What device measures body weight? Mass measuring equipment. Hourglass and fire clock

Scales (device) Scales, a device for determining the mass of bodies by the force of gravity acting on them. V. is sometimes also called instruments for measuring others. physical quantities, converted for this purpose into force or at the moment of force. Such devices include, for example, current scales And Pendant scales. The sequence of actions when determining the mass of bodies in the east is discussed in Art. Weighing.

V. is one of the oldest devices. They arose and improved with the development of trade, production and science. The simplest V. in the form of an equal-arm rocker with suspended cups ( rice. 1) were widely used in barter trade in Ancient Babylon (2.5 thousand years BC) and Egypt (2 thousand years BC). Somewhat later, unequal-shoulder V. with a movable weight appeared (see. Steelyard). Already in the 4th century. BC e. Aristotle gave a theory of such V. (rule moments of force). In the 12th century The Arab scientist al-Khazini described cups with cups whose error did not exceed 0.1%. They were used to determine the density of various substances, which made it possible to recognize alloys, identify counterfeit coins, distinguish precious stones from counterfeit ones, etc. In 1586 Galileo to determine the density of bodies, he designed special hydrostatic waves. The general theory of waves was developed by L. Euler (1747).

The development of industry and transport led to the creation of vehicles designed for heavy loads. At the beginning of the 19th century. decimal Vs were created. ( rice. 2) (with a weight-to-load ratio of 1:10 - Quintenz, 1818) and hundredth V. (V. Fairbanks, 1831). At the end of the 19th - beginning of the 20th centuries. With the development of continuous production, weighing machines appeared for continuous weighing (conveyor, dosing, etc.). In various branches of agriculture, industry, and transport, weighers of a wide variety of designs began to be used for weighing specific types of products (in agriculture, for example, grains, root vegetables, eggs, etc.; in transport - cars, railways. carriages, airplanes; in industry - from the smallest details and assemblies in precision instrument making to multi-ton ingots in metallurgy). For scientific research, designs of precision tests were developed - analytical, microanalytical, assay, etc.

Depending on their purpose, weights are divided into standard (for calibrating weights), laboratory (including analytical) and general purpose, used in various fields of science, technology and the national economy.

According to the principle of operation, voltages are divided into lever, spring, electric strain gauge, hydrostatic, and hydraulic.

Lever valves are the most common; their action is based on the law of equilibrium. lever The fulcrum of the lever (“rocker arms” V.) can be in the middle (equal-arm V.) or be shifted relative to the middle (unequal-arm and single-arm V.). Many lever machines (for example, commercial, automobile, portion, etc.) are a combination of levers of the 1st and 2nd types. The supports for the levers are usually prisms and cushions made of special steel or hard stone (agate, corundum). On equal-arm lever weights, the body being weighed is balanced by weights, and some excess (usually 0.05–0.1%) of the weight of the weights over the body weight (or vice versa) is compensated by the moment created by the rocker arm (with an arrow) due to the displacement of its center of gravity relative to the original position ( rice. 3). The load compensated by the displacement of the center of gravity of the rocker arm is measured using a reading scale. The value of division s of the lever V. scale is determined by the formula

s = k(P o c / lg),

where P 0 ‒ the weight of the rocker arm with the arrow, c ‒ the distance between the center of gravity of the rocker arm and the axis of its rotation, l ‒ the length of the rocker arm, g ‒ acceleration

free fall, k is a coefficient that depends only on the resolution of the reading device. The division value, and, consequently, the sensitivity of the V., can be changed within certain limits (usually by moving a special weight that changes the distance c).

In a number of lever laboratory V., part of the measured load is compensated by the force of electromagnetic interaction - retraction of the iron core connected to the rocker arm into a stationary solenoid. The current strength in the solenoid is regulated by an electronic device that brings the voltage to equilibrium. By measuring the current strength, they determine the load V proportional to it. V. of this type are brought to the equilibrium position automatically, so they are usually used for measuring changing masses (for example, when studying oxidation processes, condensation, etc.), when it is inconvenient or impossible to use conventional V. The center of gravity of the rocker arm is combined in these V. with the axis of rotation.

In laboratory practice, weights (especially analytical ones) with built-in weights for part of the load or for the full load are increasingly being used ( rice. 4). The principle of operation of such V. was proposed by D.I. Mendeleev. Specially shaped weights are suspended from the shoulder on which the load cup is located (single-arm weights), or (less commonly) from the opposite shoulder. In single-arm V. ( rice. 5) the error due to the unequal arms of the rocker is completely eliminated.

Modern laboratory scales (analytical, etc.) are equipped with a number of devices to increase the accuracy and speed of weighing: vibration dampers of cups (air or magnetic), doors, when opened, there is almost no air flow, heat shields, mechanisms for applying and removing built-in weights, automatically operating mechanisms for selecting built-in weights when balancing B. Projection scales are increasingly being used, making it possible to expand the range of measurements on the reference scale at small angles of deflection of the rocker arm. All this allows you to significantly increase the performance of V.

In high-speed technical quadrant V. ( rice. 6) the measurement limit on the rocker arm deflection scale is 50 – 100% of the maximum load V., usually lying in the range of 20 g – 10 kg. This is achieved by a special design of a heavy rocker arm (quadrant), the center of gravity of which is located significantly below the axis of rotation.

Most types of metrological, standard, analytical, technical, and trade ( rice. 7), medical, carriage, automobile V., as well as automatic and portioned V.

The action of spring and electric strain gauges is based on Hooke’s law (see. Hooke's law).

The sensitive element in spring voltages is a spiral flat or cylindrical spring that is deformed under the influence of body weight. V.'s readings are measured on a scale along which a pointer connected to a spring moves. It is assumed that after removing the load, the pointer returns to the zero position, that is, no residual deformation occurs in the spring under the influence of the load.

With the help of spring V., they measure not mass, but weight. However, in most cases, the spring scale is graduated in units of mass. Due to the dependence of the acceleration of gravity on geographic latitude and altitude above sea level, the readings of spring winders depend on their location. In addition, the elastic properties of the spring depend on temperature and change over time; all this reduces the accuracy of spring V.

