Thousands of people around the world are engaged in repairs every day. When performing it, everyone begins to think about the subtleties that accompany the repair: in what color scheme to choose the wallpaper, how to choose the curtains in the color of the wallpaper, to correctly arrange the furniture to obtain a uniform style of the room. But rarely does anyone think about the most important thing, and this is the main thing to replace the electrical wiring in the apartment. After all, if something happens to the old wiring, then the apartment will lose all its attractiveness and become completely unsuitable for life.

Any electrician knows how to replace the wiring in an apartment, but any ordinary citizen can do this, however, when performing this type of work, he should choose high-quality materials in order to get a safe electrical network in the room.

The first action to be taken is plan future wiring... At this stage, you need to determine where the wires will be laid. Also at this stage, you can make any adjustments to the existing network, which will make it possible to arrange the lamps and in the most comfortable way in accordance with the needs of the owners.

12.12.2019

Narrow-branch devices of the knitted sub-industry and their maintenance

To determine the extensibility of hosiery, a device is used, the diagram of which is shown in Fig. one.

The design of the device is based on the principle of automatic balancing of the rocker arm by elastic forces of the test product acting at a constant speed.

The weight rocker is an equal-armed round steel rod 6 with an axis of rotation 7. On its right end, paws or a sliding form of the track 9 are attached to its right end using a bayonet lock, on which the product is put on. A suspension for loads 4 is pivotally attached to the left shoulder, and its end ends with an arrow 5 showing the equilibrium state of the rocker arm. Before testing the product, the rocker arm is brought into equilibrium with a movable weight 8.

Figure: 1. Diagram of a device for measuring the extensibility of hosiery: 1 - guide, 2 - left ruler, 3 - engine, 4 - suspension for loads; 5, 10 - arrows, 6 - rod, 7 - axis of rotation, 8 - weight, 9 - track shape, 11 - tension arm,

12 - carriage, 13 - lead screw, 14 - right ruler; 15, 16 - helical gears, 17 - worm gear, 18 - coupling, 19 - electric motor

To move the carriage 12 with the stretching lever 11, a lead screw 13 is used, at the lower end of which a helical gear 15 is fixed; through it, the rotational movement is transmitted to the lead screw. The change in the direction of rotation of the screw depends on the change in rotation 19, which is connected to the worm gear 17 by means of a coupling 18. A helical gear 16 is mounted on the gear shaft, which directly imparts movement to the gear 15.

11.12.2019

In pneumatic actuators, the adjustment force is generated by the action of compressed air on the diaphragm, or piston. Accordingly, there are membrane, piston and bellows mechanisms. They are designed to position and move the control valve gate in accordance with a pneumatic command signal. The full working stroke of the output element of the mechanisms is carried out when the command signal changes from 0.02 MPa (0.2 kg / cm 2) to 0.1 MPa (1 kg / cm 2). The limiting pressure of compressed air in the working cavity is 0.25 MPa (2.5 kg / cm 2).

In diaphragm linear thrust mechanisms, the rod reciprocates. Depending on the direction of movement of the output element, they are subdivided into mechanisms of direct action (with an increase in membrane pressure) and reverse action.

Figure: 1. The design of the direct-acting diaphragm actuator: 1, 3 - covers, 2 - membrane, 4 - support disc, 5 - bracket, 6 - spring, 7 - stem, 8 - support ring, 9 - adjusting nut, 10 - connecting nut

The main structural elements of the diaphragm actuator are a membrane pneumatic chamber with an arm and a moving part.

The diaphragm pneumatic chamber of the direct action mechanism (Fig. 1) consists of covers 3 and 1 and membrane 2. Cover 3 and membrane 2 form a sealed working cavity, cover 1 is attached to the bracket 5. The movable part includes support disc 4, to which the membrane is attached 2, a rod 7 with a connecting nut 10 and a spring 6. The spring at one end abuts against the support disk 4, and the other through the support ring 8 into the adjusting nut 9, which serves to change the initial tension of the spring and the direction of movement of the rod.

