What instruments for measuring mass. Mass measuring instruments
"Electrical Appliances" - Lamp sockets, etc. Mixer. Thermal. Electrical engineering. Goals and objectives. Circuit breakers. Household electrical appliances. Educational topic: Household electrical appliances. Alternating current. Direct current. Electrical installation devices. Wiring. Types of electrical wiring. Appliances. The list of electrical appliances is very long.
“Weight and mass” - Progress of the experiment. WEIGHT and WEIGHTLESSNESS. Scientific data and observations. Project overview. You can get closer to weightlessness if you move at a certain speed along a convex trajectory. Who and when first began to study the fall of bodies in the air? The book “Unsolved Mysteries of Humanity” published by Reader's Digest.
“Weight of the backpack” - Recommendations for students: Weigh the backpacks without school supplies from the students in our class. Perform exercises to strengthen the muscles of the torso. Subject of research: schoolchildren’s posture. Project - research. I will maintain my health, I will help myself. Our backpacks. Research results: “What’s in our backpacks?”
“Magnifying devices” - Lenses. A hand-held magnifying glass provides magnification from 2 to 20 times. The product will indicate the magnification that the microscope is currently providing. Tripod. Historical reference. Biology - science about life, living organisms living on earth. Tube. Biology is the science of life. Laboratory work No. 1. 4. Place the finished preparation on the stage opposite the hole in it.
“Weight and air pressure” - What is the atmosphere? How can you weigh gas? What causes atmospheric pressure? Does the atmosphere have weight? Measuring atmospheric pressure. Let's answer the questions: Can the atmosphere “pressure”? What causes gas pressure? Why does water rise after the piston? What is the name of the device for measuring atmospheric pressure?
“Measuring instruments” - The thermometer is a glass tube sealed on both sides. Pressure gauge. Dynamometer. Medical dynamometer. To measure means to compare one quantity with another. Each device has a scale (division). Aneroid barometer. Barometer. Thermometer. Devices make a person's life much easier. Strength meter. Types of dynamometers.
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.
The simplest device for determining mass and weight is a lever scale, known from about the fifth millennium BC. They are a beam that has a support in its middle part. There are cups at each end of the beam. The measurement object is placed on one of them, and weights are placed on the other standard sizes until the system is brought into equilibrium. In 1849, the Frenchman Joseph Beranger patented an improved scale similar type. They had a system of levers under the cups. This type of device has been very popular for many years in trades and kitchens.
A variant of lever scales is the steelyard, known since antiquity. In this case, the suspension point is not in the middle of the beam; the standard load has a constant value. Equilibrium is established by changing the position of the suspension point, and the beam is pre-graduated (according to the lever rule).
Robert Hooke, an English physicist, established in 1676 that the deformation of a spring or elastic material is proportional to the magnitude of the applied force. This law allowed him to create spring scales. Such scales measure force, so they will show different numerical results on Earth and on the Moon.
Currently, various methods based on receiving an electrical signal are used to measure mass and weight. In the case of measuring very large masses, for example a heavy vehicle, pneumatic and hydraulic systems are used
Instruments for measuring time
The first time meter in history was the Sun, the second was the flow of water (or sand), the third was the uniform combustion of special fuel. Having originated in ancient times, solar, water and fire clocks have survived to our time. The tasks that watch creators faced in ancient times were very different from modern ones. Time meters were not required to be particularly accurate, but they had to divide the days and nights into the same number of hours of varying lengths depending on the time of year. And since almost all instruments for measuring time were based on fairly uniform phenomena, the ancient “watchmakers” had to resort to various tricks to do this.
Sundial.
The oldest sundial was found in Egypt. Interestingly, early Egyptian sundials used the shadow not of a pillar or rod, but of the edge of a wide plate. In this case, only the height of the Sun was measured, and its movement along the horizon was not taken into account.
