Hey Friends! Welcome to another article about Instrumentation Devices or Sensors!
Today in this blog, We are going to see the different types of thermometers used in the industry and How to choose the best that is suited to your application?
So, Let’s not waste more time and take a deep dive into this.
Table of Contents
Different Types of Thermometer
A thermometer is used to measure the temperature of an item. This device is often called industrial thermometers and can be classified according to the substance used to create it:
1) Expansion of Solid
- Bimetal or Bi-Metallic Thermometers
2) Expansion of Liquid
- Liquid in Glass Thermometer
- Liquid in Metal Thermometer
3) Expansion of Gas
- Gas Thermometer
Bimetal or bi-metallic thermometers:
The bimetallic thermometer uses a bimetallic strip as the temperature sensing element. This strip is made of two different metals with different temperature co-efficient are welded together. The metals are normally copper, steel, and brass.
The bimetallic strip is working on the principle of thermal expansion property of the metal with temperature. Every metal has a different temperature coefficient.
The temperature coefficient shows the relation between the change in the physical dimension of metal and the temperature that causes it. The expansion or contraction of metal depends on the temperature coefficient.
The strip is in the shape of a coil normally. Whenever this strip is heated up, the two metals start expanding their length based on their thermal expansion rate. This rate is different for both metals, thus the strip is forced to bend towards the side of low thermal co-efficient metal.
This movement of the strip is used to deflect a pointer over a calibrated scale, which is showing the temperature to the user.
Advantages
- Low Cost
- Durability
- Easy Installation
- Accuracy over a wide range of temperatures.
Disadvantages
- Possibility of calibration change because of use or environment.
- Bi-metallic thermometers are not as accurate as glass stem thermometers.
Liquid-filled thermometers:
The liquid or gas-filled thermometers use a liquid or gas as the temperature sensing element. The liquid or gas expands as the temperature rises in the tube and indicates the temperature.
When choosing a liquid of gas-filled thermometer, there are several parameters to consider, including:
- Liquid in glass
- Liquid in metal
Liquid in glass
A liquid in a glass thermometer is a small glass capillary tube with a liquid-filled bulb at the lower end. Typically liquid used in this thermometer is mercury or alcohol.
As the temperature of the liquid increases, it expands and rises into the capillary tube. The level of the liquid indicates the temperature which is marked outside the glass.
Liquid in Metal
This type of thermometer uses liquid as a thermometric substance to measure the temperature. The basic design of this type of thermometer is a liquid is filled in the metal tube, which is either a c shape or coil shape.
As the temperature of the liquid increases, it tries to expand and pressure will increase in that metal tube where the volume is constant. This pressure will be converted into temperature at a calibrated scale.
Gas Thermometer
A certain type of gas is filled as a substance in the metal tube, which is the shape of C or Coil. The thermometric substance used normally is nitrogen, helium, argon as a gas in gas thermometer.
How to choose the thermometer for a specific application:
There are several parameters or specifications you should consider while choosing the thermometer for industrial applications:
- Display Characteristics
- Dimensions
- Stem Material
- Stem Adjustments
- Operating Environments
Display Characteristics ⇒
Thermometers display options include:
- Display Range and Scale Divison
- Celsius or Fahrenheit or Both Fahrenheit and Celsius Display
- Maximum and Minimum Readings
- Glass or Plastic as a Viewing Window
The display range is the minimum and maximum values of the temperature that is being displayed. Scale division is the smallest division of degrees, sometimes referred to as resolution.
Thermometer Dimensions ⇒
While buying a thermometer, buyers may need to clarify some parameters like,
- Stem extension — The stem is a highly thermal conductor that effectively extends the thermometer bulb into the environment.
- Scale length is the length of the thermometer’s readable face. It is the overall length of the measuring portion of the thermometer
- The insertion portion is included in the total stem length. The insertion portion is the part of the stem that gets immersed into the environment.
- Mounting options can be varied and include duct mounts, tanks, or process lines mounts and handheld.
Stem Material ⇒
The most common material used as stem materials is Brass, Aluminium, and Stainless Steel.
Stem Adjustment ⇒
The industrial thermometers may be installed at fixed or sometimes variable places. So it is necessary sometimes that we should buy a thermometer with an adjustable stem angle. However, most of the industrial thermometer is available with a permanent stem angle.
An adjustable stem angle provides flexibility to use as a user can adjust it as per requirement.
A thermometer with a permanent stem angle is best suitable for application in which wall mountings are needed.
Operating Environment ⇒
The thermometer can be installed in industrial application where some environmental factors user should consider like,
- A thermometer is used to operate in some specific temperature range, which is called as Operating temperature range.
- The thermometer is designed to withstand some shock and vibration while it is in use. The more level of vibration and shock may affect the accuracy of the thermometer.
- The thermometer used in the outdoor area may affect some wheater conditions like water, humidity, wind, and sunlight.
- The thermometer must be tightly sealed, which resists washdown and wet environment applications.
This is the basic information about the different types of thermometers used in the industry. I hope you like this article, please comment below for more information and give me feedback about my articles.
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