电气技术专业英语电气技术专业英语

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中国电力出版社中国电力出版社

Unit 7 Sensors Unit 7 Sensors

课件制作课件制作 : : 吴岱曦吴岱曦

IndexIndex

• TextText– 1. Introduce to sensors 1. Introduce to sensors – 2. Presence detection2. Presence detection

– 3. Angular position detection 3. Angular position detection

• Reading materialsReading materials– 1. Inductive Sensors 1. Inductive Sensors – 2. Encoders 2. Encoders – 3. Velocity detection3. Velocity detection– 4. Game System Basics4. Game System Basics

• ExercisesExercises– 1. Put the Phrases into English 1. Put the Phrases into English – 2. Put the Phrases into Chinese 2. Put the Phrases into Chinese – 3. Sentence Translation3. Sentence Translation– 4. 4. TranslationTranslation

TextText

1. Introduce to sensors1. Introduce to sensors

• Sensors convert physical phenomena Sensors convert physical phenomena to measurable signals, typically to measurable signals, typically voltages or currents. Consider a voltages or currents. Consider a simple temperature measuring simple temperature measuring device, there will be an increase in device, there will be an increase in output voltage proportional to a output voltage proportional to a temperature rise. temperature rise.

• A computer could measure the voltage, A computer could measure the voltage, and convert it to a temperature. The basand convert it to a temperature. The basic physical phenomena typically measuric physical phenomena typically measured with sensors includeed with sensors include ：：– angular or linear positionangular or linear position– accelerationacceleration– temperaturetemperature– pressure or flow ratespressure or flow rates

• Sensors are also called transducers. This Sensors are also called transducers. This is because they convert an input phenois because they convert an input phenomenon to an output in a different form. menon to an output in a different form. This transformation relies upon a manufThis transformation relies upon a manufactured device with limitations and impactured device with limitations and imperfection. As a result sensor limitations aerfection. As a result sensor limitations are often characterized withre often characterized with ： ：

• AccuracyAccuracy - This is the maximum - This is the maximum difference between the indicated and difference between the indicated and actual reading. For example, if a actual reading. For example, if a sensor reads a force of 100N with a sensor reads a force of 100N with a ±1% accuracy, then the force could ±1% accuracy, then the force could be anywhere from 99N to 101N.be anywhere from 99N to 101N.

• ResolutionResolution - This is the smallest - This is the smallest increment that the sensor can detect, increment that the sensor can detect, this may also be incorporated into the this may also be incorporated into the accuracy value. For example if a sensor accuracy value. For example if a sensor measures up to 10 centimeter of linear measures up to 10 centimeter of linear displacements, and it outputs a displacements, and it outputs a number between 0 and 100, then the number between 0 and 100, then the resolution of the device is 0.1 resolution of the device is 0.1 centimeter. centimeter.

• LinearityLinearity - In a linear sensor the input - In a linear sensor the input phenomenon has a linear relationship phenomenon has a linear relationship with the output signal. In most sensors with the output signal. In most sensors this is a desirable feature. When the this is a desirable feature. When the relationship is not linear, the relationship is not linear, the conversion from the sensor output conversion from the sensor output (e.g., voltage) to a calculated quantity (e.g., voltage) to a calculated quantity (e.g., force) becomes more complex.(e.g., force) becomes more complex.

2. Presence detection2. Presence detection

• There are two basic ways to detect There are two basic ways to detect object presence; contact and object presence; contact and proximity. Contact implies that there proximity. Contact implies that there is mechanical contact and a resulting is mechanical contact and a resulting force between the sensor and the force between the sensor and the object. Proximity indicates that the object. Proximity indicates that the object is near, but contact is not object is near, but contact is not required. required.

11 ） ） Contact switches Contact switches

• Contact switchesContact switches （（ Fig 7.1Fig 7.1 ） ） are availare available as normally open and normally closable as normally open and normally closed. Their housings are reinforced so that ed. Their housings are reinforced so that they can take repeated mechanical forcthey can take repeated mechanical forces. These often have rollers and wear paes. These often have rollers and wear pads for the point of contact. ds for the point of contact.

• Lightweight contact switches can be Lightweight contact switches can be purchased for less than a dollar, but purchased for less than a dollar, but heavy duty contact switches will heavy duty contact switches will have much higher costs. Examples of have much higher costs. Examples of applications include motion limit applications include motion limit switches and part present detectors. switches and part present detectors.

Fig 7.1 Contact switches Fig 7.1 Contact switches

22 ） ） Optical (Photoelectric) SensOptical (Photoelectric) Sensors ors • Optical sensors require both a light sourOptical sensors require both a light sour

ce (emitter) and detector. Emitters will pce (emitter) and detector. Emitters will produce light beams in the visible and invroduce light beams in the visible and invisible spectrums using LEDs and laser diisible spectrums using LEDs and laser diodes. Detectors are typically built with podes. Detectors are typically built with photodiodes or phototransistors. hotodiodes or phototransistors.

