What is a sensor?
Introduction of induction sensors
Sensor means sensor, and is derived from the word sens meaning sense, and can convert quantities such as pressure, heat, humidity, temperature, and به into continuous (analog) or discontinuous (digital) electrical quantities. Sensors are used in a variety of measuring devices, analog and digital control systems such as PLC. The function of the sensors and their ability to connect to various devices, including PLC, has made the sensor an integral part of the automatic control device. The sensors send information to the controller system based on the type and task defined for them, and the system operates according to the defined program.
Non-contact sensors are sensors that operate at a distance from the object and without connection to it, for example, the proximity of a piece senses and activates its existence. This operation, as shown in the figure below, can attract a relay, contactor or send an electrical signal to the input floor of a system.
Application of these sensors in industry
1- Production count: induction, capacitive and optical sensors
2- Fabric motion control and: Optical and capacitive sensor
3- Diagnosis of sheet rupture: optical sensor
4- Tank level control: Optical and capacitive sensor and capacitive level control
5- Fabric deflection control: optical and capacitive sensor
6- Speed measurement: induction and capacitive sensor
7- Traffic control: optical sensor
8- Measuring the distance of the part: analog induction sensor
Advantages of contactless sensors
High switching speed (switches on and off): Sensors have a high switching speed compared to mechanical switches, so that some of them (induction speed sensor) work with switching speeds up to 25 KHZ.
Long service life: Due to lack of mechanical contact and lack of penetration of water, oil, dust and sparks during work and… have a long service life.
Can be used in different environments with harsh conditions: Sensors can be used in environments with high pressure, high temperature, acidic, oily, water and..
No need for force and pressure: Due to the performance of the sensor when approaching the part, no force or pressure is required.
No noise when disconnecting Due to the use of semiconductors in the output floor, no bouncing noise is generated.
Types of induction sensors
Induction sensors are non-contact sensors that react only with metals and can send direct commands to relays, solenoid valves, measuring systems and PLC electrical control circuits.
1-Optical: These sensors work in two ways. Either two sensors that are in the form of sending and receiving opposite each other or a sensor that can send and receive infrared waves and in front of it is a mirror. If the body cuts off the transmitted waves, the light does not reach the phototransistor of the receiver and turns off, and as a result, a pulse is sent to the controller (level zero).
Note: Devices that work with these sensors In case of error, check that the mirrors are clean and the correctness of sending and receiving the sensors.
2- Capacitor: These sensors work like capacitors and if an object is present in its field, it changes its capacity and sends a signal to the controller (level zero).
Note: Capacitive sensors are capable of detecting the presence of any physical object (plastic, wood, metal, etc.)
3- Induction: These sensors work like an inductor and its inductive property is used to detect the presence of an object. The field has a certain amplitude and frequency. In the presence of an object, the oscillations and amplitude are zero and a signal (zero level) is sent to the controller. Becomes.
Note: Induction sensors only sense magnetic objects, and their body detection power depends on the amplitude of the output field (supply voltage).
4- Ultrasonic: These sensors use our ultrasonic waves, which are in the range of 20 to 50 kHz.
Its important application is used in speedometers and tank surface detection and flow and اندازه measurements.
It works by measuring the wave velocity and the time difference between sending and receiving distance. These sensors work as a pulse, for example, it sends a pulse every 2 seconds and measures the distance.
5- Color code detection sensor: detection of colored tape of packaging papers
Biosensors have attracted the attention of many research centers in recent years. Biosensors based on biomaterials now cover a wide range of applications such as pharmaceuticals, food industries, environmental sciences, military industries, especially the Biowar and خه industries.
The development of biosensors began in 1950 with the construction of an oxygen electrode by Lee Land Clark in Cincinnati, USA to measure the concentration of dissolved oxygen in the blood. This sensor is also sometimes called the electrodeclarc after its manufacturer. The sensor was later used to measure blood sugar by covering the surface of the electrode with an enzyme that helped oxidize glucose. Similarly, by covering the electrode with an enzyme capable of converting urea to ammonium carbonate, a biosensor was built next to the electrode made of NH4 ++ ion, which could measure the amount of urea in the blood or urine. Each of these two early biosensors used different transducers in their signal conversion. In the first type, the blood sugar level was measured by measuring the electric current produced (ammetric), while in the urea sensor, the urea concentration is measured based on the amount of electric charge created in the sensor electrodes. Potentiometric.
