Transducers, sensors and actuators.
- Johan Alejandro Duque
- Jun 19, 2022
- 11 min read
Updated: Jun 22, 2022
¿What are they and what is it for?
A transducer is defined as a device that is capable of converting a physical variable into another that has a different domain. According to this definition, it is possible to say that a transducer is part of a sensor or an actuator; only that the difference between a sensor, an actuator and a transducer is that the transducer simply changes the domain of the variable, while the sensor provides a useful output to be used as an input variable to an information processing system and the actuator is responsible for executing the action determined by the information processing system, in general, it is said that a transducer changes the physical variable measured to an electrical signal; however, this is not always true, an example can be a scale, as it is known there are electronic and mechanical scales, in the case of electronic scales the transducer has the task of transforming the weight of an object into an electrical signal that is interpreted , while the mechanical scale transducer converts the weight of the object into a mechanical signal that runs through an indicator. So, in this way, it is said that a transducer is capable of converting a physical variable into movement, pressure, flow, an electrical signal, among others.
To better understand the differences and utilities of the types of transducers:
The sensors detect forms of energy, such as light or force, and convert them into an output of information readable by an electronic system. For example, a thermocouple that produces a measurable change in electrical voltage when heated or cooled. Or the charge that is generated when a force is applied to a piezoelectric force-measuring ring.
Actuators: It is a device with the capacity to generate a force that exerts a change of position, speed or state of some kind on a mechanical element, from the transformation of energy. In general, actuators are classified into two large groups:
By the type of energy used: pneumatic, hydraulic and electric actuator
Due to the type of movement they generate: linear and rotary actuator.
Example:
If you did not understand the above very well, this image along with an example can help, in this case it would be a thermometer, the physical magnitude is our temperature, the transducer enters there, which converts that physical magnitude into an electrical signal and thus shows your temperature (37ºC or 98.6ºF) via the thermometer display.
Transducer types
Transducers are divided into two broad branches: input transducers and output transducers. When the transducer is used as part of a sensing system, the transducer is said to be input. Therefore, an input transducer is one that is used to measure a physical variable whose output is used by an information processing system. On the other hand, when the transducer is part of an actuation system, it is said to be an output transducer. Thus, an output transducer is that device that converts the signal from the information processing system into a tangible action in the environment; for example, the movement of a motor, the activation of a valve, etc.
Aesthetic characteristics
The parameters that define the characteristics and optimal and ideal operation of a transducer are the following:
Sensitivity: The sensitivity of a sensor is defined as the minimum input required by the sensor to cause a detectable output. The graphical representation of how the sensor output changes with respect to the input is known as the output curve, where the slope of the tangent line to this curve constitutes the sensitivity of the sensor.
Accuracy: Accuracy is defined as the maximum difference between the actual sensor output and the actual value of the measured variable. Typically, the accuracy of a sensor is expressed as a percentage. In general, most sensors present a distribution around the real value of the physical variable they are sensing, regardless of whether the real value does not change.
Precision: The precision of a sensor refers to the degree of repeatability of a measurement. For example, if the same physical variable is measured with the same value, the sensor must always deliver exactly the same output each time.
Range: The range of a sensor is defined as the present interval between the minimum value and the maximum value of the physical variable that the sensor can measure.
Static linearity: The static linearity of a sensor depends mainly on environmental factors, so it is defined as the deviation that the sensor presents between the curve provided by the manufacturer under controlled conditions and the current output curve. In general, static non-linearity is expressed as a percentage. which reflects how far the sensor is from the ideal curve and the maximum value at full scale.
Offset: The offset is a sensor that is defined as a shift in the y-axis of the output curve, which is characterized by always being the same under certain operating conditions. Alternatively, the offset is the output a sensor presents when it should actually be zero.
Resolution: The resolution of a sensor is defined as the smallest change in the physical variable that it is possible to record.
Static error: When a physical variable is sensed or quantified, there is always the possibility of making an error in the measurement. In general, static errors in sensors are due to reading problems.
Dynamic characteristics
The dynamic characteristics of the sensors are presented and described below.
Response time: The response time is defined as the period that elapses since the sensed variable presents a change of state and the sensor registers it.
Hysteresis: The hysteresis in a sensor is the ability of the sensor to follow the ideal output curve due to the trend of changes in the physical variable; The main difference between hysteresis and linearity is that when a sensor exhibits hysteresis it means that the output trend crosses the ideal output curve in both directions.
Dynamic linearity: The dynamic linearity of a sensor is its ability to correctly follow the output curve given by the manufacturer when the physical variable undergoes sudden and very fast changes. In this case, the dynamic or linearity of the sensor is the degree of distortion that said sensor presents at the output, due to the abrupt changes of the phenomenon that is being sensed.
