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Aneroid gauge measures pressure using a bellows and spring arrangement connected to the pointer that points to a calibrated scale.
This aneroid gauge utilizes flexible bellows connected to a mechanical indicator to measure pressure.

An entire class of gauges uses the property that pressure due to the weight of a fluid is given by P = hρg . size 12{P=hρg "." } {} Consider the U-shaped tube shown in [link] , for example. This simple tube is called a manometer . In [link] (a), both sides of the tube are open to the atmosphere. Atmospheric pressure therefore pushes down on each side equally so its effect cancels. If the fluid is deeper on one side, there is a greater pressure on the deeper side, and the fluid flows away from that side until the depths are equal.

Let us examine how a manometer is used to measure pressure. Suppose one side of the U-tube is connected to some source of pressure P abs size 12{P rSub { size 8{"abs"} } } {} such as the toy balloon in [link] (b) or the vacuum-packed peanut jar shown in [link] (c). Pressure is transmitted undiminished to the manometer, and the fluid levels are no longer equal. In [link] (b), P abs size 12{P rSub { size 8{"abs"} } } {} is greater than atmospheric pressure, whereas in [link] (c), P abs size 12{P rSub { size 8{"abs"} } } {} is less than atmospheric pressure. In both cases, P abs size 12{P rSub { size 8{"abs"} } } {} differs from atmospheric pressure by an amount hρg size 12{hρg} {} , where ρ size 12{ρ} {} is the density of the fluid in the manometer. In [link] (b), P abs size 12{P rSub { size 8{"abs"} } } {} can support a column of fluid of height h size 12{h} {} , and so it must exert a pressure hρg size 12{hρg} {} greater than atmospheric pressure (the gauge pressure P g size 12{P rSub { size 8{g} } } {} is positive). In [link] (c), atmospheric pressure can support a column of fluid of height h size 12{h} {} , and so P abs size 12{P rSub { size 8{"abs"} } } {} is less than atmospheric pressure by an amount hρg size 12{hρg} {} (the gauge pressure P g size 12{P rSub { size 8{g} } } {} is negative). A manometer with one side open to the atmosphere is an ideal device for measuring gauge pressures. The gauge pressure is P g = hρg size 12{P rSub { size 8{g} } =hρg} {} and is found by measuring h size 12{h} {} .

Open-tube manometers have U-shaped tubes and one end is always open. When open to atmosphere, fluid at both ends will be the same, as in the first figure. When pressure at one end is greater, the fluid level will go down on that end, as in the second figure. If the pressure at one end is less, then the height of the fluid column on that side will increase, as in the third figure.
An open-tube manometer has one side open to the atmosphere. (a) Fluid depth must be the same on both sides, or the pressure each side exerts at the bottom will be unequal and there will be flow from the deeper side. (b) A positive gauge pressure P g = hρg size 12{P rSub { size 8{g} } =hρg} {} transmitted to one side of the manometer can support a column of fluid of height h size 12{h} {} . (c) Similarly, atmospheric pressure is greater than a negative gauge pressure P g size 12{P rSub { size 8{g} } } {} by an amount hρg size 12{hρg} {} . The jar’s rigidity prevents atmospheric pressure from being transmitted to the peanuts.

Mercury manometers are often used to measure arterial blood pressure. An inflatable cuff is placed on the upper arm as shown in [link] . By squeezing the bulb, the person making the measurement exerts pressure, which is transmitted undiminished to both the main artery in the arm and the manometer. When this applied pressure exceeds blood pressure, blood flow below the cuff is cut off. The person making the measurement then slowly lowers the applied pressure and listens for blood flow to resume. Blood pressure pulsates because of the pumping action of the heart, reaching a maximum, called systolic pressure    , and a minimum, called diastolic pressure    , with each heartbeat. Systolic pressure is measured by noting the value of h size 12{h} {} when blood flow first begins as cuff pressure is lowered. Diastolic pressure is measured by noting h size 12{h} {} when blood flows without interruption. The typical blood pressure of a young adult raises the mercury to a height of 120 mm at systolic and 80 mm at diastolic. This is commonly quoted as 120 over 80, or 120/80. The first pressure is representative of the maximum output of the heart; the second is due to the elasticity of the arteries in maintaining the pressure between beats. The density of the mercury fluid in the manometer is 13.6 times greater than water, so the height of the fluid will be 1/13.6 of that in a water manometer. This reduced height can make measurements difficult, so mercury manometers are used to measure larger pressures, such as blood pressure. The density of mercury is such that 1.0 mm Hg = 133 Pa .

Questions & Answers

where we get a research paper on Nano chemistry....?
Maira Reply
nanopartical of organic/inorganic / physical chemistry , pdf / thesis / review
what are the products of Nano chemistry?
Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
ya I also want to know the raman spectra
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
yes that's correct
I think
Nasa has use it in the 60's, copper as water purification in the moon travel.
nanocopper obvius
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
how nano science is used for hydrophobicity
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
what is differents between GO and RGO?
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
analytical skills graphene is prepared to kill any type viruses .
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
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Source:  OpenStax, College physics (engineering physics 2, tuas). OpenStax CNX. May 08, 2014 Download for free at http://legacy.cnx.org/content/col11649/1.2
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