Instrumentation. Measuring instruments Presentation on the topic of electrical measuring instruments galvanometer

Measuring current Ammeter AMPERMETER is a device for measuring the current flowing through a section of a circuit. To reduce the distorting effect on the electrical circuit, it must have a low input resistance. It has a sensitive element called a galvanometer. To reduce the resistance of the ammeter, a shunt resistance (shunt) is connected parallel to its sensitive element.

Increasing the measurement limits of an ammeter SHUNT is a conductor connected in parallel to an ammeter to expand its measurement limits. When the shunt is turned on in this way, part of the measured current is branched off and a current of strength n times less than the measured current will flow through the ammeter.

Galvanometer D'Arsonval GALVANOMETER D'ARSONVAL is a highly sensitive electrical measuring instrument for measuring weak currents or voltages. The principle of its operation is based on the magnetic action of current.

Measuring electrical voltage Voltmeter VOLTMETER is a device for measuring voltage in an area electrical circuit. To reduce the influence of a switched-on voltmeter on the circuit mode, it must have a high input resistance. A voltmeter has a sensing element called a galvanometer. To increase the resistance of the voltmeter, an additional resistance is connected in series with its sensitive element.

Increasing the measurement limits of a voltmeter ADDITIONAL RESISTANCE - an additional resistor connected in series with the voltmeter to expand its measurement limits. With this inclusion of additional resistance, the voltage on the voltmeter will be n times less than the measured one.

Methods for measuring resistance MEASURING BRIDGE (Wheatstone bridge) – a measuring circuit used to measure unknown values ​​of resistance, inductance, capacitance and other quantities by comparison with a reference value. Measuring instruments containing this circuit are also called measuring bridges.

Measuring resistance Ohmmeter OHMETER is a device for measuring electrical resistance, allowing you to read the measured resistance directly on the scale. In modern instruments for measuring resistance and others electrical quantities different principles are used and the results are presented in digital form.

Operating principle of an ohmmeter The simplest ohmmeter consists of a current source, a variable resistor and a sensitive current meter (micrometer), the scale of which is graduated in ohms. When connecting an unknown resistance, the microammeter needle will deflect more, the smaller the connected resistance. Therefore, on the ohmmeter scale, the zero division is on the right, and the far left is indicated by the “infinity” sign. Schematic diagram ohmmeter

Conclusion The measurement of electrical quantities such as voltage, resistance, current, etc. is carried out using various means– measuring instruments, circuits and special devices. The type of measuring device depends on the type and size (range of values) of the measured value, as well as on the required measurement accuracy.

Optical devices for the eye

The images of the objects in question are imaginary.

Angular magnification– the ratio of the angle of view when observing an object through an optical device to the angle of view when observing with the naked eye (characteristics of an optical device).

Magnifier

A magnifying glass is a converging lens or a system of lenses with a short focal length.

h d 0

The angle of view from which an object is visible to the naked eye.

d0 =25cm – distance of best vision. h – linear size of the object.

The magnifying glass is placed close to the eye, and the object is positioned in its focal plane.

h - the angle at which it is visible through a magnifying glass

F subject.

Fd – focal length of the magnifying glass.

Г 0 - angular magnification of the magnifying glass.

The magnification provided by a magnifying glass is limited by its size.

Magnifying glasses are used by watchmakers, geologists, botanists, and criminologists.

Microscope

A microscope is a combination of two lenses or lens systems.

Lens O1 facing the object is called a lens

(gives a real magnification of the image of the object). Lens O2 – eyepiece.

An object is placed between the focal point of the lens and a point at twice the focal length. The eyepiece is placed so that the image coincides with the focal

Microscope magnification is called the ratio of the visual angle φ, at which an object is visible when observed through a microscope, to the visual angle ψ when observed with the naked eye from the distance of best vision

d0 =25cm.

	Um							Microscope Magnification
								For a magnifying glass.
								For microscope,
								h’ – linear size of the image given
								lens. F2 – focal length of the eyepiece.

The linear size of the image in the lens is related to the linear size of the object by the ratio:

		f F1				F1 – lens focal length.
					Optical length of microscope tube
					(distance between rear lens and
					front focus of the eyepiece).
						Microscope magnification: from several
						tens to 1500.
			F1 F2			The microscope allows you to distinguish small
						details of an object that, when observed, Uchim.net
						with the naked eye or with a magnifying glass

Kepler tube

In 1613 it was made by Christoph Scheiner according to Kepler's design.

Kepler (1571 – 1630)

A lens is a long-focus lens that gives a truly reduced, inverted image of an object. The image of a distant object is obtained in the focal plane of the lens. The eyepiece is located from this image at its focal length.

Uchim.net

The angular magnification of a telescope is the ratio of the visual angle at which we see the image of an object in the telescope to the visual angle at which we see it

the same object directly.

