What is Bimetallic Thermometer? – Definition, Working, Construction, Spiral & Helix Strip Thermometer

Hi friends welcome to the new post. Here we will learn What is Bimetallic Thermometer. – Definition, Working, Construction, Spiral & Helix Strip Thermometer.  A bimetallic thermometer is a temperature-measuring device that works on the differential thermal expansion principle. It is mostly used in different industrial and domestic applications due to its reliability, simplicity, and cost-effectiveness. Let’s discuss its definition, working principle, construction, and variations like spiral and helix strip thermometers. So What is a Bimetallic Thermometer? 

What is Bimetallic Thermometer Definition:

A bimetallic thermometer is a temperature-measuring instrument that comes with 2 different metal strips bonded with each other. These metallic strips have different coefficients of thermal expansion which means they expand or contract at different rates when temperature varies. This differential expansion results in instruments to the end or coil and this movement is used for indication of temperature

Bimetallic Thermometer Working Principle

The operation of a bimetallic thermometer is based on the principle that when dissimilar metals are bonded together, they will expand or contract differently when exposed to temperature changes. The metal strips normally come with high coefficient of thermal expansion than other. When temperature varies one strip expands or contracts more than another resulting in composite strip bending or coil

Bimetallic Thermometer Construction

A typical bimetallic thermometer has these parts that are

1. Bimetallic Strip: it is the main component of the thermometer. It has two metal strips, normally steel and copper, that are bonded together.
2. Pointer: Connected to the free end of the bimetallic strip, the pointer moves as the strip bends or coils.
3. Dial: The thermometer’s faceplate or dial displays temperature markings. The pointer moves about these markings to show the temperature.
4. Casing: The casing or housing protects the inner components of the thermometer and offers a clear viewing window for the dial.

Spiral and Helix Strip Thermometer:

Spiral and helix strip thermometers are certain types of bimetallic thermometers:

• Spiral Strip Thermometer: In this design, the bimetallic strip is coiled into a spiral shape. As temperature varies, the spiral expands or contracts, making the connected pointer move around the dial to indicate the temperature.
• Helix Strip Thermometer: In place of a spiral shape, the bimetallic strip is wound into a helical or coiled shape. Like the spiral strip thermometer, varies in temperature cause the helix to expand or contract, resulting in pointer movement on the dial.

Bimetallic Stemmed Thermometer

A bimetallic stemmed thermometer is a thermometer that comes with 2 different metals with different coefficients of thermal expansion for temperature measurements. The 2 metals are bonded together to make a strip, which is then bent into a coil. When the temperature varies, the 2 metals expand at different rates, causing the coil to twist. This twisting motion is then transformed into a temperature reading by a pointer and scale.

Bimetallic stemmed thermometers are used in homes and businesses to measure the temperature of liquids, gases, and solids. They are also used in scientific and industrial applications.

Characteristics of bimetallic stemmed thermometers:

• They are low-cost and easy to use.
• They have a different range of measurement capabilities, from -80 to 500 degrees Celsius.
• They are correct and reliable.
• They are durable and can withstand harsh environments.

 bimetallic stemmed thermometer limitations:

• it can slow to respond to variation temperature.
• it can be damaged if they are not handled properly.
• They are not as correct as some other types of thermometers, such as digital thermometers.

Overall, bimetallic stemmed thermometers are versatile and reliable for measuring temperature. They are a find option for many applications, like business homes, , and scientific use.

Here are some more details about bimetallic stemmed thermometers:

• The 2 metals that are normally used are brass and steel. Brass has a higher coefficient of thermal expansion than steel, so when the temperature rises, the brass side of the strip expands more than the steel side. it resulted in the coil twisting.
• The pointer is connected to the coil, and it moves along the scale as the coil twists. The scale is calibrated so that the pointer points to the temperature reading.
• Bimetallic stemmed thermometers are made of glass or plastic. The glass or plastic protects the internal components of the thermometer from damage.
• These thermometers can be used to measure temperatures in different environments, including indoors, outdoors, and in industrial settings.

Bimetallic thermometer is used for

Bimetallic thermometers are used in different applications, which are

• Thermostats: They are commonly used in thermostats to control the temperature of a room or appliance. When the temperature gets a certain point, the bimetallic strip bends and on the switch, turning the appliance on or off.
• Ovens: These thermometers are used in ovens to measure the oven temperature. The thermometer is normally located in the oven door, and the temperature is shown on a dial or digital display.
• Air conditioners: They are also used in air conditioners to measure the temperature of the air in the unit. The thermometer is normally located in the evaporator coil, and the temperature is used to control the operation of the compressor.
• Industrial processes: Bimetallic thermometers are used in different industrial processes to measure the temperature of liquids, gases, and solids. They are also used to find the temperature of ovens, furnaces, and other heat-treating equipment.