08.12.2019

Today there are several types of lamps for. Each of them have their own pros and cons. Consider the types of lamps that are most often used for lighting in a residential building or apartment.

The first type of lamps - incandescent lamp... This is the cheapest type of lamp. The advantages of such lamps include its cost, simplicity of the device. The light from these lamps is the best for the eyes. The disadvantages of such lamps include a short service life and a large amount of electricity consumed.

The next type of lamps is energy-saving lamps... Such lamps can be found for absolutely any type of base. They are an elongated tube containing a special gas. It is the gas that creates the visible glow. In modern energy-saving lamps, the tube can have a wide variety of shapes. The advantages of such lamps: low power consumption compared to incandescent lamps, daylight, a large selection of socles. The disadvantages of such lamps include the complexity of the design and flicker. The flickering is usually subtle, but the eyes will tire of the light.

28.11.2019

Cable assembly - a kind of mounting assembly. The cable assembly consists of several local ones, terminated on both sides in an electrical installation shop and tied into a bundle. The installation of the cable route is carried out by laying the cable assembly in the cable route fastening device (Fig. 1).

Ship cable route - an electrical line mounted on a ship from cables (cable bundles), cable routing fixing devices, sealing devices, etc. (Fig. 2).

On the ship, the cable route is located in hard-to-reach places (along the sides, ceiling and bulkheads); they have up to six turns in three planes (Fig. 3). On large ships, the maximum cable length reaches 300 m, and the maximum cable section area is 780 cm 2. On individual ships with a total cable length of over 400 km, cable corridors are provided for placing the cable route.

Cable routes and cables passing through them are subdivided into local and trunk routes, depending on the absence (presence) of sealing devices.

Trunk cable routes are subdivided into routes with end boxes and pass-through boxes, depending on the type of cable box application. This makes sense for the selection of technological equipment and cable routing technology.

21.11.2019

In the field of development and production of instrumentation and automation devices, the American company Fluke Corporation occupies one of the leading positions in the world. It was founded in 1948 and since that time has been constantly developing, improving technologies in the field of diagnostics, testing, analysis.

Innovation from an American developer

Professional measuring equipment from a multinational corporation is used for servicing heating, air conditioning and ventilation systems, refrigeration units, checking air quality, calibrating electrical parameters. The Fluke brand store offers to purchase certified equipment from an American developer. The complete range includes:

• thermal imagers, insulation resistance testers;
• digital multimeters;
• analyzers of the quality of electrical energy;
• rangefinders, vibrometers, oscilloscopes;
• calibrators of temperature, pressure and multifunctional devices;
• visual pyrometers and thermometers.

07.11.2019

A level gauge is used to determine the level of various types of liquids in open and closed storages and vessels. It is used to measure the level of a substance or the distance to it.
To measure the liquid level, sensors are used that differ in type: radar, microwave (or waveguide), radiation, electrical (or capacitive), mechanical, hydrostatic, acoustic.

Principles and features of radar level transmitters

Standard instruments cannot determine the level of chemically aggressive liquids. Only a radar level gauge is able to measure it, since it does not come into contact with liquid during operation. In addition, radar level gauges are more accurate than, for example, ultrasonic or capacitive ones.

Electric motor - stator winding

From time to time in the process of work, you need to find the number of revolutions of the asynchronous electric motor, on which there is no tag. And not every electrician can cope with this task. But my worldview is that every electrical fitter should understand this. At your own workplace, as they say - on duty, you understand all the properties of your own engines. And we ran to a new workplace, and there are no tags on any engine there. Finding the number of revolutions of an electric motor is even very simple and simple. Determined by the winding. To do this, remove the motor cover. It is better to do this with the back cover, since the pulley or half-coupling does not need to be removed. Quite remove the shroud

cooling and impeller and motor cover are available. After removing the cover, the winding can be seen quite well. Find one section and see how many

Engine - 3000 rpm

it takes place around the circumference of a circle (stator). Now remember, if the coil takes half a circle (180 degrees) - this is a 3000 rpm engine.

