What instrument measures body weight. Means of measuring mass. Hourglass and Fireglass

Scales (instrument) 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 a force or a moment of force. Such devices include, for example, current scale And Pendant scales. The sequence of actions in determining the mass of bodies in V. is considered in Art. Weighing.

V. is one of the oldest instruments. They arose and improved with the development of trade, production and science. The simplest V. in the form of an equal-shoulder yoke with hanging 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-shouldered weights with a mobile weight appeared (see Fig. Bezmen). Already in the 4th c. BC e. Aristotle gave the theory of such V. (rule moments of forces). In the 12th century The Arab scientist al-Khazini described the bowls with cups, the error of which 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 Mr. Galileo To determine the density of bodies, he designed special hydrostatic velocities. The general theory of volatility was developed by L. Euler (1747).

The development of industry and transport led to the creation of V., designed for heavy loads. At the beginning of the 19th century decimal V. were created. ( rice. 2) (with a weight-to-load ratio of 1:10 - Kvintenz, 1818) and centesimal V. (W. Fairbanks, 1831). At the end of the 19th - beginning of the 20th centuries. With the development of in-line production, weighing machines for continuous weighing (conveyor, dosing, etc.) appeared. In various branches of agriculture, industry, and transport, V. of a wide variety of designs began to be used for weighing specific types of products (in agriculture such as grains, root vegetables, eggs, etc.; in transport - cars, railroad. wagons, planes; in industry - from the smallest details and nodes in precision instrumentation to multi-ton ingots in metallurgy). For scientific research, designs were developed for accurate V. - analytical, microanalytical, assay, etc.

Depending on the purpose of the test, they are divided into exemplary (for checking weights), laboratory (including analytical), and general-purpose instruments used in various fields of science, technology, and the national economy.

According to the principle of operation, V. are divided into lever, spring, electrotensometric, hydrostatic, and hydraulic.

The most common are lever winders; their action is based on the law of equilibrium. lever . The fulcrum of the lever (“rocker arm” V.) may be in the middle (equal-arm V.) or be displaced relative to the middle (unequal-arm and one-arm V.). Many lever v. (for example, trading, automobile, portion, etc.) are a combination of levers of the 1st and 2nd kind. The levers are usually supported by prisms and cushions made of special steels or hard stone (agate, corundum). On equal-armed lever weights, the weighed body is balanced by weights, and a certain excess (usually by 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 yoke (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 is measured using a reading scale. The division price s of the scale of lever V. is determined by the formula

s = k (P o c / lg),

where P 0 – weight of the rocker arm with arrow, s – distance between the center of gravity of the rocker arm and its axis of rotation, l – 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 V., can be changed within certain limits (usually by moving a special weight that changes the distance c).

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

In laboratory practice, V. (especially analytical) with built-in weights for part of the load or for the full load ( rice. 4). The principle of operation of such V. was proposed by D.I. Mendeleev. Weights of a special shape are suspended from the shoulder, on which the load cup is located (single-arm weights), or (less often) on the opposite shoulder. In single shoulder V. ( rice. 5) completely eliminates the error due to the unequal arm.

Modern laboratory weighing machines (analytical, etc.) are equipped with a number of devices for increasing the accuracy and speed of weighing: vibration dampers for cups (air or magnetic), doors that, when opened, almost no air flow occurs, thermal screens, mechanisms for applying and removing built-in weights, automatically operating mechanisms for selecting built-in weights when balancing V. Increasingly, projection scales are used to expand the measurement range on the reference scale at small angles of deflection of the rocker arm. All this allows to significantly increase the speed of V.

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

Most types of metrological, exemplary, analytical, technical, and commercial ( rice. 7), medical, wagon, automobile V., as well as V. automatic and portioned.

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

The sensitive element in spring ventilators is a spiral flat or cylindrical spring, which deforms under the weight of the body. V.'s indications are counted on a scale along which a pointer connected to a spring moves. It is assumed that after the load is removed, the pointer returns to the zero position, that is, no residual deformations occur in the spring under the action of the load.

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

In torsional (torsion) windmills, 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 torque generated by the load.

The action of electrostrain gauges is based on the transformation of the deformation of elastic elements (pillars, 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, electrostrain gauges (wagon, automobile, crane, etc.) are used for weighing large masses.

Hydrostatic waves are mainly used to determine the density of solids and liquids. Their action is based on the law of Archimedes (cf. Hydrostatic weighing).

