UNCLASSIFIED
Quest metal detector intermediate tests
Ian M Dibsdall, David J Allsopp and Steven M Bowen QinetiQ/FST/TR042527 May 2004
Copyright © QinetiQ ltd 2004
Administration page
Customer Information Customer reference number N/A Project title T&E of Quest Metal Detector Customer Organisation DFID Customer contact Mr A.Willson Contract number CNTR 01 2395 Milestone number N/A Date due May 2004
Principal author Ian M Dibsdall 01252 374589 MCES Bldg 412 Cody Technology Park, [email protected] Farnborough GU14 0LS
Release Authority Name David W Lewis Post Project Manager Date of issue April 2004
Record of changes Issue Date Detail of Changes 1.0 May 2004 Initial issue.
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List of contents
Administration page 2 List of contents 3 1 Introduction 4 1.1 Authority 4 1.2 Background 4 1.3 Support 4 1.4 Aims 4 2 Outline of tests 5 2.1 General 5 2.2 QinetiQ Pyestock 5 2.3 QinetiQ Longcross test area 5 3 Test procedures and results 6 3.1 In-air detection range 6 3.2 Maximum detection depth in sand 10 3.3 Signal to noise measurements 11 3.4 Results Location accuracy 12 3.5 Sensitivity profile (footprint) 12 3.6 Resolution Tests 15 3.7 Sensitivity drift 19 3.8 Optimum sweep speed 21 3.9 Interference from nearby detectors 23 3.10 Effect of moisture on the sensor head 24 3.11 Blind tests against buried targets 25 3.12 Size, mass and moment of inertia 25 4 Summary and discussion of results 27 4.1 Comparison with off the shelf detectors 27 5 Conclusions 29 6 Recommendations 31 A. Detection Data Plots 32 B. Detection Data Plots 46 List of abbreviations 48 Acknowledgement 49 References 50 Initial distribution list 51 Report documentation page 53
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1 Introduction
1.1 Authority
QinetiQ undertook this evaluation of the Quest Ltd low-power metal detector under tasking from the Department for International Development (DFID).
1.2 Background
Quest Technology Ltd has produced a prototype metal detector that operates with an extremely low power consumption. QinetiQ, working on behalf of DFID carried out an initial assessment of the detector in February 2004. The results [1] indicated that it would be worthwhile carrying out more formal ‘intermediate’ testing, in accordance with recent European guidelines (the ‘CEN guidelines’ [2]), under the International Test and Evaluation Project for humanitarian demining (ITEP). The results of the intermediate testing can be directly compared to results of similar tests with a range of off the shelf detectors being carried out in parallel at the European Commission Joint Research Centre in Ispra, Italy (JRC). Technical details of the detector are proprietary to Quest Ltd, with whom QinetiQ have a non-disclosure agreement. No proprietary information is contained in this report.
1.3 Support
The tests were supported and observed by Mr Ben Remfrey of Quest Ltd and Mr Chris Richardson of Roke Manor Research, acting as a consultant to Quest Ltd.
1.4 Aims
The aims of the tests were to: • Produce quantitative performance figures for the Quest detector, with the further aims of: - determining if field testing would be appropriate in the near future - providing Quest with information on the strengths and weaknesses of the detector to assist future development • Develop and prove testing methods in accordance with the CEN guidelines.
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2 Outline of tests
2.1 General
Most tests were based on procedures developed at JRC Ispra [5]. The procedures were amended to take account of the slightly different equipment available to QinetiQ. The following is a list of the tests, carried out at two locations.
2.2 QinetiQ Pyestock
1 In-air detection ranges for - chrome steel spheres from 4 to 15mm diameter - stainless steel spheres from 4 to 15.88mm diameter - aluminium spheres from 5 to 15.88mm diameter - targets representative of AP and AT mine components1 2 Signal to noise measurements 3 Maximum detection depth in sand 4 Location accuracy (manual blind test)
2.3 QinetiQ Longcross test area
1 Sensitivity profile (footprint) measurement (mechanised movement) 2 Measuring optimum sweep speed (mechanised movement) 3 Blind tests against buried targets and clutter (compared to an in-service detector). 5 Size, mass and moment of inertia measurements
2.4 Other tests
1 Measurement of sensitivity drift 2 Interference from nearby detectors 3 Effect of moisture on the sensor head
1 A subset of the International Test Operations Procedures (ITOPS) target set.
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3 Test procedures and results
3.1 In-air detection range
3.1.1 Method The area in which the tests were conducted was first swept to ensure that there was no interference from other metal objects. Each target in turn was mounted on the measurement jig (as shown in Figure 1) and set to a zero height position.
Due to the lack of mechanical support and flexing of the head, the detector would give an alarm if the head came into contact with the jig. Consequently, the detector was held stationary and the jig holding the target at a known height was swept underneath the detector head.