Engine - 1500 rpm

If three sections fit in a circle (120 degrees), this is a 1500 rpm engine. Well, if the stator accommodates four sections (90 degrees) - this engine is 1000 rpm. This is how it is quite simple to find the number of revolutions of an "unknown" electric motor. This can be seen perfectly in the presented figures.

Engine - 1000 rpm

This is a way of detecting when the winding coils are wound in sections. And there are “loose” windings, which cannot be found in this way. This method of winding is rare.

There is another way to determine the number of revolutions. In the rotor of the electric motor, there is a residual magnetic field that can induce a small EMF in the stator winding if we turn the rotor. This EMF can be "caught" - with a milliammeter. Our task is as follows: it is necessary to find the winding of one phase, regardless of how the windings are connected, a triangle or a star. And we connect a milliammeter to the ends of the winding, rotating the motor shaft, see how many times the milliammeter needle deviates in one rotor revolution, and from this table you can see what kind of engine you are determining.

(2p) 2 3000 r / min
(2p) 4 1500 r / min
(2p) 6 1000 r / min
(2p) 8 750 r / min

These are the usual and I think two understandable ways of determining the number of revolutions on which there is no tag (plate).

In the USSR, the TCh10-R device was produced, maybe someone has preserved it. Who has not seen and did not know about such a meter, I suggest looking at a photo of your own. The set includes two nozzles - for measuring revolutions along the shaft axis and the second one for measuring along the circumference of the shaft.

You can also measure the number of revolutions using the "Digital Laser Tachometer"

"Digital Laser Tachometer"

Technical properties:

Spectrum: 2.5rpm ~ 99999rpm
Resolution / step: 0.1 rpm for spectrum 2.5 ~ 999.9 rpm, 1 rpm 1000 rpm or more
Accuracy: +/- 0.05%
Working distance: 50mm ~ 500mm
Lowest and highest value is also indicated
For those who really need it - just a super thing!
L. Ryzhenkov

Whatever machine you assembled, for sure more than once, testing the machine, you thought: you need a tachometer. But he was always at your fingertips, of course, if you have such simple components as a small motor and a voltmeter. Get to know the proposed device and make sure that in just five minutes you will have a compact and accurate homemade tachometer at your disposal.

So, let's start assembling. As already mentioned, a homemade tachometer consists of two main parts: a DC motor and a voltmeter. If you don't have such a motor, you can easily buy it at a flea market for the price of a loaf of bread or cheaper, for the price of two loaves you can buy a new one in an electronic component store. If there is no voltmeter, it will cost more than a motor, but in the same flea market its price will be quite acceptable. The voltmeter is connected to the contacts of the motor, and that's it, the tachometer is ready. Now you need to test the finished tachometer in operation. When the shaft of the motor generator rotates, a voltage proportional to the speed will be generated. Consequently, the speed will be proportional to the readings of the voltmeter.

You can calibrate such a tachometer in different ways. For example, build a reference graph of the dependence of voltage on the armature rotation frequency or make a new voltmeter scale, on which the number of revolutions is recorded instead of voltages.

Since the graph reflects a linear relationship, it is enough to mark two or three points and draw a straight line through them. Obtaining control points is the most problematic stage in preparing a homemade tachometer for work. If there is access to branded machines, control points can be easily obtained by clamping a rubber tube put on the motor shaft in the chuck of a drilling or lathe and turning on the machine in various gears, fixing the voltmeter readings (the spindle rotation speed in each gear is indicated in the machine's passport). Otherwise, for calibration, you will have to use either a drill or a motor in the operating mode for which the speed is known. And even if it was possible to measure the voltage at the motor contacts for only one speed, the second point is the intersection of the axes (x) and (y) (that is, the speed and voltage), although the measurement accuracy based on the dependence based on two points will be low.

To measure the rotational speed, the shaft of the engine under study is connected to the motor with a small piece of rubber tube or using various adapters. If the voltmeter reads off scale when measuring high speeds of rotation, a switch with additional resistors is introduced into the circuit. You will also need to rebuild the graph for each switch position.

