One of the most important physical parameters that are most often studied, observed and corrected, whether it is a person's everyday life, production cycles or laboratory research, is the temperature indicator. Depending on the properties, technical features and the determining mechanism of operation, there is a certain classification of temperature measuring devices into separate types: conventional liquid devices or complex, advanced electronic and laser meters, which are a worthy alternative to the familiar household thermometer. Of course, the place of application of such devices is a fundamental and decisive factor.
Types of instruments for measuring temperature
Devices for carrying out the necessary research, including a device for measuring air temperature, differ in design, as well as in the principle of operation, whichused for measurements. Sufficiently widespread use in contact and remote thermometers, otherwise called pyrometers. In addition, the classification of temperature measuring instruments groups:
- Glass and metal liquid expansion thermometers, working on the property of changing the volume of bodies at different temperatures. Their range of action is from -190 to +500 °С.
- Manometric thermometers that use the relationship between the changing temperature of a gaseous substance placed in a closed volume and pressure. Work at values from -160 to +600 °C.
- Electrical resistance thermometers operate by relying on the ability of conductor materials to change electrical resistance as they heat up and cool down. Effective at temperatures from -200 to +650 °С.
- Thermoelectric converters - thermocouples. Are involved in the range from 0 to +1800 °C. These temperature measuring instruments use the property of two different metals and metal alloys to generate an electromotive force when the temperature of the junction changes.
- Device for determining temperature from +100 to +2500 °С - radiation pyrometer (photoelectric, optical, radiation). The action is due to the fact that the fixed indicator affects the amount of heat radiated by the body. Refers to the non-contact type of measurement. There are stationary and mobile, low- and high-temperature pyrometers.
Thermometers and sensors
According to another classification of heat-fixing devicesthey are divided into thermometers and temperature sensors.
The first are mechanical instruments, including gas-filled gauges, bimetals, glass temperature meters and combination controllers.
Thermal sensors are ultra-precise advanced electronic devices for fixing temperature readings in liquids and solids. These should include resistance thermometers, thermocouples, transducers of sensor readings and signaling devices equipped with relay mechanisms.
The latest thermal detectors are equipped with a USB interface, memory for saving and analyzing studies, and a laser pointer.
Water temperature meters
Each individual device for measuring the temperature of water, cold and hot solutions is characterized by a special principle of operation. There are universal devices that are also suitable for measuring air indicators.
Liquid thermometers
Glass liquid meters are known as the most elementary and accurate thermometers, which are available in straight and angled. And the scope of their application is the analysis of technological equipment, as well as public utilities (measurements in pipelines). The devices are suitable for values from -35 to +600 ° C, and mercury is most often used as a sensitive element, and readings are recorded on a scale.
Depending on the place of application and structural features, medical, technical, electrocontact, liquid, stick and other devices are distinguished.
A specific device for measuring water temperature is selected taking into account the permissible measurement error.
Devices for determining air temperature
The first device for measuring air temperature is a glass thermometer, the active liquid element in which can be mercury, ethyl alcohol, toluene and other substances.
High-precision mercury meters are stick and with an embedded glass scale. They are in demand in laboratory research in various fields of production and medicine. The stick thermometer is equipped with a transparent heat-resistant graduated capillary tube, and the second type of meters is characterized by the fact that the scale divisions are located behind it on a separate plate, and the entire mechanism is protected by a case made of durable glass.
If there are electrical contacts in the device, it is called a thermal alarm, and the sensitive liquid inside the tank and capillary shows the real temperature of the surrounding space.
Features of thermostats and alarms
In addition to the above, there are other devices for measuring temperature. For example, as temperature controllers and signaling devices, rod dilatometers are used with sensitive parts made of dissimilar metal alloys, which elongate when heated by a different amount.
The same principle characterizes another type of thermometer - bimetallic, with an inserted temperature-sensitive spring soldered to a pair of metalplates with different thermal expansion. In the process of heating, the spring bends towards the plate of a lower thermal coefficient, and the required temperature indicator is found by the magnitude of the bend.
Electrothermometer
For remote recording of the thermal parameters of the environment in the range from -15 to +125 ° C, a non-contact temperature measuring device - an aspiration electrothermometer - is excellent. Its device includes a meter and a sensor connected to each other by a cord.
The sensitive element is the thinnest copper wire of the sensor, wound in a spiral on a thread frame.
What are the devices for measuring body temperature
Body temperature is routinely measured with a thermometer. But today there are many other thermometers that differ in appearance and basic principles of operation.