Initially the maximum detection range for the each target was found using the audible tone. To gauge the sensitivity of the detection circuit, measurements were also taken of the detection circuit voltage using a data logging oscilloscope. The voltage measurements were taken in exactly the same way as the tone measurements, with the exception of a “detection” being declared as a repeatable signal for the target at a higher level than noise or clutter (see section 3.3).
Figure 1 Test set-up for measuring the maximum detection height in air
3.1.2 Results In general, the results taken using the oscilloscope showed a distinct improvement in detection distance over the measurements taken using the audio output. This is illustrated in Figure 2 to Figure 4.
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Chrome Balls
250
200
150
100
Detection depth (mm) Audio tone Measured Voltage
50
0 0 5 10 15 20 25 30 Ball diameter (mm)
Figure 2 Detection depth vs diameter for audio tone (blue) and analogue output (pink) for Chrome targets
Stainless Steel Balls
250
200
150
100
Detection distance (mm) Audio tone Measured Voltage
50
0 0 5 10 15 20 25 30 Ball diameter (mm)
Figure 3 Detection depth vs diameter for audio tone (blue) and analogue output (pink) for Stainless Steel targets
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Aluminium Balls
200
180
160
140
120
100
80
Detection distance (mm) 60 Audio tone Measured Voltage 40
20
0 0 2 4 6 8 10 12 14 16 18 Ball diameter (mm)
Figure 4 Detection depth vs diameter for audio tone (blue) and analogue output (pink) for Aluminium targets.
The results taken using the audio tone were compared with the results, from various commercially available metal detectors, gathered from the similar tests carried out at JRC. The comparisons of the results for the chrome balls, stainless steel balls, aluminium balls and the ITOP targets can be seen in Figure 5 to Figure 8. The results for the Quest metal detector using the audio tone are shown in blue and the results using the voltage output are shown in red.
Chrome Ball in air
400
350
300 De te Quest Quest Voltage cti250 on Foerster di Scheibel Atmid st 200 Ceia an Minelab F1A4 ce Guartel MD8+ (m150 Minelab F3 m) Vallon VHM3
100
50
No Dat a 0 3mm 4mm 5mm 6mm 7mm 8mm 9mm 10mm 15mm Ball diameter
Figure 5 Comparison of detection distance for Quest detector and various off-the-shelf metal detectors (Chrome targets).
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Stainless steel Balls in air
400
350
300 De te Quest cti 250 Quest Voltage on Foerster Di Scheibel Atmid st 200 Ceia an Minelab F1A4 ce Guartel MD8+ (m 150 Minelab F3 m) Vallon VHM3
100
50
0 4mm 5mm 6mm 7mm 8mm 10mm 12.7mm 14mm 15.9mm Ball diameter
Figure 6 Comparison of detection distance for Quest detector and various off-the-shelf metal detectors (Stainless Steel targets).
Aluminium Balls in air
350
300
De 250 te Quest cti Quest Voltage on 200 Foerster Di Scheibel Atmid st Ceia an Minelab F1A4 150 ce Guartel MD8+ (m Minelab F3 m) Vallon VHM3 100
50
0 5mm 5.6mm 6.35mm 7.4mm 8.6mm 15.9mm Ball diameter
Figure 7 Comparison of detection distance for Quest detector and various off-the-shelf metal detectors (Aluminium targets).
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ITOPs in air (Audio tone)
400
350
300
Quest 250 Foerster Scheibel Atmid Ceia 200 Minelab F1A4 Guartel MD8+ 150 Minelab F3 Vallon VHM3 Detection Distance (mm) 100
50
0 CEG I KMO ITOP
Figure 8 Comparison of detection distance for Quest detector (Audio Tone Only) and various off-the-shelf metal detectors (ITOP targets).
3.2 Maximum detection depth in sand
3.2.1 Method The aim of this test was to measure the effect of the sand on the detection capability of the detector. Earlier tests [1] using soil had presented some unusual results (detection anomalies could not be linked to a precise source), so this test was carried out using clean sand.
The detector was swept over the sandbox with a sweep height of 30mm. The target was suspended in a Perspex tube, previously inserted into the sandbox. The detector was then swept over the target and if an alarm was produced, the target was lowered until the maximum detection depth was found. The depth to the top of the target was then measured and recorded.
Figure 9 Set-up for maximum detection depth in sand
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Due to the difference between the detection distance measured from the audio tone and the measurements from the oscilloscope, it was considered more useful to take maximum detection depth measurements in sand using the oscilloscope. The results can be seen in Table 1.
Type Diameter (mm) Detection distance in Detection distance in air sand (mm) (mm) Chrome 3 51 72 Chrome 20 177 (no data) Chrome 25 206 207 Stainless 4 70 77 Stainless 10 124 (no data) Stainless 15.9 171 187 Al 5 90 107 Al 8.6 123 (no data) Table 1 Comparison of detection distances (recorded using voltage output) measured in sand and air.
