Computer & Electronic Systems Year 2, Semester 4. Industrial Automation. Sensors and Actuators

Transcription

1 Computer & Electronic Systems Year 2, Semester 4 Industrial Automation Sensors and Actuators

2 Preview Definition Examples Sensor Properties Sensor/Controller Interface Application Circuits Actuators Open-Loop and Closed-Loop Control Sensors and Actuators 1 2

3 Definitions Transducer: A device which transforms energy from one domain (magnetic, thermal, mechanical, optical, chemical, electrical) into another Sensors: devices which monitor a parameter of a system, ideally without disturbing that parameter. Actuators: devices which impose a state on a system, ideally independent of the load applied to them Sensors and Actuators 1 3

4 Definitions A sensor is a device which produces a proportional output signal when exposed to a physical phenomenon (e.g. temperature, displacement, force). A sensor responds to a change in the physical phenomenon. Sensors and Actuators 1 4

5 Types of Sensors Sensors can be classified as follows Active or Passive Active sensors are sensors that require an external power source (e.g. accelerometer) Passive sensors are sensors where the power required to produce the output is derived from the sensed physical phenomenon (e.g. thermometer) Analog or digital Analog sensors produce continuous signals that are proportional to the sensed parameter. Digital sensors produce digital outputs. Sensors and Actuators 1 5

6 Examples of Sensors Examples of sensors Magnetic sensors Photo sensors Temperature sensors - Analog Devices ADT7461 (e.g. to monitor Pentium processor temperature) Accelerometers - Analog Devices ADXL193 (e.g. automotive airbag), ADXL330 (Nintendo Wii) Motion sensors - speed gun Proximity sensors Electrical sensors - Voltmeter, Ammeter GPS Sensor "Without disturbing that parameter" implies that the sensors must be small and low-power devices in order to reduce energy exchange. Sensors and Actuators 1 6

7 Examples of Sensors acoustic dot mag ultrasound Sensors and Actuators 1 7

8 Examples of Sensors Board with multiple sensors: Accelerometer Temperature Sensor Light Sensor Sensors and Actuators 1 8

9 Accelerometers Accelerometers used extensively in the automotive industry Airbag release is the most well known application. Others are suspension control, brake control and fuel cut off. Nintendo Wii Remote Vibration control (e.g. hard-disk drive) Used to measure motion of patients with Parkinson s disease. Sensors and Actuators 1 9

10 Accelerometers An accelerometer is a device that measures the acceleration and provides an electrical output. The accelerometer measures acceleration but can be used to provide information on velocity and position as well. This can be done by integrating the output of the accelerometer once to get the velocity and twice to get the position. Sensors and Actuators 1 10

11 Sensor Properties Using example of Temperature sensor Full-scale Range: Typical value C. Saturation point and noise impact the usable range Accuracy: Typical value 1 C. Measure of error and uncertainty Resolution: Typical value 0.25 C Smallest change in temperature that can be detected Determined by the noise level Repeatability Sensors and Actuators 1 11

12 Sensor Properties Nonlinearity: Typical value 1% Ideal sensor should be completely linear How input/output transfer function compares to a straight line Sensitivity: Typical value 10mV/ C How output reflects input Efficiency Ratio of the output power to the input power More important for actuators Conversion time: 100ms Sensors and Actuators 1 12

13 Sensor Properties Response time How fast the output reaches a fraction of the expected signal level Overshoot How much does the output signal go beyond the expected signal level Drift and stability How the output signal varies slowly compared to time Offset The output when there is no input Sensors and Actuators 1 13

14 Sensor/Controller Interface Serial Interfaces - 2-wire I2C (Inter-Integrated Circuit): Clock, Data - 3-wire SPI (Serial Peripheral Interface): Clock, Data In, Data Out Parallel Interface - 10-bit Digital data, Clock, Read/Write Sensors and Actuators 1 14

15 Sensor/Controller Interface What commands/data would a temperature sensor give to it s controller? What commands/data would a controller give to a temperature sensor it is controlling? Sensors and Actuators 1 15

16 Communication from Sensor to Controller Sample Messages: - Ready to transmit measurement data - Transmission of the actual measurement data representing temperature measured - Have measured a temperature outside allowable range alarm that limits have been exceeded Sensors and Actuators 1 16

17 Communication from Controller to Sensor Sample Commands: - Take a temperature measurement - Give me the last measured temperature - Exit sleep mode (power-up) - Enter sleep mode (power-down) - Perform a calibration Sensors and Actuators 1 17

18 Interface Signals Controller to Sensor: Data In Clock In Power-Down/Power-Up Perform Measurement Enable Calibration Sensor to Controller: Data Ready Data Out Outside Limit Alarms Sensors and Actuators 1 18

19 Temperature Sensor Sensors and Actuators 1 19

20 Temperature Sensing + Fan Control Application Sensors and Actuators 1 20

21 Digital and Analog Outputs Sensor with a digital output can connect directly to its controller Sensor with an analog output must have that output signal digitised by an Analog-to-Digital Converter (ADC) before being sent to the controller In this case, the controller will have the additional function of controlling the ADC as well as the sensor Sensors and Actuators 1 21