Basic of Analog and Digital sensors.ppt
- 2. Types of Signals Analog: An analog signal is a continuous signal and is often represented by a V(t). A dimmer light switch continuously increases/decreases the current. Digital : A digital signal is a discrete time signal, binary signal. An On/Off light switch applies a fixed, predetermined voltage.
- 3. Analog and Digital Signals Light intensity Temperature Pressure
- 4. Analog-to-Digital Conversion Sampling – converts the continuous signal into a series of discrete analog signals at periodic intervals Quantization – each discrete analog is converted into one of a finite number of (previously defined) discrete amplitude levels Encoding – discrete amplitude levels are converted into digital code Variable Time Analogue Signal 1001 1101 0101 Discrete Variables
- 5. Features of an ADC Sampling rate – rate at which continuous analog signal is polled e.g. 1000 samples/sec Quantization – divide analog signal into discrete levels Resolution – depends on number of quantization levels Conversion time – how long it takes to convert the sampled signal to digital code Conversion method – means by which analog signal is encoded into digital equivalent Example – Successive approximation method
- 6. Sensors and Actuators Sensor (e.g., thermometer) a device that detects/measures a signal or stimulus acquires information from the “real world” Actuator (e.g., heater) a device that generates a signal or stimulus real world sensor actuator intelligent feedback system sensor input signal (measurand) microcontroller signal processing communication sensor data analog/digital network display Typical Electronic Sensor System
- 7. Analog Sensors Sensors that produce continuous analog output signal and these sensors are considered as analog sensors. This continuous output signal produced by the analog sensors is proportional to the measurand. Practical examples of various types of analog sensors are as follows: accelerometers, pressure sensors, light sensors, sound sensors, temperature sensors, and so on.
- 8. Accelerometers Analog sensors that detect changes in position, velocity, orientation, shock, vibration, and tilt by sensing motion are called as accelerometers. These accelerometers are available as analog and digital sensors, based on the output signal. Analog accelerometer produces a constant variable voltage based on the amount of acceleration applied to the accelerometer.
- 9. Light sensor Analog sensors that are used for detecting the amount of light striking the sensors are called as light sensors. These analog light sensors are again classified into various types such as photo-resistor, Cadmium Sulfide (CdS), and, photocell.
- 10. Sound Sensor Analog sensors that are used to sense sound level are called as sound sensors. These analog sound sensors translate the amplitude of the acoustic volume of the sound into an electrical voltage for sensing sound level. This process requires some circuitry, and utilizes microcontroller along with a microphone for creating an analog output signal.
- 11. Pressure Sensor The analog sensors that are used to measure the amount of pressure applied to a sensor are called as analog pressure sensors. Pressure sensor will produce an analog output signal that is proportional to the amount of applied pressure. These piezoelectric sensors are used for the generation of electric charge.
- 12. Analog Temperature sensor Temperature sensors are widely available as both digital and analog sensors. Typically used analog temperature sensors are thermistors. Thermistor is a thermally sensitive resistor that is used for detecting changes in temperature. If the temperature increases, then the electrical resistance of thermistor increases. Similarly, if temperature decreases, then the resistance decreases.
- 13. Ultrasonic sensors The high frequency sound waves generated by active ultrasonic sensors are received back by the ultrasonic sensor for evaluating the echo. Thus, the time interval taken for transmitting and receiving the echo is used for determining the distance to an object. But, passive ultrasonic sensors are just used for detecting ultrasonic noise which is present under specific conditions.
- 14. Digital Sensors Electronic sensors or electrochemical sensors in which data conversion and data transmission takes place digitally are called as digital sensors. These digital sensors are replacing analog sensors as they are capable of overcoming the drawbacks of analog sensors. In digital sensors, the signal measured is directly converted into digital signal output inside the digital sensor itself.
- 15. Digital Sensors Button Motion Bumper Switch Sensor Lever Limit Switch Sensor Ultrasonic sensor
- 16. Digital Temperature Sensor DS1620 is a digital temperature sensor that provides temperature of device with 9-bit temperature readings. It acts a thermostat with its three thermal alarm outputs. If the temperature of device is greater than or equal to user defined temperature TH, then THIGH is driven high. If the temperature of the device is less than or equal to user defined temperature TL, then the TLOW is driven high. If the temperature of the device exceeds TH and remains high until it falls below that of TL, then the TCOM is driven high.
- 17. Digital Accelerometers The method of generation of variable frequency square wave output by the digital accelerometer is called as pulse-width modulation. The output PWM signal, pulse width or duty cycle is proportional to the acceleration value.
- 18. Sensors for a Robot Touch sensors tell the robot when it bumps into something. Light sensors measure light intensity. gyroscopes tell the robot which direction is up. Heat Sensors which measure temperature. Ultra Sonic Rangers tell the robot how far away objects are. 1. Resistive 2. Infra-red 3. Light 4. Sonar 5. Other
- 21. Actuators Hardware devices that convert a controller command signal into a change in a physical parameter The change is usually mechanical (e.g., position or velocity) An actuator is also a transducer because it changes one type of physical quantity into some alternative form An actuator is usually activated by a low-level command signal, so an amplifier may be required to provide sufficient power to drive the actuator
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