• The emitter and detector are The emitter and detector are positioned so that an object will block positioned so that an object will block or reflect a beam when present. A or reflect a beam when present. A basic optical sensor is shown in Fig basic optical sensor is shown in Fig 7.2.7.2.

Fig 7.2 A Basic Optical Fig 7.2 A Basic Optical SensorSensor

• In the figure the light beam is In the figure the light beam is generated on the left, focused generated on the left, focused through a lens. At the detector side through a lens. At the detector side the beam is focused on the detector the beam is focused on the detector with a second lens. If the beam is with a second lens. If the beam is broken the detector will indicate an broken the detector will indicate an object is present. object is present.

• The oscillating light wave is used so The oscillating light wave is used so that the sensor can filter out normal that the sensor can filter out normal light in the room. The light from the light in the room. The light from the emitter is turned on and off at a set emitter is turned on and off at a set frequency. When the detector frequency. When the detector receives the light it checks to make receives the light it checks to make sure that it is at the same frequency. sure that it is at the same frequency.

• If light is being received at the right If light is being received at the right frequency then the beam is not frequency then the beam is not broken. The frequency of oscillation broken. The frequency of oscillation is in the KHz range, and too fast to is in the KHz range, and too fast to be noticed. A side effect of the be noticed. A side effect of the frequency method is that the sensors frequency method is that the sensors can be used with lower power at can be used with lower power at longer distances. longer distances.

3. Angular position 3. Angular position detectiondetection

• Potentiometers measure the angular Potentiometers measure the angular position of a shaft using a variable position of a shaft using a variable resistor. A potentiometer is shown in resistor. A potentiometer is shown in Fig 7.3. The potentiometer is resistor, Fig 7.3. The potentiometer is resistor, normally made with a thin film of normally made with a thin film of resistive material. A wiper can be resistive material. A wiper can be moved along the surface of the moved along the surface of the resistive film. resistive film.

• As the wiper moves toward one end As the wiper moves toward one end there will be a change in resistance there will be a change in resistance proportional to the distance moved. proportional to the distance moved. If a voltage is applied across the If a voltage is applied across the resistor, the voltage at the wiper can resistor, the voltage at the wiper can be detected and the wiper rotates be detected and the wiper rotates the output voltage will be the output voltage will be proportional to the angle of rotation. proportional to the angle of rotation.

• Potentiometers are popular because Potentiometers are popular because they are inexpensive, and don’t they are inexpensive, and don’t require special signal conditioners. require special signal conditioners. But, they have limited accuracy, But, they have limited accuracy, normally in the range of 1% and they normally in the range of 1% and they are subject to mechanical wear.are subject to mechanical wear.

Fig 7.3 principle of a Fig 7.3 principle of a potentiometer potentiometer

• Potentiometers measure absolute Potentiometers measure absolute position, and they are calibrated by position, and they are calibrated by rotating them in their mounting rotating them in their mounting brackets, and then tightening them in brackets, and then tightening them in place. The range of rotation is normally place. The range of rotation is normally limited to less than 360 degrees. Some limited to less than 360 degrees. Some potentiometers can rotate without potentiometers can rotate without limits, and the wiper will jump from limits, and the wiper will jump from one end of the resistor to the other.one end of the resistor to the other.

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Reading materialsReading materials

1. Inductive Sensors1. Inductive Sensors

• Inductive sensors use currents induced Inductive sensors use currents induced by magnetic fields to detect nearby by magnetic fields to detect nearby metal objects. The inductive sensor metal objects. The inductive sensor uses a coil (an inductor) to generate a uses a coil (an inductor) to generate a high frequency magnetic field as high frequency magnetic field as shown in Fig 7.4. If there is a metal shown in Fig 7.4. If there is a metal object near the changing magnetic object near the changing magnetic field, current will flow in the object. field, current will flow in the object.

• This resulting current flow sets up a This resulting current flow sets up a new magnetic field that opposes the new magnetic field that opposes the original magnetic field. The net effect original magnetic field. The net effect is that it changes the inductance of is that it changes the inductance of the coil in the inductive sensor. By the coil in the inductive sensor. By measuring the inductance the sensor measuring the inductance the sensor can determine when a metal have can determine when a metal have been brought nearby.been brought nearby.

• These sensors will detect any metals, These sensors will detect any metals, this work by setting up a high frequency this work by setting up a high frequency field. If a target nears the field will field. If a target nears the field will induce eddy currents. These currents induce eddy currents. These currents consume power because of resistance, consume power because of resistance, so energy is in the field is lost, and the so energy is in the field is lost, and the signal amplitude decreases. The signal amplitude decreases. The detector examines filed magnitude to detector examines filed magnitude to determine when it has decreased determine when it has decreased enough to switch. enough to switch.