The smaller targets (e.g. Chrome ball 3mm diameter) showed the greatest reduction in detection distance in-soil (51mm) compared to in-air (72mm), whilst larger targets did not appear to be affected by the presence of the sand.
3.3 Signal to noise measurements
3.3.1 Method
The data recorded for in-air and in-soil detection depths was analysed to determine the signal to noise ratio. Note that the signal was recorded from the detector’s opto-isolated output interface, which had an adjustable offset and gain. The gain was fixed during the recording of the data and the offset set to an agreed “null” position between each target sweep (approximately 2.5V). The data was first shifted to zero mean and then separated into “target” and “background” sections. The root mean square value was calculated for each section and the signal to noise ratio calculated in dB. A “detection” on the voltage output was declared when the target signal (a pair of reflected pulses for the outward and return parts of a sweep) was larger than the background noise and clutter (e.g. variation due to movement of the head, zero drift etc.). This corresponds to approximately 4-6dB in the data plots (see Annex A).
3.3.2 Results
Very large or targets close to the detector head would saturate the detector’s output, resulting in “clipped” data. These were not included in signal to noise calculations. The background level of noise was relatively constant throughout the duration of these tests. Targets were detectable in the data (by eye) down to approximately 5dB, however the background “null” level was found to vary if the detector was flexed slightly. This variation can be seen in the in-soil tests – particularly the 130mm measurement (See Annex A) – and was larger than the signal from the target itself. Once the head is mechanically supported or encapsulated, there is likely to be far less flexure in the circuit board and a correspondingly lower variation in the null output of the detector.
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3.4 Results Location accuracy
3.4.1 Method A 15mm-chrome ball was placed under an opaque non-metallic surface so that the operator could not see the location of the target. The operator was then asked to pinpoint the target. The detection position was marked and the distance from the actual target position was measured.
3.4.2 Results
Three tests were carried out and for each test the distance from the actual position to the marked position was within the diameter of the target.
3.5 Sensitivity profile (footprint)
3.5.1 Method The sensitivity profile or footprint of the detector was measured using a 10mm diameter chrome ball at heights of 20mm, 32.5mm, 45mm, 57mm, 70mm, 82.5mm and 95mm.
A scanning frame was programmed to give a two-dimensional scan of 400x400mm, recording the true X,Y position and the detector’s analogue voltage output at each step. The forward step in both the x and y directions was 20mm. At each measurement point the frame was stationary and the motors briefly turned off to avoid any potential problems with interference from the servo drive.
The resulting data was also filtered to remove the zero baseline drift (as each test took approximately 10 minutes to run) and shift the resulting data to a nominal zero.
3.5.2 Results The datasets are presented below as both a 2D image and graph of the voltage output vs. sample number. The image shows a plan view of the detector’s response to the target, gradually fading into the background noise as the distance between the target and detector was increased. Note that the colour map is scaled in every plot to show the maximum span of the data, as the longest range target would not be visible if a common scale was used.
The detector exhibits a pattern typical of a “figure of eight” type coil, with a positive and negative half with a null running through the middle - useful for pinpointing the location of targets.
For the short range targets (20 and 32.5mm) the detector’s output also exhibited a voltage inversion , visible in the 20mm data as a blue (negative) centre to the red (positive) side of the coil. This was possibly due to the opto-isolator interface unit, and should be investigated by Quest.
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2D scan Peak signal for each measurement Figure 10 10mm Chrome ball result at a detector height of 20mm
2D scan Peak signal for each measurement Figure 11 10mm Chrome ball result at a detector height of 32.5mm
2D Scan Peak signal for each measurement Figure 12 10mm Chrome ball result at a detector height of 45mm
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2D scan Peak response for each measurement Figure 13 10mm Chrome ball result at a detector height of 57mm
2D Scan Peak response for each measurement Figure 14 10mm Chrome ball result at a detector height of 70mm
2D scan Peak response for each measurement Figure 15 10mm Chrome ball result at a detector height of 82.5mm
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2D scan Peak response for each measurement Figure 16 10mm Chrome ball result at a detector height of 95mm
3.6 Resolution Tests
3.6.1 Method
The aim of these tests was to measure the capability of the metal detector to detect minimum metal mines in the presence of a large metallic object (e.g. railway line, fence etc). Two tests were carried out - the first used a 10mm chrome ball bearing and a 1m length steel rod with 10mm x 10mm cross section to simulate a small AP mine lying next to a rail. The second test used a small AP mine next to a larger AT mine. Both tests were carried out using the metal detector mounted on the scanning frame and a 2D scan carried out.
Figure 17 Photo of resolution test - 10mm chrome ball next to 1m steel rod with 10x10mm cross section
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Figure 18 Test layout for the AP and AT resolution test
3.6.2 Results The results in Figure 19 show the response of the metal rod with a ball bearing separated by 25mm, with the detector scanned at a height of 50mm.
