Optical instruments that arm the eye. Presentation on the topic of electrical measuring instruments, the device was prepared by a student. Presentation of measuring instruments, gymnasium 1567

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Analog measuring instruments are devices whose readings are a continuous function of changes in the quantity being measured.

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An analog electrical measuring device is, first of all, an indicating device, i.e., a device that allows readings to be taken. To do this, for all analog electrical measuring instruments, regardless of the purpose and the type of measuring mechanism used in it, any device contains components and elements common to all analog instruments: a reading device, consisting of a scale located on the dial of the device, and a device indicator for creating a counteracting and calming moments support device.

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Measuring circuit Measuring mechanism Reading device The measuring circuit is a converter of the measured quantity x into some intermediate electrical quantity y (current, voltage), functionally related to the measured quantity x, i.e. y=f1(x). The electrical quantity y, which is current or voltage, directly affects the measuring mechanism (the input quantity of the mechanism). The measuring circuit contains resistance, inductance, capacitance and other elements. The measuring mechanism is a converter of the electrical energy supplied to it into the mechanical energy necessary to move its moving part relative to the stationary one, i.e. α = f2(y). The input quantities create mechanical forces acting on the moving part. Usually in mechanisms the moving part can only rotate around an axis, therefore the mechanical forces acting on the mechanism create a moment M. This moment is called torque M = Wm / α., where Wm is energy magnetic field The reading device is a pointer (arrow), a pen, rigidly connected to the moving part of the measuring mechanism and a fixed scale (a paper medium that combines the functions of a scale and a medium of recorded information). The moving part converts the angular movement of the mechanism into the movement of the pointer, and the value α is measured in scale division units. X Y α

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The common elements of analog electromechanical devices are: a housing (made of metal or plastic), a fixed and moving part (a coil, a ferromagnetic core or an aluminum rotating disk), a counteracting device (spiral or tape spring), a damper (liquid or magnetic induction), a zero position corrector and reading device (scale and pointer).

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Depending on the physical phenomena underlying the creation of torque, or, in other words, on the method of converting electromagnetic energy supplied to the device into mechanical energy of movement of the moving part, electromechanical devices are divided into the following main systems: magnetoelectric, electromagnetic, electrodynamic, ferrodynamic, electrostatic, induction.

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The principle of operation of IMs of various groups of devices is based on the interaction of: magnetoelectric IMs - magnetic fields of a permanent magnet and a current-carrying conductor; electromagnetic - the magnetic field created by a current-carrying conductor and a ferromagnetic core; electrodynamic (and ferrodynamic) - magnetic fields of two systems of conductors with currents; electrostatic - two systems of charged electrodes; induction - an alternating magnetic field of a conductor with current and eddy currents induced by this field in a moving element - as a result, an MVR torque is created.

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Depending on the method of creating a counteracting moment Ma, electromechanical SIs are divided into two groups: - with a mechanical counteracting moment; - with electrical counter-torque (logometers).

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A ratiometer is an electrical measuring device for measuring the ratio of the strengths of two electric currents. The moving part is made in the form of two frames located perpendicularly. When a current flows through the frame of the ratiometer, when interacting with the magnetic field of a permanent magnet of an elliptical shape (the fixed part of the ratiometer), a torque is created that moves the needle of the device. When the currents in both frames are equal, their torques are equal, the arrow of the device takes the zero position. If the currents are different, the moving part of the device moves in such a way that the frame with a large current ends up in a position with a large gap of the permanent magnet (due to its ellipticity). As a result, the torque generated by the frame decreases and becomes equal to the torque of the frame with a lower current. A ratiometer is usually used in instruments for measuring resistance, inductance, capacitance, and temperature. A ratiometer is a device in which there are no spiral springs that create a counteracting moment when the needle is turned, and the readings of which do not depend on the magnitude of the current, but depend on the multiple ratio of the currents in the coils. Logometers of magnetoelectric, electrodynamic, ferrodynamic, electromagnetic systems are common. For example, a logometer is a magnetoelectric megohmmeter, a device for measuring temperature complete with a resistance thermometer, etc.

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Magnetoelectric ammeters and voltmeters are the main measuring instruments in direct current circuits. Devices of the magnetoelectric system are based on the principle of interaction of the coil current (frame with current) and the magnetic field of a permanent magnet. The fixed part consists of a permanent magnet 1, its pole pieces 2 and a fixed core 3. There is a strong magnetic field in the gap between the pole pieces and the core. The moving part of the measuring mechanism consists of a light frame 4, the winding of which is wound onto an aluminum frame, and two semi-axes 5, fixedly connected to the frame frame. The ends of the winding are soldered to two spiral springs 6, through which the measured current is supplied to the frame. An arrow 7 and counterweights 8 are attached to the frame. A frame is installed in the gap between the pole pieces and the core. Its axle shafts are inserted into glass or agate bearings. When current passes through the winding of the frame, the latter tends to turn, but its free rotation is counteracted by spiral springs. And the angle at which the frame nevertheless turns, it turns out, corresponds to a certain current strength that flows through the winding of the frame. In other words, the angle of rotation of the frame (arrow) is proportional to the current strength. Ammeters and voltmeters have basically the same measuring mechanisms. Their difference lies only in the electrical resistance of the frames. An ammeter has a much lower frame resistance than a voltmeter.