The capabilities of the device can be significantly expanded. If a roller friction adapter with a diameter of 31.8 mm is made, the tachometer will also measure the linear speed, expressed in meters per minute. To do this, the number of revolutions per minute, determined according to the schedule, is divided by 10.

The measurement accuracy depends practically only on the accuracy of the graph and the voltmeter division value. Such a simple and very cheap home-made tachometer can be widely used wherever you need to quickly determine the frequency or speed of rotation of shafts, pulleys and other parts.

Do-it-yourself digital tachometer from a smartphone

If you own an iPhone, I highly recommend installing the best RPM app shown below. And do not stop at the stroboscope from the phone flash, it will just help you understand how the stroboscope-tachometer works. Having made very simple electronic circuits with your own hands, you will receive stroboscopic and laser tachometers that are not inferior (and in some situations superior) to branded tachometers. You will find diagrams, photos and descriptions of tachometers in this application. See a video demonstrating this application below.

DIY homemade stroboscopic tachometer from iPhone

DIY homemade laser (optical) tachometer from iPhone

Comparative measurements of engine speed with laser and stroboscopic tachometers

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Old and used Soviet-made asynchronous machines are considered the highest quality and most durable. However, as many electricians know, the nameplates on them can be completely unreadable, and in the engine itself they could be rewound. You can determine the nominal speed by the number of poles in the winding, but if we are talking about machines with a phase rotor or there is no desire to disassemble the case, you can resort to one of the proven methods.

Determination of speed using a graphic drawing

There are circular graphical figures to determine the engine speed. The bottom line is that a paper circle with a given pattern glued to the end of the shaft, while rotating, forms a certain graphic effect when illuminated by a light source with a frequency of 50 Hz. Thus, after going through several figures and comparing the result with the tabular data, you can determine the nominal speed of the motor.

Typical installation dimensions

Industrial production in the USSR, like most modern ones, was produced according to state standards and has an established correspondence table. Based on this, it is possible to measure the height of the center of the shaft relative to the landing plane, its and rear diameters, as well as the dimensions of the mounting holes. In most cases, these data will be enough to find the required engine in the table and not only determine the speed, but also establish its electrical and net power.

With a mechanical tachometer

Very often it is necessary to determine not only the nominal characteristic of an electric machine, but also to know the exact number of revolutions at a given moment. This is done when diagnosing electric motors and to determine an accurate indicator of the slip coefficient.

In electromechanical laboratories and in production, special devices are used - tachometers. With access to such equipment, the speed of an induction motor can be measured in a few seconds. The tachometer has a dial or digital dial and a measuring rod, at the end of which there is a hole with a ball. If you lubricate the centering hole on the shaft with a viscous wax and press the measuring rod firmly against it, the dial will display the exact RPM.

With a stroboscopic effect detector

If the engine is in service, you can avoid having to detach it from the actuator and remove the rear cowl just to reach the centering hole. The exact number of revolutions in these cases can also be measured using a stroboscopic detector. To do this, a white longitudinal risk is applied to the motor shaft and a light catcher of the device is installed opposite it.

When the engine is turned on, the device will determine the exact number of revolutions per minute by the frequency of the appearance of the white spot. This method is used, as a rule, in the diagnostic examination of powerful electrical machines and the dependence of the rotational speed on the applied load.

Using a cooler from a personal computer

A very original method can be used to measure engine speed. It uses a blade cooling fan from a personal computer. The propeller is attached to the end of the shaft with double-sided tape, and the fan frame is held by hand. The fan wire connects to any of the motherboard connectors, where measurements can be made, while the cooler itself does not need to be powered. An accurate RPM reading can be obtained through the BIOS utility or a diagnostic utility running under the operating system.

The rotational speed of an asynchronous electric motor is usually understood as the angular frequency of rotation of its rotor, which is shown on the nameplate (on the nameplate of the motor) in the form of revolutions per minute. A three-phase motor can also be powered from a single-phase network, for this, parallel to one or two of its windings, depending on the mains voltage, but the design of the motor will not change from this.