With the development of astronomy, the complex movement of the Sun was understood: daily along with the sky around the axis of the world and annual along the zodiac. It became clear that the shadow would show the same periods of time, regardless of the height of the Sun, if the rod was directed parallel to the axis of the world. But in Egypt, Mesopotamia, Greece and Rome, day and night, the beginning and end of which marked the sunrise and sunset, were divided, regardless of their length, into 12 hours, or, more roughly, according to the time of changing of the guards, into 4 “guards” of 3 hours each. Therefore, it was necessary to mark on the scales unequal hours tied to certain parts of the year. For large sundials that were installed in cities, vertical gnomon-obelisks were more convenient. The end of such an obelisk described symmetrical curved lines on the horizontal platform of the foot, depending on the time of year. A number of these lines were applied to the base, and other lines corresponding to the clock were drawn across. Thus, a person looking at the shadow could recognize both the hour and approximately the month of the year. But the flat scale took up a lot of space and could not accommodate the shadow that the gnomon casts when the Sun is low. Therefore, in watches of more modest sizes, the scales were located on concave surfaces. Roman architect of the 1st century. BC. Vitruvius in his book “On Architecture” lists more than 30 types of water and sundials and reports some of the names of their creators: Eudoxus of Cyidae, Aristarchus of Samos and Apollonius of Pergamon. Based on the architect’s descriptions, it is difficult to get an idea of the design of this or that clock, but many of the remains of ancient time meters found by archaeologists were identified with them.
Sundials have a big drawback - the inability to show time at night and even during the day in cloudy weather, but compared to other watches they have important advantage- direct connection with the luminary that determines the time of day. That's why they didn't lose practical significance even in the era of mass distribution of accurate mechanical watch that require verification. The stationary medieval sundials of the countries of Islam and Europe differed little from the ancient ones. True, during the Renaissance, when learning began to be valued, complex combinations of scales and gnomons came into fashion, serving for decoration. For example, at the beginning of the 16th century. a time meter was installed in Oxford University Park, which could serve visual aid on the construction of various sundials. Since the 14th century, when mechanical tower clocks began to spread, Europe gradually abandoned the division of day and night into equal periods of time. This simplified the sundial scales, and they were often used to decorate the facades of buildings. To Wall Clock could show morning and evening time in the summer; they were sometimes made double with dials on the sides of a prism protruding from the wall. In Moscow, a vertical sundial can be seen on the wall of the building of the Russian Humanitarian University on Nikolskaya Street, and in the park of the Kolomenskoye Museum there is a horizontal sundial, unfortunately, without a dial and a gnomon.
The most grandiose sundial was built in 1734 in the city of Jaipur by the maharaja (ruler of the region) and astronomer Sawai-Jai Singh (1686-1743). Their gnomon was a triangular stone wall with a vertical leg height of 27 m and a hypotenuse 45 m long. The scales were located on wide arcs along which the shadow of the gnomon moved at a speed of 4 m per hour. However, the Sun in the sky does not look like a point, but a circle with an angular diameter of about half a degree, so due to the large distance between the gnomon and the scale, the edge of the shadow was unclear.
Portable sundials were very diverse. IN early middle ages Mostly high-altitude ones were used, which did not require orientation to the cardinal points. In India, watches in the form of a faceted staff were common. On the edges of the staff, hour divisions were applied, corresponding to two months of the year, equidistant from the solstice. The gnomon was a needle, which was inserted into holes made above the divisions. To measure time, the staff was suspended vertically on a cord and turned with a needle towards the Sun, then the shadow of the needle showed the height of the luminary.
In Europe, similar watches were designed in the form of small cylinders, with a number of vertical scales. The gnomon was a flag mounted on a rotating pommel. It was installed above the desired hour line and the clock was rotated so that its shadow was vertical. Naturally, the scales of such watches were “tied” to a certain latitude of the area. In the 16th century In Germany, universal high-altitude sundials in the form of a “boat” were common. The time in them was marked by a ball placed on the thread of a plumb line, when the instrument was pointed at the Sun so that the shadow of the “bow” exactly covered the “stern”. Adjustment in latitude was made by tilting the “mast” and moving a bar along it, on which the plumb line was attached. The main disadvantage of altitude clocks is the difficulty of determining the time from them closer to noon, when the Sun changes altitude extremely slowly. In this sense, a clock with a gnomon is much more convenient, but it must be set according to the cardinal points. True, when they are supposed to be used for a long time in one place, you can find time to determine the direction of the meridian.
