 10 is low pass filtered by filter 13 and buffered by amplifier 14 before being applied to a first differentiator circuit comprising capacitor 17 and resistor 18. The signal is buffered and amplified by amplifier 19. The output of amplifier 19 is applied to a second differentiator comprised of capacitor 23 and resistor 24. The signal is applied to the inverting input of voltage comparator 26 and buffer amplifier 34.

[0057]Note that resistors 16, 18, 22 and 24 are variable and are ganged together. The four variable resistors can be either a ganged potentiometer or four integrated circuit, electronic potentiometers.

[0058]The variable resistors can be adjusted by the operator to allow a faster or slower movement of the searchcoil to be chosen to suit the prevailing ground mineral conditions.

[0059]The outputs of comparators 25 and 26 are normally low due to a negative reference voltage being applied to the non-inverting inputs of both comparators. The junctions of diodes 27 and 28 as well as 29 and 30 are held low if either or both comparators 25 or 26 have a low output.

[0060]The low comparator output/s remove the base bias voltage from NPN transistor 31 which is provided by resistor 32, thus turning the transistor and LED indicator lamp 33 off. The audio input to amplifier 38 is also reduced below a level to where amplifier 38 can output an audio indication signal.

[0061]Metallic objects which cause a negative output from demodulator 9 will cause comparator 25 to have a low output. The output from demodulator 10 will be positive during this time. The effect is to keep transistor 36 off and inhibit the audio indication signal from amplifier 34. The low output from comparator 25 also removes the base voltage from transistor 31 keeping it, and the LED indicator lamp 33 switched off.

[0062]Metallic objects which cause a positive output from both sampling demodulators 9 and 10 cause the junctions of diodes 27 and 28 as well as diodes 29 and 30 to be open circuits. Base current now flows into transistor 31 through resistor 32 turning it on and causing LED indicator lamp to turn on. The positive going all metal signal from buffer amplifier 34 is now chopped by transistor 36 into audio pulses.

[0063]Transistor 36 chops the positive voltage from buffer amp 34. Transistor 36 is driven by audio oscillator 37. The chopped audio signal is amplified by amplifier 38 which drives loudspeaker 39 to provide an audio indicator signal.

Ratiometric Signal Indicator

[0064]The ratio of the resistive and the reactive signal components are measured and displayed to the operator as a reading on meter 44. To use this feature, the discrimination potentiometer 76 of FIG. 2 is set to where ferrous metallic objects cause a negative output signal and non-ferrous metallic targets cause a positive output from demodulator 9.

[0065]Analog divider 42 outputs a voltage related to the ratio of the signals from both demodulators 9 and 10. Comparator 40 squares the signal from demodulator 10 after the first differentiator comprising capacitor 17 and resistor 18. This signal is primarily resistive and is in quadrature to the signal at the output of the second differentiators comprised of capacitor 23 and resistor 24 and capacitor 21 and resistor 22.

[0066]The squared output of comparator 40 fires a monostable which provides a gating clock to sample and hold 43 at a time when the signals at the outputs of the second differentiators are at a peak value. The output of the sample and hold is output to meter 44.

[0067]The ratios of the voltage peaks and the polarity of the signal from demodulator 9 is an indication of the type of metal and the possible identity of the metallic object which the searchcoil is passing over.

Precision Sample Reference

[0068]As the resonant frequency of the tuned receive coil is completely independent of any timing signals, the problem remains as to how to provide a precision reference to clock the sampling circuits. The problem is solved by part of the timing circuit 1. Refer to FIG. 2.

[0069]Astable 57 clocks monostable 55 to provide a continuous source of transmit pulses. Potentiometer 58 sets the transmit pulse repetition frequency. Monostable 55 sets the transmit pulse width which is set by potentiometer 56.

[0070]At a time after the termination of the transmit pulse and after the decaying sinusoidal signal from metallic objects (when present) has substantially decayed, the timing circuit injects a short pulse of about 2 .mu.s duration through capacitor 89 and resistor 90 in FIG. 1 directly into receive coil 5. The pulse shocks the receive coil into a burst of damped oscillation as shown in FIG. 3b, FIG. 3c and FIG. 3d.

[0071]The damped oscillation or "reference burst" is not effected by metallic objects being present in the searchcoil's field, as it is applied directly to the receive coil at a time when the current through the transmit coil is zero.

[0072]The damped oscillation or reference burst is measured to provide a reference for the sampling circuits.

[0073]Flip flop 46 is clocked by the leading edge of a reference pulse from the burst pulse timing monostable 52. This sets the Q output of flip flop 46 high and its /Q low. The transition of /Q to low is coupled to the reset of flip flop 47 via a differentiator made from capacitor 48 and resistor 49. This rapidly resets flip flop 47.

