This presentation for Metal Detector System. The goal is to analyze, design, model, simulate and construct the Metal Detector System. A very simple Design Pattern was used to modulate the system with the use of less number of components. Coils were designed in consideration to the principles of induction for the Metal Detector System. Standard components were used to construct the Signal Processing Unit (ASPU). The design for the ASPU was simulated and tested using advanced simulation software called Pspice. The final Product fulfills the requirements as expected.
3. Technical University of Denmark
Transducer
• Transmitter coil fed with 10 KHz AC signal
– Creation of B-field
• Inner coil’s B-field equal each other = 0
• Adding coin => Adding B-field = voltage drop
• B = Btran – Bcoil
• Vi = dφB/dt
• Ii(t) = Vi(t)/R
• 𝐿 =
𝑅∗ 3
𝜋∗2∗𝑓
• 𝐿 = (
𝑁2∗ 𝜇∗𝐴
𝐼
)
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2018
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Transducer
• Transducer: Idle • Transducer: Coin
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2018
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Analog Signal Processing Unit(ASPU)
• Amplifier
• Full Wave Precision Rectifier
• Active Low Pass Filters In Cascade
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2018
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Amplifier
• Op Amp is connected with feedback to produce a closed loop operation
• The inverting amplifier circuit amplifies voltage by a factor: A = –R2/R1
• So that the gain can be controlled by controlling the resistor value
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2018
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Full Wave Precision Rectifier
• Use of Full Wave Rectifier is to convert AC signal to a positive DC signal
• It is also known as Super Diode
• First part of circuit is active when signal is positive for each half cycle
• The output from the first part generates a half wave rectification which is added to the sine wave as an input to the second
part of the circuit
• It generates full wave rectification at the output
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2018
9. Technical University of Denmark
Active Low Pass Filters
• Two Active Low Pass Filters have been used to average the average of the rectified signal- The Pulsating DC.
• Is called the Cascaded Active Low Pass Filters.
• The resistor has a constant resistance while capacitor varies its impedance
• High resistance is optimized at a very low frequencies and very low resistance optimized at higher frequencies
• The filters are acting as a voltage divider
• We needed to find out R=XC=10k which is the cutoff frequency at -3db and is calculated using
• 𝑓𝑐 =
1
2𝑝𝑖𝑅2𝐶
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2018
10. Technical University of Denmark
Active Low Pass Filters
• Gain of Op-Amp Av = 𝑥 =
−R2
R1
• Capacitor value calculated using C =
1
2𝑝𝑖𝑓𝑐𝑅2
• Resistance calculated using R2 =
1
2𝑝𝑖𝑓𝑐 𝐶
• Transfer Function for the filters
𝑂𝑢𝑡
𝐼𝑛
= 𝐾
1
1+𝑠𝑅𝐶
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2018
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Active Low Pass Filters
• Raise time is approx. 5ms as show in the figure above marked with white line defined as 10% - 90% of the steady state
value in our case it’s the 5V
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2018
12. Technical University of Denmark
Active Low Pass Filters
• In figure below we can see the bode plot of the two low pass filters in cascade. Since the cutoff frequency for both filters is
the same, we have two poles laying at the cutoff frequency
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2018
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Active Low Pass Filters
• The poles Y1 and Y2 are laying at value of 41.147 DB
• The Cutoff frequency is laying at 106 Hz approx. -6db. Raise time is of approx. 5ms
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2018
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Results
• Metal Detector: Idle • Metal Detector: Coin
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2018
15. Technical University of Denmark
Conclusion
Part Requirement Nr Description Mandatory /
Optional
State
System
R1 Test object: 5 crowns Mandatory Approved
R2 Testing distance: 1 cm Mandatory Approved
R3 Max output: 4.5 V - 5.5V Mandatory Approved
R4 Min output: 0 V - 0.5 V Mandatory Approved
R5 Peak to peak: <20 mV Mandatory Approved
Transducer
R6 Operating value: 10 kHz Mandatory Approved
R7 Min output: ~ 0
Max output: 0 <
Mandatory Approved
R8 Use of function generator Mandatory Approved
R9 Handmade & calculations Mandatory Approved
R10 Formulas Mandatory Approved
ASPU R11 Convert signal Mandatory Approved
R12 3-dB bandwidth of max. 4
kHz
Mandatory Approved
Additional R13 Use of potentiometers or
variable resistors
Optional Rejected
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2018
