Features of the counter field are that. Test on the topic: Databases - Knowledge Hypermarket. What are the forms for?

1. information structures, stored in external memory
2. software that allows you to organize information in the form of tables,
3. software tools that process tabular data,
4. software tools that search for information,
5. information structures stored in the OP.

2. The most common in practice are:

1. distributed databases;
2. hierarchical databases;
3. network databases;
4. relational databases.

3. What are the forms for?

1. for storing database data;
2. for selecting and processing database data;
3. to enter database data and view it;
4. For automatic execution groups of commands;
5. to perform complex program actions?

4. A distributed database is a database

1. stored on one computer.
2. different parts of which are stored on many computers,interconnected by a network.

5. The button indicates

1. sorting records in ascending order;
2. sort records in descending order;
3. displaying records starting with these letters;
4. counting the number of records in the database

6. Does a table that does not have any records contain any information?

1. an empty table does not contain any information;
2. an empty table contains information about the database structure;
3. an empty table contains information about future records;
4. a table without records cannot exist.

7. What is the purpose of the “table” object?

1. for data storage
2. for data archiving
3. to enter and delete data
4. for data sampling

8. A fragment of the database provides information about family relationships. Based on the given data, determine the surname and initials of grandmother Ivanova A.I.

Table 1

Table 2

1. Tseys T.N.
2. Petrenko A.I.

c) Chernykh I.A.

d) Petrenko N.N.

9. The database structure will change if

1. add/delete record;
2. add/remove field.
3. edit entry;
4. swap entries;

1. to destroy unnecessary records
2. to find the information you need
3. to make new entries
4. to display the necessary information on the screen

11. What is special about the counter data type?

1. used to enter integers and real numbers
2. tends to automatically increase
3. has the property of automatic recalculation when deleting a record
4. used to enter fonts

12. Determine the database type:

1. Relational b) Hierarchical c) Network

13. The database contains information about school students: last name, class, test score, practical task, total points. What type of field should the TOTAL POINTS field be?

1. symbolic b) logical c) numeric d) any type e) Date

14. How many records are there in the database?

Electricity meters first appeared in the 19th century. Their appearance was associated with massive research into electromagnetism conducted by scientists and their inventions powered by electricity. Infrastructure developments and debates over consumer choice of DC or AC led to the discovery of the transformer, and attempts to account for AC electrical energy fueled breakthrough innovation. In 1888, Oliver B. Shellenberger developed the first alternating current meter.

Operating principle and design of the electricity meter

To make an accounting active electricity alternating current, induction single-phase and three-phase devices are needed, and to account for direct current, which is used in electric transport, railways, etc. – electrodynamic counter.

The counting disk mechanism of the electric meter records the number of revolutions of its moving part, which is proportional to the amount of electricity consumed.

In an induction electric meter, the aluminum disk (the moving part of the device) rotates when electricity is consumed using eddy currents, which are induced by the magnetic field of the meter coil. Here the interaction of two fields occurs: the magnetic field of the eddy currents and the magnetic field of the coil. The meter is designed in such a way that for its operation two currents are created, one of which flows in a circuit parallel to the load, and the other in the circuit of the load current itself. Both of these currents flow in coils that are placed on cores made of iron. Their names are appropriate: “ampere coil” and “voltaic coil”. The iron cores of the coils are magnetized by alternating current. Using a variable electric current contributes to the fact that the poles of electromagnets are constantly changing. Due to this, the effect of passing a magnetic field between them occurs. The arrangement of the coils and the magnetic field between them is calculated so that they form eddy currents in the body of the disk, and the direction of these currents will induce the magnetic field to pull the disk along with it, creating rotation. The speed of rotation of the disk will be proportional to the magnitude of the currents in both coils, that is, the speed of rotation, based on practical calculations, will be directly proportional to the product of the cosine of the phase shift (power consumption) and the voltage U and current strength I. Using simple connecting techniques from mechanics, a rotating disk is connected to the digital readings of the device. The operating principle of an electronic type meter is that voltage and AC, which leads to the creation of pulses at the output. The number of these pulses is proportional to the energy to be measured.

Types of electricity meters and their classification

There are several types and types of electricity meters, which differ in the type of measured values, design and type of connection. Meters are divided into devices that are directly connected to the power circuit and devices that are connected to the power circuit using special instrument transformers.

According to the type of design, electricity meters are divided into:

1. Induction (electromechanical) is an electric meter in which a moving element made of a conductive material is influenced by a magnetic field created by stationary current-carrying coils. The disk acts as a moving element. The magnetic field of the coils induces currents that flow through the disk. The amount of energy consumed is directly proportional to the number of revolutions of this disk.
2. Electronic (static) is an electric meter, the solid-state (electronic) elements of which are affected by alternating current and voltage, which creates pulses at the output, the number of which is equal to the amount of measured energy. In such meters, the measurement of active electricity is based on the fact that analog input signals of current and voltage are converted into a counting pulse.
3. A hybrid electric meter is a cross between devices with a digital interface and a measuring electronic or induction part, with a mechanical calculation device. Such devices are rare.

Meters can also be classified according to the measured values: single-phase - measure alternating current 220 volts, 50 Hz, as well as three-phase, designed to measure voltage of 380 V and a frequency of 50 Hz. In high-voltage circuits, where the voltage reaches 600 V, three-phase meters with current transformers are used, which measure electricity with a voltage of 100 V.