Later, portable sundials began to be equipped with a compass, which made it possible to quickly set them in the desired position. Such watches were used until the middle of the 19th century. to check the mechanical ones, although they showed true solar time. The greatest lag of the true Sun from the average during the year is 14 minutes. 2 seconds, and the greatest advance is 16 minutes. 24 seconds, but since the lengths of neighboring days do not differ much, this did not cause any particular difficulties. For amateurs, a sundial with a noon gun was produced. A magnifying glass was placed above the toy cannon, which was positioned so that at noon the sun's rays collected by it reached the ignition hole. The gunpowder caught fire, and the cannon fired, naturally, with a blank charge, notifying the house that it was true noon and it was time to check the clock. With the advent of telegraph time signals (in England since 1852, and in Russia since 1863), it became possible to check watches in post offices, and with the advent of radio and telephone “talking clocks”, the era of sundials ended.
Water clock.
The religion of ancient Egypt required the performance of night rituals with precise adherence to the time of their performance. Time at night was determined by the stars, but water clocks were also used for this. The oldest known Egyptian water clock dates back to the era of Pharaoh Amenhotep III (1415-1380 BC). They were made in the form of a vessel with expanding walls and a small hole from which water gradually flowed out. The time could be judged by its level. To measure watches of different lengths, several scales were applied to the inner walls of the vessel, usually in the form of a series of dots. The Egyptians of that era divided night and day into 12 hours, and for each month they used a separate scale, near which its name was placed. There were 12 scales, although six would have been enough, since the lengths of days located at the same distance from the solstices are almost the same. There is also another type of clock in which the measuring cup was not emptied, but filled. In this case, water came into it from a vessel placed above in the form of a baboon (this is how the Egyptians depicted the god of wisdom Thoth). The conical shape of the watch bowl with flowing water contributed to a uniform change in the level: when it decreases, the water pressure drops and it flows out more slowly, but this is compensated by a decrease in its surface area. It is difficult to say whether this shape was chosen to achieve uniform “running” of the watch. Perhaps the vessel was made in such a way that it would be easier to examine the scales drawn on its inner walls.
The measurement of equal hours (in Greece they were called equinoxes) was required not only by astronomers; they determined the length of speeches in court. This was necessary so that those speaking for the prosecution and defense were on equal terms. In the surviving speeches of Greek orators, for example, Demosthenes, there are requests to “stop the water,” apparently addressed to the servant of the court. The clock was stopped while the text of the law was read or a witness was interviewed. Such a clock was called a “clepsydra” (Greek for “stealing water”). It was a vessel with holes in the handle and bottom into which a certain amount of water was poured. To “stop the water,” they apparently plugged the hole in the handle. Small water clocks were also used in medicine to measure pulse. Problems of measuring time contributed to the development of technical thought.
A description of a water alarm clock has been preserved, the invention of which is attributed to the philosopher Plato (427-347 BC). "Plato's Alarm Clock" consisted of three vessels. From the upper one (clepsydra) water flowed into the middle one, which contained a bypass siphon. The receiving tube of the siphon ended near the bottom, and the drain tube entered the third empty closed vessel. This in turn was connected by an air tube to the flute. The alarm clock worked like this: when the water in the middle vessel covered the siphon, it turned on. The water quickly poured into the closed vessel, displaced the air from it, and the flute began to sound. To regulate the time the signal turned on, the middle vessel should be partially filled with water before starting the clock.
The more water was pre-filled into it, the earlier the alarm went off.
The era of designing pneumatic, hydraulic and mechanical devices began with the work of Ctesibius (Alexandria, II-I centuries BC). In addition to various automatic devices that served mainly to demonstrate “technical miracles,” he developed a water clock that automatically adjusted to changes in the length of night and day periods of time. Ctesibius's clock had a dial in the form of a small column. Near her were two figurines of cupids. One of them cried continuously; his “tears” flowed into a tall vessel with a float. The figurine of the second cupid was moved using a float along the column and served as a time indicator. When at the end of the day the water raised the indicator to the highest point, the siphon was triggered, the float was lowered to its original position, and a new daily cycle of operation of the device began. Since the length of the day is constant, the clock did not need to be adjusted to suit the different seasons. The hours were indicated by transverse lines marked on the column. For summer time, the distances between them in the lower part of the column were large, and in the upper part small, depicting short night hours, and in winter, vice versa. At the end of each day, the water flowing from the siphon fell on the water wheel, which, through gears, slightly turned the column, bringing a new part of the dial to the pointer.
Information has been preserved about the watch that Caliph Harun al Rashid gave to Charlemagne in 807. Egingard, the king’s historiographer, reported about them: “A special water mechanism indicated the clock, which was still marked by striking from the fall a certain number balls into a copper basin. At noon, 12 knights rode out from as many doors that closed behind them.”
