Application of bimetallic strips and thermometers
- The bimetallic strip is used in control devices.
- The spiral strip is used in air conditioning thermostats.
- The helix strip is used for process application such as refineries, oil burners, tyre vulcanisers etc.,
Why are bimetallic strips used in thermostats?
Bimetallic strips are used as switches in thermostats. bi-metalic strips bend when heated Two metals making up the strip have different rates of expansion, so as heat is applied and the metals expand, one metal will expand faster than the other, causing that side to grow longer faster than the other side.
What is the use of the bimetallic strip in a thermostat?
Bimetallic in both refrigerator and electric iron is used as a thermostat, a device to sense the temperature of the surrounding and break the current circuit, if it goes beyond a set temperature point.
What is a bimetal thermometer?
Definition: A Bimetallic thermometer is a device that uses two different metal strips to convert temperature displacement into mechanical.
Which thermometer is used to measure atmospheric temperature?
Temperature refers to how hot or cold the atmosphere is as measured by a thermometer (in Celsius (C) or Fahrenheit (F), or Kelvin (K) ). A traditional thermometer consists of mercury, red spirit or green spirit in a glass tube and operates on the principle that the liquid expands more that the glass does when heated.
What is bimetallic thermometer?
Bimetallic Thermometer. Definition: The bimetallic thermometer uses the bimetallic strip which converts the temperature into the mechanical displacement. The working of the bimetallic strip depends on the thermal expansion property of the metal. The thermal expansion is the tendency of metal in which the volume of metal changes with ...
How are bimetallic thermometers constructed?
Constructions of Bimetallic Thermometer. The bimetallic strip is constructed by bonding together the two thin strips of different metals. The metals are joined together at one end with the help of the welding. The bonding is kept in such a way that there is no relative motion between the two metals.
What is a spiral strip thermometer?
Spiral Strip bimetallic thermometer – In bimetallic strip thermometer, the spiral-shaped strip is used. This type of thermometer is used for measuring the ambient temperature. Because of the thermal expansion property of metal the deformation occurs in the spring with the variation of temperature. The pointer and dials attached to the spring, which indicates the variation of temperature.
What happens to the bimetallic strip of a thermometer?
Thereby, the length of metals changes at different rates. When the temperature increases, the strip bends towards the metal which has a low-temperature coefficient. And when the temperature decreases, the strip bends towards the metal which has a high-temperature ...
What is the working principle of bimetallic thermometer?
The working principle of bimetallic thermometer depends on the two fundamental properties of the metal. The metal has the property of thermal expansion, i.e., the metal expand and contract concerning the temperature. The temperature coefficient of all the metal is not same.
Why is a thermometer not used for industrial applications?
This thermometer is not used for industrial application because of low sensitivity and small deflection. The sensitivity of the thermometer increases with the increase of the length of the strip.
What is a bimetallic helix strip?
Helical Types Bimetallic Strip – The helix type bimetallic strip is mostly used for industrial applications. In this thermometer, the helix shape strip is used for measuring the temperature. The free end of the strip is connected to the pointer. The deflection of the strip shows the variation of temperature.
What temperature range is a bimetallic thermometer used for?
Bimetallic thermometers are widely used in industry. Their typical range is from 40–800 (°F). They are often used for two-position temperature control in residential and industrial thermostats.
How are thermometers classified?
Thermometers can be classified in a number of ways, but mainly they are grouped according to the nature of physical contact between the sensor and the measured object; as contact and noncontact thermometers. When measuring a variable which characterizes thermal energy flow, temperature sensing can be regarded as direct. But when an external energy is needed, as an interrogating medium to capture information about the abilities of the body under measurement to store, dissipate, transmit, or transform energy, temperature measurement is considered to be accomplished by an inferential method [13]. The measurement systems may be manually operated or automatic. They can be grouped as electric or nonelectric according to the energy form of the output signal. Frequent classification is one done according to a type of physical variable (the measurand) which is used to sense temperature: radiation thermometers, resistance thermometers, thermometers based on the expansion of solid, liquid, or gas, etc. In practice, the choice of thermometer is usually performed on the basis of measurement temperature range and required precision. Classification of thermometers by measuring range is given in Fig. 2.3.
