To correctly answer the question posed in the task, it is necessary to distinguish them from each other.
Body weight is a physical characteristic that does not depend on 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.
"Electrical Appliances" - Lampholders, etc. Mixer. Thermal. Electrical engineering. Targets and goals. Circuit breakers. Household electrical appliances. Educational theme: Household electrical appliances. Alternating current. Direct current. Electrical devices. Wiring. Types of electrical wiring. Appliances. The list of electrical appliances is very large.
"Weight and mass" - The course of the experiment. WEIGHT AND WEIGHTNESS. Scientific data and observations. Project overview. You can approach 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? Humanity's Unsolved Mysteries by Reader's Digest.
"Weight of the backpack" - Recommendations to students: Weigh the backpacks without school supplies from the students of our class. Perform exercises to strengthen the muscles of the body. Subject of research: posture of a schoolboy. The project is research. I will keep my health, I will help myself. Our backpacks. Research results: "What's in our backpacks?".
"Magnifiers" - Lenses. A hand magnifier gives magnification from 2 to 20 times. The product will indicate the magnification that the microscope is currently giving. Tripod. History reference. Biology is the science of life, living organisms that live on earth. Tube. Biology is the science of life. Laboratory work №1. 4. Place the finished preparation on the object table opposite the hole in it.
"Weight and pressure of air" - What is the atmosphere? How can you weigh a gas? What causes atmospheric pressure? Does the atmosphere have weight? Measurement of atmospheric pressure. Let's answer the questions: Can the atmosphere "press"? What causes gas pressure? Why does water rise with the piston? What is the name of the instrument 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 life very easy. Silomer. Types of dynamometers.
The simplest instrument for determining mass and weight is the lever balance, known from about the fifth millennium BC. They are a beam having a support in its middle part. There are cups at each end of the beam. An object of measurement is placed on one of them, and weights of standard sizes are placed on the other until the system is brought into equilibrium. In 1849, the Frenchman Joseph Beranger patented an improved scale of this type. They had a system of levers under the cups. Such a device has been very popular for many years in trade and kitchens.
A variant of the balance scale 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-calibrated (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 on the Earth and on the Moon they will show a different numerical result.
Currently, various methods based on obtaining an electrical signal are used to measure mass and weight. In the case of measuring very large masses, such as a heavy vehicle, pneumatic and hydraulic systems are used.
Instruments for measuring time
The first in the history of time was the Sun, the second - the flow of water (or sand), the third - the uniform combustion of a special fuel. Originating in ancient times, solar, water and fire clocks have survived to our time. The challenges faced by watchmakers in antiquity were very different from those of today. Time meters were not required to be particularly accurate, but they had to divide days and nights into the same number of hours of different 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 go to various tricks for this.
Sundial.
The oldest sundial found in Egypt. It is interesting that in the early sundial of Egypt, the shadow was not used 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 lengths of time, regardless of the height of the Sun, if the rod is 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 sunrises and sunsets, were divided, regardless of their length, by 12 hours, or, more roughly, by the time of the changing of the guards, into 4 "guards" of 3 hours each. Therefore, it was required to mark unequal hours on the scales, tied to certain parts of the year. For large sundials that were installed in cities, vertical obelisk gnomons were more convenient. The end of the temes 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 foot, and other lines were drawn across, corresponding to the hours. 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, 1st century BC. Vitruvius in the book "On Architecture" lists more than 30 types of water and sundials and reports some of the names of their creators: Eudoxus of Cyida, Aristarchus of Samos and Apollonius of Pergamon. According to the descriptions of the architect, 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.
A sundial has a big drawback - the inability to show the time at night and even during the day in cloudy weather, but they have an important advantage compared to other watches - a direct connection with the luminary that determines the time of day. Therefore, they have not lost their practical significance even in the era of the mass distribution of accurate mechanical watches that require verification. The stationary medieval sundials of the countries of Islam and Europe differed little from the ancient ones. True, in the Renaissance, when learning began to be valued, complex combinations of scales and gnomons, which served as decoration, came into fashion. For example, at the beginning of the XVI century. a time meter was installed in Oxford University Park, which could serve as a visual aid for the construction of a variety of 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 often began to decorate the facades of buildings. So that wall clocks could show morning and evening time in 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 the 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, therefore, due to the large distance between the gnomon and the scale, the edge of the shadow was fuzzy.