The Arab scientist Ridwan created in the 12th century. clock for the great mosque in Damascus and left a description of it. The clock was made in the form of an arch with 12 windows indicating the time. The windows were covered with colored glass and illuminated at night. The figure of a falcon moved along them, which, when it reached the window, dropped balls into the pool, the number of which corresponded to the hour that had come. The mechanisms connecting the clock float to the indicators consisted of cords, levers and blocks.
In China, water clocks appeared in ancient times. In the book "Zhouli", which describes the history of the Zhou dynasty (1027-247 BC), there is a mention of a special servant who "looked after the water clock." Nothing is known about the structure of these ancient watches, but, given the tradition Chinese culture, we can assume that they differed little from the medieval ones. A book by an 11th century scientist is devoted to a description of the design of a water clock. Liu Zaya. The most interesting design described there is a water clock with a surge tank. The clock is arranged in the form of a kind of ladder, on which there are three tanks. The vessels are connected by tubes through which water flows sequentially from one to another. The upper tank supplies the rest with water, the lower one has a float and a ruler with a time indicator. The most important role is assigned to the third “equalization” vessel. The flow of water is adjusted so that the tank receives a little more water from the top than flows out of it into the bottom (the excess is discharged through a special hole). Thus, the water level in the middle tank does not change, and it enters lower vessel under constant pressure. In China, the day was divided into 12 double hours “ke”.
A tower astronomical clock, remarkable from a mechanical point of view, was created in 1088 by astronomers Su Song and Han Kunliang. Unlike most water clocks, they did not use changes in the level of flowing water, but its weight. The clock was placed in a three-story tower, designed in the form of a pagoda. On the top floor of the building there was an armillary sphere, the circles of which, due to the clock mechanism, maintained parallelism to the celestial equator and the ecliptic. This device anticipated the mechanisms for guiding telescopes. In addition to the sphere, in a special room there was a star globe, which showed the position of the stars, as well as the Sun and Moon relative to the horizon. The tools were driven by a water wheel. It had 36 buckets and automatic scales. When the weight of water in the bucket reached the desired value, the latch released it and allowed the wheel to rotate 10 degrees.
In Europe, water public clocks were used for a long time along with mechanical tower clocks. So in the 16th century. On the main square of Venice there was a water clock, which every hour reproduced the scene of the worship of the Magi. The Moors appeared and struck a bell to mark the time. Interesting clock from the 17th century. are kept in the museum of the French city of Cluny. In them, the role of a pointer was played by a water fountain, the height of which depended on the elapsed time.
After its appearance in the 17th century. pendulum clock In France, an attempt was made to use water to keep a pendulum swinging. According to the inventor, a tray with a partition in the middle was installed above the pendulum. Water was applied to the center of the partition, and when the pendulum swung, it pushed it into the right side. The device did not become widespread, but the idea behind it to drive the hands from a pendulum was later implemented in an electric clock.
Hourglass and fire clock
Sand, unlike water, does not freeze, and a clock where the flow of water is replaced by the flow of sand can work in winter. Hourglass with a pointer indicator was built around 1360 by the Chinese mechanic Zhai Siyuan. This clock, known as the “five-wheeled sand clepsydra,” was driven by a “turbine” on which sand fell onto the blades. A system of gear wheels transmitted its rotation to the arrow.
IN Western Europe The hourglass appeared around the 13th century, and its development is associated with the development of glass making. Early clocks consisted of two separate glass bulbs held together with sealing wax. Specially prepared “sand”, sometimes from crushed marble, was carefully sifted and poured into a vessel. The flow of a dose of sand from the top of the clock to the bottom quite accurately measured a certain period of time. The clock could be adjusted by changing the amount of sand poured into it. After 1750, watches were already made in the form of a single vessel with a narrowing in the middle, but they retained a hole plugged with a stopper. Finally, from 1800, hermetic watches with a sealed hole appeared. In them, the sand was reliably separated from the atmosphere and could not become damp.
Back in the 16th century. Churches generally used frames with four hourglasses set at the quarter, half, three-quarter and hour. By their condition it was possible to easily determine the time within the hour. The device was equipped with a dial with an arrow; when the sand flowed out of the last upper vessel, the attendant turned the frame over and moved the arrow one division.
