Temperature measurement and its methods:
Temperature indicates the amount of molecular activity of a substance. Being hot and cold is a mental description of the amount of molecular activity. Temperature sensors use standard and universal scales to express the amount of temperature. Since these scales are based on fixed points in nature (such as the freezing point of water), therefore Sensors, Provide a temperature description that is both quantitative and objective.
Temperature measurement scales are:
- Celsius (Celsius);
- Absolute (Kelvin);
Types of temperature sensors:
There are two types of temperature sensors in industrial applications:
The contact type is the most common and most used in measuring temperature. Three main methods of measuring contact temperature
- Temperature resistant sensors (RTDs);
The common building characteristics in the contact type are as follows:
- Sensor element;
- Sensor body;
- Interface wires;
- Screw adapter
Temperature measurement with non-contact instruments is more complex and can be done using the following technologies:
Types of thermometers:
1- Ordinary thermometer (Thermometer standard)
This thermometer is a very narrow glass tube with a chamber at the end filled with mercury or alcohol. There is a complete vacuum inside the thermometer tube. Heating and cooling the tank causes the liquid inside the tank to heat up and cool down, and subsequently causes the liquid to go up and down inside the glass tank, by observing the liquid level inside the thermometer tube and reading the number written on the glass body. It is determined at that moment.
In addition to the normal air temperature, it is often necessary to measure and stabilize the maximum temperature that has occurred during a certain period, such as a day and night. For this purpose, the maximum thermometer is used. This type of thermometer with a slight difference is almost similar to conventional thermometers in that its capillary tube is very narrow at the point where it leads to the tank. When the temperature rises, the mercury in the tank expands and the resulting force can cause
The mercury is expelled from the narrow tube above the tank to the top of the tube. Thus, the height of the mercury inside the tank increases and the liquid inside the tank contracts as the temperature decreases, but the narrowness of the tube prevents the liquid from returning to the tank and the liquid level. Inside the tube remains the place where the highest temperature occurred before, so the upper level of mercury indicates the maximum temperature occurred.
3- Minimum Thermometer
Minimum thermometers are used to stabilize the lowest temperature that has occurred in a given period. Minimum thermometers are similar to conventional thermometers except that the liquid inside Reservoir This type of thermometer uses thinner liquids such as alcohol instead of mercury. In addition, a glass needle with round ends is left inside the capillary tube, which is used as an indicator. When the air temperature decreases, the upper surface of the alcohol decreases with the contraction of the liquid inside the capillary tube by applying a surface tension force. The needle index also moves down the tank. As the temperature rises, the alcohol passes through the needle again inside the capillary tube and ascends upwards, but the needle remains at the lowest point previously lowered by surface tension. .
Thus, the upper part of the glass index shows the lowest temperature that has occurred, while the end of the alcohol surface at the top of the tube indicates the instantaneous temperature of the air.
4 – Min-Max Thermometer
This thermometer is a combination of two minimum and maximum thermometers. This thermometer is made of a U-shaped glass tube whose two ends are closed. The lower part of the U-shaped tube with Mercury Filled. In addition to mercury, the upper part of the left tube is completely filled with alcohol, but half of the volume of the right tube, the end of which is an expanded tank, is filled with alcohol, and the other half is filled with a type of gas. At the highest level of mercury and in the alcohol in both columns, there are colored glass indicators with a needle embedded in the middle, which rises and falls due to heating and cooling, followed by expansion and contraction of the mercury surface. The highest level of mercury in the left branch is the minimum temperature and the highest level of mercury in the right branch is the maximum temperature.
5 – Thermograph
The protractor is a purely mechanical device made of a metal element whose curvature changes with temperature. One side of the temperature-sensitive metal element, which has a curvature, is attached to a long, movable lever arm that may Is to indicate the temperature directly on a simple calibrated scale or to attach the end of an arm to a stylus. As the air temperature changes, the curvature of the metal changes, and this causes the pen to deviate at the end of the arm, depending on how the temperature changes.Mechanical Graph up and down on the paper and record the temperatures.
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