Hi friends, welcome to the new post. Here, we will learn What it is. – Definition, Working, Construction, Spiral & Helix Strip Thermometer. The bimetallic thermometer is a temperature-measuring instrument that operates at the differential thermal expansion principle. It is used in industrial and domestic uses due to its reliable, simple, and cost-effective structure. Let’s discuss its definition, working principle, construction, and variations like spiral and helix strip thermometers. So What is a Bimetallic Thermometer?
What is a Bimetallic Thermometer? Definition:
A bimetallic thermometer is a temperature-measuring device that comes with two different metal strips connected to each other. These strips of metals come with different coefficients of thermal expansion, which means expanding or contracting at differnt rates when temperature changes. This differential expansion causes the instrument to end or coil, and this motion is used for temperature measuring.
Bimetallic Thermometer Working Principle
The working of this device is based on when dissimilar metals are connected, they expand or contract when face temperature changes. Metal strips have a higher coefficient of thermal expansion than others. If temperature changes, one strip expands or contracts higher than another, causing the strips to bend.
Bimetallic Thermometer Construction
A typical bimetallic thermometer has these parts that are
- Bimetallic Strip: It is the essential component of the thermometer. That’s two strips made of steel and copper and connected
- Pointer: it is connected with the free end of the bimetallic strip pointer moves as strips bonds or coils
- Dial: The thermometer’s faceplate or dial displays temperature values. The points move over markings to indicate temperature.
- Casing: it protects the internal component of the meter and provdies 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: this mete strip is coiled in a spiral shape. When temperature changes, the spiral expands or contracts, making connected points move over the dial to show temperature.
- Helix Strip Thermometer: In place of a spiral shape, the bimetallic strip is wounded in a helical or coiled shape. Like the spiral strip thermometer, temperature changes cause the helix to expand or contract, resulting in pointer movement on the dial.
Bimetallic Stemmed Thermometer
A bimetallic stemmed thermometer has two different metals and different coefficients of thermal expansion for temperature measurements. The two metals are connected to make a strip and then bend in the coil. When temperature changes, two metals expand at different rates, resulting in coil twisting. This twist is then converted into a temperature reading through a pointer and scale. This meter is used to measure liquid, gas, and cold temperatures. Also used in scientific uses
Characteristics of bimetallic stemmed thermometers:
- Low cost, easy to use
- durable and handle harsh conditions
- Accurate meter
- 80 to 500 degrees Celsius. temperate ranges
Bimetallic stemmed thermometer limitations:
- Slow response
- Damaged if not handled accurately
- It is not as accurate as other meters, such as digital thermometers
The bimetallic thermometer is used for
Bimetallic thermometers are used in different applications, which are
- field testing devices used to measure low and medium temperatures. It can directly measure the temperature of liquid, steam, and gas in the range from-80℃~500℃ in various production processes.
- An electrical contact bimetal meter is employed for temperature control and alarm at the production loctaion
- It measures temperature from -80℃~500℃
- An explosion-proof bimetal meter can directly measure the existence of explosives like hydrocarbons.
Bimetallic Thermometer Advantages and Disadvantages
|Simple and easy to use
|Not as accurate as other types of thermometers
|Durable and long-lasting
|It can be damaged if not properly used
|Can be used in a variety of applications
|Calibration may be required over time
|Nearly linear response to temperature change
|Suitable for wide temperature ranges
Bimetallic thermometer calibration
- First of all, take a glass and fill it with ice water.
- Then, fill the glass with cold water
- Put meter stem in ice water
- Wait till the dial on the meter stops motion
- Set the thermometer so it can read 32°F (0°C).
Bimetallic thermometer temperature range:
The temperature range of this meter is based on the type of meter and material used. But mostly bimetallic meters have a temperature range of -70 to 600 degrees Celsius (-94 to 1,112 degrees Fahrenheit). Some thermometers come with 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:
- Type of metals used in the bimetallic strip.
- length of the strip.
- Shape of the strip.
- Calibration of the thermometer.
Factors that affect the Response of the Bimetallic Thermometer’s Temperature Sensing Element:
- Different thermal expansion coefficients for metals used in the strip must exist. So they expand at different rates when get heated. Metals with high coefficient of thermal expansion are used in thermometers that measure high temperatures.
- The thick bimetallic strip responses have slow temperature changes. As it takes more heat to bend
- The long strip is more sensitive to temperature change. The longer strip bends more when heated
- The shape of strips also affects the response to changes in temperature. Strips found in spiral shapes more sensitive to changes in temperature than bimetallic strips is in a straight line.
- The thermal conductivity of the bimetal strip is measuring how well it works. The larger thermal conductivity fast strip will affected with temperate change.
- Strip surface areas are surfaces exposed to heat. The large area exposed faster strip will respond to temperature.
How to select a Bimetallic Thermometer?
- A bimetallic meter should have a temperature range of about 1000 centigrade; you will need a different meter than what is needed to measure up to 100 degrees Celsius.
- it must be accurate to use. Such as if needed to measure temperature with an accuracy of ±1 degrees Celsius, then a differnt meter is used than if you only need an accuracy of ±5 degrees Celsius.
- Made with application-based materials such as measuring the temperature of corrosive liquid needs a meter that makes material resistant to corrosion
- It should be made for durable and reliable operation. So it can operate in harsh conditions
- Its size must be enough so it can be used in confined places
- the process must be reasonable
What is a bimetallic thermometer?
The bimetal thermoeter uses two metal spring for temperature measuring component. This method uses coil spring created with two differnt metals that connectd. Meals can becopper, steel, or brass.
What is the working principle of a bimetallic thermograph?
The working principle of bimetal thermometer is that two metals have differntexpansion coefficient. If temperarus cahgnes lenght of two metals also cahgnes. When two metals connected shape will bent
What are the advantages and disadvantages of bimetallic thermometers?
cheap requires frequent calibration to maintain accuracy durable fairly slow response can be used for thermograph
What are the parts of a bimetallic thermometer?
its main parts are a stem, a bimetallic strip, dial with pointer, and instrument connection. Dia of stem is 6-9.6mm diameter and a 63-1000mm length and bimetal helix facing away from the case.
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?
its wokng based on thermal expansion of liquids. Heat sensitive liquids are used in meter such as mercury
What is the range of a bimetallic thermometer in Celsius?
The bimetallic thermometer working rane is up to 300°C to within ±1% of the scale range
What are the uses of bimetallic thermometers?
Bimetallic thermometers used in indsutries. its nrmal range is from 40 to 800 (°F). So used for two-position temperature control in residential and industrial thermostats
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, 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 allowable errors of the thermometer are (+1.5) and (+1.0) in range
How accurate is a bimetallic thermometer?
it can be accurate to about 1% full span In general, bimetallic thermometers are not as correct as some other types of thermometers, like digital thermometers.
What is the ice point method?
It is comon technique used to calibrate dial and digital thermometer
How do you zero a thermometer?
Place meter probe in ice water. Esnrue the sensing area is in water. Wait 30 seconds or till reading stays steady. Sete meter so it can read 32˚F (0˚C).