Transducers
Contents
Recall the Advantages of Transducers 1
Recall Strain Gauge and its Types 4
Recall the important terms related to Strain Gauge 5
Recall the Applications of Bridgman Gauge 11
Define Transducers
A transducer is a device or instrument that converts one form of energy into another. In other words, it is a device that senses or measures a physical quantity such as temperature, pressure, or strain, and converts it into an electrical signal that can be measured and analysed.
Transducers are used in a wide range of applications, from monitoring environmental conditions and industrial processes to medical and scientific research. They can be designed to measure a variety of physical parameters, such as force, acceleration, displacement, and flow, among others.
Transducers can be classified based on their method of operation, such as mechanical, electrical, magnetic, optical, or thermal. Examples of transducers include sensors, actuators, accelerometers, pressure sensors, and strain gauges, among others.
Transducers play a critical role in many fields, including engineering, medicine, and science, and are essential components of many modern technologies, such as electronic devices, control systems, and automation systems.
Recall the Advantages of Transducers
The advantages of transducers include:
- Ability to measure and convert a wide range of physical quantities into electrical signals
- High accuracy and precision in measurements
- Non-intrusive nature, which minimises disturbance to the measured system
- Ease of integration with electronic instrumentation and control systems
- Ability to operate in harsh environments or in remote locations
- Low power consumption and small size for portable applications.
Classify Transducers
Transducers can be classified based on the physical quantity they measure or the type of energy conversion they perform. Here are some common classifications:
- Based on the physical quantity: temperature, pressure, displacement, strain, force, acceleration, flow, level, etc.
- Based on the type of energy conversion: electrical, mechanical, thermal, optical, magnetic, chemical, etc.
- Based on the direction of energy flow: input transducers (convert physical quantity to electrical signal) and output transducers (convert electrical signal to physical quantity).
- Based on the mode of operation: active transducers (use an external power source to provide the output signal) and passive transducers (generate the output signal without an external power source).
- Based on the sensing principle: resistive, capacitive, inductive, piezoelectric, etc.
Recall Inverse Transducers
An inverse transducer is a device that takes an output signal and produces an input signal that would produce the same output signal if passed through a direct transducer. In other words, an inverse transducer is the inverse function of a direct transducer.
Direct transducers convert physical input signals, such as temperature or pressure, into electrical signals that can be measured and analysed. Inverse transducers, on the other hand, take electrical signals and convert them into physical output signals.
Inverse transducers are used in a variety of applications, such as control systems, instrumentation, and signal processing. They are particularly useful in feedback control systems, where the output of a system is used to adjust the input in order to maintain a desired output.
Examples of inverse transducers include electroacoustic transducers, which convert electrical signals into acoustic signals, and photoelectric transducers, which convert light signals into electrical signals.
Describe the Construction and Working of following Transducers: i. Potentiometer ii. Linear Variable Differential Transformer(LVDT) iii. Hall-Effect Transducers
i. Potentiometer:
A potentiometer is a passive transducer that converts the displacement or position of an object into an electrical signal. The potentiometer consists of a resistive element called a track or a strip, a wiper that moves along the track, and a knob that is used to move the wiper. The resistive element is usually made of carbon, and the wiper is usually made of a conductive material such as copper. As the wiper moves along the track, the resistance between the wiper and one end of the track changes. This change in resistance is proportional to the displacement or position of the object being measured. A voltage is applied across the resistive element, and the output voltage is taken across the wiper and one end of the resistive element. The output voltage is proportional to the displacement or position of the object being measured.
ii. Linear Variable Differential Transformer (LVDT): An LVDT is an inductive transducer that is used to measure linear displacement or position. It consists of a primary winding, two secondary windings, and a movable core. The primary winding is excited with an AC voltage, which induces a voltage in each of the secondary windings. The voltage induced in each secondary winding is proportional to the displacement of the movable core. When the core is in the central position, the voltage induced in both secondary windings is equal and opposite, and the net output voltage is zero. As the core moves, the voltage induced in one of the secondary windings increases, while the voltage induced in the other secondary winding decreases. The net output voltage is proportional to the displacement of the core.
iii. Hall-Effect Transducers:: A Hall-effect transducer is a solid-state device that is used to measure magnetic fields. It consists of a thin slice of semiconducting material, usually a crystal of gallium arsenide, with a thin layer of metal on one side. When a magnetic field is applied perpendicular to the surface of the semiconductor, it causes a voltage to be generated across the metal layer. The voltage is proportional to the strength of the magnetic field. Hall-effect transducers are used in a variety of applications, including position sensors, speed sensors, and current sensors.