[0074]s previously stated in reference to FIG. 1, the same reference pulse is injected into the receive coil via capacitor 89 and resistor 90. This shock excites receive coil 5 and causes a damped sinusoidal oscillation. The oscillation starts with a sinusoidal signal starting at zero degrees and going positive.

[0075]Comparator 45 squares the sinusoidal oscillations from the receive coil into a series of pulses. Each time the sinusoidal burst signal goes through its negative zero crossing, a positive going pulse is output from the comparator.

[0076]The first pulse from comparator 45 clocks Q of flip flop 47 high. The second pulse clocks flip flop 47 low, as its /Q output is connected to the D input. The transition of Q to low is coupled to the reset of flip flop 46 by capacitor 50 and resistor 51, which resets flip flop 46 to Q=low.

[0077]The result of this is to provide a single pulse of a width equal to 360 degrees or one cycle of the reference burst from the Q output of flip flop 46.

[0078]The pulse from flip flop 46 is passed to OR gate 59. The positive edge of the pulse from the OR gate triggers monostable 60 setting its Q output to a logic high. The logic high enables constant current source 61, which linearly charges capacitor 62.

[0079]Constant current source 61 and capacitor 62 form the charging part of a linear ramp circuit. Capacitor 62 is discharged by FET 63 when monostable 60 times out. Buffer amplifier 64 buffers the ramp.

[0080]Monostable 53 has its timing adjusted by voltage controlled resistor 54.

[0081]The output of monostable 53 is connected to a differentiator circuit consisting of capacitor 65 and resistor 66. The differentiator provides a sample clock pulse with a duration in the range of 2 .mu.s-5 .mu.s to analog switch 70.

[0082]The Q output of flip flop 47 is connected to a differentiator circuit consisting of capacitor 67 and resistor 68. The differentiator provides a sample clock in the range of 2-5 .mu.s to analog switch 69.

[0083]Both analog switches sample and hold a voltage from the linear ramp and apply their sampled voltages to difference amplifier 75 via buffer amplifiers 73 and 74. The output of difference amplifier 75 is now either positive, negative or at zero volts depending on the voltage being higher or lower on capacitor 71 than the voltage on capacitor 72 or if the two voltages are equal.

[0084]The output of difference amplifier 75 is thus an error voltage which adjusts voltage controlled resistor 54 until the pulse width outputs of flip flop 46 and monostable 53 are equal. The above method automatically adjusts the pulse width of monostable 53 to that of a pulse from flip flop 46 even though these two pulses occur during completely different time intervals. The ramp period equals 360 degrees of one sinusoid from the reference burst.

[0085]Buffer amplifier 74 outputs the buffered voltage from capacitor 72. When both monostables have the same pulse width then the voltage on either capacitor 71 or 72 represents a ramp voltage time equal to 360 degrees of one sinewave of the sinusoidal reference burst.

[0086]The linear ramp is applied to the inverting inputs of voltage comparators 78 and 79. The voltage from buffer amplifier 74 is divided by potentiometers 76 and 77. The wipers of the potentiometers are applied to the non-inverting inputs of comparators 78 and 79.

[0087]The comparators now switch states from high to low according to the ratio of the peak ramp voltage to the divided voltage on the comparators inverting inputs.

[0088]Two half monostables formed by capacitors 80 and 82, resistors 81 and 83 and Schmitt triggers 84 and 85 both output a short sample clock pulse at the times set by potentiometers 76 and 77. This method provides sampling pulses which can be set over a wide range.

[0089]The accuracy of the sampling pulse timing is not effected by the resonant frequency of the receive coil.

[0090]A microcomputer with an internal counter/timer can be used to measure the time from the burst pulse which is used to shock excite the receive coil and a second zero crossing of the squared damped oscillation of the burst signal. The same microcomputer can also provide the sample clock signals to the demodulators.

[0091]The invention provides a metal detector which transmits energy from high voltage flyback pulses which occur at the termination of each of a continuous train of high current pulses. A transmit coil is energized by a continuous train of high current pulses. A receive coil is connected to a parallel capacitor forming a parallel tuned circuit. Signals intercepted by the receive coil are sampled and processed. Indicators alert the operator of the equipment when the signal processing yields results that meet predetermined criteria.

[0092]The transmit and receive coils are balanced for a minimum output from the receive coil when no metallic objects are in the transmitted magnetic field.

[0093]A reference burst or decaying sinusoidal oscillation is generated by a voltage pulsed directly into the receive coil at a time when signals from metallic objects are substantially zero.

[0094]Accurate measurement of a cycle of the reference burst produces accurate timing and sample demodulator clock pulse generation.

[0095]Sampling pulses are derived for the processing so that the signals intercepted by the said receive coil can be separated into resistive and reactive signal components.

[0096]High pass filtering of the resistive and reactive signal components uses two differentiator circuits in each signal channel and causes an output indication only when both signals are of the same polarity, thus indicating the presence of a non ferrous metallic object in the field produced by the transmit coil.