Fig 7.4 principle of an inductive Fig 7.4 principle of an inductive sensorsensor

2. Encoders2. Encoders

• The encoder contains an optical disk The encoder contains an optical disk with fine windows etched into it, as with fine windows etched into it, as shown in Fig 7.5, Light from emitters shown in Fig 7.5, Light from emitters passes through the openings in the passes through the openings in the disk to detectors. As the encoder disk to detectors. As the encoder shaft is rotated, the light beams are shaft is rotated, the light beams are broken. broken.

• There are two fundamental types of There are two fundamental types of encoders; absolute and incremental. encoders; absolute and incremental. An absolute encoder will measure An absolute encoder will measure the position of the shaft for a single the position of the shaft for a single rotation. The same shaft angle will rotation. The same shaft angle will always produce the same reading. always produce the same reading. The output is normally a binary or The output is normally a binary or grey code number. grey code number.

• An incremental (or relative) encoder An incremental (or relative) encoder will output two pulses that can be used will output two pulses that can be used to determine displacement. Logic to determine displacement. Logic circuits or software is used to circuits or software is used to determine the direction of rotation, and determine the direction of rotation, and count pulses to determine the count pulses to determine the displacement. The velocity can be displacement. The velocity can be determined by measuring the time determined by measuring the time between pulses. between pulses.

Fig 7.5 encoderFig 7.5 encoder

3. Velocity detection3. Velocity detection

11 ） ） TachometersTachometers Tachometers measure the velocity of a roTachometers measure the velocity of a ro

tating shaft. A common technique is to tating shaft. A common technique is to mount a magnet to a rotating shaft. Whemount a magnet to a rotating shaft. When the magnetic moves past a stationary n the magnetic moves past a stationary pick-up coil, current is induced. For each pick-up coil, current is induced. For each rotation of the shaft there is a pulse in throtation of the shaft there is a pulse in the coil, as shown in Fig 7.6.e coil, as shown in Fig 7.6.

• When the time between the pulses is When the time between the pulses is measured the period for one rotation measured the period for one rotation can be found, and the frequency can be found, and the frequency calculated. This technique often calculated. This technique often requires some signal conditioning requires some signal conditioning circuitry. circuitry.

Fig 7.6 A Magnetic Fig 7.6 A Magnetic TachometerTachometer

• Another common technique uses a Another common technique uses a simple permanent magnet DC simple permanent magnet DC generator (note: you can also use a generator (note: you can also use a small DC motor). The generator is small DC motor). The generator is hooked to the rotating shaft. hooked to the rotating shaft.

• The rotation of a shaft will induce a The rotation of a shaft will induce a voltage proportional to the angular voltage proportional to the angular velocity. This technique will introduce velocity. This technique will introduce some drag into the system, and is some drag into the system, and is used where efficiency is not an issue.used where efficiency is not an issue.

22 ） ） Venturi valveVenturi valve

• When a flowing fluid or gas passes throuWhen a flowing fluid or gas passes through a narrow pipe section (neck) the presgh a narrow pipe section (neck) the pressure drops. If there is no flow the pressursure drops. If there is no flow the pressure before and after the neck will be the sae before and after the neck will be the same. The faster the fluid flow, the greater me. The faster the fluid flow, the greater the pressure difference before and after the pressure difference before and after the neck. This is known as a Venturi valvthe neck. This is known as a Venturi valve. e.

• Fig 7.7 shows a Venturi valve being used Fig 7.7 shows a Venturi valve being used to measure a fluid flow rate. The fluid floto measure a fluid flow rate. The fluid flow rate will be proportional to the pressuw rate will be proportional to the pressure difference before and at the neck (or are difference before and at the neck (or after the neck) of the valve. fter the neck) of the valve.

Fig 7.7 Venturi valveFig 7.7 Venturi valve

• Venturi valves allow pressures to be reaVenturi valves allow pressures to be read without moving parts, which makes thd without moving parts, which makes them very reliable and durable. They work em very reliable and durable. They work well for both fluids and gases.well for both fluids and gases.

4. Game System Basics4. Game System Basics

• The basic pieces really haven't changed The basic pieces really haven't changed that much since the birth of the Atari that much since the birth of the Atari 2600. Here's a list of the core 2600. Here's a list of the core components that all video game components that all video game systems have in common: User control systems have in common: User control interface, CPU, RAM, Software interface, CPU, RAM, Software kernel ,Storage medium for kernel ,Storage medium for games ,Video output ,Audio output, games ,Video output ,Audio output, Power supply . Power supply .