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When the direction of the current changes, the direction of the torque (determined by the left-hand rule) changes. When a magnetoelectric system device is connected to an alternating current circuit, the coil is acted upon by mechanical forces that rapidly change in value and direction, the average value of which is zero. As a result, the instrument needle will not deviate from the zero position. Therefore, these instruments cannot be used directly for measurements in alternating current circuits. Calming (damping) of the needle in the devices of the magnetoelectric system occurs due to the fact that when the aluminum frame moves in the magnetic field of the permanent magnet NS, eddy currents are induced in it. As a result of the interaction of these currents with the magnetic field, a moment arises that acts on the frame in the direction opposite to its movement, causing the vibrations of the frame to quickly calm down.

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1) with a moving coil and a fixed magnet; 2) with a moving magnet and a fixed coil. with external magnet with internal magnet symbol 1 – fixed permanent magnet; 2 - magnetic circuit; 3- core; 4 – frame; 5 – spring; 6-arrow

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Advantages: high sensitivity, high accuracy, uniform scale, low intrinsic power consumption, low influence of external magnetic fields due to the strong intrinsic magnetic field. Disadvantages: design complexity, high cost, unsuitable for operation in alternating current circuits, sensitivity to overloads and current changes.

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Application: as DC ammeters and voltmeters with measurement limits from nanoamps to kiloamps and from fractions of millivolts to kilovolts, DC galvanometers, AC galvanometers and oscillographic galvanometers; In combination with various types of AC-DC converters, they are used for measurements in AC circuits.

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Prepare presentations: Magnetoelectric galvanometers Magnetoelectric logometers Magnetoelectric ohmmeters Magnetoelectric ammeters and voltmeters

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Electromagnetic system devices operate on the principle of drawing a metal armature into a coil when a electricity. The operating principle of electromagnetic system devices is based on the interaction of a magnetic field created by a stationary coil, through the winding of which the measured current flows, with one or more ferromagnetic cores mounted on an axis. Fixed coil 3 is a frame with a wound insulated copper tape. When a measured current flows through the coil, a magnetic field is created in its flat slit. Core 5 with arrow 4 is mounted on axis 1. The magnetic field of the coil magnetizes the core and draws it into the slot, turning the axis with arrow. Spiral spring 2 creates a counteracting moment Mpr 1 – axis 2 – spiral spring 3 – coil 4 – arrow 5 – core 6 – damper

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Advantages: simplicity of design, ability to measure direct and alternating currents, ability to withstand large overloads, low cost. Disadvantages: influence of external magnetic fields on instrument readings, uneven scale (quadratic, i.e. compressed at the beginning and stretched at the end), low sensitivity, low accuracy, high power consumption.

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EM system devices are used mainly as panel ammeters and AC voltmeters of industrial frequency of accuracy class 1.0 and lower classes for measurements in AC circuits, in portable multi-range devices of accuracy class 0.5.

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Purpose of instrumentationControl and measuring
devices are intended for
parameter control,
characterizing the work
the car as a whole and individual
its units.

Requirements for instrumentation

Informativeness - assessed by time,
necessary for correct reading
information or number of errors in
reading information with limited
reading time.
Low sensitivity to pulsations and
change in voltage in the on-board network
car.
Resistance to vibration, changes
temperature, exposure to aggressive
environment.

Instrumentation classification

1. By way of displaying information
control and measuring instruments are divided into:
◦ pointing;
◦ signaling.
Indicating instruments have a scale on which
the values ​​of the measured parameter are indicated.
Signaling devices inform about
critical value of the measured parameter, about
functional state of a node or unit
car using sound or light
signal.

Instrumentation classification

2. By design devices
are divided into:
mechanical;
electrical;
◦ magnetoelectric,
◦ electromagnetic,
◦ pulse systems.
electronic.

Instrumentation classification

3. According to the intended purpose, control and measuring equipment
devices are divided into:
temperature meters (thermometers),
pressure meters (manometers),
fuel level meters,
battery charging mode meters (ammeters),
car speed and distance meters
ways (speedometers, odometers),
engine speed meters
(tachometers),
econometricians,
tachographs.

Instrumentation

Any instrumentation consists of two main
nodes: sensor and pointer.
The sensor converts the measured
physical quantity to electrical quantity
size, located on
controlled unit.
The pointer converts electrical
the value of the angle of deflection of the arrow,
located on the instrument panel.

Thermometers

For measuring temperature in cars
systems are most often installed with
magnetoelectric
ratiometric index and
thermistor sensor,
less commonly, pulse systems.