Advantages and disadvantages of bimetallic thermometers

• Simple and easy to use: They are very simple to use. They do not need any power source, and they can be read directly without any calibration. It makes them a good option for applications where ease of use is important.
• Durable and long-lasting: They are made of durable materials, and they can handle a lot of wear and tear. They are also inexpensive, making them a cost-effective option for many applications.
• Can be used in a variety of applications: It can be used in a wide variety of applications, like thermostats, ovens, air conditioners, and industrial processes. They are different options for measuring temperature in different environments.
• Nearly linear response to temperature change: The bimetallic strip in a bimetallic thermometer bends in linearly in response to variations in temperature. So it is best for applications where accurate temperature measurement is significant
• Suitable for wide temperature ranges: Bimetallic thermometers can be made to work over a wide range of temperatures, from very cold to very hot. .

 Bimetallic thermometers disadvantages:

• Not as accurate as other types of thermometers: Bimetallic thermometers are not as correct as other types of thermometers, like digital thermometers or thermocouples. Since the bimetallic strip can be affected by humidity and vibration.
• Can be damaged if not properly used: These thermometers can be damaged if they are not accurately used. For instance, they should not be exposed to excessive heat or humidity.
• Calibration may be required over time: The bimetallic strip in a bimetallic thermometer can lose its accuracy over time. This is why it is good to calibrate bimetallic thermometers regularly.

Types of bimetallic thermometer

There are 2 main types of bimetallic thermometers: helix strip and spiral strip.

• Helix strip bimetallic thermometer is created with a bimetallic strip that is wound in a helix shape. This thermometer is more compact and can handle higher temperatures than the spiral strip type. It is mostly used in industrial applications like refineries and oil burners.
• Spiral strip bimetallic thermometer is created of a bimetallic strip that is wound in a spiral shape. it is more sensitive to temperature changes than the helix strip type and is often used in thermostats..

Bimetallic thermometer calibration

Bimetallic thermometers can be calibrated using 2 techniques methods: the ice point method and the boiling point method.

Ice point method: This method is the best method to calibrate a bimetallic thermometer. To calibrate using this method, use these

1. Fill a glass with ice water.
2. Insert the thermometer into the ice water so that the sensing element is fully submerged.
3. Wait for the thermometer reading to stabilize.
4. Use a calibration screwdriver to adjust the thermometer reading till it reads 0 degrees Celsius (32 degrees Fahrenheit).

Boiling point method: This process is not as correct as the ice point method, but it is easier to perform. To calibrate using this method,

1. Bring a pot of water to a boil.
2. Insert the thermometer into the boiling water so that the sensing element is fully submerged.
3. Wait for the thermometer reading to stabilize.
4. Use a calibration screwdriver to vary the thermometer reading until it reads 100 degrees Celsius (212 degrees Fahrenheit).

Bimetallic thermometer temperature range:

The temperature range of a bimetallic thermometer can change based on the type of thermometer and the materials used. But, most bimetallic thermometers have a temperature range of -70 to 600 degrees Celsius (-94 to 1,112 degrees Fahrenheit). Some bimetallic thermometers can have a temperature range of up to 1,000 degrees Celsius (1,832 degrees Fahrenheit).

 the factors that can affect the temperature range of a bimetallic thermometer:

• The type of metals used in the bimetallic strip.
• The thickness
• The length of  strip.
• The shape of  strip.
• The calibration of the thermometer.

Factors that affects the Response of the Bimetallic Thermometer’s Temperature Sensing Element:

• The materials used in the bimetallic strip: The metals used in the bimetallic strip must have different coefficients of thermal expansion. So that they should expand at different rates when they are heated. The metals with the highest coefficients of thermal expansion are used in bimetallic thermometers that are needed to measure high temperatures.
• The thickness of the bimetallic strip: The thicker the bimetallic strip, its response will be slow changes in temperature. Since it takes more heat to cause a thick bimetallic strip to bend.
• The length of the bimetallic strip: The longer the bimetallic strip, the more sensitive it will be to vary in temperature. Since longer bimetallic strips will bend more when it is heated.
• The shape of the bimetallic strip: The shape of the bimetallic strip can also affect its response to variations in temperature. For instance, a bimetallic strip that is wound in a spiral shape will be more sensitive to vary in temperature than a bimetallic strip that is in a straight line.
• The thermal conductivity of the bimetallic strip: The thermal conductivity of the bimetallic strip is a measurement of how well it conducts heat. The larger the thermal conductivity, the faster the bimetallic strip will affected by varying temperatures.
• The surface area of the bimetallic strip: The surface area of the bimetallic strip is the amount of surface that is exposed to the heat. The larger the surface area, the faster the bimetallic strip will respond to changes in temperature.