• The user control interface allows the The user control interface allows the player to interact with the video game. player to interact with the video game. Without it, a video game would be a Without it, a video game would be a passive medium, like cable TV. Early passive medium, like cable TV. Early game systems used paddles or game systems used paddles or joysticks, but most systems today use joysticks, but most systems today use sophisticated controllers with a variety sophisticated controllers with a variety of buttons and special features. of buttons and special features.

• Ever since the early days of the Ever since the early days of the 2600, video game systems have 2600, video game systems have relied on RAM to provide temporary relied on RAM to provide temporary storage of games as they're being storage of games as they're being played. Without RAM, even the played. Without RAM, even the fastest CPU could not provide the fastest CPU could not provide the necessary speed for an interactive necessary speed for an interactive gaming experience. gaming experience.

• The software kernel is the console's The software kernel is the console's operating system. It provides the operating system. It provides the interface between the various pieces interface between the various pieces of hardware, allowing the video of hardware, allowing the video game programmers to write code game programmers to write code using common software libraries and using common software libraries and tools. tools.

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ExercisesExercises

• Ready to go?Ready to go?

1. Put the Phrases into 1. Put the Phrases into EnglishEnglish

1.1. 可测信号可测信号2.2. 温度测量器件温度测量器件3.3. 线性传感器线性传感器4.4. 实际读数实际读数5.5. 精确值精确值

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6.6. 行程开关行程开关7.7. 光电传感器光电传感器8.8. 振荡频率振荡频率9.9. 绝对位置绝对位置10.10.转动的范围转动的范围

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2. Put the Phrases into 2. Put the Phrases into ChineseChinese

• 1) 1) physical phenomena physical phenomena • 2) 2) pressure or flow ratespressure or flow rates• 3) 3) relies uporelies uponn

• 4) 4) indicated readingindicated reading• 5) 5) the smallest incrementthe smallest increment

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• 6) 6) linear displacementlinear displacement• 7) 7) resolution of the deviceresolution of the device• 8) 8) linear relationshiplinear relationship• 9) 9) output signaloutput signal• 10) 10) along the surface of the resistive filalong the surface of the resistive fil

mmShow the Answer

3. Sentence Translation3. Sentence Translation

• 1) 1) Sensors are also called transducers. TSensors are also called transducers. This is because they convert an input phehis is because they convert an input phenomenon to an output in a different fornomenon to an output in a different form.m.

• 11 ）传感器也被叫做换能器。这是因为它们）传感器也被叫做换能器。这是因为它们可以将输入量转换成另一种形式的输出可以将输入量转换成另一种形式的输出

• 量。量。

• 2) 2) In a linear sensor the input phenomeIn a linear sensor the input phenomenon has a linear relationship with the ounon has a linear relationship with the output signal.tput signal.

• 22 ）在线性传感器中，输入量和输出信号成）在线性传感器中，输入量和输出信号成线性关系。线性关系。

• 3) 3) Contact implies that there is mechaniContact implies that there is mechanical contact and a resulting force betweecal contact and a resulting force between the sensor and the object.n the sensor and the object.

• 33 ）接触意味着有机械碰撞并在传感器和物）接触意味着有机械碰撞并在传感器和物体之间产生相应的作用力。体之间产生相应的作用力。

• 4) 4) The oscillating light wave is used so tThe oscillating light wave is used so that the sensor can filter out normal light hat the sensor can filter out normal light in the room.in the room.

• 44 ）传感器使用振荡（一定频率的）光波，）传感器使用振荡（一定频率的）光波，这样可以过滤房间里平常的光。（这种光这样可以过滤房间里平常的光。（这种光能传感器白天也可以使用。 ）能传感器白天也可以使用。 ）

• 5) 5) Potentiometers are popular because Potentiometers are popular because they are inexpensive, and don’t require they are inexpensive, and don’t require special signal conditioners.special signal conditioners.

• 55 ）电位计价格便宜而且不需要特别信号条）电位计价格便宜而且不需要特别信号条件，所以很受欢迎。件，所以很受欢迎。

44 ．． TranslationTranslation

• Most desktop displays use liquid Most desktop displays use liquid crystal display (LCD) or cathode ray crystal display (LCD) or cathode ray tube (CRT) technology, while nearly tube (CRT) technology, while nearly all portable computing devices such all portable computing devices such as laptops incorporate LCD as laptops incorporate LCD technology. technology.

• Because of their slimmer design and Because of their slimmer design and lower energy consumption, monitors lower energy consumption, monitors using LCD technology (also called flat using LCD technology (also called flat panel or flat screen displays) are panel or flat screen displays) are replacing the venerable CRT on most replacing the venerable CRT on most desktops.desktops.

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This is the End of the This is the End of the ExercisesExercises

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