Hydraulic V. are similar in design hydraulic press. Reading of indications is made on the manometer graduated in units of mass.

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

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

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

Weighing error at full load

Metrological...........

Exemplary 1st and 2nd category

Exemplary 3rd category and

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

Analytical, semi-microanalytical, microanalytical, assay

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

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

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

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

Twisting ..............

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 accurate weighing methods.

Lit .: Rudo N. M., Libra. Theory, device, adjustment and verification, M. - L., 1957; Malikov L. M., Smirnova N. A., Analytical electric balances, in the book: Encyclopedia of measurements of control and automation, c. 1, M. ‒ L., 1962: Orlov S. P., Avdeev B. A., Weighing equipment of enterprises, M., 1962; Karpin E. B., Calculation and design of weight measuring 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 for measuring forces of a different origin than gravity. 1. Scales for accurate weighing. At present, the system proposed is mainly used ... ... Big Medical Encyclopedia

Ov; pl. 1. A device for determining weight and mass. Laboratory c. Aptekarskie v. Electronic c. V. Themis (book; about justice). 2. [capitalized] 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 physical. quantities converted for this purpose into a force or moment of force. Such devices include, for example, current scales and torsion ... ... Physical Encyclopedia Big Polytechnical 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 the specified technological standards, and other operations.

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

Scales VLR-20 (Fig. 4.3) have the largest weighing limit of 20 g, the division value of the dividing device is 0.005 mg.

On the basis of 6 scales, a hollow rack 9 is installed; in the upper part of the rack, a bracket with insulator levers 11 and a support pad 15 are mounted. An illuminator 5, a condenser 4 and an objective 3 of an optical readout device are installed on the base 6. Support prism 17, saddles with load-receiving prisms 13 and arrow 1 with microscale 2 are fixed on equal-arm rocker arm 16.

The regulation of the equilibrium position of the movable system on the rocker arm is carried out by calibration nuts 19 at the ends of the rocker arm. By adjusting the position of the center of gravity of the rocker by vertical movement of the adjusting nuts 18, located in the middle of the rocker, you can set the given scale division value. Cushions 14 of earrings 12 rest on load-receiving prisms 13, on which pendants with 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 in the upper part of the scales.

The girenalizatsiya mechanism 20, located on the board 8, allows you to hang weights of 10 on the right suspension; 20; 30 and 30 mg, providing balancing with built-in weights in the range from 10 to 90 mg. The mass of superimposed weights is counted on a digitized limb associated with the weight application mechanism.

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

1.2. Laboratory two-prism balance(Fig. 4.5) consist of an asymmetric rocker arm 1, installed with the help of a support prism 2 on the pad 5 of the balance base. Suspension 9 is connected to one shoulder of the rocker through the load-receiving prism 6 and pillow 11 with the load-receiving cup. On the same suspension rail 10 is fixed, on which built-in weights 7 are hung, with a total mass T 0 . On the other shoulder of the rocker, a counterweight 4 is fixed, balancing the rocker. The microscale 3 of the optical reading device is rigidly attached to the rocker arm 1. When measuring the mass, a weighed load 8 with a mass of T 1, and part of the weights 7 with a mass of T T.

If T 1 > T d, 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 is the mass of the suspension, counterweight, rocker arm; T oh and T 1 - mass of all built-in weights and cargo; T g is the mass of the 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 pad; A 2 - distance from the axis of rotation of the rocker to the center of gravity of the counterweight; A k - distance from the axis of rotation of the rocker to its center of gravity, α 1 , α 2 - angles depending on the installation of the lines of the prisms of the rocker; g \u003d 9.81 m / s 2.

Compensating moment

Error δ y, depending on the gravitational moment of stability and the deflection angle 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 highest weighing limit of 100 g, with a named scale and built-in weights for full load. The balance has a pre-weighing device that allows you to increase the speed of mass measurement and simplify the weighing operations associated with the selection of weights that balance the moving balance system.

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

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

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

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

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

In the initial position, the rocker 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 isolation mechanism is first placed in the PV position. In this case, the lever 3 rests against the rocker, the built-in weights are removed from the suspension, the suspension is lowered onto the load-receiving prism of the rocker. After that, the rocker with the support prism 2 is lowered onto the pillow, deviated 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 - weight of the weighed body.