In torsional (torsional) batteries, the sensitive element is an elastic thread or spiral springs ( rice. 8). The load is determined by the angle of twist of the spring thread, which is proportional to the torsional moment created by the load.

The action of electrical strain gauges is based on converting the deformation of elastic elements (columns, plates, rings) that perceive the force of a load into a change in electrical resistance. The transducers are highly sensitive wire strain gauges, glued to elastic elements. As a rule, electric strain gauges (carriage, automobile, crane, etc.) are used for weighing large masses.

Hydrostatic measurements are used primarily to determine the density of solids and liquids. Their action is based on Archimedes' law (see. Hydrostatic weighing).

Hydraulic V. are similar in design hydraulic press. The readings are taken using a pressure gauge calibrated in mass units.

All types of V. are characterized by: 1) ultimate load - the greatest static load that the V. can withstand without breaking them metrological characteristics; 2) division value - the mass corresponding to a change in the reading by one scale division; 3) the limit of permissible weighing error - the largest permissible difference between the result of one weighing and the actual mass of the body being weighed;

4) permissible variation of readings - the largest permissible difference in V.’s readings when repeatedly weighing the same body.

Weighing errors on some types of V. at maximum load.

Weighing error at maximum load

Metrological..........

Exemplary 1st and 2nd categories

Exemplary 3rd category and

technical 1st class............

Analytical, semi-microanalytical, microanalytical, assay

Medical........................

Household...................

Automotive........................

Carriage................

Torsional...............

1 kg

20 kg ‒ 1 kg

200 g - 2 g

20 kg ‒ 1 kg

200 g ‒2 g

200 g

100 g

20 g

2 g

1 g

150 kg

20 kg

30 kg ‒ 2 kg

50 t ‒ 10 t

150 t ‒ 50 t

1000 mg ‒ 20 mg

5 mg ‒ 0.5 mg

0.005 mg*

20 mg ‒ 0.5 mg*

1.0 mg ‒ 0.01 mg*

100 mg ‒ 20 mg

10 mg - 0.4 mg

1.0 mg ‒ 0.1 mg*

1.0 mg ‒ 0.1 mg*

0.1 mg ‒ 0.01 mg*

0.02 mg ‒ 0.004 mg*

0.01 mg ‒ 0.004 mg*

50 g

10 g

60 g ‒5 g

50 kg ‒ 10 kg

150 kg ‒ 50 kg

1.0 mg - 0.05 mg

0.01 mg - 0.001 mg

* Using precision weighing methods.

Lit.: Rudo N.M., Libra. Theory, structure, adjustment and verification, M. - L., 1957; Malikov L. M., Smirnova N. A., Analytical electric scales, in the book: Encyclopedia of Control and Automation Measurements, v. 1, M. - L., 1962: Orlov S.P., Avdeev B.A., Weighing equipment of enterprises, M., 1962; Karpin E. B., Calculation and design of weighing mechanisms and dispensers, M., 1963; Gauzner S.I., Mikhailovsky S.S., Orlov V.V., Recording devices in automatic weighing processes, M., 1966.

N. A. Smirnova.

Great Soviet Encyclopedia. - M.: Soviet Encyclopedia. 1969-1978 .

See what “Scales (device)” is in other dictionaries:

Scales - get a worker at the Academician - SCALES, a device for determining the weight of bodies. In a broader sense, some instruments measure forces of origin other than gravity. 1. Scales for accurate weighing. Currently, the system proposed by... is mainly used. Great Medical Encyclopedia

Ov; pl. 1. Device for determining weight and mass. Laboratory c. Pharmacy v. Electronic v. V. Themis (book; about justice). 2. [with a capital letter] One of the twelve constellations of the Zodiac. 3. About a person born at the end of September October, when... encyclopedic Dictionary

A device for determining the mass of bodies by the force of gravity acting on them. V. sometimes called also instruments for measuring other physics. quantities converted for this purpose into force or moment of force. Such devices include, for example, current balances and torsion... ... Physical encyclopedia Big Polytechnic Encyclopedia

General information

Modern scales are a complex mechanism that, in addition to weighing, can provide registration of weighing results, signaling in case of mass deviation from specified technological standards and other operations.

1.1. Laboratory equal-arm scales(Fig. 4.1) consist of a rocker arm 1 mounted using a support prism 2 on the flange 3 of the base of the scales. The rocker arm has two load-receiving prisms 5, 11 through which, using cushions 4 and 12, suspensions 6 and 10 are connected to the rocker arm 1. The scale 8 of the optical reading device is rigidly attached to the rocker arm. When measuring mass, a weighed load 9 with a mass m is installed on one pan of the scale, and balancing weights 7 with a mass m g are placed on the second pan. If m > m g, then the balance beam is deflected by an angle φ (Fig. 4.2).

The VLR-20 scales (Fig. 4.3) have a maximum weighing limit of 20 g and a dividing device division value of 0.005 mg.

A hollow stand 9 is installed on the base of 6 scales; a bracket with insulating levers 11 and a support pad 15 are attached to the upper part of the rack. An illuminator 5, a condenser 4 and a lens 3 of an optical reading device are installed on the base 6. A support prism 17, saddles with load-receiving prisms 13 and a pointer 1 with a microscale 2 are fixed to the equal-arm rocker arm 16.

The equilibrium position of the moving system on the rocker arm is adjusted using calibration nuts 19 at the ends of the rocker arm. By adjusting the position of the center of gravity of the rocker by vertically moving the adjusting nuts 18 located in the middle of the rocker, it is possible to set the specified weight division price. The load-receiving prisms 13 support the cushions 14 of the earrings 12, on which the pendants with the load-receiving cups 7 are suspended.

The scales have two air dampers 10. The upper part of the damper is suspended on an earring, and the lower part is mounted on a board 8 at the top of the scales.

The weight application mechanism 20, located on the board 8, allows you to hang weights weighing 10 on the right suspension; 20; 30 and 30 mg, providing balancing with built-in weights ranging from 10 to 90 mg. The mass of the applied weights is counted on a digitized dial connected to the weight application mechanism.

