Here we will go into detail about temperature sensors. A temperature sensor is an electronic device that senses the temperature of its surroundings and converts input data into electronic output data to record or signal changes in temperature. There are different types of temperature sensors. Some of them require direct contact with the physical target to be identified, introduced as contact temperature sensors. In contrast, others indirectly detect the temperature of targets, known as non-contact temperature sensors.
temperature sensorsQuantifying the amount of thermal or even cold energy produced by an object or system and allowing us to 'sense' or detect any physical change in that temperature and produce an analogue or digital output. A temperature sensor is an important product when using industrial tools. Temperature sensors are offered by a number of vendors and companies rangingManufacturer, and manydistributorand there are manysell temperature sensorsauf Linquip.
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Visit the Linquip website for a complete list of temperature sensor services to meet all your needs. Linquip can connect you to a variety of temperature sensor service providers and experts who can help. Linquip offers a team of temperature sensor experts and subject matter experts to help you test your devices.
Here we would like to introduce you to what a temperature sensor is and how it works, what applications there are and what types there are.
What is the temperature sensor?
Temperature sensors are simple devices that take the degree of cold or heat and convert it into a simple unit. But have you ever thought about how the temperature of soil, wells, large concrete dams or houses is recorded? Well this is done using some of the special temperature sensors. Visiton hereto clearly see what a temperature sensor is.
We use them in many applications in our daily lives, for example in water heaters, refrigerators, microwave ovens or in the form of thermometers. In general, they have a wide range of applications, geotechnical monitoring being one of them. They are used in this field to control the condition of concrete structures, bridges on land or water, etc. for structural changes in them according to seasonal changes.
Temperature sensors are designed to periodically monitor and check special structures such as road bridges, train tracks, concrete or earth dams, etc. A thermometer is the most common form of these, used to record the degree of temperature in any given location.
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A thermocouple is another common example of this. A thermocouple, or T/C for short, is made of two dissimilar metals that produce an electrical output voltage that is directly related to the change in temperature. Another example of this is an RTD (resistance temperature detector). The RTD is a variable resistor that changes its electrical resistance directly with a change in temperature. Acquiring an RTD is very repeatable, accurate and nearly linear.
temperature sensor works
As discussed earlier, a temperature sensor is an instrument designed to detect the cold or hot condition of the target object. The basic operation of this sensor is based on the voltage across its diode. The temperature change is directly related to the resistance of this diode.
Diode resistance is detected and converted into simple, readable temperature values such as Fahrenheit, Kelvin or Celsius and displayed in meaningful formats rather than readings. These temperature sensors are used to detect the internal temperature of various structures like power plants. clickon hereto see exactly how much the diode resistance and temperature variations account for.
The basic operating principle of temperature sensors is the voltage variation in theMOSFETterminals. As the voltage drops, the temperature also drops according to the voltage drop between the emitter in the MOSFET and the base sensor terminals.
In addition, some devices have a kind of vibrating wire in the sensor structure, which works on the principle of voltage changes followed by temperature changes. Depending on the function, the oscillating wire is modeled in different metals. They have different linear coefficients with temperature changes in their expansion.
They essentially comprise a magnetic wire that has a high tensile strength. Two sections are tuned for different metals, so any change in temperature will directly affect the stress on the wire and therefore its main oscillation frequency.
In modern, high-tech temperature sensors, the base metal is aluminum because aluminum has a higher coefficient of thermal effect than steel. As the temperature signal is converted to frequency, the readings used for other vibration sensors can also be used for temperature control.
Formula for temperature sensors
The temperature-related frequency is also proportional to the voltage “σ” in the wire and can be described as follows:
f = 1/2 * [σg/ρ] / 2L (Hz)
σ = thread tension
ρ = yarn density
L = wire length
g = acceleration due to gravity
Types of temperature sensors
Temperature sensors come in a variety of types, sizes and shapes. However, two main classifications are contact and non-contact sensors.
Contact sensors are a group of sensors that detect the degree of temperature in an object through direct contact with it. They can be used to detect liquids, solids or gases over a wide temperature range. Among them are thermocouples and thermistors. Thermocouples tend to be inexpensive because their basic design and materials are simple. The other common type of them is a thermistor. With thermistors, resistance decreases with increasing temperature.
Non-contact sensors have no contact with the object. Then they measure the temperature using radiation from the heat source. Their most common type is theInfra-red(IV). IRs remotely sense an object's energy and send a signal to electronic circuits, which detect the object's temperature using a specific calibration chart.
