Podcast
Questions and Answers
What happens to the resistance of an NTC thermistor as temperature increases?
What happens to the resistance of an NTC thermistor as temperature increases?
Which material is commonly used in the manufacturing of PTC thermistors?
Which material is commonly used in the manufacturing of PTC thermistors?
Which of these is NOT a typical application of an NTC thermistor?
Which of these is NOT a typical application of an NTC thermistor?
What is the function of a bimetallic strip in a temperature sensor?
What is the function of a bimetallic strip in a temperature sensor?
Signup and view all the answers
According to the formula $R = R_o(1 + αΔT)$, what does $ΔT$ represent?
According to the formula $R = R_o(1 + αΔT)$, what does $ΔT$ represent?
Signup and view all the answers
What is the primary mechanism by which liquid expansion sensors operate?
What is the primary mechanism by which liquid expansion sensors operate?
Signup and view all the answers
In the formula given: $R = R_o(1 + \alpha\Delta T)$ , what does Ro represent?
In the formula given: $R = R_o(1 + \alpha\Delta T)$ , what does Ro represent?
Signup and view all the answers
What is a characteristic of both liquid expansion and bimetallic sensors, as described in the text?
What is a characteristic of both liquid expansion and bimetallic sensors, as described in the text?
Signup and view all the answers
What is the primary function of a sensor?
What is the primary function of a sensor?
Signup and view all the answers
Which of the following best describes a transducer?
Which of the following best describes a transducer?
Signup and view all the answers
What distinguishes a passive transducer from a self-generating transducer?
What distinguishes a passive transducer from a self-generating transducer?
Signup and view all the answers
Which of the following is an example of a self-generating transducer?
Which of the following is an example of a self-generating transducer?
Signup and view all the answers
What principle does a thermocouple use to measure temperature?
What principle does a thermocouple use to measure temperature?
Signup and view all the answers
Why is standardization important for thermocouples?
Why is standardization important for thermocouples?
Signup and view all the answers
What is a typical application for thermocouples enclosed in a metal casing?
What is a typical application for thermocouples enclosed in a metal casing?
Signup and view all the answers
What is the typical temperature range for thermocouple measurements?
What is the typical temperature range for thermocouple measurements?
Signup and view all the answers
What is the primary constituent of Alumel?
What is the primary constituent of Alumel?
Signup and view all the answers
Which of the following thermocouple pairings is NOT commonly used?
Which of the following thermocouple pairings is NOT commonly used?
Signup and view all the answers
In the equation for thermocouple EMF, $E = c(T_1 – T_2) + k(T_1^2 – T_2^2)$, what do 'c' and 'k' represent?
In the equation for thermocouple EMF, $E = c(T_1 – T_2) + k(T_1^2 – T_2^2)$, what do 'c' and 'k' represent?
Signup and view all the answers
What is the typical resistance of a platinum resistance temperature sensor at 0°C?
What is the typical resistance of a platinum resistance temperature sensor at 0°C?
Signup and view all the answers
Which material is NOT typically used to make thermistors?
Which material is NOT typically used to make thermistors?
Signup and view all the answers
What is a key advantage of resistance-type sensors over thermocouples?
What is a key advantage of resistance-type sensors over thermocouples?
Signup and view all the answers
A copper-constantan thermocouple has constants $c = 3.75 \times 10^{-2} mV/°C$ and $k = 4.5 \times 10^{-5} mV/°C^2$. If the hot junction is at 100°C and the cold junction is at 0°C, what is the calculated EMF?
A copper-constantan thermocouple has constants $c = 3.75 \times 10^{-2} mV/°C$ and $k = 4.5 \times 10^{-5} mV/°C^2$. If the hot junction is at 100°C and the cold junction is at 0°C, what is the calculated EMF?
Signup and view all the answers
What is a key characteristic of thermistors compared to platinum resistance sensors?
What is a key characteristic of thermistors compared to platinum resistance sensors?
Signup and view all the answers
What is the fundamental principle behind positive displacement flow meters?
What is the fundamental principle behind positive displacement flow meters?
Signup and view all the answers
Which type of flow meter infers flow rate based on the speed of a spinning component?
Which type of flow meter infers flow rate based on the speed of a spinning component?
Signup and view all the answers
In a turbine flow meter, how is the fluid flow rate typically determined?
In a turbine flow meter, how is the fluid flow rate typically determined?
Signup and view all the answers
What is the function of the tapered tube in a variable area float type flow meter?
What is the function of the tapered tube in a variable area float type flow meter?
Signup and view all the answers
In a rotating vane type inferential flow meter, what causes the vane to rotate?
In a rotating vane type inferential flow meter, what causes the vane to rotate?