An optical reading device is used to project a scale image onto a screen using an illuminator, a condenser, a lens and a system of mirrors and allows the change in mass to be measured in the range from 0 to 10 mg. The scale has 100 reading divisions with a division value of 0.1 mg. The dividing mechanism of the optical reading device allows one division of the scale to be divided into 20 parts and, increasing the resolution of the reading, provides a measurement result with a resolution of 0.005 mg.

1.2. Laboratory double prism balance(Fig. 4.5) consist of an asymmetrical rocker 1, installed with the help of a support prism 2 on the pad 5 of the base of the scales. A suspension 9 with a load-receiving cup is connected to one arm of the rocker through a load-receiving prism 6 and a cushion 11. A rail 10 is attached to the same suspension, on which built-in weights 7 are hung, with a total mass of T 0 . A counterweight 4 is attached to the other arm of the rocker arm, balancing the rocker arm. The microscale 3 of the optical reading device is rigidly attached to the rocker 1. When measuring mass, a weighing weight 8 with a mass of T 1, and from the rack using a weight mechanism, part of the weights 7 with a mass of T T.

If T 1 > T g, then the balance beam deviates by an angle φ (Fig. 4.6). In this case, the gravitational moment of stability will be

Where T P, T etc, T k - mass of suspension, counterweight, rocker arm; T about and T 1 - mass of all built-in weights and load; T g - mass of removed weights; A 1 - distance from the axis of rotation of the rocker to the points of contact of the load-receiving prism with the suspension cushion; A 2 - distance from the axis of rotation of the rocker to the center of gravity of the counterweight; A k is the distance from the axis of rotation of the rocker to its center of gravity, α 1, α 2 are angles depending on the installation of the lines of the rocker prisms; g = 9.81 m/s2.

Compensating moment

Error δ y, depending on the gravitational moment of stability and the angle of deviation φ, is determined by the formula:

(4.3)

Error δ to, depending on the compensating moment, will be

(4.4)

Scales VLDP-100 (Fig. 4.4) with the largest weighing limit of 100 g, with a named scale and built-in weights for full load. The scales have a pre-weighing device that allows you to increase the speed of mass measurement and simplify weighing operations associated with the selection of weights that balance the moving scale system.

On the short arm of the rocker 1 there is a saddle with a load-receiving prism 9, and on the long arm there is a counterweight, an air damper disk and a microscale 4 of the optical device. During weighing, an earring 11 rests on the load-receiving prism 9 of the rocker arm with a cushion 10, to which a suspension 7 with a load-receiving cup 6 is attached.

The scales have a weighting mechanism 8, which serves to remove from the suspension and apply three decades of built-in weights weighing 0.1-0.9 to it; 1-9 and 10-90

The pre-weighing mechanism has a horizontal lever 3, whose free end rests against the rocker arm. The second end of the lever is rigidly attached to a torsion spring, the axis of rotation of which is parallel to the axis of rotation of the rocker arm.

Rice. 4.1. Equal-armed scales	Rice. 4.2. Scheme of the action of forces in equal-armed scales
Rice. 4.3. Laboratory equal-arm scales VLR-20	Rice. 4.4. Laboratory scales VLDP-100
Rice. 4.5. Double prism scales	Rice. 4.6. Scheme of the action of forces in two-prism balances

The isolating mechanism 5 has three fixed positions: IP - initial position, PV - preliminary weighing, TV - precise weighing.

In the initial position, the rocker arm 1 and the suspension 7 are on the stops of the isolating mechanism 5. The lever of the pre-weighing mechanism is in the lower position, the built-in weights are hung on the suspension.

When weighing a load placed on a cup, the isolating mechanism is first placed in the PV position. In this case, lever 3 rests on the rocker arm, the built-in weights are removed from the suspension, and the suspension is lowered onto the load-receiving prism of the rocker arm. After this, the rocker arm is lowered onto the cushion by the support prism 2, deflected by a certain angle at which the counteracting moment created by the torsion spring of the pre-weighing mechanism balances the moment proportional to the difference T k = T 0 - T 1 where T 0 - mass of built-in weights; T 1 - mass of the body being weighed.

Using the scale of the optical reading device and the dial of the dividing device, the preliminary value of the measured mass is counted, which is set on the counters of the weighting mechanism.

When moving the isolating mechanism to the TV position, first isolate the rocker arm and suspension, after which weights with a mass of T d. Lever 3 is pulled down all the way, releasing the rocker arm, the suspension is connected to the rocker arm through a load-receiving prism and a cushion, and the rocker arm sits on the cushion with the support prism and precise weighing is performed.

The value of the measured mass is counted by the counter of the weighting mechanism, the scale and the dial of the dividing device.

1.3. Quadrant scales are simple, reliable in operation, and have high accuracy. Unlike other laboratory scales, the weight receiving cup of quadrant scales is located in the upper part, which creates significant ease of use. Quadrant scales are used in production lines, in centralized control systems, and in control systems associated with mass measurement.

Quadrant scales (Fig. 4.7) consist of an asymmetrical rocker 1 (quadrant), installed using a support prism 2 on a corner pad 3, fixed to the base of the scales. The suspension 6, using corner pads 8, is installed on the load-receiving prism 7, mounted on the rocker arm 1. The load-receiving cup 9 in the quadrant scales is attached to the upper part of the suspension 6. To prevent the suspension from tipping over when a load is placed on the cup 9, the lower part of the suspension is attached to the base of the scales through hinge joints using a lever 5 called a string. The microscale 4 of the optical reading device is rigidly attached to the quadrant. A rail is attached to the suspension, on which built-in weights are located.

The use of corner cushions and hinge joints in the lower part of the suspension in quadrant scales made it possible to increase the working angle of deflection φ of the quadrant several times compared to the deflection angle in equal-arm or two-prism scales. For example, in quadrant scales, when the maximum load is applied to the suspension, the deflection angle is 12°, and in equal-arm and double-prism scales it is less than 3°. With a large deflection angle, naturally the range of mass measurement on the scale will also be larger, which makes it possible to reduce the number of built-in weights used in the scales. However, hinges with a string are a source of additional errors, reducing weighing accuracy. Therefore, the quadrant scales produced generally have accuracy class 4.