Recall Strain Gauge and its Types
A strain gauge is a type of sensor used to measure the strain or deformation of an object. It works by detecting the small changes in electrical resistance that occur when a material is subjected to stress.
There are several types of strain gauges, including:
- Metal Foil Strain Gauge: This type of gauge is made from a thin strip of metal foil, such as constantan or nickel-chromium. The foil is bonded to a substrate material, such as paper or plastic, and then attached to the object being measured. As the object is subjected to strain, the foil stretches or compresses, causing a change in its electrical resistance.
- Semiconductor Strain Gauge: In this type of gauge, a semiconductor material such as silicon is used instead of metal foil. The semiconductor is doped to create regions with different electrical properties, and the resulting changes in resistance are used to measure strain.
- Piezoelectric Strain Gauge: A piezoelectric strain gauge works by converting mechanical strain into an electrical signal. It uses a piezoelectric material, such as quartz or tourmaline, which generates a voltage when subjected to mechanical stress.
- Optical Strain Gauge: This type of gauge uses light to measure strain. It typically consists of a length of optical fibre, which is subjected to strain and causes changes in the way light travels through the fibre. These changes can be detected and used to measure strain.
Strain gauges are used in a wide variety of applications, including structural engineering, aerospace, and manufacturing. They can be used to measure the deformation of materials under stress, to monitor the performance of machinery and equipment, and to help ensure the safety and reliability of critical systems.
Recall the important terms related to Strain Gauge
Some important terms related to strain gauges include:
- Strain: The amount of deformation experienced by the object being measured, typically expressed as a percentage of the object’s original length or width.
- Sensitivity: The amount of change in electrical resistance per unit strain.
- Gauge factor: The ratio of the change in electrical resistance to the applied strain. For metallic foil strain gauges, the gauge factor is typically around 2.
- Poisson’s ratio: The ratio of lateral strain to axial strain in a material. This can affect the accuracy of strain gauge measurements.
- Wheatstone bridge: An electrical circuit commonly used to measure the small changes in resistance that occur in strain gauges due to applied strain. The Wheatstone bridge compares the resistance of the strain gauge to that of a reference resistor and produces an output voltage proportional to the strain.
Describe the following: i. Load Cells, ii. Piezo-Electric Transducers iii. Photovoltaic Transducers
i. Load Cells:
Load cells are devices used for measuring forces or weights. They work on the principle of strain gauges, where a strain gauge is attached to a structure that is under stress. When the stress is applied, the strain gauge deforms and its resistance changes. This change in resistance is proportional to the applied force, and hence the force can be measured. The load cell can be classified into various types, such as hydraulic load cells, pneumatic load cells, and strain gauge load cells.
ii. Piezo-Electric Transducers:
Piezoelectric transducers are sensors that convert mechanical stress into electrical charge. They use piezoelectric materials, such as quartz, which produce a voltage when pressure is applied to them. When the piezoelectric crystal is deformed, it generates a charge, which can be measured as a voltage across its terminals. Piezoelectric transducers are used in a variety of applications, including microphones, accelerometers, and pressure sensors.
iii. Photovoltaic Transducers:
Photovoltaic transducers are devices that convert light energy into electrical energy. They work on the principle of the photoelectric effect, where photons from light energy knock electrons out of a material and create a current. Photovoltaic cells, also known as solar cells, are the most common type of photovoltaic transducer. They are used in a variety of applications, such as solar panels for generating electricity, sensors for measuring light, and electronic displays.