The most common devices to which our thermometer belongs work on the thermal expansion of mercury, kerosene, alcohol and other liquids. They are inexpensive, practical, and reasonably accurate, especially the mercury ones, although the poisonous contents in the fragile glass case carry some risk.
An electronic or digital device for measuring body temperature shows the desired value thanks to the built-in sensor, but its cost is much higher than the price of liquid "colleagues". These thermometers are contact.
Infrared pyrometers do not require direct contact withperson, acting remotely. An ultra-sensitive sensor reads the amount of radiation in 2-15 seconds, displaying the result on the display. These non-contact temperature measuring instruments are perfect for families with small children, sleeping sick situations, etc. In addition, they are applicable to household cooking, and more powerful types are used in electric power, construction sites, metallurgy and other industries.
When a remote pyrometer is needed
There are often situations when it is impossible or simply inconvenient to measure the temperature by contact. It is in such cases that you will need a pyrometer - a device for remote temperature measurement, namely:
- when measuring indicators of highly heated bodies or a toxic environment;
- with difficult access, and with a small error, you can make measurements at a distance of tens of meters;
- when observing mechanisms in motion, and this will take a fraction of a second;
- when diagnosing the electrical safety of a building, when such a meter is convenient for remote scanning in numerous remote areas.
What devices can measure the temperature of the metal
In the metallurgical industry, molten metal alloys require a rugged instrument to measure high temperatures.
The pyrometers already described earlier are considered as such. They fix heat radiation at a distance,characterizing the actual temperature of the metal. In difficult conditions of ultra-high heat indicators, the non-contact method is ideal. The LCD displays the following data:
- actual temperature Fahrenheit and Celsius;
- border temperatures;
- battery charge.
Maximum accuracy of the measured variable can only be achieved when there is no interference between the object and the remote instrument in the form of heat-absorbing vapors or solids. If it is necessary to take measurements of the metal alloy in the transport ladle or during bottling, then the condition should be accepted that the temperature indicator will be less than the actual one and will be determined by calculations.
In order to avoid the inaccuracy of this method, another device is used to measure the temperature of the metal, namely the black body simulator. It is immersed in the melt and is presented in the form of a pipe with a sealed or open end, a hollow cone or a cup made of refractory metal. Either way, the temperature meter must have superior heat resistance, chemical resistance, and excellent thermal conductivity to deliver exceptionally accurate readings.
Measuring engine temperature
Long-term operation, as well as periodic repairs of machines and mechanisms, require the presence of special equipment, which includes a device for measuring engine temperature. These include thermocouples, thermistors, and expansion thermometers.
Thermocouples – very handy and widedevices known among motorists for measuring the temperature of surfaces, windings and the internal cavity of the engine. Using these temperature sensors, you can record data even in hard-to-reach areas of the engine, in grooves and cores. They are two insulated wires of different metal with ends soldered on one side, which are placed at a certain measurement point. The second ends are connected to a millivoltmeter and a thermometer, and the sum of their readings determines the actual temperature value.
Mercury and alcohol expansion thermometers are very convenient for taking the necessary measurements in accessible areas: the winding, the open surface of various parts, as well as the air flow leaving (or entering) from the engine. Thermistors in the form of a copper wire winding are mounted simultaneously in several places of the engine, turning them on in turn, taking fixed readings and determining the average value.
Secondary instruments used in temperature measurements
Let's try to define what an industrial secondary temperature measuring device is. In fact, this automatic device is an important addition to the main meter, capturing and converting recorded indicators into a readable form. It is necessary for the implementation of clear control, signaling and timely temperature regulation in those exceptional cases when deviations from the parameters specified by the operating conditions occur. Stationary and portable secondary electrical appliances are separated separately.
Usually secondary appliancesfor temperature measurement have a durable protective steel case and are equipped with a graduated scale. The values are recorded according to the diagram recorded from thermocouples, strain gauges, resistance thermometers, converters and other devices.
Considering various ways of presenting information, secondary devices should be divided into recording and indicating, single and multi-channel, dual-function and single-range. In the presence of a signaling mechanism, these devices instantly indicate an unacceptable temperature change that is different from the required value. This helps to maintain the logical flow of all reactions and technological processes in which they are involved.
With all the variety of devices that record the temperature indicators of gases, liquids and solids, one should seriously approach the choice of the desired device. The primary factors that must be taken into account are the permissible limits of temperature values, the maximum distance at which measurements can be taken (sighting), accuracy. And, of course, the scope of use of a particular type of thermometer is taken into account.