Laboratory quadrant scales model VLKT-5 (Fig. 4.8) belong to accuracy class 4 and are designed for measuring mass up to 5 kg. The measuring system of scales includes a rocker arm 3, a suspension bracket 2 with a load-receiving cup 1, and a “string” b. The prismatic “string” is one of the sides of the articulated parallelogram. The “string” and steel prisms of the rocker rest on angular self-aligning cushions. To calm the vibrations of the moving system, the scales have a magnetic damper 5. The scales also have a mechanism for compensating for fluctuations in the level of the workplace, a device for compensating the mass of the container and a weighting mechanism. When weighing, special grips driven by the handles of the weighting mechanism are removed from the weight-receiving suspension or built-in weights 7 weighing 1, 1 and 2 kg are placed on it. The mass values ​​of the removed weights are counted from a digitized drum associated with the weighting mechanism. The optical reading device includes a backlight lamp, a condenser, a lens and a microscale 4, mounted on the rocker arm. The image of the microscale, enlarged using an optical system, is transmitted to the frosted glass of the screen 8, where the value of the mass determined when the rocker arm deviates from its initial position is indicated.

A cylindrical spiral spring 9, attached at one end to the suspension, is a measuring element of the dividing mechanism. The second end of this spring, connected by a drive to the digitized drum of the mechanical counter, can move vertically when the counter handle of the dividing mechanism is rotated. When the drum of a mechanical counter rotates to a full capacity equal to 100 divisions, the spring stretches, transmitting to the rocker a force equivalent to the force created by changing the mass of the load by 10 g, and the result of the measurement made using the dividing mechanism is counted on the digitized drum of the mechanical counter with a discreteness of 0 ,1 g. The microscale mounted on the rocker has 100 divisions with a division value of 10 g. Therefore, the measuring range of the optical reading device and dividing mechanism with a resolution of 0.1 g is 1000 g.

The quadrant scales model VLKT-500 (Fig. 4.9), designed for measuring mass up to 500 g (measurement error ±0.02 g), are designed in a similar way.

Before measuring body weight at level 1, the scales are installed in a horizontal position using adjustable supports 4. To put the scales into operation, it is necessary to connect the power cord 5 to the electrical network and turn on the switch 2. Using the handle 7, set the digital drum of the mechanical counter to position “00” and use the handwheels 3 (“coarse”) and 6 (“fine”) tare weight compensation devices bring the zero scale division to a symmetrical position. In this case, the handle 9 of the weighting mechanism is in the position for measuring in the range of 1-100 g. The body under study is placed on the load-receiving cup 10 and the handle 7 combines the scale division with the reading marks on the screen 8.

Torsion scales WT-250 (Fig. 4.10) are designed for weighing bodies weighing up to 250 g and have a measurement error of ±0.005 g. The body of the scale rests on three supports, two of which 1 are adjustable and are designed to install the scales in a horizontal position at level 2.

The scale casing has a glass screen 4, through which the dial of the measuring mechanism is visible. Before weighing, turn the lock 9 to unlock the suspension and use the flywheel 10 of the tare weight compensation device to set the pointer 5 to the zero position. The measured body 7 is placed on the suspension 6 and the safety cover 8 is closed. By rotating the flywheel 3 of the movable dial, the pointer 5 is returned to the zero position. In this case, the amount of body weight is determined by the arrow on the dial of the measuring mechanism.

1.4. Electronic digital scales. A significant advantage of the scales is that operations do not require built-in or overhead weights. Therefore, during serial production of scales and during their operation, metal is significantly saved and the number of weights subject to state verification is reduced.

Electronic digital scales of the 4th accuracy class, model VBE-1 kg (Fig. 4.11, a), based on the principle of operation discussed above. These scales have a weighing device I mounted on a base 2, and an electrical part consisting of five printed circuit boards 3, 13, 14 with connectors and mounting brackets, a transformer 15, a sensor 4 that converts linear movements into an electrical signal.

The weighing device has a stand on which a bracket 12 and a magnetic system 16 with a working coil 5 are mounted. The movable scale system consists of two frames 6, a bracket 7 and six springs 8, two of which are intermediate links in the elastic-flexible connection between the frames and the bracket. The working coil is attached to the liner 9, which is rigidly connected to the bracket 7. The movable weighing system is attached through springs 8 so that the coil in the working gap of the magnetic system can only move in the vertical direction. In the upper part of the bracket 7 there is a stand 10, on which the load-receiving cup 11 is installed.

The electrical part of the scales is made on printed circuit boards located in the scale housing. The electrical elements that generate heat are located at the rear of the scale and are separated from the weighing device by a heat shield.

The scales have an electronic device that compensates for the force generated by the container. When a container is placed on the load receiving cup, the value of its mass appears on the digital reading device, and after pressing the “Tare” button, this value is transferred to the storage device, and the digital reading device is set to zero and the scales are ready to measure the mass of the load. The tare compensation device included in the scale compensates for loads weighing up to 1000 g.

Electronic digital scales of the 4th class VLE-1 kg with improved technical characteristics (Fig. 4.11, b). This scale can be widely used in closed technological processes agro-industrial complexes. They have an output for connecting digital printing devices and computers, semi-automatic calibration and tare weight compensation over the entire weighing range. The terminal provides automatic sorting of items by weight and counting the number of items based on a given value of the mass of one item.

3. Work order: read clause 1; using formulas (4.1)-(4.4) according to the initial conditions (Table 4.1) for two-prism scales, determine: the moment of stability M y, the compensating moment M k, as well as the errors δ y and δ k, compile a report.

Rice. 4.7. Laboratory quadrant scales	Rice. 4.8. Scheme of quadrant scales VLKT-5
Rice. 4.9. General form scales VLKT-500

Table 4.1. Initial data for performing the work

- describe the purpose, design of devices and draw their diagrams (Fig. 4.1

Perform calculations to determine M y, M k, δ y and δ k;

Give answers to security questions.