Describe the following Temperature Measuring Transducers: i. Resistance Thermometer (RTD) ii. Thermocouple iii. Thermistor iv. Pyrometer v. Bimetallic Strip
i. Resistance Thermometer (RTD): A resistance thermometer (RTD) is a transducer that is used to measure temperature. The principle of RTD is that the resistance of a metallic conductor increases with temperature. The resistance is measured by passing a small current through the conductor, and measuring the voltage drop across it. The resistance of the conductor can be calculated using Ohm’s law, R=V/I. RTDs are typically made of platinum, and have a resistance of 100 ohms at 0°C. The resistance of the RTD changes linearly with temperature, which makes it easy to calibrate.
ii. Thermocouple: A thermocouple is a transducer that is used to measure temperature. It consists of two wires made of different metals, which are joined at one end to form a junction. When the junction is heated, a voltage is generated between the two wires. The voltage generated is proportional to the temperature difference between the junction and the other end of the wires. The voltage generated by the thermocouple is measured using a voltmeter, and the temperature can be calculated using a calibration table or equation.
iii. Thermistor: A thermistor is a transducer that is used to measure temperature. It is a type of resistor whose resistance changes with temperature. Thermistors are made of semiconductor materials, and have a negative temperature coefficient, which means that their resistance decreases as the temperature increases. The resistance of the thermistor is measured by passing a small current through it and measuring the voltage drop across it. The temperature can be calculated using a calibration equation.
iv. Pyrometer: A pyrometer is a transducer that is used to measure the temperature of objects that are too hot to be measured using traditional thermometers. Pyrometers work by measuring the intensity of the thermal radiation emitted by the object being measured. The intensity of the thermal radiation is related to the temperature of the object, and can be measured using a detector that is sensitive to thermal radiation.
v. Bimetallic Strip: A bimetallic strip is a transducer that is used to measure temperature. It consists of two metals that have different coefficients of thermal expansion, which causes the strip to bend when it is heated. The bending of the strip is proportional to the temperature, and can be measured using a mechanical or optical system. Bimetallic strips are often used in thermostats and other temperature control systems.
Describe the following Low Pressure Measuring Transducers: i. Pirani Gauge ii. Ionization Vacuum Gauge iii. Thermistor Gauge iv. Thermocouple Gauge v. Mc-Leod Gauge
Low Pressure Measuring Transducers:
- Pirani Gauge: Pirani gauge is a thermal conductivity gauge used to measure low vacuum pressure. It consists of a metal filament (usually made of tungsten or platinum) that is heated by passing an electric current through it. As the pressure of the gas in the chamber decreases, the heat transfer rate from the filament to the gas molecules decreases, resulting in a decrease in the filament’s temperature. This decrease in temperature is proportional to the pressure of the gas, and can be measured by monitoring the resistance change of the filament.
- Lonisation Vacuum Gauge: Ionisation vacuum gauge works by ionising the gas molecules in the vacuum chamber and measuring the resulting ion current. It consists of a filament that emits electrons when heated, and an electrode that collects the ionised gas molecules. When the gas molecules in the chamber are ionised by the electrons emitted by the filament, they create a current that can be measured by the electrode. The ion current is directly proportional to the pressure of the gas in the chamber.
- Thermistor Gauge: Thermistor gauge uses a thermistor (a type of resistor whose resistance changes with temperature) to measure the pressure of the gas in a vacuum chamber. The thermistor is placed in thermal contact with the gas, and as the gas pressure changes, the temperature of the thermistor changes, resulting in a change in its resistance. The change in resistance is proportional to the pressure of the gas, and can be measured using a Wheatstone bridge circuit.
- Thermocouple Gauge: Thermocouple gauge works by measuring the temperature difference between two dissimilar metals in contact with the gas in the vacuum chamber. As the pressure of the gas changes, the heat transfer rate to the metals changes, resulting in a change in the temperature difference between them. This change in temperature difference is proportional to the pressure of the gas, and can be measured by the thermocouple.
- Mc-Leod Gauge:The McLeod gauge works on the principle of Boyle’s law, which states that at constant temperature, the pressure and volume of a gas are inversely proportional to each other. The gauge consists of a glass tube with a bulb at one end and a capillary at the other. The tube is partially filled with mercury, and the bulb is connected to the vacuum system being measured.
Recall the following Mechanical Devices for Measuring Pressure: Bourdon Tubes, Bellows, and Diaphragms
Bourdon tubes, bellows, and diaphragms are mechanical devices used for measuring pressure in various applications. These devices operate based on the principle of elastic deformation of a material when subjected to pressure.