Dynamic error: A dynamic error in a sensor can be caused by several reasons, and among the most common are the loads induced in the sensor due to the measurement devices.
Parts of a transducer
Preamplifier: It is the one who conditions the output signal.
Getter: It is the one who provides the signal of the incoming energy.
Sensor: Part in contact with the physical magnitude.
Auxiliary mechanisms: They intervene in the process of the previous pieces.
Classification of sensors by the principle of transduction
Sensors can be classified by the type of transducer used for their implementation; however, this type of classification is usually impractical, since it does not offer a clear idea about what type of physical variable can be measured.
Classification of transducers according to the physical variable to be measured
This classification is usually the most common; however, it has the disadvantage of causing some confusion in the reader, since the same sensor can be used to measure different physical variables; For example, an ultrasonic sensor is very useful if you want to measure proximity, the level of a liquid, the presence of an object, the speed of a fluid, etc. However, its operating principle is always the same, and only depends on the type of configuration in which it is placed and how its output signal is interpreted.
Sensor types:
Temperature Sensors: Temperature is the heat intensity of an object, a temperature sensor converts temperature changes into electrical signal changes, and these can be classified into 3 types.
Thermocouples: It is a transducer that converts thermal energy into electrical energy by joining two wires of different materials. A thermocouple is available in different combinations of metals or calibrations. The four most common settings are J, K, T, and E. Each setting has a different ambient and temperature range.
2. Resistive: It is a resistive temperature detector, that is, a temperature sensor based on the variation of the resistance of a conductor with temperature.
3. Semiconductors: Semiconductor materials change their level of conductivity to
as their temperature varies, so that, at a lower temperature they are lousy but
at higher temperatures they are excellent conductors, in this way, they take advantage of this property for temperature measurement.
Thermometers:
LM35: It is a well-known analog sensor in the world of electronics because it is simple to implement and cheap, it has a compact package, it has 3 pins, 2 for power supply and one for output. It has a power supply that ranges from 4 to 30v and can measure temperatures from -50 to 150 °C.
DS18B20 Sensor: It has three pins, the first pin is called GND which is the reference to 0 of our circuit and this is connected to ground, the second is the DQ pin which is where all the sensor data will be transmitted and the The third pin is the VDD, which is the power pin where we can feed our sensor with its V range. Its power supply is from 3 to 5 V and its temperature measurement range measures from -55° to 125°.
Pressure sensors:
To measure the pressure, sensors are used that are equipped with a pressure-sensitive element and that emit an electrical signal when the pressure varies or that cause switching operations if it exceeds a certain limit value. These sensors are small, low cost and reliable.
Direct Measurement Sensor: They measure the pressure by comparing it with that exerted by a liquid of known density and height. Examples are: bucket barometer, U-tube manometer, inclined tube manometer.
U-tube manometer: Measures the pressure difference between the fluid and atmospheric pressure. Contains mercury, water, oil, among others, is accurate in the Pascal unit range of
500 [Pa] to 200 [KPa], its advantage is its versatility and its disadvantage is its length of tube necessary to measure high pressures.
Barometers: Used in the calibration of altimeters and weather stations. It is required to apply a correction for height.
Elastic Sensors
Bourdon tube: It is the most common method to measure pressures. Flattened tube of bronze or steel curved in an arc. By applying pressure to the inside of the tube, it tends to straighten, transmitting this movement to a needle by means of a suitable amplifying mechanism. Very accurate up to 200 atm. with 2–3% accuracy. max scale 7000Kg/cm2. This deformation can be transferred to a needle or a variable resistance system or to an electromagnetic field.
Diaphragm Meter: It consists of circular capsules connected to each other by welding. As pressure is applied, each capsule deforms and the displacement sum is amplified by a set of levers. It is applied for small pressures.
Bellows Gauge: Similar to the diaphragm, but in one piece flexible axially. It is applied for low pressures.
Electromechanical Sensors
They combine an elastic mechanical element plus an electrical transducer. The mechanical element may consist of a bourdon tube, bellows, diaphragm, or a combination thereof.
Digital Manometer: Digital Manometers are the ideal solution when looking for a wireless pressure transducer and display, since by uniting the sensor and the display in a single block powered by internal batteries, they can be installed at any point where measurement is required. pressure with good performance and ranges from 0.5 to 2,000 bar.
Optical Sensors
An optical sensor is classified within the physical sensors because its operation is based on the detection of light; either by its reflection, luminescence, refractive index, etc.
Optical sensors can be classified based on the nature of the optical property measured, they can be divided into:
Absorbance sensors.
Reflectance sensors.