Control questions

1. How is the equilibrium position of the moving system on the rocker in the VLR-20 scales adjusted?

2. On which arm of the rocker arm is the saddle with the load-receiving prism mounted in the VLDP-100 scales?

3. What is the design difference between quadrant scales and two-prism scales?

4. How are quadrant scales model VLKT-5 designed?

5. How is weighing performed on the VLKT-500 scales?

6. How do electronic scales model VBE-1 work?

Laboratory and practical work No. 5

Instruments for measuring mass are called scales. At each weighing, at least one of four basic operations is performed

1. determination of unknown body weight (“weighing”),

2. measuring a certain amount of mass (“weighing”),

3. determination of the class to which the body to be weighed belongs (“tariff”

level weighing" or "sorting"),

4. weighing of a continuously flowing material flow.

The measurement of mass is based on the use of the law of universal gravitation, according to which the Earth's gravitational field attracts mass with a force proportional to that mass. The force of attraction is compared with the known force created by different ways:

1) a load of known mass is used for balancing;

2) a balancing force occurs when the elastic element is deformed;

3) the balancing force is created by a pneumatic device;

4) a balancing force is created hydraulic device;

5) the balancing force is created electrodynamically using a solenoid winding located in a constant magnetic field;

6) a balancing force is created when a body is immersed in a liquid.

The first method is classic. The measure in the second method is the amount of deformation; in the third - air pressure; in the fourth - fluid pressure; in the fifth - the current flowing through the winding; in the sixth - immersion depth and lifting force.

Classification of scales

1. Mechanical.

2. Electromechanical.

3. Optomechanical.

4. Radioisotope.

Lever trade scales

Commercial mechanical scales RN-3TS13UM

Mechanical scales are based on the principle of comparing masses using levers, springs, pistons and scales.

In electromechanical scales, the force developed by the mass being weighed is measured through the deformation of the elastic element using strain gauge, inductive, capacitive and vibration-frequency transducers.

The current stage of development of laboratory scales, characterized by relatively low speed and significant susceptibility to external influences, is characterized by the increasing use in them to create a balancing force (torque) of electric power exciters with an electronic automatic control system (ACS), which ensures the return of the measuring part of the scale to its original equilibrium position. SAR electronic lab. scales (Fig. 4) includes a sensor, for example, in the form of a differential transformer; its core is fixed to the measuring part and moves in a coil mounted on the base of the scale with two windings, the output voltage of which is supplied to the electronic unit. Sensors are also used in the form of an electro-optical device with a mirror on the measuring part that directs a beam of light to a differential photocell connected to the electronic unit. When the measuring part of the scale deviates from the initial equilibrium position, the relative position of the sensor elements changes, and a signal containing information about the direction and magnitude of the deviation appears at the output of the electronic unit. This signal is amplified and converted by the electronic unit into current, which is supplied to a power exciter coil mounted on the base of the scale and interacts with a permanent magnet on its measuring part. The latter, thanks to the counteracting force that arises, returns to its original position. The current in the exciter coil is measured with a digital microammeter calibrated in mass units. Electronic scales with a top-mounted weight cup use a similar automatic balancing circuit, but permanent magnet The power exciter is mounted on a rod carrying a cup (electronic lever-less scales) or is connected to this rod by a lever (electronic lever scales).

Schematic diagram electronic lab. scales: 1 - sensor; 2-core; 3, 5-correspondences of the sensor coil and the exciter; 4-power exciter; 6-permanent magnet; 7-rod; 8-weight-receiving cup; 9-electronic unit; 10-power supply; 11-digit readout device.

Vibration frequency (string). Its action is based on changing the frequency of a tense metal string installed on an elastic element, depending on the magnitude of the force applied to it. The influence of external factors (humidity, temperature, atmospheric pressure, vibration), as well as the complexity of manufacturing, have led to the fact that this type of sensor has not found wide application.

Vibration-frequency sensor of electronic scales from TVES. An elastic element 2 is attached to the base 1, in the hole of which there is a string 3, made integral with it. On both sides of the string there are coils of the electromagnet 4 and the displacement transducer 5 inductive type. A rigid plate 6 with supports 7 is attached to the upper surface of the elastic element, on which the base of the load-receiving platform is placed. To limit the deformation of the elastic element there is a safety rod 8.

Electronic table scales.

Specifications:

weighing range - 0.04–15 kg;

resolution - 2/5 g;

sampling of tare weight - 2 kg;

average service life - 8 years;

accuracy class according to GOST R 53228 - III average;

mains power parameters alternating current- 187–242 / 49 - 51 V/Hz;

power consumption - 9 W;

dimensions- 295×315×90 mm;

weight - 3.36 kg;

overall dimensions (with packaging) - 405×340×110 mm;

weight (with packaging) - 4.11 kg.

IN Lately Electromechanical scales with a quartz piezoelectric element are widely used. This piezoelectric element is a thin (no more than 200 microns) plane-parallel rectangular quartz plate with electrodes located in the center on both sides of the plate. The sensor has two piezoelectric elements glued to elastic elements, which implement a differential loading scheme for the transducers. The force of gravity of the load causes compression of one elastic element and stretching of the other.

Scales from the Mera company with an external display device PVm-3/6-T, PVm-3/15-T, PVm-3/32-T. Three ranges: (1.5; 3; 6), (3; 6; 15), (3; 6; 32) kg.

The principle of operation of the scales is based on the transformation of the deformation of the elastic element of the load cell, which occurs under the influence of gravity of the load, into an electrical signal whose amplitude (strain gauge sensor) or frequency (strain quartz sensor) varies in proportion to the mass of the load.

Thus, in terms of the method of installation on a deformable body, transducers of this type are similar to strain gauges. For this reason, they are called strain gauge quartz transducers. In the body of each piezoelement, self-oscillations are excited at a natural frequency, which depends on the mechanical stress that occurs in the piezoelement under the influence of load. The output signal of the converter, like that of a vibration frequency sensor, is a frequency in the range of 5...7 kHz. However, strain gauge quartz converters have a linear static characteristic and this is their advantage. Sensitive elements are isolated from environment, which reduces the error due to fluctuations in ambient air humidity. In addition, using a separate temperature-sensitive quartz resonator, a correction is made for changes in temperature in the active zone of the sensor.