Signup and view all the answers
What type of flow meter directly measures the volume of fluid passing through it by trapping a known quantity with a mechanical element?
What type of flow meter directly measures the volume of fluid passing through it by trapping a known quantity with a mechanical element?
Signup and view all the answers
Which of the following accurately describes how float-type variable area flow meters work?
Which of the following accurately describes how float-type variable area flow meters work?
Signup and view all the answers
What is the key difference between positive displacement and inferential flow meters?
What is the key difference between positive displacement and inferential flow meters?
Signup and view all the answers
In a tapered plug type flow meter, what mechanism causes the plug to move and find a new balance position when the flow changes?
In a tapered plug type flow meter, what mechanism causes the plug to move and find a new balance position when the flow changes?
Signup and view all the answers
What is the main operating principle behind differential pressure flow meters such as orifice, venturi, and nozzle meters?
What is the main operating principle behind differential pressure flow meters such as orifice, venturi, and nozzle meters?
Signup and view all the answers
In differential pressure flow meters, what does 'k' represent in the formula $Q = k \Delta P$?
In differential pressure flow meters, what does 'k' represent in the formula $Q = k \Delta P$?
Signup and view all the answers
What is the fundamental principle that mechanical force sensors rely on?
What is the fundamental principle that mechanical force sensors rely on?
Signup and view all the answers
How do hydraulic-type force sensors (hydraulic load cells) measure force?
How do hydraulic-type force sensors (hydraulic load cells) measure force?
Signup and view all the answers
What is the essential function of a position sensor within actuator control systems?
What is the essential function of a position sensor within actuator control systems?
Signup and view all the answers
What is the fundamental operating principle of resistive position sensors?
What is the fundamental operating principle of resistive position sensors?
Signup and view all the answers
Which of the following is NOT a primary type of position sensor mentioned in the text?
Which of the following is NOT a primary type of position sensor mentioned in the text?
Signup and view all the answers
Which material provides the best analog output in a slider-type position sensor?
Which material provides the best analog output in a slider-type position sensor?
Signup and view all the answers
What is the primary function of the engraved lines on the transparent strip or disc in optical position sensors?
What is the primary function of the engraved lines on the transparent strip or disc in optical position sensors?
Signup and view all the answers
In an LVDT, when the core is exactly in the middle, what is the relationship between the voltages induced?
In an LVDT, when the core is exactly in the middle, what is the relationship between the voltages induced?
Signup and view all the answers
What does the output voltage in an LVDT represent?
What does the output voltage in an LVDT represent?
Signup and view all the answers
What is the primary purpose of depth gauges?
What is the primary purpose of depth gauges?
Signup and view all the answers
Which principle does ultrasonic depth measurement rely on?
Which principle does ultrasonic depth measurement rely on?
Signup and view all the answers
What is a characteristic of the wire wound tracks of a potentiometer?
What is a characteristic of the wire wound tracks of a potentiometer?
Signup and view all the answers
In a pneumatic depth gauge, what is directly related to the depth of the liquid?
In a pneumatic depth gauge, what is directly related to the depth of the liquid?
Signup and view all the answers
Study Notes
Sensors and Transducers
- Sensors detect changes in physical stimuli, converting them into measurable signals.
- Transducers convert energy from one form to another. Many convert non-electrical stimuli (like temperature, sound, or light) into electrical signals.
Transducer Classification
- Transducers are classified by their application, based on the physical quantity measured.
-
Passive transducers require external power; their output is a measure of some variation (e.g., resistance, capacitance).
- Example: Condenser microphone
-
Self-generating transducers don't need external power; they generate analog voltage or current when stimulated by physical energy.
- Example: Thermocouple
Temperature Transducers
- Thermocouples: Two dissimilar wires joined at both ends. Heating one junction creates a small electric current proportional to the temperature difference.
- The relationship between temperature and EMF (electromotive force) is generally linear within operating ranges. The specific metals used in the wires determine the characteristics. Standard types are used for consistent readings.
- Thermocouples come in various forms: insulated wires, insulated wire pairs in tubes with mineral insulation or metal enclosures (e.g., stainless steel).
- Thermocouples can measure temperatures from -270°C up to 2700°C.
- The EMF is related to the temperature difference between the hot and cold junctions and to constants of the materials. The formula is: E = c(T1 – T2) + k(T1² – T2²) where c and k are constants.
Resistance Type Sensors
- Resistance changes with temperature for conductive materials.
- A constant voltage applied results in current changes that vary with temperature.
- Resistance type sensors' resistance increases as the conductor gets hotter.
- Example: Platinum resistance thermometer
- A basic temperature sensor uses a thin resistance wire wound into a small head, the resistance directly representing the temperature.
