We will learn a little bit about sensors and transducers, how to choose a sensor, what sensors need, how they are categorized, and a few analog and digital sensor examples in this tutorial.
We communicate and control mechanical objects using electrical signals in an analog world with digital means. Sensors and transducers, which assist us in transferring data or information from one domain to another, make this possible.
Introduction
Whether an electronic or mechanical system, measurement is an essential component of any major system. Sensors, actuators, transducers, and signal processing equipment make up a measurement system. Measurement systems are not the only applications for these components and devices.
[adsense1] These are also used to communicate with the real world in systems that carry out particular tasks. The communication can be anything from reading the status of a switch signal to activating an LED at a specific output.
Sensor and Transducer Definitions
When discussing measurement systems, the terms “sensors” and “transducers” are frequently used. A component that generates signals relating to the quantity being measured is the sensor. “A sensor is a device that provides usable output in response to a specified quantity that is measured,” states the Instrument Society of America. The original meaning of the word “sensor” was “to perceive.”
A sensor is a device that provides an output signal that can be measured and/or recorded in response to changes and events in a physical stimulus. In this case, the output signal can be any signal that can be measured, usually an electrical quantity.
In a system, sensors are devices that “sense” changes in a quantity and perform an input function. The mercury thermometer is the best example of a sensor. Here the amount that is being estimated is intensity or temperature. Based on the expansion and contraction of liquid mercury, the temperature that is being measured is converted to a value that can be read on the calibrated glass tube.
Contrary to sensors, actuators are devices. An actuator converts an electrical signal into a physical event, whereas a sensor converts a physical event into an electrical signal. A system’s actuators are used to control an external device and perform the system’s output function when sensors are used as the system’s input.
The devices that transform one form of energy into another are called transducers. The energy usually comes in the form of a signal. The term “transducer” encompasses both sensors and actuators.
How to Select a Sensor
When selecting a sensor, the following factors should be taken into account:
Type of perception: the parameter being measured, such as pressure or temperature.
Working Standard: The sensor’s workings in general.
Consumption of Power: The system’s total power will be determined in large part by how much power the sensor uses.
Accuracy: When choosing a sensor, one of the most important considerations is its accuracy.
Conditions of the environment: When choosing a sensor’s quality, consider the conditions under which it will be used.
Cost: A low-cost or high-cost sensor can be used, depending on the application’s cost.
Ranging and resolution: The limit of measurement and the smallest value that can be sensed are important.
Repeatability and calibration: the capacity to repeat measurements under similar conditions and the variation in values over time.
What a Sensor or Transducer Needs to Do
A sensor must meet the following basic requirements:Range: It specifies the input’s upper and lower bounds for variation. A thermocouple can measure temperatures between 25 and 250 degrees Celsius with accuracy. It refers to the degree of precision between the actual value and the measurement. Precision is communicated as level of full reach yield.
Sensitivity: The relationship between the electrical signal at the input and the physical signal at the output is called sensitivity. It is the proportion of progress in result of the sensor to unit change in input esteem that causes change in yield.
Stability: It refers to the sensor’s capacity to continuously provide the same output for a given input.
Repeatability: It refers to the sensor’s capacity to produce the same output for various applications using the same input value.
Time to respond: It refers to the rate at which input changes step by step change output.
Linearity: The percentage of nonlinearity is used to describe it. The deviation of the actual measurement curve from the ideal measurement curve is known as nonlinearity.
Ruggedness: It is a proportion of the sturdiness when the sensor is utilized under outrageous working circumstances.
Hysteresis: The maximum difference in output at any measurable value within the sensor’s specified range when approaching the point first with an increase in input parameter and then a decrease in input parameter is referred to as hysteresis. A transducer’s inability to faithfully replicate its functionality when operated in the opposite direction is known as hysteresis.
Classification of Sensors
The classification scheme for sensors can be very simple or very complicated. This classification takes into account a significant amount of the stimulus that is being sensed.
Acoustic stimuli include the following: Wave, its spectrum, and its speed.
Electric: Conductivity, permittivity, charge, potential, the electric field, and
Magnetic: Permeability, magnetic flux, and field
Thermal: thermal conductivity, specific heat, and temperature.
Mechanical: Acceleration, force, pressure, stress, strain, mass, density, momentum, torque, shape, orientation, roughness, stiffness, compliance, crystallinity, and structural are all aspects of the structure.
Optical: emissivity, reflectivity, absorption, wave velocity, and refractive index
The phenomenon of sensors’ conversion also plays a significant role in the classification of sensors. Photoelectric, thermoelectric, and magnetoelectric are a few examples of conversion phenomena.
