Shadowing Practice: ATPL Instrumentation - Class 2: Pressure Measurement. - Learn English Speaking with Video
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Lots of aircraft systems need to have their pressure measured
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and monitored to make sure they are working in a safe and effective manner.
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We also need to know the pressure of the air around us
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which we can use for various things that we'll look at in the next few classes.
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So how do we even measure pressure?
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Let's find out.
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Hi I'm Grant and welcome to the second class in the instrumentation series.
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Today we're going to be having a look at how we measure pressure.
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Pressure is used for lots of different things in aviation
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and we use the pressure data to generate more useful information for us whilst we're flying
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which we'll look at in the next few classes.
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But for today though we're just going to focus on how we actually measure it
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so without further ado let's find out what it's all about.
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Ah I couldn't keep his right face.
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The most common and fundamental type of pressure sensor is a diaphragm.
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A diaphragm is essentially a thin circular flexible plate or membrane.
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It can be made of various materials like metal, rubber or plastic
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and the diaphragm is fixed around its edge creating a sealed chamber on one side set to a known pressure.
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When a pressure difference exists between the two sides, the known pressure and whatever we're trying to measure,
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then the diaphragm will effectively bend or deflect.
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It's kind of like a hydraulic actuator but using air or some other pressure source instead of hydraulic fluid.
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The amount of deflection is directly proportional to the pressure difference between the two sides
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and we can then attach a mechanical linkage
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or an electrical sensor to the centre of the diaphragm to measure how much this moves by
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and this movement is what gives us our pressure reading
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and what we are reading can be a few different units it can be quite confusing
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and what you'll often see is millibars and hectopascals they're exactly the same
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and then you'll see one bar which is a thousand millibars is equal to 14.5 psi pounds per square inch.
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There's not really any rhyme or reason as to why we measure some things in psi
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and other things in millibars or hectopascals.
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It can be quite confusing.
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Generally air pressure is hectopascals and components
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and things like mechanical like the engine oil pressure and hydraulic pressure is measured in psi.
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I don't know why but that just seems to be the way that I've notice things go.
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Diaphragms, anyway, are rugged and simple.
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They're often used in basic air pressure gauges with the seal side set to normal sea level pressure
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and even some basic systems like the oil pressure measurements in the engine might use this sort of diaphragm.
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A more specialized type of sensor that's very important is the aneroid capsule.
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An aneroid capsule is kind of like a diaphragm
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but instead of being a single flat disc in a container it's essentially a flexible metal box with corrugated sides
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which makes it very responsive.
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These capsules are evacuated which means
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that most of the air has been removed from the inside creating a near vacuum where the pressure is essentially zero.
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The capsule is designed to measure absolute or total pressure
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that is the pressure
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that is relative to a near vacuum not just the outside
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atmosphere as a reference just like in the diaphragm hopefully
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that makes sense when the external pressure increases this compresses the capsule
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because there's no pressure for it to resist against and
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when the external pressure decreases the capsule expands this is good in aviation
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because we don't need to feed in a reference pressure to measure the difference against.
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And in aviation, we often change pressure a lot when we climb and descend in the atmosphere.
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So getting a source of that reference pressure can be quite hard.
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This is just measuring the total absolute pressure, nothing needs to be compared against, which is good for us as we're flying.
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Bellows are just stacks of aneroid capsules joined together.
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The purpose of joining them together is that each capsule is inflating and deflating according to the pressure a small amount.
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Therefore, when we stack them together, we stack the total movement of those capsules together.
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Therefore, it's much easier to measure small and precise pressure changes, and we can measure larger total pressures in general.
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Bellows can also be pressure fed, whereby the internal structure isn't near vacuum,
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but instead has a pressure fed in just like a diaphragm
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or you might call this not an anoid capsule
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but a pressure fed capsule it's the same sort of thing
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and we can call this a pressure fed bellows therefore we can also measure pressure differentials with much more precision
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if we wanted and these sensors are great for use in things where we need to measure
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and adjust pressure to a very specific value such as the manifold pressure in a piston engine while diaphragms,
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capsules and bellows are membranes essentially, the Borden tube uses a different principle for deformation.
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A Borden tube is a C-shaped tube essentially.