The “inversion” of strong positive targets is clearly visible in the graph, but the small ball bearing target is not visible. Figure 20 and Figure 21 show the response obtained from the steel bar and chrome ball alone for comparison.
Note that the steel bar was at a slight angle for the test shown in Figure 20.
Figure 19 Response from a 1m steel rod, 10x10mm cross section with 10mm Chrome ball, height 50mm.
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Figure 20 Response from a 1m steel rod, 10x10mm cross section, height 50mm.
Figure 21 Response from 10mm-chrome ball (Averaging 10), height 50mm
Figure 22 shows the response from a TM-57 Anti-tank mine – again the “polarity inversion” feature is clearly visible in both the image and plot of this data. Figure 23 shows the response from an AP mine (inert PMA-2) .
Figure 22 Response from a TM-57 anti-tank mine
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Figure 23 Response from a PMA-2 Anti-Personnel mine
When the two targets were placed in the same scan at 60mm separation (250mm centre to centre) the response from the AT mine completely obscured that of the AP mine (Figure 24). Note that the data shown here consists of two scans combined to give complete coverage of the targets. The positive (red) feature in the upper right quadrant is due to a null offset adjustment between scans.
Figure 24 AP and AT mines with a separation of 25cm centre to centre (6cm-separation edge to edge)
Figure 25 shows the same targets, but at an increased separation of 400mm edge to edge (590mm centre to centre). The AP mine is just visible as a slightly positive (red) area at around position 1200x,300y in the 2D image. It is suggested that only an experienced operator would be able to pick out the AP mine from the AT using this detector in this scenario.
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Figure 25 AP and AT mines with a separation of 590mm centre to centre (400mm- separation edge to edge)
3.7 Sensitivity drift
3.7.1 Method
These tests were carried out to determine if the detector exhibited any significant change in sensitivity over the lifetime of the battery. The detector was left on and a target passed by the coils every hour until the detector stopped responding. The battery terminal voltage, detector output and target response were all logged. Note – Data from these tests was provided by Chris Richardson of Roke Manor Research.
3.7.2 Results
The tests ran for approximately 35 hours. The battery terminal voltage (Figure 26) shows a typical discharge characteristic (initial drop, steady discharge, rapid final drop).
QUEST P2 Battery Discharge Characteristics 9
8 e g a t
l 7 o v
l a n i
m 6 r te y r e t t 5 a B
4
3 0 5 10 15 20 25 30 35 40 Time (hours) Figure 26 Battery terminal voltage against time
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The detector’s voltage output (directly from the detection circuit, no target present) is shown in Figure 27. This is very stable throughout the battery life of the detector, only varying significantly when the battery volts drop off at the end of their life. The battery life is approximately equivalent to the F3 and VMH3 detectors tested recently at Ispra, and approximately half that of the ATMID and Minex detectors. It should be noted that the Quest detector uses smaller capacity batteries than the other detectors, so the long life reflects is lower current operation.
QUEST P2 Drift Characteristics 2.6
2.4
2.2
) 2 (V t u
tp 1.8 u O r o
t 1.6 c e t e
D 1.4
1.2
1
0.8 0 5 10 15 20 25 30 35 40 Time (hours) Figure 27 Detector voltage output with no target present
The detector’s output with a target sweep every hour is shown in Figure 28. The span of the target response (min to max deviation from background level) is shown in Figure 29. This is again very stable over the lifetime of the batteries, showing a variation of no more than 2mV in a target span of approximately 11mV.
QUEST P2 Sensitivity Test
2.4 ) (V
p e
e 2.38 w s
t e
g 2.36 r ta y l r
u 2.34 o h
th i 2.32 w t u p t u 2.3 O r o t c
te 2.28 e D 2.26
0 5 10 15 20 25 30 35 Time (hours) Figure 28 Detector output with hourly target (10mm Chrome ball) sweep
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QUEST P2 Sensitivity Test - Target Span 0.014
0.013 ) V ( 0.012 an p S e s
on 0.011 p s e R et
g 0.01 r a T
0.009
0.008 0 5 10 15 20 25 30 35 40 Time (hours) Figure 29 Target span variation over time
3.8 Optimum sweep speed
3.8.1 Method This test determined the optimum sweep speed to be used during the remaining tests. This procedure was carried out for two detection heights at a variety of sweep speeds.
The metal detector was attached to a scanning frame as shown in Figure 30, and swept over a 10mm Chrome ball at sweep speeds of 100, 200, 300, 400 and 500mm/s. The signal for each of these speed was measured at both 50mm and 80mm heights.
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Figure 30 Quest detector mounted on scanning frame
3.8.2 Results
The peak response from the metal detector was plotted against sweep speed, as shown in Figure 31 and Figure 32. The raw response of the detector from a sweep over the target at each speed can be seen in Appendix B.