On the scale of the optical reading device and the limb of the dividing device, the preliminary value of the measured mass is counted, which is set on the counters of the gyre-laying mechanism.

When transferring the isolating mechanism to the TV position, the rocker arm and suspension are first isolated, after which weights of mass T d. Lever 3 is pulled down to the stop, releasing the rocker, the suspension is connected to the rocker through the load-receiving prism and pillow, and the rocker sits on the pillow with the support prism and accurate weighing is performed.

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

1.3. Quadrant scales simple, reliable in operation, have high accuracy. Unlike other laboratory scales, the load-receiving cup of the 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, in control systems related to mass measurement.

Quadrant scales (Fig. 4.7) consist of an asymmetric rocker arm 1 (quadrant) installed with the help of a support prism 2 on an angular pad 3 fixed on the basis of the scales. Suspension 6 with the help of corner cushions 8 is installed on the load-receiving prism 7, fixed on the rocker arm 1. The load-receiving cup 9 in quadrant scales is attached to the upper part of the suspension 6. To exclude the possibility of the suspension tipping over when the load is applied to the cup 9, the lower part of the suspension is attached to the base of the scales through swivel joints using lever 5, called a string. The microscale 4 of the optical reading device is rigidly attached to the quadrant. A rail is fixed on the suspension, on which built-in weights are located.

The use of corner cushions and swivel joints in the lower part of the suspension in quadrant balances made it possible to increase the working deflection angle φ of the quadrant by several times compared to the deflection angle in equal-arm or two-prism balances. For example, in quadrant scales, when the maximum load is applied to the suspension, the deflection angle is 12°, and in equal-arm and two-prism balances it is less than 3°. With a large deflection angle, of course, 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 balance. However, hinges with a string are a source of additional errors that reduce the accuracy of weighing. Therefore, the produced quadrant balances have mainly an accuracy class of 4.

Laboratory quadrant scales model VLKT-5 (Fig. 4.8) belong to accuracy class 4 and are designed to measure masses up to 5 kg. The weighing system 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 arm rest on angular self-aligning cushions. To dampen 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 tare mass and a gyre-laying mechanism. When weighing, special grippers driven by the handles of the gyre-laying mechanism are removed from the load-receiving suspension or put on it the built-in weights 7 with a mass of 1, 1 and 2 kg. The image of the microscale, enlarged with the help of an optical system, is transmitted to the frosted glass of the screen 8, where the value of the mass is indicated, which is determined when the beam deviates from its initial position.

Cylindrical spiral spring 9, attached at one end to the suspension, is the 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 handle of the dividing mechanism counter is rotated. When the drum of the mechanical counter rotates to its full capacity, equal to 100 divisions, the spring is stretched, transferring to the rocker a force equivalent to the force created by a change in the weight 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 resolution of 0 .1 g. The microscale fixed on the rocker has 100 divisions with a division value of 10 g. Therefore, the measurement range of the optical reading device and the dividing mechanism with a resolution of 0.1 g is 1000 g.

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

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

The casing of the scales has a glass screen 4, through which the limb of the measuring mechanism is visible. Before weighing, turn the latch 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 limb, the pointer 5 is returned to the zero position. In this case, the value of the body mass is determined by the arrow on the limb of the measuring mechanism.

1.4. Electronic digital scales. A significant advantage of the scales is that the operations do not require built-in or overhead weights. Therefore, in the serial production of scales and during their operation, metal is significantly saved, 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, fixed on the 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 displacements into an electrical signal.

The weighing device has a stand, on which the bracket 12 and the magnetic system 16 with the working coil 5 are mounted. The working coil is attached to the insert 9, which is rigidly connected to the bracket 7. The movable weighing system is attached through the 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 mounted.

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

The balance has an electronic device that compensates for the force generated by the container. When a tare 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 memory device, and zeros are set on the digital reading device and the scales are ready to measure the weight of the load. The tare compensation device included in the scale compensates for loads up to 1000 g.

Electronic digital scales of the 4th class VLE-1 kg with improved technical characteristics (Fig. 4.11, b). These scales 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 according to a given value of the mass of one item.

3. Order of performance of work: read item 1; using formulas (4.1) - (4.4) according to the initial conditions (Table 4.1) for two-prism balances, determine: the stability moment M y, the compensating moment M k, as well as the errors δ y and δ k, draw up a report.

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

Table 4.1. Initial data for work performance

- 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 control questions.