Luminescence sensors (fluorescence, phosphorescence, etc).
Raman scattering sensors.
Refractive index sensors.
Some types of optical sensors are:
Color sensors: Color sensors have very common applications in the field of color adjustment in prints, control systems based on the color of objects, toys and video games, among others. These sensors have two basic aspects: one based on the use of color filters and the other on the irradiation of light and how it is reflected in the object to be detected.
Filter-based sensors provide a voltage output directly proportional to irradiance, being completely linear. It consists of a group of three photodiodes, each with a color filter: red, green and blue. In this type of sensor, the light source is independent of the sensor; the amount of light present in the system is a characteristic of the environment.
Color filters are based on the idea that an element of a given color will absorb all wavelengths except the one corresponding to the color of the object.
Those based on the irradiation of a fixed color source center their idea on the fact that when a light source is emitted on an object, it will reflect the color of its body with greater intensity.
Infrared sensors: In particular, the infrared sensor is an optoelectronic device capable of measuring the infrared electromagnetic radiation of bodies in its field of vision. All bodies emit a certain amount of radiation, this is invisible to our eyes but not to these electronic devices, since they are in the range of the spectrum just below visible light.
Proximity and level sensors
Proximity sensors are those that are limited to measuring the (go redundancy) proximity of an object with respect to the sensor, regardless of its orientation or determine if the object is close to the sensor to be detected, in addition to being able to determine the level of certain substances in a container at a certain percentage.
Proximity sensors can be classified into two groups, contact and non-contact:
Ultrasonic: Ultrasonic sensors are those that use a sonic signal to emit measurements.
This type of sensors base their operation on 3 phases:
Emission: An ultrasonic signal is generated (frequencies greater than 20 Khz).
Travel: The signal travels through the medium and is absorbed and reflected in part by the objects in the medium to be measured.
Reception: The reflected signal is captured by the receiver making measurements regarding the attenuation of the perceived wave, the time it takes to perceive the wave, the presence or absence of said wave.
The heart of these sensors is a piezoelectric material (those that generate a voltage due to an applied force).
In this way, by applying an electrical excitation to the piezoelectric material, we are able to emit an ultrasonic wave, a wave that will travel through the medium and will bounce in the form of an echo, being perceived by the receiver, which, given the deformation, will generate a voltage, which will be useful to generate the calculations necessary to obtain the measurements.
Characteristic:
It is a non-invasive means of measurement (it does not require any contact to perform the measurement).
You can obtain measurements regarding a variety of objects.
They base their operation on the Doppler effect.
They emit sound signals higher than 20khz.
They usually make use of piezoelectric materials.
They allow to measure distances from 20mm to 10m (depending on the manufacturer)
Main advantage: Any element that reflects sound can be detected regardless of its size, shape, texture or color.
Main disadvantage: The propagation speed of the sound wave is affected by changes in temperature, making it necessary to mathematically compensate for this fact.
A basic example of this type of sensor is the HC-SR04 for Arduino:
Which has 4 connection pins:
VCC: sensor supply voltage (5v).
Trig: this being the one that receives the input signal that enables the sensor measurement, that is, upon receiving the input signal, the emitter transmits the sonic signal.
Echo: Output signal that emits a high pulse with a duration corresponding to the time it takes to go from TX (transmitter) to RX (receiver).
GND: Ground connection.
Inductive: They are those that base their operation on the interaction between the object to be detected and the electromagnetic field generated by the sensor itself. Inductive sensors can be classified according to their construction format (cubic or cylindrical) or by the type of contact generated (pin or non-pin).
Its operation is similar to capacitive; the coil detects the object when there is a change in the electromagnetic field and sends the signal to the oscillator, then the trigger is activated and finally the output circuit makes the transition between open or closed.
It is here where:
An oscillator circuit: Induces the electromagnetic field emitted by the sensor.
A detector circuit: It is responsible for perceiving the change in the amplitude of the emitted field and sends a signal to the conditioning circuit.
A conditioning circuit: Sends the sensor output signal as a change from low state to high state.
The form of communication is through its pins and the connection cables, they generally have 3 pins or brown cables which connect to a 5V source, a blue cable connects to ground (GND) and the black one an input. digital as reading.
And so far the information about the transducers, sensors and actuators, I hope you have found this post useful, you would help us by leaving a "Like", sharing and leaving your opinion about it.
Bibliographic references:
Title: Sensores y Actuadores. Aplicaciones con Arduino.
Author: Leonel G. Corona Ramírez, Griselda S. Abarca Jimenez, Jesús Mares Carreño
Publisher: Grupo Editorial Patria
Year: 2014
Edition: First
ISBN: 978-607-438-936-4
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