Mass measuring device. Scales (instrument). Special purpose weights
Scale device
Scales are designed to measure the mass of goods, goods, products, people and animals. Systems can be automatic, semi-automatic or mechanical. According to the principle of operation, measuring units are divided into three categories:
- Hydraulic scales. The algorithm of operation of hydraulic mechanisms is based on the operation of piston or membrane cylinders. The pressure from the mass is transmitted through the cylinders to the fluid that is inside the piston or membrane.
The load from the physical volume is fixed by a manometer.
- lever scales. The design of the mechanism consists of several levers interconnected by earrings or steel prisms. Gravitational balancing works on the principle of a rocker arm. Lever mechanisms are divided into square and prismatic.
- Tensometric scales. Tensometric scales work on the basis of sensors, the internal resistor changes resistance from deformation.
The principle of operation of portable and stationary measuring mechanisms is based on balancing the moment created by mass pressure.
When it is necessary to measure bulk cargo of a large volume, then special electric trolleys with a forklift are used. With pressure, the force is transferred to the prisms and levers.
In electronic scales, balancing occurs automatically. There is no lever system in this mechanism. The design of electronic mechanisms is arranged in such a way that the weighted value is converted into current or voltage.
Such units can be connected to other measuring and computing devices.
Electronic mechanisms provide for the presence of strain gauges of the Tuningfork type or with the use of an inverse type magnetoelectric converter.
The built-in microprocessor allows to achieve a high level of automation, and also provides the ability to expand the functionality of the measuring device.
Types and characteristics of scales
Scales are classified according to their purpose into types:
- The main parameter of a laboratory measuring unit is accuracy. Precision have a discreteness from one gram to one milligram, analytical - no more than 0.1 milligram.
There are brands of devices with additional options. These include dynamic weighing, which involves measuring animals or non-static objects. Hydrostatic weighing involves determining the mass of liquids.
Laboratory measuring instruments are also subdivided according to the type of calibration into devices with automatic calibration, internal weight and external weight.
- Scales of simple weighing. The unit with an electronic mechanism is a compact mechanism that allows you to measure small loads. Such devices include scales for control weighing, packing and portioning.
The latter are used for simple mass measurement that does not require high accuracy, where additional functionality is not needed.
- Trading. They are used to measure the mass of goods, for packaging, for portion weighing, with the subsequent calculation of the amount based on the price per unit. This model has a display located on the stand or on the body of the device.
Many sales units are equipped with a thermal printer with the ability to print labels with a self-adhesive surface. Such devices are subject to state verification, as they are subject to metrological control.
- This model has three panels with displays that display additional information about the measured samples.
The first display shows the total weight, the second shows the value of one sample, and the third displays the number of these samples.
The electronic unit is used to measure various loads. Such models usually have additional functionality:
- waterproof for rooms with high humidity;
- corrugated surface of the platform, which allows you to measure the mass of unstable loads; the possibility of weighing large loads;
- a device with an additional power supply that measures mass while away from the mains.
- This model of the device is intended for use for medical purposes, namely for measuring and controlling the body weight of patients.
Baby measuring devices are a cradle in which the baby is placed, and the display on the main panel shows the result.
- Crane. Such scales belong to the warehouse category, they are used for weighing loads up to 50 tons. The design of the crane scale is very durable, it consists of a metal case with an indicator of indicators and a powerful hook.
- Platform. Structurally, this model is a platform, the indicator is installed either in a wall or on a rack.
- . This model is used to measure the mass of goods of any size and volume, and also solves many problems. There are two groups of such devices: electronic and mechanical.
Currently, all enterprises use only electronic versions of scales, mechanical devices are already considered obsolete, since they are inferior to modern ones in terms of reliability and price.
- Packing. Such devices are classified as simple, they are used by devices for weighing a small mass of goods not exceeding 35 kilograms.
- Electronic with receipt stamp. No modern supermarket can do without such devices. Printing a label on a product in automatic mode improves the quality of customer service.
Scales not only measure the mass of products and issue labels with a barcode and other information, but also keep records, store all kinds of parameters in memory.
- Such scales are designed for weighing goods on pallets.
The design of the pallet measuring device allows, using four sensors, to determine the weight of the cargo and display the data on the display located on the designated terminal.
These devices are used at wholesale depots, in industrial shops, at customs, at trade enterprises and in logistics centers.
- Car weights. This category of scales is designed to measure the mass of the car - both laden and empty. Weighing methods are different, it all depends on the application, design and other parameters of the device.
- Luggage scales. The luggage weight measurement unit is the simplest type of scale. There are mechanical models and electronic ones.