Thermometers

Thermistor sensor:
a - design; b - resistance dependence
temperature sensor;
1- body; 2- current-carrying spring;
Z - insulating sleeve; 4-pin bushing;
5- thermistor tablet; 6- insulator; 7-pin.

Thermometers


a - electrical circuit of the thermometer;
b - magnetoelectric design
ratiometric index;
1 - frame; 2 - magnetic screen; 3 - arrow axis;
4 - windings; 5 - permanent magnet.

Thermometers

Thermometer with ratiometric indicator:

b - electrical circuit diagram;

24 - coil frame; 22 - temperature indicator coils;
43 - temperature indicator sensor; 44 - magnet balancers and arrows;
45 - permanent magnet.

Thermometers

Thermometer with ratiometric indicator:
A - appearance magnetoelectric ratiometric indicator;
b - electrical circuit diagram;
26 - coolant temperature indicator;
24- coil frame; 22 temperature indicator coils; 43-sensor
temperature indicator; 44- magnet balancers and arrows;
45 - permanent magnet.

Pulse system thermometer

a - electrical circuit of the thermometer; b - device
thermobimetallic sensor; c - pointer device
pulse system; d - electrical circuit of the thermal alarm:
1 - sensor; 2- bimetallic plate; Z - heating
spiral; 4- contacts; 5-pointer; 6- adjustment sector; 7-
elastic plate with arrow.

Pulse system thermometer

"Cold" engine
I
Ieff
t
"Hot" engine
I
Ieff
t

Fuel level meters

a - rheostat sensor; b, c - electrical circuit of the meter
12 and 24 V, respectively;
1 - rheostat; 2- slider; 3, 5 - backup alarm contacts
fuel supply; 4-conclusions; 6-axis float; 7-float.
L1, L2, L3 - ratiometer windings; Rd - sensor resistance; RT -
temperature compensation resistor; Rext. - additional resistor

Fuel level meters with electromagnetic system indicator

1 - anchor; 2 - arrow; 3 - pole pieces;
4 - float; L1, L2 – pointer coils;
Rd - sensor resistance.

Pressure meters

a - sensor with rheostatic output;
b- pulse system;
1- fitting; 2- membrane; Z-rheostat; 4-engine
rheostat; 5 - fixed contact plate;
6-bimetallic plate with spiral and
moving contact; 7-regulator;

Pressure meters

c - diagram of a pressure gauge with a ratiometric meter;
d - diagram of the pressure gauge of the pulse system;
8 - bimetallic indicator plate;
L1, L2, L3 - ratiometer windings;
Rd, RT sensor and temperature compensation resistors.

ammeters;
◦ Electromagnetic system;
◦ Magnetoelectric system;
voltmeters;
◦ Magnetoelectric system with
moving coil

Battery charge meters

Ammeter
electromagnetic
systems
◦
◦
◦
◦
◦
1 – brass tire;
2 – arrow;
3 – permanent magnet;
4 – base;
5 – anchor.

Battery charge meters

Ammeter
magnetoelectric
systems
◦ 1 – permanent magnet;
◦ 2 – stationary
coil;
◦ 3 – shunt;
◦ 4 – arrow;
◦ 5 – stationary
permanent magnet.

Battery charge meters

Voltmeter of magnetoelectric system with moving
coil

Battery charge meters

Voltmeter:
◦ red sector - voltage 8...11V, battery not
charging;
◦ white sector – voltage 11...12V, battery not
recharges;
◦ green sector – voltage 12...15 V, battery charging and
generator set operation is normal;
◦ red sector – voltage 15...16 V, recharging
batteries, generator set is faulty.

Speedometers

By type of drive they can be:
◦ with mechanical drive (flexible shaft);
◦ with electric drive.
according to the operating principle:
◦ magnetic induction;
◦ electronic.

Speedometers

Magnetic induction
speedometer:
a - high-speed node;
1 - drive shaft;
2 - thermomagnetic shunt,
3 - magnet; 4 - card;
5 - screen-magnetic core;
6 - setting regulator;
7 - spring; 8 - arrow;
9 - drive of the counting unit;

Speedometers

Magnetic induction speedometer:
b - counting unit;
10-reel counting unit; 11-tribe.

Electric speedometer

Tachometers

Electronic tachometer circuit

Instrumentation malfunctions

Speedometer:
◦ The speedometer does not work;
◦ Incorrect speed reading;
◦ Oscillation of the speedometer needle;
Lack of instrument readings:
◦ The arrow is in its original position (wire break from the sensor);
◦ Arrow at maximum value (short to ground);
Sensor malfunction:
◦ complete refusal;
◦ violation of characteristics.
Pointer fault:
◦ mechanical damage;
◦ violation of electrical connections.

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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.

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    • 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

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    • 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 great 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

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    • - 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 such 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. Inside the coil there is a soft iron cylinder 1. This design ensures the radial direction of the lines of magnetic induction in the area where the coil turns are located (see figure). As a result, at any position of the coil of force, The magnetic field acting on it is maximum and, at a constant current strength, 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 in place 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 such 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 shaped like 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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