The results show a gradual drop in peak output as the detection speed is increased, but it should be noted that the data acquisition system in the scanning frame could not sample at a particularly high rate (~10Hz). This could result in the peak being missed at high scan speeds.
To minimise this effect a total of 10 scans were made at each speed, and the results averaged to give the data shown below.
Figure 31 shows how the average peak signal varies with sweep speed over a 10mm chrome ball at 50mm height
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Figure 32 shows how the average peak signal varies with sweep speed over a 10mm chrome ball at 80mm height
3.9 Interference from nearby detectors
3.9.1 Method
The aim of this simple test was to determine if two Quest detectors could be operated in close vicinity. One prototype detector was held stationary and the second prototype moved progressively closer. The distance between detectors was noted if an alarm sounded on either detector.
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3.9.2 Results
The detectors were found to sound an alarm when the separation was approximately 1m in any direction. The plot below shows the angle of approach (arrowed) and the minimum distance that could be achieved without either detector sounding an alarm (red dot). The data was reflected to complete the 360° plot.
Q UE ST Mutu al In terferen ce Test Angle of Approach Minimum Distance 90 1.5 120 60 0° 0.84m
1 ) m
( 150 30 e
c 45° 1.09m
n 0.5 a t s Di
h c
a 180 0 o
r 90° 1.14m p p
m A mu i
n 210 330 135° 0.9m Mi
240 300 270 180° 0.8m
Angle of Approach (Degrees) Figure 33 Minimum Distance between detectors to avoid interference
This compares well to other detectors tested at Ispra – with minimum distances ranging from ~3m (Minex, VMH3, ATMID) down to ~25cm (MD8+) .
3.10 Effect of moisture on the sensor head
3.10.1 Method
This test determines the extent to which the moisture on the sensor head affects the detection capability of the detector.
3.10.2 Results
Quest requested that these tests were left to the end of the week, due to the possibility of damage to the unprotected sensor head. Time did not permit any assessment to be carried out, so it is recommended that this test should be conducted on the detector once the head is fully encapsulated.
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3.11 Blind tests against buried targets
3.11.1 Method
An attempt was made to compare the performance of the Quest mine detector (DC coupled) with that of a Guartel MD8 in pit C of the mine lanes at QinetiQ Chertsey. The following targets were buried in the pit: • SB33
• Nr409
• VS50
• PMA3 The MD8 was first used to clear the pit of all detectable metal clutter, which may have contaminated the pit since last use. The targets were all genuine mines made free from explosive and filled with silastic as an inert explosive surrogate. All metal components were in place in the mines. The mines had been buried for over two years. The Quest and Guartel detectors were then to be used to attempt to locate the four targets. Any false alarms were to be investigated to determine their source.
3.11.2 Results
It soon became apparent that the number and density of signals from the Quest would make it impractical to search the whole pit (3x2m) and investigate every signal within the time available. A smaller area was therefore marked out (about 1x0.5m) and scanned thoroughly. About 6 signals were marked – there were more detections than this within the area, but it was not possible to accurately locate them all because they tended to overlap each other. Several of the detections were investigated by digging soil out until the signal disappeared, then scanning the pile of soil and repeatedly halving it to determine which half the detected object was in, until it was located. Two types of result were obtained: • In two cases a small object was located as the source of the detection. It was not possible to determine if the objects were metal or not, but neither of them caused a response from the MD8 on its highest sensitivity setting. The objects have been kept for later analysis if required.
• In at least three other cases, the soil was repeatedly split in two and each half continued to cause the detector to signal – but weaker than the original signal. This continued to happen as the soil samples got smaller until the detections were very weak – indicating that it was either the soil itself or perhaps small stones or particles distributed within it that were triggering the detector. It was concluded that it was not practical to search any significant area of the soil pit with the Quest detector due to the large number of signals. The sources of some signals were difficult to accurately locate as the detector was very sensitive to vertical and horizontal movement – it would often only take 10 or 20 millimetres of movement for the signal to change from zero to saturation. Hence the smallest change in height could cause a signal to disappear. The null setting of the detector also tended to drift, requiring frequent adjustment to avoid a constant tone obscuring the target signals.
3.12 Size, mass and moment of inertia
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3.12.1 Method
The physical dimensions of the detector were measured during the testing at QinetiQ Pyestock. The total mass of the detector was measured using laboratory scales, along with the mass of the head and shaft ends. As the detector had to be returned to Quest before the moment of inertia test could be carried out, a simple AutoCad Inventor model was created to calculate these parameters, using the measured dimensions, mass and centre of gravity position.
3.12.2 Results
The detector is 1.27 m long, with a total mass of 0.93 kg The head is 0.203m by 0.153m with a mass of 0.62kg. The figure below shows the CAD model created and the co-ordinate axes used. The moments of inertia were calculated about the origin, located at the top end of the detector shaft i.e. close to where it would be held.