The mechanism is a simple compact device that easily fits in your hand, the load is hung on a hook, and the display shows the result. Pocket scales are easy to take with you.
- . A device for measuring the mass of products is necessary in the kitchen of a real housewife, who observes the accuracy in the proportions and quantities of ingredients for preparing delicious dishes.
Classification of weighing measuring instruments by type of installation:
- Stationary
- Suspended
- mobile
- floor standing
- Desktop
- Embedded
According to the accuracy class, measuring devices are divided into three types:
- high class of accuracy,
- average;
- ordinary.
According to the type of lifting mechanism, groups are distinguished:
- Bunker
- Rail
- Platform
- Conveyor
- Hook
- Bucket
Some models of weighing instruments have additional options:
- Taro compensation. This option allows you to make weight measurements without tare. Before weighing, it is necessary to put an empty container on the scales, then reset the result to zero, and then weigh the load together with the container.
- Synchronization with PC/phone. This option allows you to transfer the data received from the scales to a computer or phone.
- Automatic shutdown. When the device is not in use, it automatically turns off.
Diagnostic
Diagnostic measurements in electronic scales allow you to determine physical indicators, which leads to effective weight loss. All received data is stored in the device memory.
Advantages of mechanical measuring instruments:
- The mechanism is easy to use.
- Long service life.
- Structural strength.
- Low price compared to electronic models.
- There are no batteries that require regular replacement.
- There are no special storage requirements.
Advantages of electronic measuring instruments:
- Additional options (memory, the ability to calculate body mass index and others).
- Measurement accuracy at the highest level.
- There are no bulky elements, compactness in comparison with mechanical units.
- Automatically when disconnected, the product is set to the zero position.
- Fashion design.
- High load limit.
- Automatic shutdown and inclusion when touching the surface.
- Quite a large assortment offered by manufacturers.
Flaws
Disadvantages of mechanical measuring instruments:
- Modern technologies are not used in the production of measuring mechanisms.
- Measurement accuracy is not at the highest level.
- There are no additional features.
Disadvantages of electrical measuring instruments:
- Batteries that need to be changed from time to time.
- The high cost of the device, and the more additional options it has, the higher the price.
- The device requires careful handling and storage, there is a risk of damage to electronic components.
- Difficulty in repair in case of breakdowns.
How to choose scales
When choosing a device for home use, you should follow some recommendations:
- First, it is important to check in which units of measurement the device operates. Not all devices determine the mass in kilograms, there are imported models with a measuring system in pounds. Perhaps you need pounds.
- Next, you need to verify the accuracy of the measurements of the device. Right in the store, make sure that a pack of kilogram granulated sugar weighs exactly one kilogram. For verification, test on several models. Buy a device with a minimum error.
- A device with a corrugated surface is much more convenient, the weighed load will not slip. Also look for a non-slip bottom, rubber pads at the bottom are possible.
- When buying a unit for a bathroom, sauna or pool, take a model with a waterproof case. Electronic models without this protection will fail very quickly.
- When choosing the material from which the floor options are made, give preference to metal. When buying kitchen weighing devices, choose a device with a glass bowl.
- can be checked for accuracy on the spot. Press the surface with your hand and release your hand abruptly. In a quality device, the arrow returns immediately back to zero.
- If you can't see well, buy a device with large numbers. There are also options with a separately displayed scoreboard.
Which measuring units are better - electronic or mechanical? There is no definite answer, since each species has its own buyer.
It is enough for one person to simply know their body weight with an error within one kilogram, for another it is important to know about the minimum fluctuations in weight and control other parameters, such as body mass index, the amount of water, fat, bone mass.
How to use
It is necessary to use measuring units in accordance with the instructions supplied with the purchase.
- It is important to initially install the device correctly on a flat surface so that the readings are more accurate. For adjustment and alignment, a building level is used.
There are models in which the level is built in, you only need to tighten the adjusting legs. The air bubble should be in the center of the control ring.
- The mechanism must be stable and must not wobble when in use. With the correct installation of the measuring unit, the arrow shows zero on the dial.
Also, in dial mechanical measuring devices, the frequency of oscillation of the arrow is adjusted, for this the damper rotates in a certain direction.
- Readings from a mechanical device are taken while facing directly to the dial. It is forbidden to cut and pack products on the platform.
Measuring mechanisms do not require special maintenance, it is only necessary to periodically wipe the surface with a damp cloth, the parts must not be lubricated with oil.
Precautionary measures:
- Do not use the unit for other purposes.
- Handle with care as the measuring mechanism is a precision instrument.