What is a vapor pressure thermometer?
Vapor pressure thermometers offer even lower uncertainty measurements than gas thermometry. These thermometers are based on the temperature dependence of the saturated vapor pressure of the thermometric liquid, such as helium-3 and helium-4, hydrogen, neon, nitrogen, oxygen, argon, methane, and carbon dioxide.
What are the different types of sensors used in microclimates?
The principal types are liquid-in-glass thermometers (i.e. mercury or spirit thermometers), bimetallic thermometers; electrical resistance thermometers (metal resistance sensors and thermistors) and thermocouples. The choice is determined by several factors, i.e. compatibility with the ambient conditions, measuring range, resolution, accuracy, response time, drift, compatibility with the recording instrument and cost.
What is a manometric thermometer?
Manometric thermometers, constant volume gas and vapor pressure thermometers, relay on a measurement of pressure as temperature indicators. Constant volume gas thermometry can be used for temperature measurements from parts of one kelvin to approximately 1000 K, but mainly for cryogenic temperatures. The method is used in the ITS-90 and is capable of very low uncertainty. These thermometers can take many forms and most commonly use nitrogen or helium gas as a thermometric medium. Vapor pressure thermometers offer even lower uncertainty measurements than gas thermometry. These thermometers are based on the temperature dependence of the saturated vapor pressure of the thermometric liquid, such as helium-3 and helium-4, hydrogen, neon, nitrogen, oxygen, argon, methane, and carbon dioxide. They have good sensitivity, require relatively simple measuring equipment, and are inherently reproducible [14].
What are the limitations of contact thermometers?
The limitations of contact thermometers to disclose thermal processes, especially in small systems where submicron spatial resolution is desirable scale have spurred the development of new noncontact (semi-invasive and noninvasive, Fig. 6.3) accurate thermometers using the changes in the light emitted or absorbed by a thermal probe. It is now well spread in the literature that the temperature measurements based on intensity changes require ratiometric readout. The intensity ratio between two transitions is not compromised by the well-known disadvantages of experiments based on the intensity of only one transition, such as the critical dependence on variations of the sensor concentration, eventual material inhomogeneities, and optoelectronic drifts of the excitation source and detectors [30, 31, 37].
What is resistance thermometer?
Resistance thermometers exploit the change in electrical resistance of conductors and semiconductors with temperature. The resistance is usually measured by potentiometric or bridge methods. Copper, nickel, and platinum are mainly used in metal-based devices. Platinum resistance thermometers, Fig. 2.5 B, have the largest temperature measuring range and a near linear resistance–temperature relationship. They are a common choice for precise temperature measurements and are used to define the ITS-90. For temperatures lower than 20 K, rhodium–iron, doped germanium, and carbon resistors are frequently utilized. Thermistors, that is, thermally sensitive resistors, are made of a ceramic semiconductor whose resistance is sensitive to temperature (with both a negative temperature coefficient or a positive temperature coefficient). They are cheaper, smaller, have a faster response, and present better sensitivity than platinum resistance thermometers, but have much higher levels of uncertainty in measurements and smaller measurement ranges. Current thermistors are ordinarily made of mixtures of oxides, such as nickel, manganese, iron, copper, cobalt, and titanium oxide, along with doped ceramics.
What is a bimetallic thermometer?
The bimetallic thermometer consists of a bimetallic strip. A bimetallic strip is made of two thin strips of metals which have different coefficients of expansion. The two metal strips are joined together by brazing, welding or reveting so that the relative motion between them is arrested.
What is a bimetallic strip made of?
A bimetallic strip is made up of metal A and B , having different thermal expansion co-efficient. It is bonded together.
How does a bimetallic coil react to the heat from a lighter?
Fig : A bimetallic coil from a thermometer reacts to the heat from a lighter, by uncoiling and then coiling back up when the lighter is removed.
Can bimetallics deform?
When regularly used, the bimetallic may permanently deform, which in turn will introduce errors.