AutoCad Inventor Report File: Quest.dxf 06/05/2004
Total Mass = 0.965 kg 5 2 Ixx = 1.7 x 10 kg.mm 4 2 IYY = 3.8 x 10 kg.mm 5 2 IZZ = 2.1 x 10 kg.mm
Figure 34 Moment of inertia calculations of the Quest detector
The moment of inertia in the XX axis was calculated as 1.7 x 105 kg.mm2. This is the axis of most interest, as side-to-side sweeping of the detector involves rotation about this axis. This compares favourably with other detectors measured recently at Ispra and reflects the Quest’s lightweight construction.
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4 Summary and discussion of results
4.1 Comparison with off the shelf detectors
Compared to commercial off-the-shelf detectors, some areas of the Quest prototype’s performance and mechanical design need addressing. In particular: • Detection distances in general using the audio tone are lower than the set of commercially available detectors recently tested at Ispra (with the exception of very small stainless steel targets). • The performance of the detector could be improved with modifications to the “back end” (e.g. altering the threshold level of the audio tone generator) as the detection circuit itself is more capable than the audio tone would suggest. • There was an anomalous yet repeatable response from the 3mm chrome ball – in that it produced a larger response than a 4mm ball. The targets in question have been quarantined until an explanation can be found. • Problems were found with the lack of mechanical support of the detector head, i.e. slight flexing of the head or touching the coils gave an alarm. Also, the detector would give an alarm when the head went from shade to bright sunshine (probably due to thermal expansion of the coil PCB). • The polarity of the target would invert (on the voltage output) with large metal targets or very close small targets. This would cause confusing audio signals on a two tone (left positive, right negative) output, or a false “null” in the single tone system. This is visible in the data plots as a negative spike, or as a blue target contained within the red (positive) half of the target image. • The detector has very good target location capability (for isolated targets). The second prototype detector has two tone coil which was found to be useful in pinpointing isolated targets. • The resolution test carried out did not provide conclusive results, as it was difficult to distinguish the steel rod and ball bearing from these results. It is difficult to operate most detectors near to large linear metal features (e.g. rails, fences), so the results for this detector are not unique. • The Sweep speed tests showed the greatest detection distances at the slowest speed, with a trend for gradually reducing detection distance for higher speeds. The sweep speed used during the detection tests was low (typically less than 300mm/sec). • “Blind” testing in the soil bins at QinetiQ Chertsey highlighted the fact that the detector was finding anomalies in the soil that other detectors (e.g. Guartel MD8, Minelab) could not pick up. These objects (small, hard, rust coloured nodules) were most likely the highly corroded remains of a metallic item. It is speculated that the Quest detector, operating at a higher frequency than most metal detectors, was sensitive to the concentrated iron oxide in these nodules. It is recommended that a more detailed assessment of the response of the detector to metal types, soils and uncooperative “mineralised” soils (e.g. laterite) is carried out unless the detector design is to be significantly changed. • The detector does not fold or disassemble for storage/transport, owing to the current single tube design. • The detector was not presented for testing with any protective transport case or manuals – this should be addressed after development of the unit itself to provide a complete package, comparable to existing metal detectors.
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• The Quest Detector does not currently incorporate automatic correction for drift or inbalance of the detector coils. Automatic correction with a long time constant, coupled with a manual 'zero' button, is a common and useful feature in other detectors.
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5 Further Development
(The following text in this section was provided by Quest after consideration of the test results and conclusions of this report). The prototype detector covered by this report is based on a design for an inexpensive hand held medical detector used for detecting fragments of metal in the human eye prior to an MRI scan. At this early stage it can only be considered as a concept demonstrator as it has not previously been developed, optimised or tested for mine detection. The tests have identified a number of areas in the mine detection role where significant improvements could be expected to the performance by relatively simple modifications. In light of the test results, further development and modifications will be carried out as follows: Frequency Anomaly Relationship As recommended, an investigation of the relationship between the frequency of operation and detection of anomalies in soil has begun The detector currently operates on an unusually high frequency (455 kHz). This choice of frequency is satisfactory for the medical application. Lowering the frequency should improve the discrimination between metal and flint and also increase the range in soil as the ground should then be more transparent. Initial experiments indicate that an operating frequency of about 50 kHz would be a good compromise. This could be achieved with relatively minor changes to the existing circuit if the single turn loops printed on the search head PC board were changed to 3 turns. Search Head The search head will be protected and made much more mechanically and electrically stable. This should allow the overall sensitivity of the detector to be significantly increased. Other aspects of the mechanical construction will also be improved whilst retaining the lightweight and simple design of the prototype. Power The power consumption of the prototype could be reduced by a factor of 10 or more by the use of more efficient circuitry. For instance, more than half the power is lost in the voltage regulator alone. For simplicity, RF amplification is currently achieved using fast operational amplifiers. Much lower power would be required by using some discrete component circuitry. This leaves scope for significantly increasing the loop energising power to achieve greater sensitivity if required. The energising power is currently only a few microwatts. Controls The "back end" circuit is being redesigned to include automatic drift/offset correction and a simple manual threshold/sensitivity control. Summary Work has started on making these modifications. The Quest team would welcome a meeting with DFID to discuss in detail what support the Department maybe able to provide. (End of quoted text).
