Week 4 - Analog Sensors I

Question 1

Sensors vs. Transducers

Answer 1

A sensor senses the quantity that needs to be observed or measured (known as the measurand), while the transducer converts into a form that can be observed or used in a subsequent action.

Question 2

Why is sensing used in a control system?

Answer 2

• Measure the system outputs for feedback control
• Measuring some types of system inputs (unknown inputs, disturbances etc) for feedforward control
• Measuring output signals for system monitoring, parameter adaptation, self-tuning, and supervisory control
• Measuring input and output signal pairs for experimental modelling of the plant (i.e for system identification)

Question 3

Examples of Sensors in Engineering Systems

Answer 3

• Differential Transformers
• Piezoelectric Sensors
• Strain Gauges
• Potentiometers

Question 4

Stages of Sensing and Application

Answer 4

Measurand —> Sensor —> Transducer —> Signal Conditioning/Conversion —> Communication, application

Question 5

Terminology

Answer 5

Measurand (measurement) : Variable that is measured.

Sensor/Transducer : Two stages: 1) measurand is sensed; 2) The sensed signal is converted into the form of the device output

Analog and Digital Sensor/Transducer Devices: For a digital converter, the output needs to be digitised using an analog-to-digital converter (ADC). (Also called as digital transducer)

Sensor Signal Conditioning : Processing of the sensor output, such as amplification, filtering, etc.

Question 6

Pure Tranducer

Answer 6

Depend on non-dissipative coupling in the transduction stage.

Question 7

Passive Transducer (Self-Generating Tranducer)

Answer 7

Depend on their power transfer characteristics for operation and do not need an external power source. Pure transducers are essentially passive devices

Examples are: Electromagnetic, thermoelectric, radioactive, piezoelectric, and photovoltaic transducers.

Question 8

Active Sensor/Transducer

Answer 8

Need external source of power for operation, and does not depend on its own power conversion characteristics for this purpose.

Example: resistive transducer, such as a potentiometer, which depends on its power dissipation through a resistor to generate the output signal.

Question 9

In selecting a sensor/s for a particular application, we need to know…

Answer 9

The application and purpose, and what quantities (variables and parameters) need to be measured in the application.

Question 10

For quantities that cannot be measured (due to inaccessibility, lack of sensors, etc):

Answer 10

1. Estimate the quantity by using other quantities that can be measured
2. Develop a new sensor for the purpose

Question 11

Sensors for Mechatronics

Answer 11

• Motion sensors (position, proximity, rectilinear and angular velocity, acceleration)
• Effort sensors (force, torque, tactile)
• Others including thermo-fluid sensors and cameras

Question 12

Motion Transducers

Answer 12

Motion typically refers to one or more of the following four kinematic variables:

• Displacement (position, distance, proximity, size and gauge)
• Velocity (rate of change of displacement)
• Acceleration (rate of change of velocity)
• Jerk (rate of change of acceleration)