- Do not use in hazardous areas using flammable liquids and gases.
- Do not use the device in an area affected by electromagnetic or electrostatic waves, as the readings will be incorrect.
- You cannot disassemble the device yourself.
The warranty period is usually several years, during which time the warranty card must be kept. The coupon specifies the date of purchase, the brand of goods and the store's seal is required (note that the coupon is invalid without a seal).
If during the service period any damage to the device occurs due to the fault of the manufacturer, then the repair is carried out at the expense of the seller. It is important that the unit is operated in accordance with the conditions specified in the instructions.
The warranty does not apply in the following cases:
- Defects arose in the event of force majeure (power surges, traffic accidents, fire or natural disasters).
- The operating conditions specified in the manual are violated.
- If the buyer independently or with the help of third parties repaired the product.
- Failure to comply with safety standards.
- Making changes to the design of the product by the buyer.
- Damage due to improper transportation of goods by the buyer. If the delivery is carried out by the manufacturer or seller, then the guarantee is valid.
- The presence of mechanical damage on the body or platform of the device.
- Use of equipment at high humidity (over 90%) and elevated temperatures over 25 degrees.
- Penetration of liquid, dust, insects or other foreign objects into the mechanism of the product.
- In case of equipment breakdown due to the use of low-quality or expired parts.
Also, the warranty does not apply to components and individual structural elements.
During operation of the measuring unit, malfunctions are periodically possible. You can fix the problems yourself:
- If there is no indication on the display, the machine may not be connected to the network. Or the batteries are out of order, in which case they must be replaced with working batteries.
- If the weighing result is incorrect, the calibration or zeroing may not have been performed.
- In case of problems with the power cord, you can replace the electric plug or simply clean the contacts.
Do not try to repair the device yourself, if you do not understand the technique, entrust this matter to professional craftsmen, call the service department. Or take advantage of the warranty if your warranty period has not expired.
Spare parts for a specific model are purchased in specialized stores that are focused on the sale of such units.
Manufacturers offer additional components for measuring devices: buttons, indicators, legs, keyboard stickers, transformers, shock absorbers for the platform, platforms themselves, sensors, power supplies,.
Scale Manufacturers
Bosch
Bosch offers customers about a dozen different models of floor measuring devices. The official website contains all possible options. The design is stylish, the case is thin.
In addition to weighing units, the company sells all kinds of household appliances:,
Polaris sells various options for measuring devices: desktop and, as well as floor-standing for weighing people. The site contains all the necessary information on this product.
The company also sells climate control equipment, water heaters, household appliances, and dishes. Modern design developments and a unique approach to consumers are an integral part of the company's activities.
Scarlett offers home and kitchen appliances, health and beauty products. The site presents mechanical and electronic models of measuring devices.
The models of this company are distinguished by their bright design, there is a collection of scales with Disney comics.
Supra
Supra offers a wide range of kitchen measuring devices and floor standing units. The official website of the company will allow you to get acquainted with the entire range of products.
Tefal
Tefal sells household appliances, including measuring units. The presented models on the site look aesthetically pleasing and elegant. The product is guaranteed by the manufacturer.
To correctly answer the question posed in the task, it is necessary to distinguish them from each other.
Body weight is 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.
11. General information about the mass. Classification of instruments and means for measuring and dosing mass.
1.1. Relationship between mass and body weight
Body mass is called PV, which is a measure of its inertial and gravitational properties, i.e. the mass of a body m is its physical property, determined by the ratio between the force of gravity G acting on this body and the acceleration imparted by it to the body: G = mg , H
Gravity acceleration = Acceleration forces of attraction + Centripetal acceleration
The weight of a body is the force P with which this body acts due to gravity towards the Earth on a support that keeps the body from free fall.
If the body and the support are stationary relative to the Earth, then the weight of the body is equal to its gravity: P = G.
The mass of a body m, in contrast to its gravity G, is independent of the location of the body on Earth or on another planet
1.2. Mass reference
The unit of mass is the international prototype of the kilogram, kept at the International Bureau of Weights and Measures in Sevres (a suburb of Paris).
The prototype (ME No. 12) is a straight circular cylinder of platinum-iridium (90% platinum, 10% iridium) 39 mm high and 39 mm in diameter, the mass of which, to the nearest 0.01 mg, should remain unchanged for more than 1000 years. The mass of working standards approved for comparison by national prototypes can be determined with an accuracy of (1÷3) 10 -9
Scheme for transferring a unit of mass
2. Classification of instruments and means for measuring and dosing mass
2.1. Giri
Weights are divided into: standard weights; general purpose weights; weights for special purposes.