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6 Conclusions
The Quest detector prototype is a lightweight, relatively low power detector. As a prototype, it is acknowledged that there are limitations to its mechanical and electronic performance which can still be addressed. The detection performance using audio tone alone (as specified in the CEN standard, and in the same way an end user would use the detector) did not compare well to the range of commercial detectors tested recently at Ispra. However, when the detection circuit was examined (picking off the voltage before the back-end audio tone generator) it was found that the inherent performance of the detector was approximately 30% greater than the tone alone would suggest. These results were still not quite up to the same level as the commercial detectors, but for a very simple detection circuit they are impressive. The audio tone of the P2 prototype did not have the significant “lag” that was highlighted during the Initial Assessment [1], making target location much easier and more accurate. The mechanical stability of the search head had not been altered between the Initial Assessment[1] and these tests – it was recommended that the head was either enclosed or encapsulated. This would probably have avoided the problems encountered with flexing of the head causing an unbalance of the circuit (and therefore an alarm) and solar loading on the search head causing expansion (and again, an alarm). The battery life of ~35 hours was not as high as expected from the initial “extremely low power” description of the circuit (comparing directly to battery life measurements of 30 and 70 hours from two other commercial detectors). However, this performance was achieved using a small rechargeable battery, so the comparison should only be drawn in terms of operational life. In this case the Quest is directly comparable with two of the other commercial detectors. The detection of several highly corroded lumps (undetectable to two other metal detectors) in the soil bins suggests that the high frequency search head is capable of picking up very low metal content targets, but could also potentially cause problems in mineralised soils (e.g. Laterite).
The Quest prototype shows promise as a simple, lightweight, low power metal detector, provided its detection performance, user interface and mechanical design can be more fully developed.
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7 Recommendations
It is recommended that:
1) The Quest Detector is further developed to improve its detection performance. 2) The audio interface “back end” circuit is reconsidered so that it more fully represents the true detection performance of the detector. 3) An automatic drift/offset correction (with manual “zero” function) is incorporated into the detector. 4) The mechanical aspects of the detector (particularly protecting the search head) are addressed. 5) An investigation of the relationship between the frequency of operation and detection of anomalies in soil is carried out. 6) The low power, lightweight and simple design aspects of the prototype are retained. 7) Future developments are tested to a similar standard to show the level of improvement in the system.
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A. Detection Data Plots This section contains plots of the detector’s voltage output recorded during maximum detection distance tests. A Tektronix TDS220 storage scope (serial number B080915) was used to record the voltage output from the opto-isolated “interface box” as the detector was swept across a target. The double peak shows the outward and return pass over the target. The signal to noise ratio (SNR) was calculated using the RMS signal and noise levels.
IN-AIR: 3mm Chrome Ball
27mm, SNR = 23.9 dB 57mm, SNR =10.4 dB
67mm, SNR =10.0 dB 72mm, SNR =6.0 dB
77mm, SNR =5.7 dB
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IN-AIR: 4mm Chrome Ball
27mm, SNR =20.6 dB 37mm, SNR =16.4 dB
47mm, SNR =12.1 dB 57mm, SNR =9.4 dB
62mm, SNR =6.0 dB
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IN-AIR: 12mm Chrome Ball
67mm, SNR = (CLIPPED) 107mm, SNR =24.3 dB
117mm 127mm, SNR =15.7 dB
137mm, SNR =10.1 dB 147mm, SNR =7.5 dB
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IN-AIR: 25mm Chrome Ball
167mm, SNR =22.0 dB 177mm, SNR =18.5 dB
187mm, SNR =15.7 dB 197mm, SNR =13.8 dB
207mm, SNR =11.4 dB 217mm SNR not measured
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IN-AIR: 4mm Stainless Steel
57mm, SNR =15.6 dB 67mm, SNR =8.5 dB
77mm, SNR =6.9 dB
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IN-AIR: 15.9mm Stainless Steel
137mm, SNR =20.1 dB 157mm, SNR =11.5 dB
167mm, SNR =10.3 dB 177mm, SNR =9.9 dB
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IN-AIR: 25mm Stainless Steel
167mm, SNR =19.9 dB 187mm, SNR =12.6 dB
207mm, SNR =12.3 dB 217mm, SNR =6.3 dB
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IN-AIR: 5mm Aluminium ball
77mm, SNR =15.1 dB 97mm, SNR =8.0 dB
107mm, SNR =6.6 dB
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IN-AIR: 15.9mm Aluminium ball
137mm, SNR =16.6 dB 157mm
177mm, SNR =9.2 dB 187mm, SNR =7.3 dB
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IN-SOIL: 5mm Aluminium ball
78mm, SNR =11.6 dB 90mm, SNR =9.6 dB
IN-SOIL: 8.6mm Aluminium ball
96mm, SNR =21.2 dB 102mm, SNR =15.5 dB
123mm, SNR =8.7 dB
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IN-SOIL: 3mm Chrome ball
37mm, SNR =12.7 dB 51mm, SNR =13.2 dB
62mm, SNR =8.7 dB
IN-SOIL: 20mm Chrome ball
144mm, SNR =18.9 dB 170mm, SNR =10.7 dB
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177mm, SNR =11.0 dB
IN-SOIL: 25mm Chrome ball
200mm, SNR =10.0 dB 206mm, SNR =6.9 dB
IN-SOIL: 10mm Stainless ball
124mm, SNR =15.4 dB 130mm, SNR =11.4 dB
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IN-SOIL: 15.9mm Stainless ball
135mm, SNR =20.0 dB 144mm, SNR =17.5 dB
166mm, SNR =7.8 dB 171mm, SNR =6.3 dB
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B. Detection Data Plots This section contains plots of the detector’s average response from a sweep over a 10mm chrome ball at various velocities.