- Bourdon Tubes: A Bourdon tube is a C-shaped metallic tube that is closed at one end and connected to the pressure source at the other end. When the pressure is applied to the tube, it tends to straighten out, and this deformation is transferred to the pointer via a linkage mechanism, resulting in the movement of the pointer on the pressure scale. Bourdon tubes are widely used in gauges for measuring gas or liquid pressure.
- Bellows: A bellows is a thin-walled, accordion-shaped metallic container that is subjected to pressure. The bellows’ walls expand or contract in response to the pressure changes, which is transferred to the pointer via a linkage mechanism, resulting in the movement of the pointer on the pressure scale. Bellows are used in applications that require high accuracy and sensitivity.
- Diaphragms: A diaphragm is a thin, elastic metallic membrane that is sealed around the edges and connected to the pressure source. When pressure is applied to one side of the diaphragm, it deflects and moves the pointer attached to the other side of the diaphragm. Diaphragms are commonly used in pressure gauges for measuring the pressure of gases or liquids that are corrosive or highly viscous.
All these devices work on the principle of elastic deformation of the material when subjected to pressure, and their calibration is dependent on the material’s mechanical properties and its geometrical dimensions.
Describe Bridgeman Gauge
The Bridgman gauge is a mechanical device used for measuring high pressure, typically in the range of several hundred to several thousand atmospheres. It consists of a small cylinder that is filled with a liquid, usually mercury, and a piston that is pushed into the cylinder by the pressure being measured. The change in volume of the liquid is then measured to determine the pressure.
The piston is usually made of a hard, wear-resistant material such as tungsten carbide, and is designed to move freely and smoothly within the cylinder. The cylinder is sealed at both ends to prevent any leakage of the liquid, and is typically made of a high-strength material such as stainless steel.
The Bridgman gauge is commonly used in high-pressure experiments in the fields of physics, chemistry, and materials science, where precise measurements of pressure are often required. It is also used in industrial applications where high-pressure equipment must be tested and calibrated, such as in the oil and gas industry.
One of the key advantages of the Bridgman gauge is its high accuracy and precision, which make it an ideal choice for measuring pressure in high-pressure experiments. However, it is a relatively complex and expensive device, and is typically used only in specialised applications where its unique capabilities are required.
Recall the Applications of Bridgman Gauge
Bridgman gauge is commonly used for the measurement of high-pressure ranges up to 50,000 psi. It is used in various applications including:
- Hydraulic and pneumatic systems: Bridgman gauge is used for the measurement of pressure in hydraulic and pneumatic systems. It helps to ensure the safe operation of these systems by providing accurate pressure measurements.
- Calibration of other pressure sensors: Bridgman gauge is also used as a reference standard for calibrating other pressure sensors. It provides highly accurate and reliable measurements, making it an ideal reference standard.
- Materials research: Bridgman gauge is used in materials research to measure the pressure inside the sample cells. This helps to study the behaviour of materials under high pressure and high-temperature conditions.
- Geophysical research: Bridgman gauge is used in geophysical research to measure the pressure of fluids and gases inside the Earth’s crust. This helps to understand the dynamics of the Earth’s interior and the movement of tectonic plates.
Recall the following Transducer for the measurement of Flow: i. Turbine Flow Metre ii. Hot Wire Anemometer iii. Thermistor Flow Meter iv. Electromagnetic Flow Metre v. Ultrasonic Flow Meter
i. Turbine Flow Metre: It consists of a rotor with blades attached to a shaft. The fluid flow causes the rotor to rotate at a speed proportional to the fluid velocity. The rotation is sensed by a magnetic pickup which produces an output signal proportional to the flow rate.
ii. Hot Wire Anemometer: It measures the flow velocity by sensing the cooling effect of a fluid flowing past a heated wire. The wire is maintained at a constant temperature, and the cooling effect is proportional to the velocity of the fluid.
iii. Thermistor Flow Meter: It measures the flow velocity by sensing the change in resistance of a thermistor immersed in a fluid. The change in resistance is proportional to the velocity of the fluid.
iv. Electromagnetic Flow Metre: It measures the flow velocity by sensing the voltage induced in a fluid flowing through a magnetic field. The voltage is proportional to the flow rate of the fluid.
v. Ultrasonic Flow Meter: It measures the flow velocity by sensing the time taken by ultrasonic waves to travel upstream and downstream through a fluid. The time difference is proportional to the velocity of the fluid.