The day may come when the patient is diagnosed with the disease without the need to see a doctor and only on the basis of information provided by a COBD or Chip-on-Board Doctor, and then the required drugs are injected directly into the blood. This will greatly reduce the dose of the drug and at the same time dramatically reduce the side effects of the drug Side-Effect, because the drug is sent directly to the required place in the body.
What a biosensor does is convert a biological response into an electrical signal and consists of two main components: the Receptor and the Detector. The selectivity of a biosensor is determined by the receiving section. Enzymes, antibodies, and lipid layers are good examples of receptors.
The task of the detector is to convert physical or chemical changes by detecting the decomposed material (Analyte) into an electrical signal. It is quite clear that the detectors are not selectable in the type of reaction performed. , Optical, piezoelectric and thermal.In the electrochemical type, the operation takes one of the forms: amprometric, potentiometric, and impedance. -sensitive are FET or ISFET.
The biosensor generally consists of an immobilized static biological system such as a cell bundle, an enzyme, or an antibody and a measuring device. In the presence of a certain systemic biological molecule, it changes the properties of the environment. A measuring device that is sensitive to these changes produces a signal commensurate with the amount or type of changes. This Rasppe signal can be converted into an intelligible signal for electronic devices.
The advantages of biosensors over other existing measuring devices can be summarized as follows:
Many non-polar molecules form in living organs that do not respond to most existing measurement systems. Biosensors can receive this answer.
They are based on the built-in Immobilized biological system themselves, thus having side effects on other weavers.
Continuous and very fast control of metabolic activities is possible by these sensors.
Human body motion detection sensor PIR
As you know, the use of motion detection sensors is booming today, both in terms of security and protection and in terms of saving and optimization, PIR or PASSIVE INFRA RED sensors are sensors that receive infrared wavelengths of the environment.
Any object with a temperature above zero degrees Celsius has infrared or infrared radiation. But this wave has different wavelengths for different temperatures. What this sensor does is actually receive these waves in the suffering of the human body and detect it. This sensor is used in devices that detect the movement of the human body, even in part, and is at a high level in terms of accuracy and reliability. By this, you have a motion detector that is only sensitive to the movements of the human body.
Application of this type of sensor
It is useful in security issues, such as alarms, and can be very useful in issues related to energy efficiency.
Transmitter It is a device that receives a weak electrical signal and converts it to acceptable levels for controllers and electronic circuits, such as a feedback loop at the level of microvolts or millivolts or milliamperes, and this weak signal can pass through. TransmitterConvert to a signal at levels of zero to ten volts or 4 to 20 mA.
Transmitters It typically uses components such as op-amp to amplify and linearize these weak signal levels. Sensors and their accessories, such as transducers, are grouped into large instruments and classified according to the type of energy that can be used and the conversion methods.
A transducer is by definition a component that is responsible for converting energy states into each other, meaning that if a pressure sensor is accompanied by a transducer, the pressure sensor measures the parameter and delivers the specified value to the transducer, then The transducer converts it into a comprehensible electrical signal for the controller and, of course, can be transmitted by metal wires. To change the frequency, however, it should be noted that the selected sensor must be a type of sensor that converts physical parameters into electrical and can, for example, convert the measured temperature into a very weak signal that enters the transducer in the next step and then Electronic circuits will be delivered.
To understand this, let’s look at the differences between two temperature sensors: a thermocouple and a mercury temperature sensor, two types of temperature sensors that both perform the same function, but the thermocouple provides an electrical signal on the output side, while The mercury temperature of the output manifests itself in the form of changes in height in the mercury inside.
Pressure is measured with the help of sphygmomanometers. The main sphygmomanometers, which are named according to the mechanism of experts, are:
- U-shaped tube barometer
- Barometer McLeod
- Mercury barometer
- Thermocouple barometer
- Acoustic barometer
- Capacitive barometer
- Ideal gas barometer
- U-shaped tube barometer
The simplest and most famous of these is the U-shaped barometer, in which some mercury is poured into a U-shaped tube and the difference between the ambient air pressure, which is p0, and the material inside the barometer, which exerts pressure on the mercury liquid, is measured by the difference in column height. . So this way we can get the real pressure: P = P0 + ρg) h – h0
In the latter relation P is the pressure and ρ density of matter and P0 is the atmospheric pressure, h0 is the height of the liquid column at atmospheric pressure, g is the acceleration of gravity and h is the height of the liquid column at the pressure of matter.