The following classifications of sensors can be made based on their applications:
I. Displacement, Position and Proximity Sensors
Inductive proximity sensors, eddy current proximity sensors, differential transformers, optical encoders, hall effect sensors, pneumatic sensors, proximity switches, and rotary encoders II are all examples of resistive elements. Temperature Detectors, Resistance Temperature Sensors, Thermistors, Thermocouples, and Bimetallic Strips Photodiode and phototransistor light sensors, as well as a light-dependent resistor IV. Fluid Pressure Diaphragm Pressure Gauge Tactile Sensor Piezoelectric Sensors Capsules, Bellows, Pressure Tubes VI. Velocity and Motion Pyroelectric Sensors Tachogenerator Incremental Encoder Fluid Stream and Level
Turbine Meter
Hole Plate and Venturi Cylinder
VII. IR Sensor Eighth Pair of Infrared Transmitter and Receiver Cell IX, Force Strain Gauge, Load Touch Sensors: Capacitive Touch Sensors; Resistive Touch Sensors: Capacitive Touch Sensors: X. UV Sensors: Ultraviolet Light Detector Photo Stability Sensors: UV Photo Tubes: Germicidal UV Detectors All sensors can be divided into two categories based on the need for power or signal. Active and passive sensors are the two types.
Active sensors require a power signal from an outside source to function. The sensor generates output based on this signal, which is known as an excitation signal. An example of an active sensor is the strain gauge. The output electrical signal is not generated by it on its own because it is a pressure-sensitive resistive bridge network. By relating the applied force to the resistance of the network, it is possible to measure the force. By passing current through it, the resistance can be measured. The excitation signal is current.
Passive sensors, on the other hand, respond to an input stimulus by directly generating the electrical signal for the output. A passive sensor gets all the power it needs from the measurand. A passive thermocouple is a sensor.
BACK TO TOP Commonly Used Sensors and Transducers Some of the most common sensors and transducers for various stimuli (the quantity to be measured) are photo diodes, photo transistors, light dependent resistors, and solar cells. For sensing light, the input devices or sensors are photo diodes. The result gadgets or actuators are LEDs, presentations, lights and fiber optics.
The thermostat, thermistor, thermocouple, and resistance temperature detector are the sensors used to measure temperature. Heaters serve as the actuators.
Potentiometer, proximity sensor, and differential transformer are the inputs for position sensing. Motor meter and panel meter are the output devices.
The strain gauge and load cell are the sensors that are used to measure pressure. The actuators are lifts and jacks and electromagnetic vibrations.
Microphones serve as the input devices, and loudspeakers and buzzers serve as the output devices.
Tachogenerator and Doppler Effect sensors are the ones used to measure speed. Motors and brakes are the actuators.
BACK TO TOP A Simple Transducer-Based System A public address system is an illustration of a system that employs sensors and actuators.
Analogue Sensors
Over a range of values, an analogue sensor produces output signals that change continuously. In most cases, the voltage that is output is proportional to the measurand. the quantity being measured, such as speed, temperature, pressure, strain, or other variables. are analog quantities because they are all continuous in nature.
An analog sensor is a Cadmium Sulfide Cell (CdS Cell) that measures light intensity. A CdS cell’s resistance changes when light hits it at different intensities. Variable output voltage reveals the change in resistance when connected to a voltage divider network. The output of this circuit can range from 0 V to 5 V. An analog sensor is a thermocouple or thermometer. Using a thermocouple, the following setup is used to measure the temperature of the liquid in the container.
Thermocouple Sensor The following is an illustration of the setup’s output signal:
The thermocouple’s output Over time, an analog sensor’s output typically changes smoothly and continuously. As a result, analog sensor-based circuits have a slower response time and lower accuracy. Analog to Digital converters can be used to utilize these signals in a microcontroller-based system.
In most cases, analog sensors need an external power supply and some kind of amplification to produce the right output signals. Op amps are very useful for filtering and amplifying.
Returning to the Top Digital Sensors A digital sensor generates discrete digital signals. There are only two states for a digital sensor’s output: “ON” and “OFF.” Logic 1 is ON, and logic 0 is OFF. The best illustration of a digital sensor is a switch with a push button. The switch can only be in one of two states in this scenario: When pushed, it is either ON or OFF, depending on whether it is released or not.
A light sensor is used in the following setup to measure speed and generate a digital signal.
An illustration of digital sensors can be found in the above arrangement, where the transparent slots on the rotating disc are connected to the motor’s shaft. The light sensor informs the counter of the presence or absence of the light by sending a logic 1 or logic 0 signal. The disc’s speed is shown by the counter. Since more counts can be counted in the same amount of time if the transparent slots on the disc are increased, accuracy can be improved.
When compared to an analog sensor, the accuracy of a digital sensor is generally higher. The number of bits used to represent the measurand affects the accuracy. The accuracy increases with the number of bits.Analog Signal a An analog sensor is a thermocouple or thermometer. Using a thermocouple, the following setup is used to measure the temperature of the liquid in the container.