Describe the following Transducers for the Measurement of Angular Speed: i. Tacho-generator ii. Magnetic Pick-up iii. Photoelectric Tachometer iv. Stroboscope
i. Tacho-generator: A tachogenerator is a type of electromechanical transducer that converts the mechanical speed of a rotating shaft into an electrical voltage proportional to its speed. It operates on the principle of electromagnetic induction, where a magnetic field is generated by a permanent magnet or an electromagnet, and a coil rotating in the magnetic field produces an output voltage that is proportional to the speed of the rotating shaft.
ii. Magnetic Pick-up: A magnetic pick-up is a transducer that detects changes in the magnetic field produced by a rotating ferromagnetic object, such as a gear tooth or a flywheel. It works on the principle of electromagnetic induction, where a magnetic field is generated by the ferromagnetic object, and a coil placed in close proximity to the object produces an electrical signal that is proportional to the speed of the object.
iii. Photoelectric Tachometer: A photoelectric tachometer is a transducer that measures the speed of a rotating object by detecting changes in the intensity of light passing through a small hole or slot on the object. It works on the principle of photoelectric effect, where a light beam is directed at the rotating object, and a photodetector detects changes in the amount of light passing through the hole or slot as the object rotates. The output signal is then processed to determine the speed of the object.
iv. Stroboscope: A stroboscope is a non-contact optical transducer that measures the speed of a rotating object by using a flashing light source that is synchronised with the rotational speed of the object. It works on the principle of stroboscopic effect, where the flashing light source appears to freeze the motion of the rotating object at certain intervals, allowing the user to count the number of rotations per minute (RPM) of the object.
Recall Synchros
Synchros, also known as Synchro Transmitters or Synchro Receivers, are electromechanical devices used to transmit and receive angular information between two or more rotating shafts. Synchros operate on the principle of electromagnetic induction and are commonly used in navigation, control systems, and military applications.
Here are a few examples of Synchros and their applications:
- Control systems: Synchros are commonly used in control systems to accurately measure the angle and position of rotating shafts. For example, a Synchro Transmitter may be used to transmit the position of an aircraft’s control surfaces to the cockpit instruments, allowing the pilot to monitor the aircraft’s attitude and make adjustments as needed.
- Navigation: Synchros are also used in navigation systems to accurately measure the angle and position of rotating devices, such as radar antennas and gyroscopes. For example, a Synchro Receiver may be used to receive the position information from a radar antenna and display it on a navigation screen.
- Military applications: Synchros are used extensively in military applications, such as gun turrets and missile guidance systems. For example, a Synchro Transmitter may be used to transmit the position of a gun turret to the gunner’s controls, allowing the gunner to aim and fire the weapon accurately.
The formula for calculating the output voltage of a Synchro is:
Vout = K * (Sinθ * Cosωt + Cosθ * Sinωt)
Where Vout is the output voltage, K is the conversion factor, θ is the angle of rotation, t is time, and ω is the angular velocity. This formula is used to convert the angular position of the rotating shaft into a proportional electrical signal that can be transmitted and received by other Synchros.
Recall Hygrometers
Hygrometers are instruments used to measure the relative humidity of the air or other gases. There are several types of hygrometers available, each with its own method of measuring humidity. Here are a few examples:
- Psychrometer: A psychrometer is a type of hygrometer that consists of two thermometers, one of which has a wet wick or cloth around its bulb. As the water evaporates from the wick, it cools the thermometer, and the difference in temperature between the two thermometers is used to calculate the relative humidity.
- Hair hygrometer: A hair hygrometer is a mechanical hygrometer that uses a human or animal hair to measure humidity. The hair lengthens or shortens as the humidity changes, and the change in length is used to calculate the relative humidity.
- Capacitive hygrometer: A capacitive hygrometer measures humidity by using a capacitor that changes in capacitance as the humidity changes. The change in capacitance is then used to calculate the relative humidity.
- Dew-point hygrometer: A dew-point hygrometer measures humidity by cooling a surface until water vapor in the air condenses onto it, and then measuring the temperature at which condensation occurs. The dew point temperature is then used to calculate the relative humidity.
Hygrometers are used in a variety of applications, including weather forecasting, industrial processes, and building maintenance. It is important to regularly calibrate hygrometers to ensure accurate measurements.