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One end of the tube is sealed and it's free to move, move up and down left and right, while the other end is fixed but this is open to the pressure source.
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When pressure is applied, the tube attempts to straighten out.
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It's kind of like one of those things at parties that you blow into and they make a honking noise.
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You know, they're sort of curled up like this and you blow them and you go, it's basically one of those, but it doesn't make a honking noise.
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The straightening movement is mechanically linked to a needle via gears and other linkages.
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and by the movement of this C-shaped tube moves the dial and that's how we display the pressure.
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Burden tubes are pretty robust and can handle much higher pressures than simple diaphragms
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which makes them ideal for systems that have quite high pressure such as the hydraulic system.
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Pressure transducers are basically small electric diaphragms.
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A small metal diaphragm deforms and the metal moving presses on a resistive element
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that will change its resistance depending on the pressure that's put on it.
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There's electricity flowing through the resistive element, so when it changes, the voltage across it changes,
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which can then be measured and translated into a pressure reading and sent to a dial or a digital display.
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The main advantage of a transducer is that it doesn't need to be fed with the source of the pressure.
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we aren't sending the engine oil or hydraulic fluid into the sensor to be measured specifically.
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If you think about measuring oil pressure using a burden tube for example, the previous one that we saw, we would need to send some of the oil to the pressure gauge which is in the cockpit
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requiring extra tubes to send the oil out of the way to the instrument and then back again back into the engine.
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Because the data generated by a transducer is electronic we don't need extra pipes and tubes to send it to the sensor.
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We just place one of these sensors in an existing tube or pipe and then wire up.
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This means we can place the sensors at the source
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and not worry about leaks from let's say the hydraulic reservoir to the cockpit.
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It also means it's easy to add redundancy and multiple sensors to the same thing therefore improving reliability and minimizing false readings.
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This means that you'll see electronic transducers
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to sense pressure all over the place in large aircraft where we want multiple sensors for everything to make sure
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that there's no problems.
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In summary then we've got a diaphragm which is basically a disc that deforms.
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That deformation is used to measure a pressure difference therefore we
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need to have a reference pressure fed into a diaphragm on one side
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and then the other side is the thing we want to measure
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and then it will be the pressure difference between the reference and the measured pressure that we're actually getting a reading for.
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We also have aneroid capsules which is essentially a bellows but without all the components.
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What will happen inside an aneroid capsule is you'll have zero pressure near enough
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and then we're going to measure the total pressure
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that is surrounding the aneroid capsule because
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if there's less pressure the capsule will expand and
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if there's more pressure the capsule will deflect and we're just going to measure that movement.
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The problem is we only get a small amount of movement
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so what we can do is we can add loads of aneroid capsules together to create a bellows.
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The same principle applies if there's lots of pressure around the outside of this, this whole thing will compress.
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If there's less pressure around the outside, the thing will expand.
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The advantage of having them all stacked together is we get a lot of movement
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and we can be much more precise with our measurements of total pressure
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which you might use for things where you want to set a pressure reading like in a piston engine.
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You get a board on tube which is a party hooter.
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You blow it and it straightens out.
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It's the same principle with this except instead of blowing on it you're measuring some sort of pressure.
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At this end the c-shape tries to straighten out.
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The straightening of this section here pulls on mechanical linkages,
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gears etc and moves a dial to display how much is straightening out
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and therefore how much pressure is being fed into the source there.
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You also get pressure transducers, essentially electronic diaphragms.
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The diaphragm deflects, the metal diaphragm here deflects and
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that metal diaphragm pushes on a resistive element
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and the resistive element changes its resistance according to how much pressure is put on it.
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we measure the voltage across the resistor and by measuring
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that voltage we can then convert that into a display which shows how much pressure is being put on the diaphragm.
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So that's just how we measure pressure
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and in the next few classes we'll look at how to actually use that pressure for giving us some useful information.
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Vocabulario y notas de pronunciación para esta lección
Este vídeo tiene 125 frases y 1728 palabras para practicar shadowing. La parte hablada dura 10:57. El hablante habla a un ritmo natural de unas 158 palabras por minuto, cercano a una conversación cotidiana. Solo el 80 % de las palabras está entre las 3.000 más comunes del inglés, por lo que el vocabulario es exigente.