What are the two types of bimetallic thermometers?
Types of Bimetallic Thermometer. These thermometers are classified into two types like the spiral strip and helical type. These two thermometers are used to keep the thermometer size in a manageable limit.
What is the working principle of bimetallic thermometer?
The working principle of this thermometer mainly depends on two basic temperature properties of the metal like the following. Once the temperature changes, then there will be a change in the physical dimension of the metals. Whenever the temperature rises, the metal strip turns in the direction ...
How is a helical bimetal thermometer connected?
The helical bimetal is connected at one end in a measuring tube. A metal rod that can be turned in the direction of the helical coil, is connected to another end. A pointer in this thermometer can be connected to the higher side of the metal rod.
How to design a thermometer?
The designing of this thermometer can be done by wrapping the bimetallic strip into this thermometer. The inside of the spiral can be connected in the direction of the housing, and a pointer can be connected to the outside of the spiral. The temperature which is measured can be read off a standardized scale.
What happens when a thermometer is heated?
Whenever the measuring tube is heated up, then the helical bimetal winds up to turn the metal rod. The equivalent temperature will be read off over the calibrated scale. In these thermometers, switch contacts can also be used to close an electrical circuit once the temperature is increased or decreased.
What is a thermometer used for?
The thermometer is one kind of mechanical device, used to measure the temperature rise in different applications using different principles. Measuring the temperature in industries is very important as they affect on many things which we rely on. This article discusses an overview of the bimetallic thermometer and its working.
What type of thermometer is used in AC thermostats?
A spiral strip-type thermometer is utilized in AC thermostats.
What temperature is a bimetallic thermometer used for?
Bimetallic thermometers are generally employed in the range of-30 to 550°C.
What is a bimetallic thermometer?
The bimetallic thermometer is of solid expansion type of thermometer. The bimetallic strip or a bimetallic thermometer, or a bimetallic sensor is the temperature sensing element formed by joining two materials having different thermal expansion coefficients. The two types of materials used are brass which has a high coefficient of thermal expansion and invar (a nickel-iron alloy) which has a low coefficient of thermal expansion.
What happens when a cantilever is subjected to a temperature?
When this element is subjected to a temperature that is to be measured, the strip senses the temperature. Due to this, the free or movable end of the cantilever will deflect. This deflection of the cantilever beam is proportional to the temperature applied. If the free end of the strip is provided with a pointer scale arrangement, the pointer moves over the calibrated scale to indicate the applied temperature.
Can a cantilever be used for industrial applications?
The cantilever type bimetallic strip cannot be used for industrial applications since it exhibits small deflection and low sensitivity. By increasing the length of the bimetallic strip the sensitivity can be increased.
How does a bimetal thermometer work?
Bimetal thermometers are thermometers based on the functional principle that metals expand differently depending on the change in temperature. A bimetal thermometer always consists of two different metal strips that have a different thermal expansion coefficient. The two strips are joined together inseparably and thus form the bimetal strip. When the temperature changes, the different metals expand to different degrees, which leads to a mechanical deformation of the bimetal strip. This mechanical deformation can be detected in a rotary movement. The measuring system works in the form of a helical or spiral tube. This movement is transmitted to the pointer of the thermometer via the pointer shaft, which thus enables the temperature to be measured.
What is a bimetal thermometer and how does a bimetal thermometer measure?
The two strips are joined together inseparably and thus form the bimetal strip. When the temperature changes, the different metals expand to different degrees, which leads to a mechanical deformation of the bimetal strip. This mechanical deformation can be detected in a rotary movement. The measuring system works in the form of a helical or spiral tube. This movement is transmitted to the pointer of the thermometer via the pointer shaft, which thus enables the temperature to be measured.
What are the three types of thermometers used in industrial applications?
In industrial temperature measurement, primarily, three types of dial thermometers are used: bimetal thermometers, gas-actuated thermometers and expansion thermometers. Which measurement principle should be used depends on a number of different factors, such as response time, temperature limits & application range.
What is a 52 bimetallic thermometer?