Hourglasses are not afraid of pitching and therefore, until the beginning of the 19th century. were widely used at sea to time watches. When an hour's portion of sand flowed out, the watchman turned the watch over and struck the bell; This is where the expression “break the bells” comes from. The ship's hourglass was considered an important instrument. When the first explorer of Kamchatka, student of the St. Petersburg Academy of Sciences Stepan Petrovich Krasheninnikov (1711-1755), arrived in Okhotsk, ship construction was underway there. The young scientist turned to Captain-Commander Vitus Bering with a request for help in organizing a service for measuring sea level fluctuations. For this, an observer and an hourglass were needed. Bering appointed a competent soldier to the position of observer, but did not give him a watch. Krasheninnikov got out of the situation by digging a water meter opposite the commandant's office, where, according to naval custom, bells were regularly sounded. The hourglass turned out to be a reliable and convenient device for measuring short periods of time and in terms of “survivability” it was ahead of the sunglass. They were recently used in physiotherapy rooms of clinics to control the time of procedures. But they are being replaced by electronic timers.
The combustion of material is also a fairly uniform process on the basis of which time can be measured. Fire clocks were widely used in China. Obviously, they served as a prototype, and are now popular in South-East Asia, smoking sticks are slowly smoldering rods that produce aromatic smoke. The basis of such watches were flammable sticks or cords, which were made from a mixture of wood flour and binders. They were often of considerable length, made in the form of spirals and hung over a flat plate into which the ashes fell. By the number of remaining turns one could judge the elapsed time. There were also “fire alarm clocks”. There, the smoldering element was placed horizontally in a long vase. In the right place, a thread with weights was thrown over it. The fire, having reached the thread, burned it out, and the weights fell with a ringing sound into the copper saucer placed. In Europe, candles with divisions were in use, playing the role of both night lights and time meters. To use them in alarm mode, a pin with a weight was inserted into the candle at the required level. When the wax around the pin melted, the weight along with it fell with a ringing sound into the cup of the candlestick. For rough measurement of time at night they were also used. oil lamps with glass vessels equipped with a scale. The time was determined by the oil level, which decreased as it burned out.
General information
Modern scales represent complex mechanism, which, 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. Top part the damper is suspended on the earring, and the lower one is mounted on board 8 in the upper part 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 |
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 Rice. 4.3. Laboratory equal-arm scales VLR-20 |   Rice. 4.4. Laboratory scales VLDP-100 |
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 Rice. 4.5. Double prism scales |  Rice. 4.6. Scheme of the action of forces in two-prism balances |
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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 articulated 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 zeros are set on the digital reading device 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 view of the VLKT-500 scales |
|
A 
b Table 4.1. Initial data for performing the work
| Option No. | T P , G | T etc , G | T To , G | T O , G | A k, m | A 1m | A 2 , m | α 1 = α 2 ,º | φ,º |
| 0,15 | 0,08 | 0,16 | 1,0 | ||||||
| 0,26 | 0,11 | 0,22 | 0,9 | 2,9 | |||||
| 0,32 | 0,17 | 0,32 | 0,8 | 2,8 | |||||
| 0,18 | 0,15 | 0,30 | 0,7 | 2,7 | |||||
| 0,20 | 0,12 | 0,22 | 0,6 | 2,6 | |||||
| 0,16 | 0,09 | 0,17 | 0,5 | 2,5 | |||||
| 0,27 | 0,12 | 0,24 | 1,5 | 2,9 | |||||
| 0,33 | 0,18 | 0,34 | 1,4 | 2,8 | |||||
| 0,19 | 0,16 | 0,31 | 1,3 | 2,7 | |||||
| 0,23 | 0,14 | 0,24 | 1,2 | 2,6 | |||||
| 0,17 | 0,07 | 0,15 | 1,1 | 2,5 | |||||
| 0,28 | 0,13 | 0,27 | 1,0 | 2,4 | |||||
| 0,34 | 0,19 | 0,36 | 2,0 | 3,2 | |||||
| 0,20 | 0,17 | 0,34 | 1,8 | 3,1 | |||||
| 0,21 | 0,15 | 0,25 | 1,7 | 3,0 | |||||
| 0,29 | 0,14 | 0,28 | 1,6 | 2,9 | |||||
| 0,35 | 0,20 | 0,37 | 1,5 | 2,8 | |||||
| 0,21 | 0,18 | 0,36 | 1,4 | 2,7 | |||||
| 0,24 | 0,13 | 0,26 | 1,3 | 2,6 | |||||
| 0,19 | 0,07 | 0,16 | 1,2 | 2,5 | |||||
| 0,30 | 0,15 | 0,29 | 1,1 | 2,4 | |||||
| 0,36 | 0,21 | 0,39 | 1,0 | 2,3 | |||||
| 0,22 | 0,19 | 0,38 | 0,9 | 2,2 | |||||
| 0,21 | 0,11 | 0,23 | 0,8 | 2,1 | |||||
| 0,14 | 0,09 | 0,18 | 0,7 | 2,0 | |||||
| 0,31 | 0,16 | 0,30 | 0,6 | 3,0 | |||||
| 0,37 | 0,22 | 0,41 | 0,5 | 2,9 | |||||
| 0,23 | 0,20 | 0,43 | 1,5 | 2,8 | |||||
| 0,25 | 0,10 | 0,20 | 1,4 | 2,7 | |||||
| 0,18 | 0,06 | 0,14 | 1,3 | 2,6 |
- 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 design difference quadrant scales from double prism ones?