General purpose weights
Special purpose weights
2.2. Weighing instruments
Scales - a device for measuring mass, by using the effect of gravitational forces
Dosers - technological scales for determining the necessary components of a product in the production process
By purpose, weighing and weighing devices can be divided into groups:
Depending on the method of converting the measuring signal, scales and weighing dispensers are divided into:
mechanical;
electromechanical;
optomechanical;
radioisotope
Depending on the purpose, design, installation method scales and weight dispensers are divided into:
Scales of discrete action:Laboratory; Desktop; Platform; for metallurgy
Continuous balance:Conveyor; Tape
Dosers of discrete action:Portion; For packing; Automatic lines
Continuous dispensers:With adjustable material supply to the conveyor; With adjustable conveyor belt speed
Depending on the method of converting the measuring signal, scales and weighing dispensers are divided into:
|
Scales |
|||
|
Mechanical |
Electromechanical |
Opto-mechanical |
radioisotope |
|
Lever |
With capacitive transducers |
With mirror pointing device |
Absorption |
|
Spring |
With strain gauge converters |
With interference pointing device |
scattered radiation |
|
Piston |
With inductive converters | ||
|
With piezoelectric converters | |||
The lever scales consist of:
The load receiving device on which the weighed load is placed;
Lever system that perceives the load from the load receptor;
pointing device;
Beds or bases (foundations) on which all devices are mounted.
In addition to these main parts, the balance may contain a number of auxiliary devices:
- arrester - to stop oscillations,
- insulated - to release the prisms from the load,
- plumb or level - to control the installation in the working position,
- damper - for the transformation of periodic oscillations into aperiodic ones,
- optical device - to increase the resolution.
The lever is a rigid body, to which forces are applied, tending to rotate this body around an axis (support point).
There are levers of the 1st and 2nd kind:
In a type 1 lever, forces are applied on both sides of the fulcrum and act in the same direction.
In a lever of 2 types, forces are applied on one side of the fulcrum and act in opposite directions.
The levers are characterized by: Moment of force; Lever gear ratio(The reciprocal is the ratio of the shoulders)
Spring scales consist of:
Torsional - the applied load is balanced by the torque of the elastic thread.
Torsion - the load is balanced by the torque of the spring (flat spiral).
The spring must have the properties:
The spring characteristic must be linear over the entire measuring range;
Rigidity, that is, the ratio of distance to load, remains constant with temperature changes;
Hysteresis, that is, the divergence of the increasing and decreasing branches of the spring characteristic, must be small;
Fatigue phenomena must not occur in the spring material.
By purpose, laboratory scales are divided into scales:
general purpose,
exemplary,
special purpose
special design
Depending on the method of installation, balances for statistical weighing are divided into:
desktop (from 1 to 50 kg);
mobile (from 50 to 6000 kg);
stationary (from 5 to 1000 tons)
According to the type of reading device used for statistical weighing, balances are distinguished :
with balance indicator;
with rocker scale balancing device;
with a dial reading device;
with a projection reading device;
with discrete-digital reading device;
Basic MX scales for statistical weighing - verification division value - e
e scales for statistical weighing with analog reading devices is taken equal to the price of the smallest division of the scaled
e scales with discrete readout devices can exceed the value of the unit of readout discreteness d an integer number of times r , not exceeding 10
There are two weight accuracy classes for statistical weighing:
Scales with a number of calibration divisions of more than 500 e are classified as weighing instruments of an average accuracy class, having the designation;
Scales with a number of calibration divisions of 500 e or less are classified as instruments of the usual accuracy class, having the designation
SUBJECT : BODY WEIGHT. UNITS OF POWER. DYNAMOMETER.
The purpose of the lesson : give the concept of body weight, establish the differences between body weight and gravity; enter a unit of force; Learn how to measure body weight.
Equipment: computer, screen, projector, floor scales, dynamometer, measuring cylinders, weights.
Lesson plan:
Organizational moment (1 min)
Checking homework (7 min)
Learning new material (18 min)
a) body weight. Units of power.
b) Dynamometers. Types of dynamometers.
c) Body weight and its calculation.
4. Physical education (task G. Oster)
5. Solution of the problem. Consolidation of the material covered (10 min)
6. The results of the lesson. Homework (1 min)
During the classes.
1. Organizational moment.
2. Actualization of knowledge.
Let's start the lesson by remembering with you some physical quantities and terms that we met earlier.
Physical dictation:
What is the value of gravity? What is measured?
How is gravity directed?
What is the value of elastic force? What is measured?
What is the direction of the elastic force?
Write down the formula of Hooke's law?