Control questions

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

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

3. What is the constructive difference between quadrant and two-prism balances?

4. How are the VLKT-5 quadrant balances arranged?

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

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

Laboratory and practical work No. 5

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

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

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

3. definition of the class to which the body to be weighed belongs ("tari-

level weighing" or "sorting"),

4. weighing continuously flowing material flow.

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

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

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

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

4) balancing force is created hydraulic device;

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

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

The first way is classic. 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 - the depth of immersion and lifting force.

Weight classification

1. Mechanical.

2. Electromechanical.

3. Optical-mechanical.

4. Radioisotopes.

Lever trading scales

Trade mechanical scales RN-3Ts13UM

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

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

The modern stage in the development of laboratory scales, which are 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 balance to its original equilibrium position. ATS electronic lab. balance (Fig. 4) includes a sensor, for example, in the form of a differential transformer; its core is fixed on the measuring part and moves in a coil mounted on the base of the balance 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, directing a light beam to a differential photocell connected to the electronic unit. When the measuring part of the balance deviates from the initial equilibrium position, the relative position of the sensor elements changes, and a signal appears at the output of the electronic unit containing information about the direction and magnitude of the deviation. This signal is amplified and converted by the electronic unit into a current, which is fed into the exciter coil, fixed on the base of the balance and interacting with a permanent magnet on their measuring part. The latter, due to the emerging opposing force, returns to its original position. The current in the exciter coil is measured with a digital microammeter calibrated in units of mass. Top cup electronic scales use a similar automatic balancing scheme, but permanent magnet the exciter is mounted on the rod carrying the cup (electronic leverless scales) or connected to this rod by a lever (electronic lever scales).

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

Vibrofrequency (string). Its action is based on changing the frequency of a stretched metal string mounted on an elastic element, depending on the magnitude of the force applied to it. The influence of external factors (humidity, temperature, atmospheric pressure, vibrations), 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 of the company "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 an electromagnet 4 and a 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 loading platform is placed. To limit the deformation of the elastic element, there is a safety rod 8.

Electronic desktop scales.

Specifications:

weighing range - 0.04–15 kg;

discreteness - 2/5 g;

sampling of tare weight - 2 kg;

average service life - 8 years;

accuracy class according to GOST R 53228 - III medium;

mains power settings 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 have been 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 tension of the other.

Mera scales with remote indicating 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 action of the gravity of the load, into an electrical signal, the amplitude (strain gauge) or frequency (quartz strain gauge) of which changes in proportion to the weight of the load.

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

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

scattered radiation increases with increasing material thickness. Radioisotope balances are distinguished by low measurable forces, versatility and insensitivity to high temperatures, and electromechanical scales with tensometric transducers - low cost and high measurement accuracy.

Weighing and weighing devices

By purpose, weighing and weighing devices are divided into the following six groups:

1) scales of discrete action;

2) scales continuous action;

3) dispensers of discrete action;

4) continuous dispensers;

5) exemplary 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; desktop scales with the maximum weighing limit (LLL) up to 100 kg, platform scales, mobile and mortise with LLL up to 15 tons; scales platform stationary, automobile, trolley, wagon (including for weighing on the go); scales for the metallurgical industry (these include charge feeding systems for powering blast furnaces, electric car scales, coal-loading scales for coke oven batteries, weighing carts, 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 pointers and digital indicating and printing pointing devices and consoles. To automate weighing, printing devices for automatically recording weighing results, summing up the results of several weighings and devices that provide remote transmission of weight readings are used.

To the second group include conveyor and belt scales of continuous action, which continuously record the mass of the transported material. Belt 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 belt conveyor. Belt scales are independent belt conveyors of small length, 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 branches of the national economy.

to the fourth group include continuous feeders used in various technological processes where a continuous supply of material with a given capacity is required. In principle, continuous dispensers are performed with the regulation of the supply of material to the conveyor or with the regulation of the speed of the belt.

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

Sixth group includes various weighing devices that are used to determine not the mass, but other parameters (for example, counting 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 is displaced, as well as the core of the inductive transducer. 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 a three-position relay with a switch contact, which allows you to drop 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 value, but the event - the object is good or bad, i.e. whether the controlled value is within the specified limits or not.

Weights GOST OIML R 111-1-2009 is an interstate standard.

1. Reference weights. To reproduce and store the unit of mass

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

3. Calibration weights. For weight adjustment.

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

Reference 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, which differ mainly in the accuracy of mass reproduction.