This sphygmomanometer is basically made of an empty air tube, one side of which is blocked and the other side, which is open, is immersed in a container full of mercury. External air pressure pushes mercury from the source into the tube. Mercury rises in the pressure gauge to the extent that its weight inside the tube is exactly equal to the force exerted by the air pressure, and then remains in a state of exchange and stillness. As the air pressure changes, the level of mercury inside the tubing will rise and fall. Under normal conditions, mercury rises to 29.92 inches or 760 mm in the tube, which is a pressure equivalent to 1013.15 mm. The mercury inside the barometer tube has a convex surface due to its surface tension property, which must be read as the highest convex surface when determining the pressure.
Metal Barometer (Aneroid)
A metal sphygmomanometer is a mechanical device consisting of a canned cylindrical chamber without air; As the air pressure changes, this chamber contracts or expands. With a relatively complex system consisting of a number of levers and pulleys, these changes are magnified and transmitted to a hand that moves on a graduated plate. A moving indicator that can be fixed at one point is mounted on the barometer to measure pressure changes from the last reading.
The barometer is similar to a metal barometer, except that the effect of pressure changes in the airless chamber is transmitted to a pen, and the pen draws a continuous line on paper wrapped around a rotating cylinder. The vertical axis of this screen is calibrated in units of pressure and the horizontal axis is calibrated in terms of time, which usually has one line every two hours. Precise barographs have also been developed that can measure pressure changes up to eleven millibars. These devices are called microbarographs.
Sensors in the robot
Sensors are often used to perceive contact, tension, proximity, visual and audio information. The function of the sensors is such that due to the factor changes to which they are sensitive,
They generate small voltage levels in response, which by processing these electrical signals can be used to interpret the received information and use it for further decisions.
Sensors can be divided into different categories from different perspectives, which are as follows:
- Environmental sensor: These sensors receive information from the outside environment and the status of objects around them.
- Feedback sensor: This sensor receives information about the robot’s position, including the position of the arms, their speed and acceleration, and the force exerted on the drivers.
- Active sensor: These sensors have both a receiver and a transmitter, and they work in such a way that a signal is sent by the sensor and then received.
- Passive sensors: These sensors have only a receiver and detect the signal sent from an external source, so they are cheaper, simpler and less efficient.
The sensors are divided into three parts in terms of the distance they must have to the intended target:
- Contact sensor: These types of sensors are found in various drive connections, especially in the final factors, and can be divided into two parts.
- Contact detection sensors
- Power-pressure sensors
- Proximity sensors: This group is similar to contact sensors, but in this case it does not have to be in contact with the object to feel. These sensors are generally more difficult to build than the previous type, but provide higher speed and accuracy to the system.
There are two main ways to use sensors:
- Static sensing: In this method, the stimuli are fixed and the movements that take place take place without a moment’s reference to the sensors. For example, in this method, first the position of the object is detected and then the movement towards that point takes place.
- Sense of closed loop: In this method, the robot arms are controlled during movement according to the information of the sensors. This is the case with most sensors in vision systems.
Now, in terms of application, we will get acquainted with examples of different types of sensors in robots:
- Body Sensors: These sensors provide information about the position and location of the robot. This information is also obtained by changing the states obtained in the switches. By receiving and processing the obtained information, the robot can be aware of the slope of its movement and in which direction it is moving. Finally, it gives a reaction commensurate with the input received from the self.
- Direction Magnetic Field Sensor Using the existing magnetic properties of the earth and the strong magnetic field, an electronic compass has been developed that can provide information about magnetic directions. These features help a robot to be aware of its direction of movement and to decide to continue moving in a certain direction. These sensors have four outputs, each of which indicates one direction. Of course, using a correct logic, it is also possible to identify eight magnetic directions.
- Touch and Pressure Sensors It seems difficult to simulate the human sense of touch. But there are simple sensors that can be used to sense touch and pressure. These sensors are used to prevent accidents and cars falling into the bumps. These sensors are also used in the robot’s arms and legs for various purposes. For example, to stop the robot from moving when agents hit an object. The sensors also help the robots apply enough force to lift a body off the ground and place it in a convenient position. According to these explanations, their function can be divided into the following four categories: 1- Achieving the goal, 2- Avoiding collisions, 3- Recognizing an object.