So, if the rotor under load makes 2760 revolutions per minute, it will be equal to 2760 * 2pi / 60 radians per second, that is, 289 rad / s, which is not convenient for perception, therefore they simply write on the plate “2760 rpm”. For an induction motor, this is the slip speed s.

The synchronous speed of this motor (excluding slip) will be equal to 3000 rpm, since when the stator windings are supplied with a mains current with a frequency of 50 Hz, every second the magnetic flux will make 50 complete cyclic changes, and 50 * 60 \u003d 3000, that's it turns out 3000 rpm - the synchronous speed of the asynchronous electric motor.

In this article, we will talk about how to determine the synchronous rotational speed of an unknown asynchronous three-phase motor, just by looking at its stator. By the appearance of the stator, by the location of the windings, by the number of slots, you can easily determine the synchronous revolutions of the electric motor if you do not have a tachometer at hand. So, let's start in order and analyze this issue with examples.

3000 rpm

About asynchronous electric motors (see -) it is customary to say that a particular motor has one, two, three or four pairs of poles. The minimum is one pair of poles, that is, the minimum is two poles. Take a look at the picture. Here you can see that the stator contains two series-connected coils for each phase - in each pair of coils, one is located opposite the other. These coils form a pair of poles on the stator.

For clarity, one of the phases is shown in red, the second in green, and the third in black. The windings of all three phases are arranged in the same way. Since these three windings are powered in turn (three-phase current), then for 1 oscillation out of 50 in each of the phases - the stator magnetic flux will turn once full 360 degrees, that is, it will make one revolution in 1/50 of a second, which means 50 revolutions will be obtained in give me a sec. So it comes out 3000 rpm.

Thus, it becomes clear that to determine the synchronous revolutions of an asynchronous electric motor, it is sufficient to determine the number of pairs of its poles, which is easy to do by removing the cover and looking at the stator.

Divide the total number of stator slots by the number of slots per winding section of one of the phases. If you get 2, then you have a motor with two poles - with one pair of poles. Hence the synchronous frequency is 3000 rpm or approximately 2910 with slip. In the simplest case, there are 12 slots, 6 slots per coil, and there are 6 such coils - two for each of the three phases.

Please note that the number of coils in one group for one pair of poles may not necessarily be 1, but also 2 and 3, however, for example, we considered the option with single groups for a pair of coils (we will not focus on winding methods within the framework of this article).

1500 rpm

To obtain a synchronous speed of 1500 rpm, the number of stator poles is doubled so that for 1 oscillation out of 50, the magnetic flux would make only half a revolution - 180 degrees.

For this, 4 sections of winding are made for each phase. Thus, if one coil occupies a quarter of all slots, then you have a motor with two pole pairs formed by four coils per phase.

For example, 6 grooves out of 24 are occupied by one coil, or 12 out of 48, which means you have a motor with a synchronous frequency of 1500 rpm, or taking into account the slip of approximately 1350 rpm. In the above photo, each section of the winding is made in the form of a double coil group.

1000 rpm

As you already understood, in order to obtain a synchronous frequency of 1000 rpm, each phase already forms three pairs of poles, so that in one oscillation of 50 (hertz) the magnetic flux would turn only 120 degrees, and would accordingly turn the rotor behind it.

Thus, at least 18 coils are installed on the stator, with each coil occupying a sixth of all slots (six coils per phase - three pairs). For example, if there are 24 slots, then one coil will take 4 of them. The resulting frequency, taking into account the slip, is about 935 rpm.

750 rpm

To obtain a synchronous speed of 750 rpm, it is necessary that the three phases form four pairs of moving poles on the stator, this is 8 coils per phase - one opposite the other - 8 poles. If, for example, 48 slots have a coil for every 6 slots, you have an asynchronous motor with synchronous speeds of 750 (or about 730, taking into account slip).

500 rpm

Finally, to obtain an asynchronous motor with a synchronous speed of 500 rpm, 6 pairs of poles are needed - 12 coils (poles) per phase, so that for each network oscillation the magnetic flux would rotate 60 degrees. That is, if, for example, the stator has 36 slots, while there are 4 slots per coil, you have a three-phase motor at 500 rpm (480, taking into account slip).