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Advanced SensorsLecture 6

Sensors Technology

AUE 2008

Bo Rohde Pedersen

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Today's Lecture

• Piezo

• Acceleration

• Movement (IR)

• Distance (IR)

• Microphones

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Piezo Sensor

• Generates a ”Voltage”

• High impedance app 1Mohm (1.000.000)

• Mechanically tough

                                            

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Applications Piezo Sensor

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Applications of Accelerometer

“Accelerometers are being incorporated into more and more personal electronic devices such as media players and gaming devices, like the Wii Remote, which has multiple accelerometers to provide another element of gameplay. In particular, more and more smartphones (such as Apple's iPhone and the Nokia N95) are incorporating accelerometers for step counters, user interface control, and switching between portrait and landscape modes. Another Apple product featuring an accelerometer is the iPod Touch.”

Accelerometers can be used to measure vibration on cars, machines, buildings, process control systems and safety installations. They can also be used to measure seismic activity, inclination, machine vibration, dynamic distance and speed with or without the influence of gravity.

accelerometers is in airbag systems for automobiles. In this case the accelerometers are used to detect the rapid negative acceleration of the vehicle to determine when a collision has occurred and the severity of the collision.

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Principal of Accelerometer

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Converting Mechanical Motionto Electrical Signals

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Converting Mechanical Motionto Electrical Signals (II)

- Piezoelectric version- Optical- Laser measurements- Electromechanical

Other ways of converting the motions to electrical signals?

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Applications of Accelerometer (II)

• Measures the Vibration

• Acceleration of Motion of a Structure

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Accelerometers (vibration sensors) Frequency Range and Level

• Dynamic Range is the +/- maximum amplitude that the accelerometer can measure before distorting or clipping the output signal

• Frequency Response is determined by the mass, the piezoelectric properties of the crystal, and the resonance frequency of the case. It is the frequency range where the output of the accelerometer is within a specified deviation, typically +/- 5%.

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Frequency Range of Accelerometer

• High Frequency Limit is the frequency where the output exceeds the stated output deviation. It is typically governed by the mechanical resonance of the accelerometer.

Low Frequency Cut-off is the frequency where the output starts to fall off below the stated accuracy. The output does not "cut-off " but the sensitivity decreases rapidly with lower frequencies.

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Passive Inferred Sensor: Movement

Device: Detection Anglers:

Connect GND to 0V and V+ to 5V.O/P connect to digital in.

The device is measuring the temperature or the change in temperature

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Passive Infrared Sensor: Driver Chip

-Daylight adjusting-Filtering noise-Drivers for sensor

KC778B is the main chip on the passive infrared sensor. Here are the features of the passive infrared sensor:

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Long Distance Measurement SensorThe device sends out infrared light and detects the reflections

Device: Block diagram:

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Principles of IR Distance Measurement

Triangulating principleLight is sent out at a known angle from the transmitter and the receiver detects the direction of the light that is received (angle). Based on the receiving angle the distance is calculated.The triangulating principle is used for the short distance measurements in the range (um/mm) with high resolution.

Time of flight principleIn the principle Time of flight is a short pulse of light sent out. This pulse is reflected and the time from the pulse being sent out till it is received again is measured. This time is corresponding to the distance.

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Output Signals

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Measurement Spread

Not the IR sensor we have!!

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Microphones Technologies

• Electrodynamic (Coil in magnetic field)

• Electrostatic (A capacitor that changes size)

• PiezoMoving Coil Microphone

                                                 

Condenser Microphones

                                           

    

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Examples of microphonesElectrodynamicBenefits: Robust, high dynamic range

Electrostatic microphone capsuleBenefits: Size, low cost

Electrostatic measuring microphoneBenefits: Flat frequency response

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Microphone Characteristics

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Output Signals of a Microphone

• A microphone amplifier amplifies the signal to standard audio line level.

• A microphone amplifier includes typically extra filtering for low frequency noise.

• Frequency range is typically 20-20.000Hz

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Links

http://www.sharp-world.com/products/device/lineup/table/085.html

http://www.acoustics.salford.ac.uk/acoustics_world/id/Microphones/Microphones.htm

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Exercise

1. Connect the IR Distance Measurement Sensor to the Teleo board (analog in) and test the spread & range of the sensor (in cm). Review the Making Things page for Max implementation. http://www.makingthings.com/products/acc_datasheets/acc_ir_dist_001.htm

2. Connect the passive infrared sensor (digital in) and find out the spread and range for motion detection. Can it detect a piece of paper? How could you use it in practice? (installations / instrument interfaces)

3. Model an installation space that will have three distinct active zones but will use only two passive infrared sensors. How would you do it?