Portable sundials were of great variety. In the early Middle Ages, mainly high-altitude ones were used, which did not require orientation to the cardinal points. In India, clocks in the form of a faceted staff were common. Hour divisions were applied on the faces of the staff, corresponding to two months of the year, equidistant from the solstice. A needle was used as a gnomon, which was inserted into holes made above the divisions. To measure time, the staff was hung 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, such watches were made in the form of small cylinders, with a number of vertical scales. The gnomon was a flag mounted on a swivel 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 XVI century. in Germany, universal high-altitude sundial in the form of a "ship" was common. The time in them was marked by a ball placed on the threads of a plumb line, when the instrument was pointed at the Sun so that the shadow of the “nose” exactly covered the “stern”. Latitude adjustment was carried out by tilting the “mast” and moving a bar along it, on which a plumb line was fixed. The main disadvantage of high-altitude clocks is the difficulty in determining the time closer to noon, when the Sun changes altitude very slowly. In this sense, a watch with a gnomon is much more convenient, but they 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 allowed them to be quickly set in the desired position. Such clocks were used until the middle of the 19th century. to check 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 sec., and the greatest lead is 16 minutes. 24 sec., but since the lengths of neighboring days do not differ much, this did not cause much difficulty. For amateurs, a sundial with a noon cannon was produced. Above the toy cannon was a magnifying glass, which was exposed so that at noon the sun's rays collected by it reached the ignition hole. The gunpowder caught fire, and the cannon fired, of course, with a blank charge, notifying the house that it was true noon and it was time to check the clock. With the advent of telegraphic time signals (in England since 1852, and in Russia since 1863), it became possible to check the clock in post offices, and with the advent of radio and telephone "talking clocks", the era of sundial ended.
Water clock.
The religion of ancient Egypt required the performance of nightly rituals with the exact observance of 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. Time could be judged by its level. To measure hours 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 each month 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 that are at the same distance from the solstices are almost the same. Another type of watch is also known, 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 portrayed the god of wisdom, Thoth). The conical shape of the bowl of the clock with flowing water contributed to a uniform change in level: when it decreases, the pressure of the water 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 the uniformity of the "running" of the watch. Maybe the vessel was made in such a way that it was easier to read 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. It was necessary that speakers from the prosecution and the defense were on an equal footing. In the surviving speeches of Greek speakers, for example, Demosthenes, there are requests to “stop the water”, apparently addressed to the servant of the court. The clock was stopped while reading the text of the law or interviewing a witness. Such clocks were called "clepsydra" (in Greek "stealing water"). It was a vessel with holes in the handle and on the bottom, into which a certain amount of water was poured. To "stop the water", obviously, they plugged a hole in the handle. Small water clocks were also used in medicine to measure the pulse. Tasks for measuring time contributed to the development of technical thought.
There is a description of a water alarm clock, the invention of which is attributed to the philosopher Plato (427-347 BC). "Plato's alarm clock" consisted of three vessels. From the upper (clepsydra) water flowed into the middle one, in which there was a bypass siphon. The receiving tube of the siphon ended near the bottom, and the drain tube entered the third empty closed vessel. He, in turn, was connected by an air tube to a flute. The alarm clock worked like this: when the water in the middle vessel covered the siphon, it turned on. Water quickly overflowed into a closed vessel, forced air out of it, and the flute began to sound. To regulate the signal switching time, it was necessary to partially fill the middle vessel with water before starting the clock.