Contact and non-contact sensors are further classified into the following common sensors, which are briefly introduced.
A thermostat is a contact sensor that contains a bimetallic section made of two different metals such as aluminum, nickel, tungsten or copper.
The basic principle of thermostats is based on the difference in the coefficient of linear expansion of metals. Therefore, it forces them to create mechanical movement due to increased heat.
Thermally sensitive resistors, or simply thermistors, are special sensors because of the way their physical appearance changes with changes in temperature. Thermistors are made of ceramic substances, such as oxides of certain metals, covered with glass. This will allow them to form easily.
Some thermistors are NTCs and have a negative temperature coefficient. Therefore, some textbooks present them as a separate group of sensors. We will discuss them fully below. But there are many thermistors that have a positive temperature coefficient. They are introduced as PTCs and their resistance increases with increasing temperature.
resistance temperature detectors
RTDs are temperature sensors made of precise conductive metals, such as platinum, covered by a coil. The electrical resistance of an RTD changes due to changes in temperature.
Thermocouple is one of the most popular temperature sensors due to its wide temperature range, accuracy, sensitivity, reliability and simplicity.
A thermocouple usually consists of two sections made of different metals, such as copper. B. Constantan and copper joined by soldering. One of these sections, introduced as the cold junction, has a specific temperature, while the other, introduced as the hot junction, is used for the measurement process.
Negative Temperature Coefficient (NTC) thermistor.
The NTC is a specific type of thermistor that basically responds directly to even small changes in temperature. The negative coefficient means that the thermistor has a high resistance at low temperatures. Therefore, as the temperature increases, the resistance immediately starts to drop.
It can be said that even a small temperature change can be accurately detected by the negative temperature coefficient thermistors according to the large resistance change per degree Celsius in them. However, due to their exponential operating principle, they require linearization. They normally work between -50 and 250 °C.
semiconductor based sensors
A semiconductor based temperature sensor works with two circuits or ICs combined. They contain two similar MOSFETs with high sensitivity. They provide accurate electrical properties, including voltage and current, for measuring temperature changes. They send an approximately linear output, but are less accurate at 1 to 5°C. They also show the slowest time responses between 5 and 60 s among temperature sensors in their temperature range.
Applications for temperature sensors
As mentioned earlier, there are different types of temperature sensors and the most common way to classify their application depends on the type of connection, which includes contact and non-contact sensors. Contact sensors, such as thermistors and thermocouples, are connected directly to the target they want to measure, while non-contact sensors detect the thermal radiation emitted by the heat source. The main application of these temperature sensors is in potentially explosive areas such as nuclear power plants.
Temperature sensors determine the heat of hydration in concrete structures in geothermal energy. They can also be used to control leachate or groundwater migration. One of the most common ways to use them is by curing concrete. It needs to be warm to rise and set properly. Seasonal change causes structural expansion and changes its overall volume.
Applications of the other temperature sensors include:
- Temperature sensors are used to verify model assumptions that will improve the most economical and safest design.
- You can record rock temperatures to identify liquefied gas storage tanks and the process of soil freezing.
- Temperature sensors can also be used in wells and onshore reservoirs and to measure water temperature.
- They are used to interpret temperature in dams to reduce stresses in volumetric variations and to control temperature variations in other installed instruments such as concrete curing.
Why do we use temperature sensors?
When dealing with high heat, hazards or inaccessible measurement points, temperature sensors are used to ensure that a process stays within a specified range, allows safe use of that application or meets a prescribed requirement. A thermometer consists of two main components: (1) a temperature sensor (such as the bulb in a mercury thermometer or the pyrometric sensor in an infrared thermometer) that changes as the temperature changes, and (2) a direction of rotation that changes to a numeric value.
Advantages of temperature sensors
Temperature sensors have some advantages compared to other practical instruments.
- Temperature sensors are inexpensive, accurate and extremely reliable in repeated experiments.
- They are desirable for both recessed and surface mount applications.
- They have a faster response time due to lower thermal mass.
- The vibrating wire type is usually fully interchangeable. This means that one indicator can be used for all sensors. It also has special technology to prove long-term stability, easy and fast issuance.
- They usually have an IP 68 rating due to their weatherproof casing.
- They have some suitable indicators for a direct representation of the temperature. Thus, they can be used for remote sensing and data logging.
- Its temperature sensors have precise linearity and low hysteresis.
- Finally, it must be said that the temperature sensors are absolutely hermetic. They are completely sealed by electron beam welding with a pure vacuum inside.
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