[0097]The differentiator circuits are tunes by ganged potentiometers or electronic chip resistors.

[0098]The ratio of the resistive and the reactive components of the metallic object are displayed as an indication as to the nature of the metallic object in the field of the searchcoil.

[0099]The invention provides exciting the transmitter coil of a metal detector with high current pulses, employing resulting high voltage flyback pulses as the primary source of transmit energy and intercepting signals from metallic objects in the transmitted magnetic field using a receive coil tuned to a resonant frequency with a parallel capacitor.

[0100]It is apparent from the foregoing that a new and improved metal detector has been provided. While only certain preferred embodiments have been described in detail as will be apparent to those familiar with the art, certain modifications and changes can be made without departing from the scope of the invention as defined by the following claims.

[0101]While the invention has been described with reference to specific embodiments, modifications and variations of the invention may be constructed without departing from the scope of the invention, which is defined in the following claims.

[Nc-Dirty-digger]

are there any updates yet? website?

[plumabob]

Dave has posted on another website that the PD is alive and well. He is in Europe about now and stated that there may be a release before Christmas. He has had some health issues and is finally feeling better.

[Boldgold]

The latest scoop on this unit:

PI Technology Forum
What ever happened to the "Pulse Devil"?Is it finished yet?
http://www.findmall.com/read.php?34,1049922,page=1

http://www.findmall.com/read.php?34,1049922,page=2
Posted by: NC-Dave [ Send a Message ]
Date: January 10, 2010 04:19PM
I am looking into the compatibility issue for other companies coils. As to the discrimination, the Nemesis will easily find the silver even if it is surrounded by iron trash. Now it won't find a one gram nugget under a trash can lid but it will find it under a half dozen large nails. As to aluminum and lead trash there is no way as yet to separate it from gold nuggets. Luckily there is far more iron trash than non ferrous trash in most places. We have all dug our share of spent bullets and cartridge cases. I have also dug up a fair amount of live ammo as well!!!

As of now the Nemesis is being tested in a test lab for conformity to European CE regulations. The regulations concern issues from radiation of undesired signals, the ability of the equipment to remain operational while subjected to strong interference and the need to prove that the electronic parts as well as the body and coil of the detector contain no lead or or other hazardous materials under something called RoHS (Removal of Hazardous Substances). All electronic equipment sold in Europe must meet the specifications. The testing also insures compliance with the regulations in place in the USA and other countries. and should be the last hurdle before I am allowed to sell the detectors world wide. It is costing me an arm and a leg but I believe that it will all be worth it in the end. Dave. * * *


Posted by: NC-Dave [ Send a Message ]
Date: January 11, 2010 07:37PM
The Reason that the Pulse Devil "Nemesis" is headed for Europe is because it was designed expressly for European conditions. Let me explain this to those here in the USA who might have been wondering "Why Europe first"?

Most detecting in Europe is done in ploughed fields and on pasture land. Almost every field has been in use in one way or another for thousands of years. Man has therefore been using iron on these sites since the iron age. The amount of iron buried in the average English field is staggering. Some sites contain everything from large layers of rust stained clay to small nails, large nails, giant nails, nuts, bolts, pieces of plow blades, pieces of sheet iron, tractor parts, etc. There are also many interesting iron items such as ancient arrows and spearheads, one thousand year old horse shoes and old knife blades.

Most detectorists hunt for coins and artifacts. the coins found in England date from the iron age and up. The prize to most detectorists are hammered silver coins. These coins were made by taking thin silver blanks and placing them in a die. the die was then hit with a hammer to imprint the design of the coin hence the name "Hammered Silver". Some of these coins are very small and they are very thin. if one uses a discrimination setting past foil on a VLF detector then many of these coins are rejected.
A dream detector for Europe will have great depth and sensitivity and fantastic iron discrimination.

Now lets take a look at what detectorists in the USA need for the sites they work. the list of features includes target ID, tone ID, coin depth indication, full range discrimination, notch discrimination, automatic ground balance, etc etc.

I do not get to do much detecting in the USA as there are not many good places to detect where I live in Charlotte, North Carolina. I do get to go detecting in England for a few weeks a year when I go there to visit my old mother and various relatives. I left England to live in the USA way back when I was just twenty years old. The Pulse devils have been a work of love. I designed them primarily for the conditions in England where I do my detecting.

OK, this said, I will be selling Pulse Devil detectors here in the USA very soon. The first detectors designed for the USA are beach detectors. They sport the same patent pending discrimination circuitry that the European Pulse Devil Nemesis uses. The discrimination control covers the full range from nails to pulltab reject.

I am working as fast as I can to get the first detectors out the door. I am getting very close to releasing the first units. Indeed I just took delivery of a long handled sand scoop today!!! I will be off to the beach to do some detecting quite soon. the only problem is that the beach is a two hundred mile drive from here. Dave. * * *