Thermometer – Temperature Sensors

Thermometer are the size of objects or tools that can sense the temperature of the environment.some effect on the body of the heat energy is exploited in the construction of the thermometer.

Heat effect of body size changes.
The change of electrical resistance of the body and heat affected.
change the color of objects with a heat effect.

Types of Thermometers

Fluid thermometer in a glass tube

This thermometer is used to measure temperature over a wide area. The structure of this type of thermometer is simple and cost is cheap. Fluid is used colored alcohol or mercury in the glass tube.

Operating principle: Often times they expand more than the increase in temperature liquids. The volume of mercury and mercury thermometer with a temperature rise in the glass tube will expand more than the volume of the glass tube. Glass tube in fluid thermometer in a thin capillary tube at the top of the bottom of the main chamber of the mercury is collected by the small police uniform cylindrical chamber portion has a structure between them.

Metallic Resistance Thermometers

Increasing temperature of most metals, electrical resistance increases. Metals used for accurate temperature measurements because of this feature. α is indicated by any metal resistance temperature coefficient. This value is in the range of temperature is resistance variation corresponding to each degree increase in temperature of the material. R = R0 (1 + α Dt)

Thermocouples (thermocouples)

depending on the rising temperature when heated at the junction between two different metals is formed by an electrical potential difference. other idle two ends of the metal to complete the circuit through a current circuit when the combined amount. This rule is an important feature of the thermocouple.
temperature between two points is a galvanometer placed on this type of circuit will flow occurring due to the difference

The advantages of the use of thermocouples:
It has a very simple structure.
It made very small and robust.
For a long time used.
Damaged parts replaced.
Ideal for remote control status.
Automatically connect to the system.
Short time data of temperature measurement.


Not necessarily in direct contact with the temperature of the thermometer to be measured it is limited to use at high temperatures.
According to a pyrometer for the measurement of radiation emitted from the heat source used in high temperature temperature measuring device.

Temperature sensing is a very safe and comfortable to use because the measurement can be put into proper distance from the heat source. to measure the temperature of molten metal in the blast furnace pyrometers can be used.

Color and temperature
Hot understood through a metal color temperature.
Color Temperature ° C
Matt red 700
Cherry red 900
Orange-red in 1000
yellow 1100
white 1300

Determination of a Thermometer Scale

two fixed points are dimensioned to be of a thermometer tube, one of the lowest of them, the other is at the highest point.

Form of comparison of the temperature scale.

Celsius thermometer

0 C, which is the lowest point of the freezing point of water. which is the boiling point of water 100 ° C is taken as the highest point. If the distance is divided into 100 equal parts.

Kelvin thermometer

We use the SI system is the Kelvin thermometer;
Water freezing point of 273 K, the boiling point of water is 373 K were the distance is divided into 100 equal parts. 1 C = 1 K

Kelvin = Celsius + 273
0 K = -273 C, 0 ° C to +273 ° C =

Fahrenheit thermometer

The freezing point of water at 32 degrees Fahrenheit scalene F, the boiling point between 212 ° F temperature is determined by dividing it into 180 equal parts 1 F for each interval.

C = (5/9) × (F-32) F = (9/5) × C to + 32

Source: Orhan KISA, Mechanical Engineer

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