GT - telescope magnification.

The magnification of the telescope is equal to the focal ratio

lens distance to eyepiece focal length.

GT F 1 F2

The Kepler tube produces an inverted image.

Binoculars

Binoculars are two telescopes connected together to view an object with both eyes.

Prism binoculars.

To reduce the size of the Kepler tubes used in binoculars and reverse the image, rectangular total reflection prisms are used.

Pipe

GalileoGalileo built the first telescope with his own hands in 1609.

Galileo Galilei (1564- 1642)

Rays coming from an object pass through a collecting lens and become converging (they would give an inverted, reduced image). They then fall on a diverging lens and become divergent. They give imaginary, direct, magnified

image of an object.

Using his telescope with 30x magnification, Galileo made a number of astronomical discoveries: He discovered mountains on the Moon, spots on the Sun, discovered the four satellites of Jupiter, the phases of Venus, and established that the Milky Way consists of many stars.

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What it is?

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• Device
• An instrument is a device for measuring physical quantities.
• It was called measuring because it is used to measure something.

To measure means to compare one quantity with another.

• Slide 4
• Each device has a scale (division). The values ​​are compared using it.
• Let's take the simplest device - a ruler and consider it. It is straight and has a scale.

The scale of the ruler is not simple; it contains two physical quantities, centimeter and millimeter. So a five-centimeter ruler has

• Fifty short lines, one mm each, spaced apart from each other (this is approximately equal to the thickness of the wire of a mesh fence) and five long lines, one cm each (this is approximately equal to the width of the little fingernail).
• That means 1cm is 10mm. Only centimeters are signed. Because millimeters are inconvenient to use.

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Purpose

• So the ruler has two purposes:
  • 1) drawing straight lines and checking the lines (whether they are straight).
  • 2)measuring the length of objects

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Dynamometer

• A dynamometer is a device for measuring force.
• The price of one division is equal to one Newton. (written 1N)
• A dynamometer can measure friction force and traction force.

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Types of dynamometers

• Medical dynamometer (for measuring the strength of different human muscle groups)
• Hand-held dynamometer-silometer. (to measure arm strength)
• Traction dynamometer. (for measuring large forces)

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Athletes use this device

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Silomer

• The strength meter consists of two oval handles connected by a spring
• When they are compressed, the metal plate transmits the action to the arrow. The price of one division is equal to 1 kg.

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With this device you can predict the weather

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Aneroid barometer

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Barometer

• A barometer is a metal instrument for measuring atmospheric pressure.
• The price of one division is equal to two mm Hg. Art.
• Its structure is similar to a monometer.

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Aneroid barometer

• Structure: this is a metal box from which air has been pumped out. A spring is attached to it so that it does not get crushed by atmospheric pressure. The spring is attached to the arrow using an additional mechanism.

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Why not measure tire pressure?

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Pressure gauge

• A pressure gauge is used to measure pressure greater or less than atmospheric pressure.
• One division of the pressure gauge is the atmosphere.
• 2 atmospheres means that the pressure is greater than atm. 2 times.

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• The device works due to elasticity.
• Structure: this is a curved metal tube sealed on one side. It is attached to the arrow using a toothed gear. If the pressure increases

Slide 21

• - is lit, then the tube straightens and gives movement to the arrow. She starts moving to the right. If the pressure decreases, the tube bends back (due to elasticity) until it takes its original shape. The arrow continues to move behind the tube constantly.

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Take a light rectangular aluminum frame 2 and wind a thin wire coil around it. The frame is mounted on two semi-axes O and O", to which the arrow of the instrument 4 is also attached. The axis is held by two thin spiral springs 3. The elastic forces of the springs, returning the frame to the equilibrium position in the absence of current, are selected so that they are proportional to the angle of deviation of the arrow from the position equilibrium. The coil is placed between the poles of a permanent magnet M with tips in the shape of a hollow cylinder. A cylinder 1 made of soft iron is placed inside the coil. This design ensures the radial direction of the magnetic induction lines in the area where the coil turns are located (see figure). the magnetic field acting on it is maximum and, at a constant current, is constant. Take a light aluminum frame 2 of a rectangular shape, wind a coil of thin wire around it. The frame is attached to two semi-axes O and O", to which the arrow of the device 4 is also attached. The axis is held by two thin spiral springs 3. The elastic forces of the springs, which return the frame to the equilibrium position in the absence of current, are selected so that they are proportional to the angle of deviation of the arrow from the equilibrium position. The coil is placed between the poles of a permanent magnet M with tips in the shape of a hollow cylinder. Inside the coil there is a cylinder 1 made of soft iron. This design ensures the radial direction of the magnetic induction lines in the area where the coil turns are located (see figure). As a result, at any position of the coil, the forces acting on it from the magnetic field are maximum and, at a constant current strength, are constant.

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