Sensors and Actuators in Embedded Systems

Flashcards covering key concepts about sensors and actuators in embedded systems, including their definitions, classifications, parameters, and selection criteria.

What are the roles of sensors and actuators in embedded systems?

Sensors provide environmental input values to the system, while actuators are the output devices used to control the environment.

What is a sensor?

A device that converts a physical phenomenon (temperature, displacement, force, pressure) into a proportional output signal.

Define the 'Range' parameter of a sensor.

The lower and upper limits within which input may vary.

Define the 'Span' parameter of a sensor.

The difference between the upper and lower limits of range.

Define 'Error' in the context of sensor parameters.

A measure of deviation in measurement value from the actual value of the quantity being measured.

Define 'Sensitivity' in the context of sensor parameters.

The change in output quantity of a sensor per unit change in the input value to the sensor.

Define 'Accuracy' in the context of sensor parameters.

The closeness between measurement and the actual value.

Define 'Resolution' in the context of sensor parameters.

The smallest detectable incremental change of input parameter that can be reflected in the output signal of the sensor.

Define 'Stability' in the context of sensor parameters.

Refers to the ability of the device to produce constant output.

Define 'Dead band/time' in the context of sensor parameters.

The range of input values for when a transducer does not produce any output.

Define 'Repeatability' in the context of sensor parameters.

It refers to the ability of the sensor to produce the same output in response to the same input being applied repetitively.

Define 'Response Time' in the context of sensor parameters.

It is defined as the speed of change in output corresponding to a stepwise change in input.

Define 'Hysteresis' in the context of sensor parameters.

It refers to a type of error displayed by the sensor devices corresponding to the situation about whether the input is on increasing trend or on decreasing trend. It is equal to the maximum difference in output at any point within the sensor’s range while approaching the point first with increasing and then with decreasing input parameter value.

Define 'Nonlinearity' in the context of sensor parameters.

The maximum deviation of the actual measured curve from the ideal one. The linearity of a sensor may be dependent on environmental factors.

How can sensors be classified based on power requirements?

Passive sensors (power provided by the sensed phenomena) and active sensors (require an external power source).

How can sensors be classified based on the output signal?

Analog sensors (produce continuous signals) and digital sensors (output can be fed directly to a processor).

Give examples of Linear/Rotational Sensors.

LVDT/RVDT, tachometer, strain gauge, encoders, Hall effect sensors, capacitive, inductive, and interferometer.

What do Acceleration Sensors Detect?

Changes in velocity or motion, often in multiple axes (X, Y, Z).

What do Force, Torque, and Pressure Sensors measure?

Physical stress, such as force applied, twisting torque, or fluid/gas pressure.

What do Flow Sensors measure?

The rate of fluid or gas flow through a pipe or channel.

What do Temperature Sensors Detect?

Thermal conditions or changes in temperature.

What do Proximity Sensors detect?

The presence or absence of an object without physical contact.

What do Light Sensors respond to?

Light intensity or specific wavelengths of light.

What are accelerometers used for?

Devices that could produce electric charge signal proportional to the vibration.

What are two common types of accelerometers?

Seismic mass type and the piezoelectric type.

What do Force sensors measure?

The linear force applied to an object, typically expressed in newtons (N), and is commonly used in applications such as load cells and weighing scales.

What do Torque sensors measure?

The rotational or twisting force applied to a shaft or axle, quantified in newton-meters (Nm), and is essential in monitoring motors, mechanical joints, and rotating machinery.

What do Pressure sensors measure?

The force exerted by a fluid or gas over a defined area, usually in pascals (Pa) or pounds per square inch (PSI), and are widely used in automotive systems, HVAC, and industrial process controls.

What are flow sensors used for?

Measures the rate at which a fluid (liquid or gas) flows through a pipe or open channel.

What is a temperature sensor used for?

A device that detects and measures the thermal energy or heat level of an object or environment and converts it into a signal that can be interpreted by a system (analog or digital).

What is a proximity sensor used for?

Useful in detecting the presence of an object without any physical contact.

What is a light sensor used for?

An electronic device that detects and measures light intensity (typically visible, infrared, or ultraviolet radiation) and converts it into an electrical signal.

What are key issues in the sensor selection process?

Accuracy, Reliability, Responsiveness, Field View and Range, Size, Ease of Interpretation, Resolution and Repeatability, Power Consumption, Availability, Cost

What is an actuator?

A component responsible for physically controlling the system.

What do Electromechanical Actuators do?

Converts electrical energy into mechanical motion through a mechanical system, usually rotational or linear.

What do Electromagnetic Actuators do?

Operates based on the magnetic field generated by electric current, causing movement or force.

What do Hydraulic Actuators do?

Uses pressurized fluid (usually oil) to produce linear or rotary motion

What do Pneumatic Actuators do?

Uses compressed air to generate motion

What do Electromechanical actuators use to generate motion?

Electric motors (DC, AC, stepper, or servo)

How do Electromagnetic actuators work?

When current flows through a coil, it creates a magnetic field that exerts force on a ferromagnetic element (e.g., a plunger or armature). This causes the element to move, performing an action such as opening a valve or closing a switch.

How do Hydraulic Actuators work?

A hydraulic pump pressurizes fluid which is then directed to a cylinder or motor. The fluid pressure acts on a piston, causing it to move linearly, or it rotates a hydraulic motor.

How do Pneumatic Actuators work?

Compressed air is supplied to one or both sides of a piston within a cylinder. The pressure differential causes the piston to move, which in turn produces mechanical work.