Radioisotope weight converters are based on measuring the intensity of ionizing radiation passed through the mass being measured. For an absorption type converter, the radiation intensity decreases with increasing material thickness, and for a scattered radiation converter, the intensity of the perceived

scattered radiation increases with increasing material thickness. The difference between radioisotope balances is their low measurable forces, versatility and insensitivity to high temperatures, and electromechanical scales with strain gauge transducers - low cost and high measurement accuracy.

Weighing and weighing devices

According to their intended purpose, weighing and weight-dosing devices are divided into the following six groups:

1) discrete scales;

2) scales continuous action;

3) discrete action dispensers;

4) continuous dispensers;

5) standard scales, weights, mobile weighing equipment;

6) devices for special measurements.

To the first group include laboratory scales various types, representing a separate group of weights with special conditions and weighing methods that require high accuracy of readings; table scales with the highest weighing limit (LWL) up to 100 kg, platform mobile and mortise scales with LWL up to 15 t; platform scales stationary, automobile, trolley, carriage (including for weighing on the move); scales for the metallurgical industry (these include charge feeding systems for powering blast furnaces, electric railcar scales, coal loading scales for coke batteries, weighing trolleys, scales for liquid metal, scales for blooms, ingots, rolled products, etc.).

Scales of the first group are made with scale-type rocker arms, dial square indicators and digital indicating and printing indicating devices and remote controls. To automate weighing, printing devices are used to automatically record weighing results, sum up the results of several weighings, and devices that provide remote transmission of scale readings.

To the second group include continuous conveyor and belt scales, which continuously record the mass of transported material. Conveyor scales differ from continuous belt scales in that they are made in the form of a separate weighing device installed on a certain section of the conveyor belt. Belt scales are independent short-length belt conveyors equipped with a weighing device.

To the third group include dispensers for total accounting (portion scales) and dispensers for packaging bulk materials, used in technological processes of various sectors of the national economy.

To the fourth group include continuous dispensers used in various technological processes that require a continuous supply of material with a given productivity. In principle, continuous dispensers are designed to regulate the supply of material to the conveyor or to regulate the belt speed.

Fifth group includes metrological scales for verification work, as well as weights and mobile verification equipment.

Sixth group includes various weighing devices that are used to determine not mass, but other parameters (for example, calculating equilibrium parts or products, determining the torque of engines, the percentage of starch in potatoes, etc.).

Control is carried out according to three conditions: the norm, less than the norm and more than the norm. The measure is the current in the electromagnet coil. The discriminator is a weighing system with table 3 and electromagnetic device 1, an inductive displacement transducer 2 with an output amplifier and a relay device 7. With a normal mass of control objects, the system is in an equilibrium state, and the objects are moved by the conveyor 6 to the place of their collection. If the mass of the object deviates from the norm, then the table 3, as well as the core of the inductive converter, shifts. This causes a change in the current strength in the inductor circuit and the voltage across the resistor R. The relay discriminator turns on the actuator 4, which drops the object from the conveyor belt. The relay device can be three-position with a switch contact, which allows you to throw objects to the right or left relative to the conveyor belt, depending on whether the mass of the rejected object is less or more than the norm. This example clearly shows that the result of control is not the numerical value of the controlled quantity, but an event - whether the object is suitable or not, i.e. whether the controlled quantity is within the specified limits or not.

Weights GOST OIML R 111-1-2009 – interstate standard.

1. Standard weights. To reproduce and store a unit of mass

2. General purpose weights. SI masses in the spheres of action of MMC and N.

3. Calibration weights. For adjusting scales.

4. Special weights. For individual needs of the customer and according to his drawings. For example, specially shaped, carat, Newtonian weights, with a radial cut, hooks, built into weighing systems, for example, for adjusting dispensers.

Standard weight E 500 kg F2(+) TsR-S (collapsible or composite)

Accuracy class F2, permissible error 0...8000 mg

Home / Classification of weights / Accuracy classes

Classification of weights by categories and accuracy classes.

In accordance with GOST OIML R 111-1-2009, weights are divided into 9 accuracy classes, differing mainly in the accuracy of mass reproduction.

Table of classification of weights by accuracy classes. Limits of permissible error ± δm. Accuracy in mg.

Mass ratings of weights indicate the highest and lowest rated weights allowed in any class, as well as the limits of permissible error that should not apply to higher and lower values. For example, the minimum nominal mass value for a class M2 weight is 100 mg, while the maximum value is 5000 kg. A weight with a nominal mass of 50 mg will not be accepted as a Class M2 weight under this standard, but instead must meet the error limits and other requirements for Class M1 (e.g., shape and markings) for that accuracy class of weights. Otherwise, the weight is not considered to comply with this standard.

Scale device

Scales are designed to measure the mass of cargo, goods, products, people and animals. Systems can be automatic, semi-automatic or mechanical. Based on the principle of operation, measuring units are divided into three categories:

• Hydraulic scales. Action algorithm hydraulic mechanisms based on the operation of piston or membrane cylinders. Pressure from the mass is transmitted through cylinders to the liquid, which is located inside the piston or membrane.

The load from the physical volume is recorded by a pressure gauge.

• Lever scales. The design of the mechanism consists of several levers connected to each other by earrings or steel prisms. Gravity balancing works on the principle of a rocker arm. Lever mechanisms are divided into square and prismatic.
• Strain gauge scales. Strain gauge scales operate on the basis of sensors; an internal resistor changes the resistance due to deformation.

The operating principle of portable and stationary measuring mechanisms is based on balancing the torque created by mass pressure.

When it is necessary to measure bulk cargo of large volume, special electric trolleys with a forklift are used. When pressure is applied, force is transmitted to prisms and levers.

In electronic scales, balancing occurs automatically. This mechanism does not have a lever system. The design of electronic mechanisms is designed in such a way that the weighed value is converted into current or voltage.