The more water was preliminarily poured 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, which served mainly to demonstrate "technical miracles", he developed a water clock that automatically adjusted to changes in the length of night and day time intervals. The clock of Ctesibius had a dial in the form of a small column. Near it were two figurines of cupids. One of them wept continuously; his "tears" came into a tall vessel with a float. The figurine of the second cupid moved along the column with the help of a float and served as a time indicator. When at the end of the day the water raised the pointer to the highest point, the siphon was triggered, the float dropped to its original position, and a new daily cycle of the device began. Since the length of the day is constant, the clock did not need to be adjusted to the different seasons. Hours were designated by the cross lines put on a column. For summer time, the distances between them in the lower part of the column were large, and in the upper part they were small, depicting short night hours, and vice versa in winter. At the end of each day, the water flowing out of 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 clock that Caliph Harun al Rashid presented to Charlemagne in 807. Egingard, the historiographer of the king, reported about them: “A special water mechanism indicated the clock, which was also marked by a strike from the fall of a certain number of balls into a copper basin. At noon, 12 knights rode out of the same number of doors that closed behind them.
The Arab scientist Ridwan created in the XII century. clock for the great mosque in Damascus and left a description of them. The clock was made in the form of an arch with 12 time windows. The windows were covered with colored glass and illuminated at night. Along them moved the figure of a falcon, which, having caught up with the window, dropped balls into the pool, the number of which corresponded to the hour that had come. The mechanisms that connected the float of the clock with 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 attendant who "took care of the water clock." Nothing is known about the structure of these ancient clocks, but, given the traditional nature of Chinese culture, it can be assumed that they differed little from the medieval ones. The book of the 11th century scientist is devoted to the description of the device of the water clock. Liu Zai. The most interesting is the design of a water clock with a surge tank described there. The clock is arranged in the form of a kind of ladder, on which there are three tanks. Vessels are connected by tubes through which water sequentially flows from one to another. The upper tank feeds 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 "equalizing" 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 drained through a special hole). Thus, the level of water in the middle tank does not change, and it enters the lower vessel under constant pressure. In China, the day was divided into 12 double hours "ke".
Remarkable from the point of view of mechanics, the tower astronomical clock was created in 1088 by astronomers Su Song and Han Kunliang. Unlike most water clocks, they did not use the change in the level of the outflowing water, but its weight. The clock was placed in a three-story tower, designed in the form of a pagoda. On the upper floor of the building stood an armillary sphere, the circles of which, due to the clock mechanism, remained parallel to the celestial equator and the ecliptic. This device anticipated the mechanisms for maintaining 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 the water in the bucket reached the desired value, the latch released it and allowed the wheel to turn 10 degrees.
In Europe, public water clocks have long been used alongside 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 who appeared struck the bell, marking the time. Interesting 17th century clock 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 the appearance in the XVII century. pendulum clocks in France, an attempt was made to use water to keep the pendulum swinging. According to the inventor, a tray with a partition in the middle was installed above the pendulum. Water was supplied to the center of the partition, and when the pendulum swung, it pushed it in the right direction. The device was not widely used, but the idea of driving the hands from the pendulum, which was embedded in it, was later implemented in an electric clock.
Hourglass and Fireglass
Sand, unlike water, does not freeze, and clocks where the flow of water is replaced by the flow of sand can work in winter. An hourglass with a pointer was built around 1360 by the Chinese mechanic Zhai Xiyuan. This clock, known as the "five-wheeled sand clepsydra", was powered by a "turbine" on the blades of which sand was poured. The system of gear wheels transmitted its rotation to the arrow.
In Western Europe, hourglasses appeared around the 13th century, and their development is associated with the development of glassmaking. Early clocks consisted of two separate glass bulbs held together with sealing wax. Specially prepared, sometimes from crushed marble, "sand" was carefully sieved and poured into a vessel. The flow of a dose of sand from the top of the watch to the bottom measured a certain period of time quite accurately. It was possible to regulate the clock 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 cork. 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. mainly in churches, frames were used with four hourglasses set to a quarter, half, three quarters of an hour and an hour. By their condition, it was easy to determine the time within the hour. The device was supplied 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.
