Physics Curiosities

Bulb Thermometer

bulb thermometer is the type of thermometer that is generally used to measure the temperature of a substance or object, and usually contains mercury or colored alcohol in the bulb (reservoir) at the end of the thermometer. When it comes to measuring the temperature of the environment, the mercury thermometer has greater precision, since the bright white color of the metal reflects radiation and therefore is not affected by it, an issue that always affects measurements with thermometers. of colored alcohol and can be very important when there is a strong heat source, such as the sun. In recent times, they are gradually being replaced by thermometers that operate electronically.

It is commonly referred to as a mercury or alcohol thermometer, without further reference to the bulb. The term “bulb thermometer” is not often used in isolation, but is common to describe wet bulb thermometers or dry bulb temperature .

It should not be confused with the globe thermometer , since in the latter the heat exchange with the environment is effected by radiation, while in the bulb thermometer, it is effected by convection (in gases or liquids) or conduction (in liquids or solids), and measure very different parameters of the environment or place where they are located.

What is the bulb thermometer and what is it for? 

With the bulb thermometer, the temperature of an object or substance is measured , which usually has mercury or colored alcohol in its bulb or reservoir that is located at one of its ends. It should be noted that, when measuring the ambient temperature, the mercury thermometer is usually more accurate due to its bright white color of the metal, with which radiation is reflected and is affected by this condition. bulb thermometer definition

The bulb thermometer is used in turn to measure the influence of humidity on the wind chill. If used with an ordinary thermometer you get a psychrometer , which is useful for measuring relative humidity, vapor pressure, and dew point.

This operation makes that depending on the type of thermometer, it is better to measure one procedure or another. Among these types of thermometers we find the bulb and capillary thermometer, one widely used more than anything in meteorology. bulb thermometer definition

Operation of a bulb and capillary thermometer

The bulb thermometer varies its operation very little depending on the state of the fluid whose temperature is to be measured.

The thermometer bulb type essentially consist of a bulb connected by a capillary to a spiral. When the temperature of the bulb changes, the gas or liquid in the bulb expands and the coil tends to unwind by moving the needle on the scale to indicate the rise in temperature in the bulb. bulb thermometer definition

Types of bulb thermometer

There are four kinds of these types of thermometers:

  • Class I : Liquid actuated thermometers.
  • Class II : Steam actuated thermometers.
  • Class III : Gas actuated thermometers.
  • Class IV : Mercury actuated thermometers.

Bulb Thermometer Parts

  • Mechanical amplifier system
  • Indicator or signal extract
  • Scale or conversion to electrical signal
  • Bourdon tube
  • Filling tube
  • Capillary
  • The bulb
  • The Mercury
  • A needle
  • Bimetallic propeller
  • Temperature scale bulb thermometer definition

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