What is special about the counter data type?

Currently, electricity is accounted for mainly at one tariff. In this case, the cost of electricity is the same and does not depend on the time of its consumption. When installing an induction meter, electricity readings are reproduced using mechanical parts. This mechanical type of data is inherent in a certain degree of error, which affects the payment for electricity. Unlike induction meters, which do not allow multi-tariff electricity calculations, electronic meters provide this opportunity.

The inter-verification period of electronic electricity meters ranges from 4 to 16 years.

In electronic meters, all readings are displayed on a liquid crystal display and have a digital data type, which practically eliminates all errors associated with mechanical influences on the device parts. Electronic meters will become great solution for apartments where high energy consumption prevails, as well as for enterprises.

Electronic and mechanical household electricity meters

Household induction (mechanical) electricity meters, due to a number of shortcomings, are being forced out of the market by electronic meters. Mechanical electricity meters are used in apartments where energy consumption is low.

Disadvantages of induction meters:

• Inability to count more than one tariff;
• Lack of automatic remote reading function;
• Significant degree of error in accounting;
• Poor protection against electricity theft;
• Inconveniences associated with operation and installation;
• Low functionality.

The advantages of electronic meters include the ability to account for electricity at tariffs that are differentiated. That is, one-, two-, three-tariff and more meters have the ability to remember and display the amount of electricity consumed, taking into account the time periods that are programmed into them. Such multi-tariff accounting is implemented using a set of counting mechanisms operating at set time intervals corresponding to different tariffs.

Operating principle and design of the electric meter (video)

In modern design of electrical systems, only electronic meters are used, because they have unlimited capabilities regarding service and are undeniable leaders in “information” terms.

An integral part of most database tables is the “Counter” field. What is the peculiarity of this column, what functions it performs and what properties it has, we will consider below. To do this, let us dwell in more detail on the concepts of databases, their objects and, in particular, tables, the element of which is the counter.

Databases

Let's take a short excursion into database computer science. A database is a set of tables with information between which there are connections. Databases are useful for storing large amounts of data related to one topic. Businesses use databases to store information about clients: names, dates of birth, address, passport and other personal data.

For each client, a record of orders is kept: product and its quantity, dates, delivery method, and other features. The information about the products itself is also contained in repositories and represents a complete set of parameters characterizing the products for sale.

Banks store information about clients, deposits and loans. It also contains financial parameters that allow you to generate reports for business analysis and submission to regulatory authorities.

A travel company works with a database that stores data about business partners, tourists, hotels and excursions. By using special applications tariffs and costs of tours are calculated.

Thus, the data contained in the database corresponds to the industry in which the company operates.

Database objects

The main database object is a table, the main storage of database information. These are the tables that we are used to seeing in classes at school or university, in books and textbooks. They consist of rows, which in databases are called records or tuples, and columns, called fields.

Queries perform the main work of interacting interface forms with other database objects, their elements and the database itself. When you simply click the Delete Row button on the DB application form, it is the query that completes the action and fulfills your requirement.

Reports are used to output information to the printer, and macros and modules are provided in the database application interface to perform procedures in response to events.

Features of database tables

As we know from the computer science course, databases consist of tables. Each row contains data related to one object. Let's give an example. The travel agency database contains the “Hotels” table, each record of which contains complete information on one of the hotels: name, category, address, link to website, phone and fax number, etc.

Each column defines exactly what values ​​are contained in it. From the same example of hotels, you can see that one of the fields is called “Name”, and it contains only the names of the hotels. Another field is the category, which records how many stars this hotel has. Thus, going through the entire column, we see the values ​​of one parameter for each of the rows.

Database fields have various types: text, numeric, monetary, logical, date and time format. This defines the restrictions that are placed on the values ​​in these columns. Having defined the “Date and Time” field type, we will no longer be able to enter a last name or first name into it, entering alphabetic characters in a numeric field is prohibited, and it is impossible to enter a cost in a logical column.

The “Counter” field type stands out. What is the peculiarity of its use, we will consider below.

Field type "Counter"

Let's look again at our hotel table. In the first column, which is called “Code”, we see numbers - serial numbers each of the hotels. They are not repeated and designate the entry in such a way that we know exactly under which number this or that hotel is contained in the table. This helps you easily find the desired hotel using this code.

The "Code" field has the "Counter" field type. What is special about this field based on the information above? First of all, this is the uniqueness of the column values. This property ensures unique record identification. The table cannot have two records with the same value for the “Code” parameter. The uniqueness of the field values ​​allows it to be used as primary key, that is, a column that is referenced by fields in other tables.

Another ability of the counter is auto-increment - the property of automatically increasing the number. Thanks to it, the user does not need to think about what number to enter for the next entry. The system itself will increase the number of the previous one and assign this number to the new one.

Example

In our experimental Access database added the "Hotels" table. The counter field is called “Code”, numbering starts from one.

The second table of the database - “Regions” - also contains a counter field. What is special about the region table? The fact is that its records are used by the hotel table to specify the location of the hotel. Here the value is selected from the dropdown list:

And by region we can see the hotels located there:

Thus, the counter field is a significant element of database tables that allows you to uniquely identify a record, automatically assign it a unique number, and then use this number when referring to rows of an object from another table.