The hourglass is not afraid of pitching, and therefore, until the beginning of the 19th century. were widely used at sea to count the time of watches. When an hourly portion of sand flowed out, the watchman turned the clock over and struck the bell; This is where the expression "beat the glass" comes from. The ship's hourglass was considered an important instrument. When the first explorer of Kamchatka, a student of the St. Petersburg Academy of Sciences, Stepan Petrovich Krasheninnikov (1711-1755), arrived in Okhotsk, ships were being built 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 post of observer, but did not give a watch. Krasheninnikov got out of the situation by digging in a water meter in front of the commandant's office, where, according to sea custom, flasks were regularly beaten off. The hourglass turned out to be a reliable and convenient device for measuring short periods of time and was ahead of the solar ones in terms of “survivability”. Until recently, they were used in the physiotherapy rooms of polyclinics to control the time of the procedures. But they are being replaced by electronic timers.
The combustion of the material is also a fairly uniform process, on the basis of which time can be measured. Fire clocks were widely used in China. Obviously, their prototype was, and now popular in Southeast Asia, smoking sticks - slowly smoldering rods that give fragrant smoke. The basis of such clocks was combustible sticks or cords, which were made from a mixture of wood flour with binders. Often they had a considerable length, were made in the form of spirals and hung over a flat plate, where the ashes fell. By the number of remaining turns, it was possible to judge the elapsed time. There were also "fire alarm clocks". There, the smoldering element was horizontally located in a long vase. In the right place, a thread with weights was thrown over it. The fire, having reached the thread, burned through it, and the weights fell with a clang into the copper saucer substituted. In Europe, candles with divisions were in use, playing the role of both nightlights and time meters. To use them in alarm mode, a pin with a weight was stuck into the candle at the right level. When the wax around the pin melted, the weight, along with it, fell with a clang into the cup of the candlestick. For a rough measurement of time at night, oil lamps with glass vessels equipped with a scale also served. The time was determined by the oil level, which decreased as it burned out.
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 a force known in magnitude, created in various 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 by a 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 balances, which are characterized by relatively low speed and significant susceptibility to external influences, is characterized by the increasing use of electric power exciters with an electronic automatic control system (ACS) to create a balancing force (torque) in them, 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 beam of light 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 basis 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. In electronic scales with the top location of the load receiving cup, a similar automatic balancing scheme is used, but the permanent magnet of the exciter is mounted on the rod that carries the cup (electronic leverless scales) or is connected to this rod by a lever (electronic lever balances).
Schematic diagram of 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 block; 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 TVES company. 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 of an 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;
AC power settings - 187–242 / 49 - 51 V / Hz;
power consumption - 9 W;
overall 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 balances 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 mass 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. Sensing elements are isolated from the 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. The difference between radioisotope balances is low measurable forces, versatility and insensitivity to high temperatures, and electromechanical balances with strain gauge transducers are 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 of 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 of various types, representing a separate group of scales with special conditions and methods of weighing, requiring 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 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 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 packing bulk materials used in technological processes of various sectors 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 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 weight of the 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 three-position 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.
| Nominal value of mass of weights | weight 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 |
The nominal mass values of the weights indicate the largest and smallest nominal mass allowed in any class, as well as the limits 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.
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; twenty; 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 reading resolution, 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 a 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.
A saddle with a load-receiving prism 9 is fixed on the short arm of the rocker arm 1, and a counterweight, an air damper disk and a microscale 4 of the optical device are fixed on the long arm. 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 is lowered by the support prism 2 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 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 technological 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 applied to the cup 9 of the load, 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 operating 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 mass measurement range 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 measuring system of the scales includes a beam 3, a suspension bracket 2 with a load-receiving cup 1 and a “string” b. A 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 oscillations 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-lay 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), designed to measure masses up to 500 g (measurement error ± 0.02 g), are similarly arranged.
Before measuring body weight at level 1, the scales are set in 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. At the same time, the handle 9 of the gyre-laying mechanism is in the position for measurement in the range of 1-100 g. The test body 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 scales case. Electrical elements that generate heat are located at the rear of the balance and 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 of 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 view of VLKT-500 scales |
|
a 
b Table 4.1. Initial data for work performance
| option number | t P , G | t etc , G | t to , G | t about , 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 control questions.
test 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
Loading...