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 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.
Modern stage development of laboratory balances, 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 scales 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. In electronic scales with an upper position of the load-receiving cup, a similar automatic balancing scheme is used, but the permanent magnet of the force exciter is mounted on a rod carrying the cup (electronic-lever-less scales) or is connected to this rod with a lever (electronic-lever scales).
Schematic diagram of electronic labs. 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 an electromagnet 4 and an inductive-type displacement transducer 5. 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.
Recently, electromechanical scales with a quartz piezoelectric element have become 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. Sensing elements are isolated from the environment, which reduces errors due to fluctuations in ambient 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 balances of various types, representing a separate group of scales 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 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 in 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 a table 3 and an 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 a 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.
| Nominal mass of weights | Kettlebell class | ||||||||
| E1 | E2 | F1 | F2 | M1 | M1-2 | M2 | M2-3 | M3 | |
| 5000 kg | |||||||||
| 2000 kg | |||||||||
| 1000 kg | |||||||||
| 500 kg | |||||||||
| 200 kg | |||||||||
| 100 kg | |||||||||
| 50 kg | |||||||||
| 20 kg | |||||||||
| 10 kg | 5,0 | ||||||||
| 5 kg | 2,5 | 8,0 | |||||||
| 2 kg | 1,0 | 3,0 | |||||||
| 1 kg | 0,5 | 1,6 | 5,0 | ||||||
| 500 g | 0,25 | 0,8 | 2,5 | 8,0 | |||||
| 200 g | 0,10 | 0,3 | 1,0 | 3,0 | |||||
| 100 g | 0,05 | 0,16 | 0,5 | 1,6 | 5,0 | ||||
| 50 g | 0,03 | 0,10 | 0,3 | 1,0 | 3,0 | ||||
| 20 g | 0,025 | 0,08 | 0,25 | 0,8 | 2,5 | 8,0 | |||
| 10 g | 0,020 | 0,06 | 0,20 | 0,6 | 2,0 | 6,0 | |||
| 5 g | 0,016 | 0,05 | 0,16 | 0,5 | 1,6 | 5,0 | |||
| 2 g | 0,012 | 0,04 | 0,12 | 0,4 | 1,2 | 4,0 | |||
| 1 g | 0,010 | 0,03 | 0,10 | 0,3 | 1,0 | 3,0 | |||
| 500 mg | 0,008 | 0,025 | 0,08 | 0,25 | 0,8 | 2,5 | |||
| 200 mg | 0,006 | 0,020 | 0,06 | 0,20 | 0,6 | 2,0 | |||
| 100 mg | 0,005 | 0,016 | 0,05 | 0,16 | 0,5 | 1,6 | |||
| 50 mg | 0,004 | 0,012 | 0,04 | 0,12 | 0,4 | ||||
| 20 mg | 0,003 | 0,010 | 0,03 | 0,10 | 0,3 | ||||
| 10 mg | 0,003 | 0,008 | 0,025 | 0,08 | 0,25 | ||||
| 5 mg | 0,003 | 0,006 | 0,020 | 0,06 | 0,20 | ||||
| 2 mg | 0,003 | 0,006 | 0,020 | 0,06 | 0,20 | ||||
| 1 mg | 0,003 | 0,006 | 0,020 | 0,06 | 0,20 |
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.