The model 52 bimetallic thermometer, with its case and stem made of stainless steel, represents the entry-level model among the process thermometers, but is also used for demanding applications in machine building.
Is bimetal thermometer cheaper than gas thermometer?
Compared to gas-actuated thermometers, bimetal thermometers are much cheaper in terms of price. This price advantage is due to their simpler construction.
How does a bimetallic thermometer work?
A bimetallic thermometer consists of a bimetallic strip, which is constructed by bonding together with two thin strips of two different meta s , such that , they cannot move relative to each other. Bimetallic strips can be arranged in various forms like flat, spiral and single helix and multiple helix configurations. As the temperature applied to the strip increases, there will be deflection of free end of strip. Length of both metals will change according to their individual coefficient of thermal expansion. Let ‘a’ be the notation used for coefficient of thermal expansion. As one end of bimetallic strip is fixed, the strip will bend at free end, but towards the side of metal having low coefficient of thermal expansion. Reverse will happen, if there is decrease in temperature. Deflection of free end is directly proportional to two quantities,
What is the helix of a thermometer?
Fig. 2 Shows Helix bimetallic thermometer, in which, a bimetallic strip is wound in the form of helix. One end of helix is fastened to the casing of bulb and another end is connected to pointer. When the bimetallic helix is heated, difference in thermal expansion of metals causes it to unwound. Due to this, pointer moves or sweeps over a circular scale to indicate the measured value of temperature.
Is temperature coefficient of expansion the same for all metals?
Temperature coefficients of expansion are not same for all metals and therefore, their rates of expansion or contraction are different. This property of difference in rates of thermal expansion is used to produce deflections proportional to temperature changes.
Does temperature affect reading accuracy?
Change in physical dimensions due to change in temperature may have an adverse effects on measured reading and accuracy of measuring instruments.
Can bimetallic thermometers measure temperature?
Bimetallic thermometers do not have ability to measure temperatures, which are rapidly changing. Therefore, they are not recommended to use for measurements of fast-changing temperatures.
What temperature can a bimetallic thermometer be used at?
Due to their metallic materials, bimetallic thermometers can be used at temperatures from below -100 °C to more than 500 °C. Bimetal strips are produced by rolling the different metal sheets one on top of the other and then heating them so that the metals bond at the joint by diffusion processes ( cold welding ).
How does a bimetal thermometer work?
In these cases, bimetal thermometers are equipped with a bimetal strip wrapped into a helical coil. The helical bimetal is firmly connected at one end to the inside of a measuring tube (the bimetal is attached to a cylindrical pin, which is pressed firmly into the stem). A rotatable metal rod is guided through this helical coil, which is connected to it at the loose end. A pointer is attached to the upper end of the metal rod. If the measuring tube is now heated, the helical bimetal winds up and rotates the metal rod. On a calibrated scale the corresponding temperature can be read off.
What is a long bimetal strip?
The longer the bimetal, the greater the bend and thus the sensitivity for temperature measurement. For this reason, a long bimetal strip is often wrapped into a coil. Depending on whether the bimetallic coil is twisted like a spiral or a screw, two different types can be distinguished.
How to make a bimetal thermometer?
The simplest design of a bimetal thermometer is to wrap the bimetallic strip into a spiral. The inner end of the spiral is firmly connected to the housing. A pointer is attached to the outer end of the spiral. The measured temperature can then be read off a calibrated scale.
What is a bimetallic strip thermometer?
In bimetallic strip thermometers the different rates of expansion of metals when heated is used to measure the temperature!
Why use bimetallic strips?
Note: Due to the electrical conductivity of the bimetallic strip, it is also frequently used as a safety component for automatic shutdown. Bimetallic strips can be found in kettles, for example, which switch off the kettle automatically by opening the electric circuit when the temperature is too high (or when the boiling point is reached).
How are temperature measurements measured?
Temperatures can be meassured based on the principle of different thermal expansion of solids. For this purpose, two metal strips (e.g. steel and brass) with different degrees of thermal expansion are firmly joined together. When heated, the metal strip deforms due to the different degrees of expansion. The deformation is a measure of the temperature and can be read off a calibrated scale.