Vocabulario clave de este vídeo
15 palabras del vídeo que vale la pena aprender, con su pronunciación y significado:
| Palabra | Pronunciación | Significado |
|---|---|---|
| capsule sustantivo | /ˈkæps(ə)l/ | cápsula |
| tube sustantivo | /tuːb/ | tubo, chisguete |
| sensor sustantivo | /ˈsɛn.sɚ/ | sensor |
| essentially adverbio | /ɪˈsɛnʃəli/ | esencialmente, en esencia |
| hydraulic adjetivo | /haɪˈdɹɔːlɪk/ | hidráulico |
| element sustantivo | /ˈɛləmənt/ | elemento |
| stack sustantivo | /stæk/ | pila, montón |
| expand verbo | /ɪkˈspænd/ | ampliar |
| principle sustantivo | /ˈpɹɪn.sɪ.pəl/ | principio |
| mechanical adjetivo | /məˈkænəkəl/ | mecánico |
| seal sustantivo | /siːl/ | sello |
| aviation sustantivo | /ˌeɪ̯.viːˈeɪ̯.ʃən/ | aviación |
| vacuum sustantivo | /ˈvæ.kjuːm/ | vacuo |
| voltage sustantivo | /ˈvəʊltɪd͡ʒ/ | voltaje, tensión |
| dial sustantivo | /ˈdaɪ.əl/ | dial |
Phrasal verbs que vas a escuchar
| Palabra | Significado |
|---|---|
| straighten out verbo | enderezar |
| find out verbo | averiguar, anoticiarse |
Pronunciación a tener en cuenta
El hablante usa 30 contracciones y formas reducidas, como we're, you'll, don't. Dilas en su forma corta, tal como las oyes.
- Los sonidos de “sh” y “zh”: essentially /ɪˈsɛnʃəli/, aviation /ˌeɪ̯.viːˈeɪ̯.ʃən/, measurement /ˈmɛʒ.ə.mənt/, precision /pɹɪˈsɪʒ.ən/, differential [dɪfəˈɹənʃəɫ]
- Palabras largas — cuida el acento: essentially /ɪˈsɛnʃəli/, mechanical /məˈkænəkəl/, aviation /ˌeɪ̯.viːˈeɪ̯.ʃən/, electricity /ɪˌlɛkˈtɹɪsɪti/, electrical /ɪˈlɛktɹɪkəl/
Cómo practicar con este vídeo
- Escucha el vídeo entero una vez sin hablar y anota las palabras que no conoces.
- Empieza a velocidad 0,75×, haz shadowing frase por frase y vuelve a la velocidad normal cuando te resulte fácil.
- Grábate y compara con el original, prestando atención a palabras como capsule, tube, sensor.
Gramática en este vídeo
Las estructuras que más usa el hablante, con las palabras exactas del vídeo:
| Estructura | En el vídeo |
|---|---|
| Oraciones condicionales if + oración, will/would + verbo — una condición y su resultado | if there's less pressure the capsule will expand · if there's more pressure the capsule will deflect |
| Voz pasiva be + participio pasado — importa lo que ocurre, no quién lo hace | can be made · is fixed · is measured |
| Oraciones de relativo who / which + oración — información extra sobre una persona o cosa | bar which is · evacuated which means · against, which is |
¿Qué es la Técnica de Shadowing?
Shadowing es una técnica de aprendizaje de idiomas respaldada por la ciencia, desarrollada originalmente para la formación de intérpretes profesionales y popularizada por el políglota Dr. Alexander Arguelles. El método es simple pero poderoso: escuchas audio en inglés nativo y lo repites en voz alta de inmediato, como una sombra que sigue al hablante con solo 1-2 segundos de retraso. A diferencia de la escucha pasiva o los ejercicios de gramática, el shadowing obliga a tu cerebro y músculos de la boca a procesar y reproducir simultáneamente patrones de habla reales. Las investigaciones muestran que mejora significativamente la precisión de la pronunciación, la entonación, el ritmo, el habla conectada, la comprensión auditiva y la fluidez al hablar, convirtiéndola en una de las metodologías más efectivas para la preparación del IELTS Speaking y la comunicación en inglés en el mundo real.