Such units can be connected to other measuring and computing devices.

Electronic mechanisms include strain gauge sensors of the Tuningfork type or using a reverse magnetoelectric converter.

The built-in microprocessor allows you to achieve high level automation, and also provides the opportunity to expand the functionality of the measuring apparatus.

Types and characteristics of scales

Scales are classified according to their purpose into types:

• The main parameter of a laboratory measuring unit is accuracy. Precision ones have a discreteness of one gram to one milligram, analytical ones - no more than 0.1 milligram.

There are brands of devices with additional options. These include dynamic weighing, which involves measuring animals or non-static objects. Hydrostatic weighing involves determining the mass of liquids.

Laboratory measuring instruments are also divided according to the type of calibration into devices with automatic calibration, internal weight and external weight.

• Simple weighing scales. The unit with an electronic mechanism is a compact mechanism that allows you to measure small loads. Such devices include checkweighing, packaging and portion scales.

The latter are used for simple mass measurements that do not require high accuracy, where additional functionality is not needed.

• Trading. They are used to measure the mass of goods, for packaging, for portion weighing, with subsequent calculation of the amount based on the price per unit. This model has a display located on the stand or on the body of the device.

Many retail units are equipped with a thermal printer with the ability to print labels with a self-adhesive surface. Such devices are subject to state inspection, since they are subject to metrological control.

• This model has three display panels that display additional information about the samples being measured.

The first display indicates the total mass, the second shows the indicator of one sample, and the third shows the number of these samples.

The electronic unit is used to measure various loads. Such models usually have additional functionality:

• waterproof for rooms with high humidity;
• corrugated surface of the platform, which allows you to measure the mass of unstable loads; possibility of weighing large loads;
• devices with additional block power supply, which measures mass while being far from the network.
• This model of the device is intended for use for medical purposes, namely for measuring and monitoring the body weight of patients.

Baby measuring machines consist of a cradle in which the baby is placed, and a display on the main panel shows the result.

• Crane. Such scales belong to the warehouse category; they are used for weighing cargo up to 50 tons. The design of the crane scales is very durable, consisting of a metal body with an indicator and a powerful hook.
• Platform. Structurally, this model is a platform; the indicator is installed either in the wall or on a stand.

• . This model is used to measure the mass of cargo of any size and volume, and also solves many problems. There are two groups of such devices: electronic and mechanical.

Currently, all enterprises use only electronic versions of scales; mechanical devices are considered obsolete, since they are inferior in reliability and price to modern ones.

• Packing. Such devices are classified as simple; they are used for weighing small masses of cargo not exceeding 35 kilograms.
• Electronic with a check stamp. Not a single modern supermarket can do without such devices. Automatically printing product labels allows you to improve the quality of customer service.

Scales not only measure the weight of products and issue labels indicating barcodes and other information, but also keep records and store all kinds of parameters in memory.

• These scales are designed for weighing cargo on pallets.

The design of the pallet measuring device allows, using four sensors, to determine the weight of the cargo and display the data on a display located on a dedicated terminal.

These devices are used in wholesale warehouses, industrial workshops, customs, trading enterprises and logistics centers.

• Car weights. This category of scales is designed to measure the weight of a vehicle, both loaded and unladen. Weighing methods are different, it all depends on the application, design and other parameters of the device.
• Baggage scales. The unit for measuring the weight of luggage is the simplest type of scale. There are mechanical and electronic models.

The mechanism is a simple compact device that fits easily in your hand, the load is hung on a hook, and the display shows the result. Pocket scales are easy to take with you.

• . A device for measuring the mass of food is necessary in the kitchen of a real housewife who maintains accuracy in the proportions and quantities of ingredients to prepare delicious dishes.

Classification of weighing measuring instruments by type of installation:

• Stationary
• Hanging
• Mobile
• Floor-standing
• Tabletop
• Built-in

According to the accuracy class, measuring devices are divided into three types:

• high accuracy class,
• average;
• ordinary.

According to the type of lifting mechanism, the following groups are distinguished:

• Bunker
• Rail
• Platform
• Conveyor
• Hook
• Bucket

Some models of weighing instruments have additional options:

• Taro compensation. This option allows you to make weight measurements without taking into account containers. Before weighing, you must place an empty container on the scales, then reset the result to zero, and then weigh the load along with the container.

• Synchronization with PC/phone. This option allows you to transfer data received from the scales to your computer or phone.
• Automatic shutdown. When not in use, the device turns off automatically.

Diagnostic

Diagnostic measurements in electronic scales allow you to determine physical indicators, which leads to effective weight loss. All received data is stored in the device’s memory.

Advantages of mechanical measuring instruments:

• The mechanism is easy to use.
• Long service life.
• Structural strength.
• Low price compared to electronic models.
• There are no batteries that require regular replacement.
• No special storage requirements.

Advantages of electronic measuring instruments:

• Additional options (memory, ability to calculate body mass index and others).
• The measurement accuracy is at the highest level.
• There are no bulky elements, compact compared to mechanical units.
• Automatically when switched off, the product is set to the zero position.
• Fashionable design.
• High load limit.
• Automatic switching off and on when touching the surface.
• Quite a large assortment offered by manufacturers.

Flaws

Disadvantages of mechanical measuring instruments:

• Modern technologies are not used in the production of measuring mechanisms.
• The measurement accuracy is not at the highest level.
• There are no additional features.

Disadvantages of electrical measuring instruments:

• Batteries that need to be changed from time to time.
• The high cost of the device, and the more it contains additional options, the higher the price.
• The device requires careful handling and storage; there is a risk of damage to electronic components.
• Difficulty in repairing in case of breakdowns.

How to choose a scale

When choosing a device for home use Some recommendations should be followed:

• First, it is important to check in which units of measurement the device operates. Not all devices determine mass in kilograms; there are imported models with a measuring system in pounds. Perhaps pounds are what you need.
• Next, you need to make sure the accuracy of the device’s measurements. Right in the store, make sure that a kilogram pack of granulated sugar weighs exactly one kilogram. To verify, check on several models. Buy a device with minimal error.
• A device with a corrugated surface is much more convenient; the load being weighed will not slip. Also make sure that there is an anti-slip bottom, perhaps rubber pads at the bottom.

