The device collects information about temperature from the source and converts it into a form that can be understood by other devices or people. The best example of a temperature sensor is a glass mercury thermometer, which expands and contracts as the temperature changes. The external temperature is the source of temperature measurement, and the observer looks at the position of the mercury to measure the temperature. There are two basic types of temperature sensors:
· Contact sensor
This type of sensor requires direct physical contact with the sensed object or medium. They can monitor the temperature of solids, liquids and gases over a wide temperature range.
· Non-contact sensor
This type of sensor does not require any physical contact with the object or medium being detected. They monitor non-reflective solids and liquids, but are useless against gases due to their natural transparency. These sensors measure temperature using Planck’s law. The law deals with heat radiated from a heat source to measure temperature.
Working principles and examples of different types of temperature sensors:
(i) Thermocouples – They consist of two wires (each of a different uniform alloy or metal) forming a measuring joint by a connection at one end that is open to the element under test. The other end of the wire is connected to the measuring device, where a reference junction is formed. Since the temperature of the two nodes is different, the current flows through the circuit and the resulting millivolts are measured to determine the temperature of the node.
(ii) Resistance Temperature Detectors (RTDS) – These are thermal resistors that are manufactured to change resistance as the temperature changes, and they are more expensive than any other temperature detection equipment.
(iii) Thermistors – they are another type of resistance where large changes in resistance are proportional or inversely proportional to small changes in temperature.
(2) Infrared sensor
The device emits or detects infrared radiation to sense specific phases in the environment. In general, thermal radiation is emitted by all objects in the infrared spectrum, and infrared sensors detect this radiation that is invisible to the human eye.
· Advantages
Easy to connect, available on the market.
· Disadvantages
Be disturbed by ambient noise, such as radiation, ambient light, etc.
How it works:
The basic idea is to use infrared light-emitting diodes to emit infrared light to objects. Another infrared diode of the same type will be used to detect waves reflected by objects.
When the infrared receiver is irradiated by infrared light, there is a voltage difference on the wire. Since the voltage generated is small and difficult to detect, an operational amplifier (op amp) is used to accurately detect low voltages.
(3) Ultraviolet sensor
These sensors measure the intensity or power of incident ultraviolet light. This electromagnetic radiation has a wavelength longer than X-rays, but still shorter than visible light. An active material called polycrystalline diamond is being used for reliable ultraviolet sensing, which can detect environmental exposure to ultraviolet radiation.
Criteria for selecting UV sensors
· Wavelength range that can be detected by UV sensor (nanometer)
· Operating temperature
· Accuracy
· Weight
· Power range
How it works:
Uv sensors receive one type of energy signal and transmit a different type of energy signal.
In order to observe and record these output signals, they are directed to an electric meter. To generate graphics and reports, the output signal is transmitted to an analog-to-digital converter (ADC) and then to a computer via software.
Applications:
· Measure the part of the UV spectrum that sunburns the skin
· Pharmacy
· Cars
· Robotics
· Solvent treatment and dyeing process for printing and dyeing industry
Chemical industry for the production, storage and transportation of chemicals
(4) Touch sensor
The touch sensor acts as a variable resistor depending on the touch position. Diagram of a touch sensor working as a variable resistor.
The touch sensor consists of the following components:
· Fully conductive material, such as copper
· Insulating spacer materials, such as foam or plastic
· Part of conductive material
Principle and work:
Some conductive materials oppose the flow of current. The main principle of linear position sensors is that the longer the length of the material through which the current must pass, the more the current flow is reversed. As a result, the resistance of a material changes by changing its position of contact with a fully conductive material.
Typically, the software is connected to a touch sensor. In this case, the memory is provided by software. When the sensors are turned off, they can remember “the location of the last contact.” Once the sensor is activated, they can remember the “first contact position” and understand all the values associated with it. This action is similar to moving the mouse and positioning it on the other end of the mouse pad in order to move the cursor to the far end of the screen.
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Touch sensors are cost-effective and durable, and are widely used
Business – healthcare, sales, fitness and gaming
· Appliances – oven, washer/dryer, dishwasher, refrigerator
Transportation – Simplified control between cockpit manufacturing and vehicle manufacturers
· Liquid level sensor
Industrial automation – position and level sensing, manual touch control in automation applications
Consumer electronics – providing new levels of feel and control in a variety of consumer products
(5) Proximity sensor
Proximity sensors detect the presence of objects that hardly have any contact points. Because there is no contact between the sensor and the object being measured, and because of the lack of mechanical parts, these sensors have a long service life and high reliability. Different types of proximity sensors are inductive proximity sensors, capacitive proximity sensors, ultrasonic proximity sensors, photoelectric sensors, Hall effect sensors and so on.
How it works:
The proximity sensor emits an electromagnetic or electrostatic field or a beam of electromagnetic radiation (such as infrared) and waits for a return signal or a change in the field, and the object being sensed is called the target of the proximity sensor.
Inductive proximity sensors – they have an oscillator as input that changes the loss resistance by approaching the conducting medium. These sensors are the preferred metal targets.
Capacitive proximity sensors – they convert changes in electrostatic capacitance on both sides of the detecting electrode and the grounded electrode. This occurs by approaching nearby objects with a change in oscillation frequency. To detect nearby targets, the oscillation frequency is converted to a DC voltage and compared to a predetermined threshold. These sensors are the first choice for plastic targets.
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· Used in automation engineering to define the operating state of process engineering equipment, production systems and automation equipment
· Used in a window to activate an alert when the window is opened
· Used for mechanical vibration monitoring to calculate the distance difference between shaft and supporting bearing
Post time: Jul-03-2023