100mm/s at 50mm 200mm/s at 50mm
300mm/s at 50mm 400mm/s at 50mm
500mm/s at 50mm Figure B-1 Detector response for various sweep speed at a height of 50mm
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100mm/s at 80mm 200mm/s at 80mm
300mm/s at 80mm 400mm/s at 80mm
500mm/s at 80mm Figure B-2 Detector response for various sweep speed at a height of 80mm
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List of abbreviations AP Anti Personnel AT Anti Tank ITEP International Test and Evaluation Project [for humanitarian demining] ITOPS International Test and Operating Procedures JRC [European Commission] Joint Research Centre (Ispra, Italy) PAT Portable appliance [electrical] test
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Acknowledgement
QinetiQ would like to thank Mr Tom Bloodworth of the EC Joint Research Centre, ISPRA, for the documents and test targets he has provided related to testing in accordance with the CEN standard.
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References
[1] I M Dibsdall “Initial assessment of the Quest low power metal detector” QinetiQ/FST/WP041356, March 2004
[2] European Committee for Standardization “Humanitraian mine action – test and evaluation – metal detectors” CWA 14747: 2003 E, June 2003
[3] T J Bloodworth “Development of tests for measuring the detection capabilities of metal detectors” Technical note I.03.168, November 2003
[4] C A Leach, Risk Assessment for “Testing of a lightweight metal detector …”, Humanitarian Demining file 290572, 13th March 2004
[5] T J Bloodworth “HSU procedures for testing according to CWA 14747: 2003”, draft procedures from tests at JRC Ispra, March 2004.
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Initial distribution list
External Ben Remfrey Quest Ltd 5 copies
QinetiQ David Allsopp Trials staff Ian Dibsdall Steven Bowen
Humanitarian Demining File (FST/LSED – Dept. M1401000, Project 290572)
Information Warehouse, Bldg 901, QinetiQ, Boscombe Down, Salisbury Wilts SP4 0JF
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Report documentation page
Originator's Report Number QinetiQ/FST/TR042527/1.0
Ian M Dibsdall, FST/LSED, Room S4, Bldg Originator's Name and Location 412, Cody Technology Park, Farnborough GU14 0LS
Customer Contract Number CNTR 01 2395
Customer Sponsor's Post/Name and Location Mr A.Willson, DFID
Report Protective Marking and any Date of issue Pagination No. of other markings references Unclassified May 2004 Cover + 53 5 Report Title Quest metal detector intermediate tests
Translation / Conference details (if translation give foreign title / if part of conference then give conference particulars) N/A
Title Protective Marking Unclassified
Authors Ian M Dibsdall, David J Allsopp, Steven M Bowen
Downgrading Statement
Secondary Release Limitations
Announcement Limitations
Keywords / Descriptors Mines, detection, metal, humanitarian, demining, trials
Abstract
Quest Technology Ltd has produced a prototype metal detector with very low power consumption, aimed at humanitarian demining. In February 2004, QinetiQ carried out an initial assessment of the detector on behalf of the Department for International Development. This document reports on further tests of the detector, in accordance with recent European guidelines (CEN Workshop Agreement CWA 14747, June 2003). The performance of the detector was assessed and compared to a range of other commercially available detectors. The tests concluded that the prototype detector was capable of greater detection distances than the audio tone would suggest (by measuring the detection circuit output), but that the range was not yet as good as the commercial detectors.
Abstract Protective Marking: Unclassified
This form meets DRIC-SPEC 1000 issue 7
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