跟读练习: ATPL Instrumentation - Class 2: Pressure Measurement. - 通过视频学习英语口语
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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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本节课学习要点
本节课围绕航空领域的压力测量展开，学习者将通过视频内容练习英语听力与口语表达，尤其是专业术语的发音和语境运用。视频中讲解了压力传感器的基本类型（如膜片、无液气压舱）、工作原理及压力单位，适合学习者通过影子跟读提升对科技类英语的理解与表达能力。
核心词汇与短语
- diaphragm：膜片（一种薄而柔韧的圆形板或膜，用于测量压力）
- aneroid capsule：无液气压舱（一种用于测量绝对压力的柔性金属盒）
- hectopascal：百帕（气压单位，与毫巴等值）
- psi (pounds per square inch)：磅每平方英寸（压力单位，常用于机械系统）
- deflection：偏转（膜片因压力差产生的弯曲变形）
影子跟读练习技巧
影子跟读（shadow speech）是提升口语流畅度的有效方法。本节课视频语速适中，讲解清晰，适合初学者练习。建议先完整听一遍视频，熟悉内容后，逐句跟读，注意模仿说话人的语调与重音。例如，在讲解“diaphragm is essentially a thin circular flexible plate”时，需强调“essentially”和“flexible”等关键词，突出语义重点。
针对专业术语，可先单独练习发音，再融入句子中。如“aneroid capsule”的重音在“aneroid”，跟读时需注意音节的划分。此外，视频中存在长句，如“the amount of deflection is directly proportional to the pressure difference between the two sides”，可先拆分句子结构，再逐步跟读，提升对复杂句式的处理能力。
选择合适的影子跟读网站（shadowing site）可辅助练习，通过反复对比自己与原音的差异，不断调整发音与节奏。坚持每天练习15-20分钟，能有效提高英语听力与口语的同步反应能力。
视频中的语法
说话人最常用的结构，并附上视频中的原话：
| 结构 | 视频中的用法 |
|---|---|
| 条件句 if + 从句，will/would + 动词 — 条件及其结果 | if there's less pressure the capsule will expand · if there's more pressure the capsule will deflect |
| 被动语态 be + 过去分词 — 强调发生了什么，而不是谁做的 | can be made · is fixed · is measured |
| 定语从句 who / which + 从句 — 补充说明人或事物 | bar which is · evacuated which means · against, which is |
什么是跟读法？
跟读法 (Shadowing) 是一种有科学依据的语言学习技巧，最初开发用于专业口译员的培训，并由多语言者Alexander Arguelles博士普及。这个方法简单而强大：您在听英语母语原声的同时立即大声重复——就像是一个延迟1-2秒紧跟说话者的影子。与被动听力或语法练习不同，跟读法强迫您的大脑和口腔肌肉同时处理并模仿真实的讲话模式。研究表明它能显着提高发音准确性，语调，节奏，连读，听力理解和口语流利度——使其成为雅思口语备考和真实英语交流最有效的方法之一。