- Heat Sensors: One of the types of heat sensors are thermistors. These sensors are passive resistance elements whose resistance varies according to their temperature. Depending on whether their resistance increases or decreases due to heat, they are defined as positive or negative thermal coefficient, respectively. Another type of heat sensor is a thermocouple, which also produces a small voltage due to changes in ambient temperature. In the use of these sensors, one end of the thermocouple is usually connected to the reference temperature and the other end is placed at the point where the temperature should be measured.
- Smell Sensors: Until recently, there was no sensor that could act like a human sense of smell. What was available was a series of sensitive sensors to detect gases, which were primarily used to detect toxic gases. The sensors are constructed in such a way that a passive resistive element, which is fed from a separate power supply with a voltage of +5 volts, is located next to a sensor, which, when heated, provides the necessary sensitivity for the sensor to respond to environmental stimuli. To calibrate this device, first a small amount of any desired odor or fragrance is applied to the system and its response is recorded, and then this response is used as a reference for comparison in later uses. Basically, in the construction of this system, several sensors operate simultaneously and then the received responses from them are transferred to the robot neural network and the necessary analysis and processing is performed on it. The important thing about the work of these sensors is that they can not detect a smell or perfume at all. Rather, they detect odors by measuring the difference between them.
The Germans have been able to detect up to 90% of heart diseases by building a special olfactory sensor. It has been reported that this sensor can detect different types of heart failure based on odors.
Joint position sensors: The most common type of sensors are encoders, which have both the power to exchange information with the computer and are simple, accurate, reliable, and noise-free. These categories of encoders can be divided into two categories:
Absolute encoders: In these decoders the position is converted to binary code or gray code BCD Binary Codded Decible. These encoders are not widely used because they are heavy and expensive and require a lot of signals to send information. As we know, using a large number of signals increases the error rate, and this is not desirable at all. After these encoders, it is used only in cases where the absoluteness of the places is very important to us and we do not have a problem with the robot’s fable-bearing load.
incremental encoders: The decoders have a pulse train and a reference pulse that is used for calibration. They achieve the desired position by counting the pulse trains relative to the reference point. From the frequency (pulse width) can be rotated quickly and from the calculation of frequency changes in the unit of time (pulse width changes) to accelerate the rotational motion. You can even understand the direction of rotation. Suppose signals A, B, and C are three signals sent from the decoder to the controller. B is a signal with a quarter delay period compared to A. Due to the phase difference between the two, the direction of rotation can be understood.
Infrared sensor without sensitivity to ambient light
This is an infrared sensor that is not sensitive to daylight and works using a PLL!
But how does it work? It uses an IC that has an oscillator set to 4.5 KHz. This frequency is sent by an infrared transmitter and picked up by the receiver and its DC voltage is subtracted (which is usually proportional to the voltage). With ambient light) is then compared with the transmitter phase by a Phase Detector, and if it is equal to zero output, the presence of a PLL in the circuit causes the circuit to be sensitive to scattered light. Of course, you can use a circuit potentiometer to adjust the sensitivity.
You can use this circuit both to detect the presence of an obstacle and to distinguish black from white. You can put the transmitter and the receiver of the circuit on top of each other, so that if there is an obstacle between the two, it can be detected, and you can put both of them next to each other. Only the reflection can be detected by the receiver. By doing this, if an obstacle is placed near these two, this distance is about 2 cm, which depends on the color of the body and the transmitter and receiver. Of course, it can be reduced with a circuit potentiometer. Distinguish black from white, but do not forget to adjust the potentiometer
The good thing about this circuit is that your settings will not be disturbed as the light increases or decreases.
One of the issues in robotics is to create an understanding of the external environment to prevent adverse contact with objects in the moving environment.
On the other hand, we may need the robot to be able to perceive distances without physical contact. Ultrasonic sensors are used for this purpose. The frequencies in this range can be considered between 40 kHz and several megahertz. Waves with these frequencies have applications such as measuring the distance, measuring the depth of a tank, and so on.
To use these waves, a series of special sensors have been designed that can be divided into two categories: industrial and non-industrial. Non-industrial sensors operate at frequencies around 40 kHz and are available in the market at low prices. In these sensors, the accuracy of work is high and they can be used only to the extent of detecting a distance or depth of a liquid.
The general mechanism of action of these sensors is to send a beam and receive its reflection and subsequently calculate the return time. In this way, distances can be easily calculated by considering the speed of sound at ambient temperature and pressure, so this sensor is available in two separate packets of receiver and transmitter.
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