Classification table of weights by accuracy classes. Limits of permissible error ± δm. Error in mg.

The nominal masses of weights indicate the largest and smallest nominal masses allowed in any class, as well as the margins of error which should not apply to higher and lower values. For example, the minimum nominal mass value for an M2 class 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 according to this standard, but instead it shall comply with the limits of error and other requirements for class M1 (e.g. shape and marking) for that class of weights. Otherwise, the weight is not considered to comply with this standard.

Scale device

Scales are designed to measure the mass of goods, goods, products, people and animals. Systems can be automatic, semi-automatic or mechanical. According to 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. The pressure from the mass is transmitted through the cylinders to the fluid that is inside the piston or membrane.

The load from the physical volume is fixed by a manometer.

• lever scales. The design of the mechanism consists of several levers interconnected by earrings or steel prisms. Gravitational balancing works on the principle of a rocker arm. Lever mechanisms are divided into square and prismatic.
• Tensometric scales. Tensometric scales work on the basis of sensors, the internal resistor changes resistance from deformation.

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

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

In electronic scales, balancing occurs automatically. There is no lever system in this mechanism. The design of electronic mechanisms is arranged in such a way that the weighted value is converted into current or voltage.

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

Electronic mechanisms provide for the presence of strain gauges of the Tuningfork type or with the use of an inverse type magnetoelectric converter.

Built-in microprocessor allows you to achieve high level automation, and also provides an 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 have a discreteness from one gram to one milligram, analytical - 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 subdivided according to the type of calibration into devices with automatic calibration, internal weight and external weight.

• Scales of simple weighing. The unit with an electronic mechanism is a compact mechanism that allows you to measure small loads. Such devices include scales for control weighing, packing and portioning.

The latter are used for simple mass measurement that does 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 the 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 sales units are equipped with a thermal printer with the ability to print labels with a self-adhesive surface. Such devices are subject to state verification, as they are subject to metrological control.

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

The first display shows the total weight, the second shows the value 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; the possibility of weighing large loads;
• devices with additional block power supply, which measures the mass, being far from the network.
• This model of the device is intended for use for medical purposes, namely for measuring and controlling the body weight of patients.

Baby measuring devices are a cradle in which the baby is placed, and the display on the main panel shows the result.

• Crane. Such scales belong to the warehouse category, they are used for weighing loads up to 50 tons. The design of the crane scale is very durable, it consists of a metal case with an indicator of indicators and a powerful hook.
• Platform. Structurally, this model is a platform, the indicator is installed either in a wall or on a rack.

• . This model is used to measure the mass of goods 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 already considered obsolete, since they are inferior to modern ones in terms of reliability and price.

• Packing. Such devices are classified as simple, they are used by devices for weighing a small mass of goods not exceeding 35 kilograms.
• Electronic with receipt stamp. No modern supermarket can do without such devices. Printing a label on a product in automatic mode improves the quality of customer service.

Scales not only measure the mass of products and issue labels with a barcode and other information, but also keep records, store all kinds of parameters in memory.

• Such scales are designed for weighing goods 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 the display located on the designated terminal.

These devices are used at wholesale depots, in industrial shops, at customs, at trade enterprises and in logistics centers.

• Car weights. This category of scales is designed to measure the mass of the car - both laden and empty. Weighing methods are different, it all depends on the application, design and other parameters of the device.
• Luggage scales. The luggage weight measurement unit is the simplest type of scale. There are mechanical models and electronic ones.

The mechanism is a simple compact device that easily fits 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 products is necessary in the kitchen of a real housewife, who observes the accuracy in the proportions and quantities of ingredients for preparing delicious dishes.

Classification of weighing measuring instruments by type of installation:

• Stationary
• Suspended
• Mobile
• floor standing
• Desktop
• Embedded

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

• high class of accuracy,
• average;
• ordinary.

According to the type of lifting mechanism, 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 tare. Before weighing, it is necessary to put an empty container on the scales, then reset the result to zero, and then weigh the load together with the container.

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

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 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.
• There are no special storage requirements.

