Such devices today are present in the vast majority of technology. Different types of temperature sensors are designed to measure this indicator for any object or substance. To calculate the value, various characteristics of the target bodies or the medium in which they are located are used.
Functional classification
All temperature sensors are divided into six main types according to the principle of their action:
- pyrometric;
- piezoelectric;
- thermoresistive;
- acoustic;
- thermoelectric;
- semiconductor.
The general principle of operation and the scheme of temperature sensors in each case will be slightly different. However, for all versions, some of the same features can be distinguished. In addition, in a particular situation, it is appropriate to use certain types of temperature sensors.
Pyrometers or thermal imagers
Otherwise, they can be called contactless. The working circuit of this type of temperature sensor is that they read heat from the heated bodies that they are pointing at. A positive point for this variety is the lack of need for direct contact and proximity to the measurement medium. Thus, experts can easily set the temperature indicators of very hot objects outside the radius of a dangerous proximity with them.
Pyrometers, in turn, are divided into several varieties, among which interferometric and fluorescent, as well as sensors working on the principle of changing the color of the solution depending on what temperature was measured, can be noted.
Piezoelectric sensors
In this case, the underlying work scheme is just one. Such devices operate through a quartz piezoresonator. The principle of action and the temperature sensor circuit are as follows. The piezoelectric effect, which includes the resizing of the used piezoelectric element, is exposed to a certain effect of electric current.
The essence of the work is quite simple. Due to the alternating supply of electric current with different phases, but with the same frequency, the oscillations of the piezoelectric generator occur, the frequency of which depends on the specific measured temperature of the body or medium. As a result, the information received is interpreted into specific values in degrees Celsius or Fahrenheit. This type is distinguished by one of the highest measurement accuracy. In addition, the piezoelectric option is used in those situations where the durability of the device is required, for example, in water temperature sensors.
Thermoelectric or thermocouple
A fairly common method of measurement. The basic principle of operation is the occurrence of electric current in closed circuits of conductors or semiconductors. At the same time, the places of adhesion must necessarily differ in temperature indicators. One end is placed in the environment where you want to measure, and the second serves to take readings. That is why this option is considered a remote temperature sensor.
Of course, there were some shortcomings. The most significant of them can be called a very large error in the measurements. For this reason, this method is rarely used in many technological industries, where such a spread of values is simply unacceptable. An example is the sensor for measuring the temperature of solids "TSP Metran-246". It is actively used by metallurgical companies in production to control this parameter in bearings. The device is equipped with an analog output signal for reading, and the range of acceptable measurements is in the range from -50 to +120 degrees Celsius.
Thermoresistive sensors
The principle of action can already be judged by the name of this type. The operation of such a temperature sensor according to the scheme lends itself to the following description: the resistance of the conductor is measured. Reliability of the design is combined with a very high accuracy of the information received. Also, these devices have a fairly high sensitivity, which allows to reduce the step of measuring values, and the simplicity of the reading elements makes them easy to operate.
For example, we can mention the sensor 700-101BAA-B00, having an initial resistance of 100 ohms. Its measuring range is from -70 to 500 degrees Celsius. The design is assembled from nickel contacts and platinum plates. This type was most widely used in industrial devices and a wide variety of electronics.
Acoustic sensors
Extremely simple instruments that measure the speed of sound in various environments. It is known that this parameter is largely dependent on temperature. At the same time, other parameters of the measured medium should be taken into account. One of the use cases is water temperature measurement. The sensor provides data on the basis of which it is possible to make a calculation, for which you also need to know the initial information about the medium being measured.
The advantages of this method are the possibility of using it in closed containers. It is usually used where there is no direct access to the measured medium. The main consumer areas of this method for quite natural reasons are medicine and industry.
Semiconductor sensors
The principle of operation of such devices is to change the pn characteristics and their transition under the influence of temperature. The accuracy of the measurement is very high. This is ensured by the constant dependence of the voltage on the transistor on the current temperature. In addition, the device is quite cheap and easy to manufacture.
For an example of such a temperature sensor, the LM75A can serve as well as possible. The measurement range is from -55 to +150 degrees Celsius, and the error is no more than two degrees. It also has a fairly small step of the order of 0.125 degrees Celsius. The supply voltage varies from 2.5 to 5.5 V, while the signal conversion time does not exceed one tenth of a second.