1) Divide these physical quantities into vector and scalar ones: mass, gravity, speed, time, length, inertia and elastic force.
(scalar: mass, time, length; vector: gravity, speed, elastic force. Inertia is not a physical quantity, it is a phenomenon).
follow-up question: define What is called body weight. (is a physical quantity that is a measure of the inertia of a body).
Additional question: What is deformation? ( deformity is a change in the shape or size of a body )
2) Draw graphically the force of gravity acting on a brick lying on the surface of the Earth.
Follow-up question: why do raindrops fall to the ground instead of flying back to the clouds? ( raindrops are affected by gravity
So, we remembered with you some physical quantities and terms that we met earlier, let's move on.
3. Learning new material.
What is the boy's weight?
Are we right to say that the boy's weight is __ kg?
Let's take a vote. Raise your hands if you think this is the right thing to say. And now those who believe that we are talking wrong. Opinions were divided. Let's not argue who is right and who is not. A new topic will help you understand this " Body weight ". Let's write it down in a notebook.
- Weight body is a physical quantity. We have already developed a plan for the study of physical quantities. Remembering it, tell me, what should we learn about body weight today?
1. Definition.
2. Vector or scalar.
3. Designation.
4. Formula.
5. Unit of measure.
6. Device for measuring.
These points of the plan will be the purpose of our lesson, and besides this, we will answer the question posed.
- (Slide4) The tiger cub lies on the board (support). When the body was placed on a support, not only the support was compressed, but also the body attracted by the Earth. A deformed, compressed body presses on a support with a force called the weight of the body.
If the body is suspended on a thread (suspension), then not only the thread is stretched, but the body itself.
- We write down: The weight of a body is the force with which the body, due to attraction to the Earth, acts on a support or suspension.
Do you think weight is a vector or a scalar quantity? ( since this is power,then vector value)
Body weight is a vector physical quantity
What is the direction of body weight? To answer this question, remember the direction of gravity. That's right, the force of gravity is always directed vertically downward, which means that the weight of the body is also, since this force arises as a result of attraction to the Earth.
Letter designation: P
Formula. P = F heavy(the body and support or suspension are stationary or move uniformly and in a straight line)
Quite often, the weight of a body is equal to the force of gravity acting on it.
F heavy attached to the body
R weight attached to the support (suspension)
In what units is force measured?
In honor of the English physicist I. Newton, this unit is named newton - 1H
1kN=1000N; 1N= 0.001kN
F heavy = m∙ g- gravity formula
P = F heavy = m∙ g m= P/g ; g= P/m
F heavy - gravity [N]
m - weight [kg]
g – free fall acceleration [N/kg]
g = 9,8 [N/kg]; g = 10 [N/kg];
(Slide5) in practice, they measure the force with which one body acts on another.
To measure force - use a DYNAMOMETER
used : for tightening nuts - there is such a torque wrench so that the nut does not turn off and tighten securely; measure carpal muscle toneForgeneral performance and human strength,
Experience Let's take a dynamometer and hang a weight of 102 g on it. At rest, its weight is 1 N. And indeed, if the weight hangs motionless on the hook of the dynamometer, then it will show exactly 1 N. But if the dynamometer is pumped up - down or to the left - to the right, it will show that the weight of the kettlebell has changed. In the figure, for example, it is equal to 4 N. The mass of the bodies and the force of gravity did not change in this case.
So, numerous experiments show that the weight of a body is equal to the force of gravity acting on it, when the body and its support (suspension) are at rest or move together uniformly and in a straight line.
P = F heavy .
Note also that the numerical values of weight and gravity can be equal, but the points of their application are always different. . The force of gravity is always applied to the body itself, and its weight is always applied to the suspension or support..
[ P ] = [ 1 Newton ] = [ 1 H ]
Exercise 9 (2.3) (solve)
Summarizing:
What is the name of the force measuring device?
A dynamometer is a device.... (for measuring body weight)
What is Misha's weight? Are we right to say that Misha's weight is __ kg?
( no, because body weight is measured with a dynamometer) and is measured in N, body weight is measured with a weighing device --- kg) (Slide 7)
What is the formula for gravity?
What did you find difficult in the lesson?
What turned out to be difficult for you?
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 history time meter 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 length 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, according to the time of the changing of the guard, 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, which were installed in cities, vertical obelisk gnomons were more convenient. The end of the tems of such an obelisk described symmetrical curved lines on the horizontal platform of the foot, depending on the season. 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 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 activated, 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 flows sequentially 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 of conducting 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, shipbuilding was going on 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 substituted copper saucer. 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.
