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ST13 – (Complex) Sensor systems

(Complex) sensor systems

Lecturer:Smilen Dimitrov

Sensors Technology – MED4

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ST13 – (Complex) Sensor systems

Introduction

• The model that we introduced for ST

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ST13 – (Complex) Sensor systems

Introduction

• We have discussed

– The units of voltage, current and resistance, from both a microscopic and macroscopic (electric circuits) perspective

– The definition of an elementary electric circuit, Ohm’s law and Kirschoff Laws

– Solving and measurement of voltage divider circuit and more complicated circuits - and applications in sensors

– Resistive based sensors– AC current, capacitors, and capacitive based sensors– Semiconductor structures – diode, transistor and operational

amplifier (and sensor applications)

• This time we briefly touch upon (complex) sensor systems

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ST13 – (Complex) Sensor systems

Simple sensors

• What we have discussed so far, can be categorized as simple sensors – Situation where we use a basic electronic element that behaves as

a sensor• For these sensors, the most important characteristic is that

– There is a direct functional relationship between the measured physical property (light, force, temperature), and a basic electric property (resistance R, capacitance C) etc.

– The principle of sensing need be discussed only through electronic behaviour on a microscopic level

• Examples– Photoresistor: resistance is directly related to light intensity– Force sensing resistor: resistance is directly related to pressure– Microphone: capacitance is directly related to pressure

• Interfacing with a DAQ can be from simple (using only voltage divider) to more complex (strain gauge – Wheatstone bridge – instrumentation amp)

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ST13 – (Complex) Sensor systems

Simple sensors

• Certain semiconductor structures can also be seen as simple sensors

– since the sensing mechanism can be discussed through behaviour of semiconductors ( microscopic level )

• Photodiode• Phototransistor

• Interfacing these to a DAQ can be a bit more complicated– as typically very small voltages are involved during proper

operation

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ST13 – (Complex) Sensor systems

(Complex) Sensor systems

• However, there are sensors units that are sold, that may represent entire electro-mechanical systems, whose principle of operation may involve mechanics

– Thus, the sensing principle for these units cannot be discussed only through the electronic behaviour of matter on a microscopic level

• Therefore we cannot call these units “simple” sensors– In lack of better term, we can use “complex sensors” or

“sensor systems” for such units

• Typical representatives of these units (that we have access to at school) are:

– Sharp GP2D12 IR Range Finder– Accelerometer– Gyroscope

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ST13 – (Complex) Sensor systems

Sharp GP1S036HEZ photointerrupter tilt sensor

• Listed in datasheet as “Transmissive Photointerrupter with Tilt Direction (4-direction) Detecting”:

– http://sharp-world.com/products/device/lineup/data/pdf/datasheet/gp1s036hez_e.pdf – (also: http://www.active-robots.com/products/sensors/sharp/gp1s036hez.pdf )

• Not an electrically simple sensor – because it is a mechanical system, composed of a light

emitting diode and two phototransistors

• “GP1S36J0000F is a compact-package, phototransistor output, transmissive photointerrupter, with opposing emitter and detector in a molding that provides a ball built-in case sensing. The compact package series is a result of unique technology combing transfer and injection molding. This is a 2-phase output device, suitable for detection of the position (4 direction).”

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ST13 – (Complex) Sensor systems

GP1S036HEZ photointerrupter tilt sensor

• Detection description in datasheet:

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ST13 – (Complex) Sensor systems

Sharp GP1S036HEZ photointerrupter tilt sensor

• Connecting: http://www.istop.com/~micro/electronics/notes.htm – Resistor values should allow the transistors to flip between OFF (out:

Vcc) and SAT (out 0.2V) – and thus provide maximum range of output voltage values

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ST13 – (Complex) Sensor systems

Sharp GP2D12 Range Finder

• Also known as: “analog distance”, “infrared proximity” or “range” sensor (Sharp calls it “Optoelectronic Device”)

– Datasheet http://document.sharpsma.com/files/GP2D12-DATA-SHEET.PDF • Popular in robotics

• Relatively easy to interface to a DAC – only three wires (gnd, Vcc and out)

• Provides analog voltage as measure of the distance to the nearest obstacle

http://www.acroname.com/robotics/info/articles/sharp/sharp.html

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ST13 – (Complex) Sensor systems

Sharp GP2D12 Range Finder

• Simple principle explanation: http://www.oopic.com/gp2d12.htm

• A small light detector is positioned 3/4 of an inch away from an IR emitter and is used to compute the distance and/or presence of the IR reflection in the field of view.

• This sensor uses triangulation to detect the distance: If the IR light reflects off an object, it returns to the detector and creates a triangle between the point of reflection, the emitter, and the detector. The angles in this triangle vary based on the distance to the object, and from those angles, the distance to the object can be calculated.

• output of these sensors is non-linear with respect to the distance being measured

• The output is not a constant voltage. It has pulses that are as much as 0.01 volts.

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ST13 – (Complex) Sensor systems

Accelerometer

• Typical – produced by Analog Devices, come in several packages– ADXL202 – two axis accelerometer

http://www.analog.com/en/prod/0,2877,ADXL202,00.html – ADXL330 – three axis accelerometer

http://www.analog.com/en/prod/0,,764_800_ADXL330%2C00.html

• More expensive than typical electronic elements

• Quite difficult to solder:

– Very small device

– SMD device (surface mounted)

– Needs to be set on a PCB before you can interface

• Otherwise relatively easy to interface to a DAC – Xfilt and Yfilt are analog output voltages

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ST13 – (Complex) Sensor systems

Accelerometer

• Simple principle explanation: http://itp.nyu.edu/physcomp/sensors/Reports/ADXL202Accelerometer

• On a micro level, The ADXL202 uses moveable polysilicon masses to detect various movements.

• Any movement drives the mass out of phase with the plates that surround it,

– inciting the differential capacitor formed between them to produce a square wave whose amplitude is proportional to acceleration.

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ST13 – (Complex) Sensor systems

Gyroscope

• Note that the typical meaning of a gyroscope is as a mechanical device:

– A gyroscope is a device for measuring or maintaining orientation, based on the principles of angular momentum. The device is a spinning wheel or disk whose axle is free to take any orientation.

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ST13 – (Complex) Sensor systems

Gyroscope

• Typical – produced by Analog Devices – ADXRS150 yaw rate gyro

http://www.analog.com/en/prod/0,2877,ADXRS150,00.html

• Even more expensive than an accelerometer• Near impossible to solder with an iron

– It is SMD (surface mounted device)– It is also a grid ball array element – should be soldered in an

oven– Needs to be set on a PCB before you can interface

• Should be relatively easy to interface with a DAQ – “rate” pin should be output analog voltage

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ST13 – (Complex) Sensor systems

Gyroscope

• Simple principle explanation: http://itp.nyu.edu/physcomp/sensors/Reports/ADXRS150 • A gyroscope measures angular rate, or how quickly an object turns.

The rotation is typically measured in reference to one of three axes: Yaw, Pitch, and Roll. The ADXRS 150 is, by nature, a yaw axis Gyro, measuring rate of turn on a Z-axis.

• Gyroscopes measure angular rate by means of Coriolis Acceleration. • The ADXRS series of gyros are constructed using a micromachined

mass carved from polysilicon, which is tethered to a frame so that it can move only along one direction.

• Silicon beams inside the substrate of the unit form two nominally equal capacitors. As the item which the gyro is mounted to turns, the mass in the center, mounted to a set of springs, exerts force in one direction or another