Advantages of electronic measuring instruments:

• Additional options (memory, the ability to calculate body mass index and others).
• Measurement accuracy at the highest level.
• There are no bulky elements, compactness in comparison with mechanical units.
• Automatically when disconnected, the product is set to the zero position.
• Fashion design.
• High load limit.
• Automatic shutdown and inclusion 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.
• 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 in it additional options, the higher the price.
• The device requires careful handling and storage, there is a risk of damage to electronic components.
• Difficulty in repair in case of breakdowns.

How to choose scales

When choosing a device for home use some guidelines should be followed:

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

• When buying a unit for a bathroom, sauna or pool, take a model with a waterproof case. 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 buying kitchen weighing devices, choose a device with a glass bowl.
• can be checked for accuracy on the spot. Press the surface with your hand and release your hand abruptly. In a quality device, the arrow returns immediately back to zero.
• If you have trouble seeing, buy a device with big numbers. There are also options with a separately displayed scoreboard.

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

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

How to use

It is necessary to use measuring units in accordance with the instructions supplied with the purchase.

• It is important to initially install the device correctly on flat surface for more accurate readings. For adjustment and alignment, a building level is used.

There are models in which the level is built in, you only need to tighten the adjusting legs. The air bubble should be in the center of the control ring.

• The mechanism must be stable and must not wobble when in use. At correct installation of the measuring unit, the arrow shows zero on the dial.

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

• Readings from a mechanical device are taken while facing directly to the dial. It is forbidden to cut and pack products on the platform.

Measuring mechanisms do not require special technical care, it is only necessary to periodically wipe the surface with a damp cloth, the parts must not be lubricated with oil.

Precautionary measures:

• Do not use the unit for other purposes.
• Handle with care as the measuring mechanism is a precision instrument.
• Do not use in hazardous areas using flammable liquids and gases.
• Do not use the device in an area affected by electromagnetic or electrostatic waves, as the readings will be incorrect.
• You cannot disassemble the device yourself.

The warranty period is usually several years, during which time the warranty card must be kept. The coupon specifies the date of purchase, the brand of goods and the store's seal is required (note that the coupon is invalid without a seal).

If during the service period any damage to the device occurs due to the fault of the manufacturer, then the repair is 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 arose in the event of force majeure (power surges, traffic accidents, fire or natural disasters).
• The operating conditions specified in the manual are violated.
• If the buyer independently or with the help of third parties repaired the product.
• Failure to comply with safety standards.
• Making changes to the design of the product by the buyer.

• Damage due to improper transportation of goods by the buyer. If the delivery is carried out by the manufacturer or seller, then the guarantee is valid.
• Availability mechanical damage on the body or platform of the machine.
• Use of equipment at high humidity (over 90%) and elevated temperatures over 25 degrees.
• Penetration of liquid, dust, insects or other foreign objects into the mechanism of the product.
• In case of equipment breakdown due to the use of low-quality or expired parts.

The warranty also does not cover parts and individual elements designs.

During operation of the measuring unit, malfunctions are periodically possible. You can fix the problems yourself:

• If there is no indication on the display, the machine may not be connected to the network. Or the batteries are out of order, in which case they must be replaced with working batteries.
• If the weighing result is incorrect, the calibration or zeroing may not have been performed.
• In case of problems with the power cord, you can replace the electric plug or simply clean the contacts.

Do not try to repair the device yourself, if you are not versed in technology, entrust this matter 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 the sale of such units.

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

Scale Manufacturers

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, the case is thin.

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

Polaris sells various options measuring devices: desktop and, as well as floor 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.

Scarlett offers home and kitchen appliances, health and beauty products. The site presents mechanical and electronic models of measuring devices.

The models of this company are distinguished by their bright design, there is a collection of scales with Disney comics.

Supra

Supra offers a wide range of kitchen measuring devices and floor standing units. The official website of the company will allow you to get acquainted with the entire range of products.

Tefal

Tefal sells household appliances, including measuring units. The presented models on the site look aesthetically pleasing and elegant. The product is 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 the kilogram. The physical essence at the conceptual level lies in the ability of the body 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. At the same time, like any force, it depends on the acceleration that is given to the body. On our planet, all bodies are affected by the same acceleration (acceleration of free fall; 9.8 m / s 2). Accordingly, on another planet, the weight of the body will change.

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

Devices for measuring weight and body mass

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

In order to measure body weight, you must use a device called a dynamometer. Its name is translated as a measure of strength, which corresponds to the meaning of the term body weight defined in the previous section. As well as scales, they are of a mechanical type (lever, spring) and electronic. Weight is measured in Newtons.