How to select a Bimetallic Thermometer?

• Temperature range: The bimetallic thermometer must have a temperature range that is good for the application. For instance, if you need to measure temperatures up to 1,000 degrees Celsius, you will need a different thermometer than if we need to measure temperatures up to 100 degrees Celsius.
• Accuracy: It should be correct enough for the application. For instance, if you need to measure temperatures with an accuracy of ±1 degrees Celsius, then a different thermometer be used than if you only need an accuracy of ±5 degrees Celsius.
• Materials: it must be made of materials that are supported by the application. For instance, if you are measuring the temperature of a corrosive liquid, you will need a thermometer that creates a material that is resistant to corrosion.
• Construction: They should be constructed in a process that is durable and reliable. For instance, if you are using the thermometer in harsh conditions, you will need a thermometer that is made of durable materials and is well-sealed.
• Size and weight: The size and weight of the bimetallic thermometer must be good for the application. For instance, if you need to use the thermometer in a confined space, you will need a small and low-weight thermometer.
• Cost: The price of the bimetallic thermometer should be reasonable for the application.

Faqs

• What is a bimetallic thermometer?

A bimetallic thermometer is a temperature measurement device that uses a bimetallic strip to transfomr the temperature into mechanical displacement.

• What is the working principle of a bimetallic thermograph?

The working principle of a bimetallic thermometer is depend on the different thermal expansion coefficients of the 2 metals used to make the bimetallic strip. When the temperature varies, the 2 metals expand at different rates, resulting the bimetallic strip to bend. The amount of bending is proportional to the temperature change, and this can be used to measure the temperature.

• What are the advantages and disadvantages of bimetallic thermometers?

The benfits of bimetallic thermometers are their simplicity, durability, and low cost. They are also relatively insensitive to shock and vibration. However, they are not as correct as some other types of thermometers, and they can be affected by the surrounding conditons

• What are the parts of a bimetallic thermometer?

The main parts of a bimetallic thermometer are the bimetallic strip, the pointer, the scale, and the case. The bimetallic strip is considered as the heart of the thermometer and is responsible for converting the temperature variation into mechanical displacement. The pointer is connected to the bimetallic strip and moves along the scale as the strip bends. The scale is calibrated to show the temperature. The case protects the thermometer from the surrounding affects

• What are the examples of bimetallic?

Some examples of bimetallic devices ares thermostats, oven thermometers, and car temperature gauges.

• What is the principle of thermometer working?

The principle of thermometer working is based on the expansion and contraction of liquids and gases with temperature change. When the temperature of a liquid or gas increases, it expands and the level of the liquid or gas in the thermometer increases. When the temperature reduces, the liquid or gas contracts and the level of the liquid or gas in the thermometer falls.

• What is the range of a bimetallic thermometer in Celsius?

The range of a bimetallic thermometer can chagnes based on the type of thermometer. However, most bimetallic thermometers have a range of -20 to 120 degrees Celsius.

• What are the uses of bimetallic thermometers?

Bimetallic thermometers are used in different applications, including:

* Thermostats * Oven thermometers * Car temperature gauges * Industrial process control * Medical applications * Scientific research

• Is a bimetallic thermometer a controller?

No, a bimetallic thermometer is not a controller. A controller is a instruemtns that uses a feedback loop to maintain a desired temperature. A bimetallic thermometer is just a device that measures temperature.

• How do you calibrate a bimetallic thermometer?

To calibrate a bimetallic thermometer, you needed to compare it to a reference thermometer that is consider to accurate. it can be done by placing both thermometers in a bath of water that is at a known temperature. The 2 thermometers must read the same temperature. If they do not, you can adjust the bimetallic thermometer until it reads the accurate temperature.

• What is the error of bimetallic thermometer?

The error of a bimetallic thermometer is the difference among the actual temperature and the temperature that the thermometer reads. The error of a bimetallic thermometer can changes based on the type of thermometer and the temperature range.

• How accurate is a bimetallic thermometer?

The accuracy of a bimetallic thermometer based on the type of thermometer and the temperature range. In general, bimetallic thermometers are not as correct as some other types of thermometers, like digital thermometers. However, they are still correct enough for many applications.

• What is ice point method?

The ice point method is a technique of calibrating a thermometer. In this process, the thermometer is placed in a bath of melting ice and the temperature is recorded. This is the standard reference temperature for thermometers.

• How do you zero a thermometer?

To zero a thermometer, we need to adjust the thermometer so that it reads zero when it is placed in a bath of melting ice. It be done by turning the adjusting screw on the thermometer until the pointer reads zero.