- This type is unaffected by the gauge end temperature, unlike thermocouples.
- Platinum is frequently used.
-
Thermistors: Semiconductor materials designed with a strong temperature-resistance relationship; available in negative temperature coefficient- (NTC) or positive temperature coefficient-(PTC) types.
- NTC thermistors: resistance decreases as temperature increases
- PTC thermistors: resistance increases as temperature increases
- Typical range of NTC thermistors is -200°C to 1000°C.
- Thermistors are typically suitable for use in daily-use temperature measurements, in an acceptable range (-20°C to 120°C).
Liquid Expansion and Vapour Pressure Sensors
- These measure temperature by monitoring liquid expansion or evaporation.
- The liquid-filled sensor head and connecting tube are completely filled.
- An increase in temperature results in expansion or evaporation of the liquid creating pressure.
- The pressure is measured using a pressure gauge.
- These sensors are robust and can operate over a wide range.
- Often used as thermometers, or for controlling temperature using thermostats and alarms.
- Example uses: mercury thermometers, evaporating liquids used in refrigerators.
Bimetallic Sensors
- This relies on differing expansion rates of two rigidly-joined metals.
- When heated, one metal expands more than the other.
- The difference causes the bimetal strip to bend. This bend is linked to a pointer on a dial, or limit switches to set off alarms or act as a thermostat.
Pressure Transducers
- These measure pressure changes.
- Bourdon Tube: A hollow tube with an elliptical cross-section. Pressure difference causes the tube to straighten, moving a needle on a dial or a secondary device, such as an air nozzle (commonly used in gauges to measure pressure)
- Piston Type: Pressure acts directly on a piston, compressing a spring. The piston's position relates directly to the pressure; a window in the outer case indicates the pressure with a pressure gauge. (Found commonly in hydraulic instruments)
- Bellows: Made from flattened metal capsules which expand when pressurized. The movement is proportional to the difference between the inside and outside pressure; useful for precise measurement of low pressures
Speed Transducers
- Optical Types: Light beam sensors that either reflect or interrupt a light beam, counting pulses over a fixed time. Electronic processing calculates speed.
- Magnetic Pickups: Inductive coil placed near a rotating body with a small magnet on it generating a pulse with each coil passage. Discontinuities in magnetic materials also trigger pulses.
- Tachometers: These are commonly built into electric motors to measure their rotational speed. The voltage frequency is proportionate to the rotational speed.
Flow Meters
- These quantify liquid, gas or vapor flow, using a variety of methods; based on types of displacement, inferential, variable area or differential pressure methods.
- Positive Displacement Types: Mechanical elements that rotate once for a precise amount of fluid; the flow rate depends on shaft rotations and speed, measurable mechanically or electronically. Examples: meshing motor.
- Inferential Types: Calculate flow by an effect of the flow produced - rotation of rotors is detected (mechanically or electronically) for turbine and rotating vane types.
- Variable Area Types: Utilizing a float inside a tapered tube with a flow rate affecting the pressure; examples: float type, tapered plug.
- Differential Pressure Types: Measures the flow rate by determining differential pressure (using orifice, Venturi or nozzle methods or pitot tubes). The working principle relies on changes in fluid velocity and corresponding changes in pressure. The volumetric flow rate is related to the differential pressure by the formula Q = √kΔP.
Force Sensors
- Mechanical Types: Based on the deflection of a spring proportional to the force applied; the deflection (movement) is measured on a scale.
- Hydraulic Types: Capsules filled with liquid that become pressurized when squeezed; the pressure represents the force and can be measured using a pressure gauge.
- Electrical Strain Gauge Types: Employing metal cylinders with strain gauges. Stretched or compressed cylinders change the resistance, thus enabling force to be measured in voltage or resistance changes.
Position Sensors
- Resistive Types: Using a potentiometer that is made up of a resistor tracks (made from carbon or resistive material). The movement of a slider along the track picks off the voltage depending on its position or angle.
- Optical Types: Employing light emitted onto photoelectric cells along lines engraved on a transparent strip or disc, to calculate position or angle.
- Inductive Types: A primary coil and two secondary coils used to generate voltage changes proportional to the position of a movable magnetic core.
Depth Gauges
- Instruments used to measure the liquid or powdered depth of tanks.
- Various methods are employed, often involving the use of electricity or air pressure for measuring depth based on fluid properties.
- Example: Ultrasound sensors use sound waves to determine the depth.
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Related Documents
Description
Test your knowledge on temperature sensors and thermistors in this comprehensive quiz. It covers topics like NTC and PTC thermistors, the function of bimetallic strips, and the principles behind various types of sensors. Perfect for students aiming to deepen their understanding of thermodynamics and sensor technology.