• When buying a unit for a bathroom, sauna or swimming pool, take a model with a waterproof casing. Electronic models without this protection will fail very quickly.
• When choosing the material from which they are made floor options, give preference to metal. When purchasing kitchen weighing instruments, choose one with a glass bowl.
• can be checked for accuracy on site. Press the surface with your hand and quickly release your hand. In a high-quality device, the needle returns immediately back to the number zero.
• If you have difficulty seeing, buy a device with large numbers. There are also options with a separately displayed display.

Which measuring units are better - electronic or mechanical? There is no definite answer, since each type has its own buyer.

For one person, it is enough to simply know his body weight with an error within one kilogram, for another it is important to know about minimal fluctuations in weight and control other parameters, such as body mass index, amount of water, fat, bone mass.

How to use

Measuring units must be used in accordance with the instructions included with purchase.

• It is important to initially install the device correctly on flat surface so that the readings are more accurate. A building level is used for adjustment and leveling.

There are models in which the level is built-in; you just need to tighten the adjusting feet. The air bubble should be in the center of the control ring.

• The mechanism must be stable and should not swing during use. At correct installation The arrow of the measuring unit shows zero on the dial.

Also, in dial mechanical measuring devices, the oscillation frequency of the needle is adjusted; for this, the damper rotates in a certain direction.

• Readings from a mechanical device are taken while facing the dial directly. It is prohibited to cut or package food on the platform.

Measuring mechanisms do not require special technical care, you only need to periodically wipe the surface with a damp cloth; parts should not be lubricated with oil.

Precautionary measures:

• Do not use the unit for purposes other than its intended purpose.
• Handle with care as the measuring mechanism is a high-precision instrument.
• Do not use in hazardous areas with flammable liquids or gases.
• Do not use the device in an area exposed to electromagnetic or electrostatic waves, as the readings will be incorrect.
• You cannot disassemble the device yourself.

The warranty period is usually several years; during this period you must keep the warranty card. The coupon contains the date of purchase, the brand of the product and must be stamped by the store (please note that without the stamp the coupon is invalid).

If during the service period any breakdowns of the device occur due to the fault of the manufacturer, then repairs are carried out at the expense of the seller. It is important that the unit is operated in accordance with the conditions specified in the instructions.

The warranty does not apply in the following cases:

• Defects occurred in the event of force majeure (power surges, traffic accidents, fire or natural disasters).
• The operating conditions specified in the manual have been violated.
• If the buyer independently or with the help of third parties repaired the product.
• Failure to comply with safety standards.
• Changes to the design of the product by the buyer.

• Damage caused by improper transportation of goods by the buyer. If delivery is carried out by the manufacturer or seller, then the warranty applies.
• Availability mechanical damage on the body or platform of the device.
• Using equipment at high humidity (more than 90%) and elevated temperatures of more than 25 degrees.
• Penetration of liquid, dust, insects or other foreign objects into the product mechanism.
• If equipment breaks down due to the use of low-quality or expired parts.

Also, the warranty does not apply to components and individual elements designs.

During operation of the measuring unit, malfunctions may occur from time to time. You can fix the problems yourself:

• If there is no indication on the display, then the device may not be connected to the network. Or the batteries are damaged, in which case they need to be replaced with working batteries.
• If the weighing result is incorrect, then calibration or zeroing may not have been performed.
• If there is a problem with the power cord, you can replace the power plug or simply clean the contacts.

Do not try to repair the device yourself, if you do not understand technology, entrust this task to professional craftsmen, call service department. Or take advantage of the warranty if your warranty period has not expired.

Spare parts for specific model are purchased in specialized stores that are focused on selling such units.

Manufacturers offer additional components for measuring devices: buttons, indicators, legs, keyboard stickers, transformers, shock absorbers for the platform, the platforms themselves, sensors, power supplies, .

Manufacturers of scales

Bosch

Bosch offers customers about a dozen different models of floor measuring devices. All are posted on the official website possible options. The design is stylish and the body is slim.

In addition to weighing units, the company sells all kinds of household appliances: ,

Polaris sells various options measuring devices: tabletop and floor-mounted for weighing people. The site contains all necessary information for this product.

The company also sells climate control equipment, water heaters, household appliances, and dishes. Modern design developments and a unique approach to consumers are an integral part of the company's activities.

The Scarlett company offers appliances for the home and kitchen, accessories for beauty and health. The site presents mechanical and electronic models of measuring devices.

The models of this company differ in their bright design, there is a collection of scales with Disney comics.

Supra

Supra offers a large selection of kitchen measuring devices and floor units. The official website of the company will allow you to familiarize yourself with the entire range of products.

Tefal

Tefal sells household appliances, including measuring units. The models presented on the site look aesthetically pleasing and elegant. The products are guaranteed by the manufacturer.

To correctly answer the question posed in the task, it is necessary to distinguish them from each other.

Body weight is physical characteristic, independent of any factors. It remains constant anywhere in the Universe. Its unit of measurement is kilogram. The physical essence at the conceptual level lies in the body’s ability to quickly change its speed, for example, to slow down to a complete stop.

The weight of a body characterizes the force with which it presses on the surface. Moreover, like any force, it depends on the acceleration given to the body. On our planet, all bodies are subject to the same acceleration (gravitational acceleration; 9.8 m/s2). Accordingly, on another planet, body weight will change.

Gravity is the force with which the planet attracts a body; it is numerically equal to the weight of the body.

Devices for measuring weight and body mass

The instrument for measuring mass is the well-known scale. The first type of scales were mechanical ones, which are still widely used today. Later they were joined by electronic scales, which have very high measurement accuracy.

In order to measure body weight, you need to use a device called a dynamometer. Its name translates as a force meter, which corresponds to the meaning of the term body weight defined in the previous section. Just like scales, they come in mechanical types (lever, spring) and electronic. Weight is measured in Newtons.