Thousands of people around the world are involved in repairs every day. When it is performed, everyone begins to think about the subtleties that accompany the repair: in what color scheme choose wallpaper, how to choose curtains in the color of the wallpaper, arrange the furniture correctly to get uniform style premises. But few people think about the most important thing, and this main thing is the replacement of electrical wiring in the apartment. After all, if something happens to the old wiring, 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 this is within the power of any ordinary citizen, 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 plan future wiring. At this stage, you need to determine exactly where the wires will be laid. Also at this stage, you can make any adjustments to the existing network, which will allow you to place the fixtures and fixtures as comfortably as possible in accordance with the needs of the owners.
12.12.2019
Narrow-industry devices of the knitted sub-industry and their Maintenance
To determine the extensibility of hosiery, a device is used, the scheme of which is shown in fig. one.
The design of the device is based on the principle of automatic balancing of the rocker by the elastic forces of the product under test, acting at a constant speed.
The weight beam is an equal-armed round steel rod 6, which has an axis of rotation 7. On its right end, paws or a sliding form of the trace 9 are attached with a bayonet lock, on which the product is put on. On the left shoulder, a suspension for loads 4 is hinged, and its end ends with an arrow 5, showing the equilibrium state of the rocker arm. Before testing the product, the rocker arm is balanced by a movable weight 8.
Rice. 1. Scheme 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 - trace shape, 11 - stretching lever,
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 a 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 with the worm gear 17 by means of a coupling 18. A helical gear 16 is mounted on the gear shaft, directly communicating the movement of the gear 15.
11.12.2019
In pneumatic actuators, the displacement force is created by the action of compressed air on the membrane, or piston. Accordingly, there are membrane, piston and bellows mechanisms. They are designed to set and move the valve of the regulating body in accordance with the 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 ultimate pressure of compressed air in the working cavity is 0.25 MPa (2.5 kg / cm 2).
In membrane linear mechanisms, the stem performs a reciprocating motion. Depending on the direction of movement of the output element, they are divided into mechanisms of direct action (with an increase in membrane pressure) and reverse action.
Rice. Fig. 1. The design of the direct acting membrane actuator: 1, 3 - covers, 2 - membrane, 4 - support disk, 5 - bracket, 6 - spring, 7 - stem, 8 - support ring, 9 - adjusting nut, 10 - connecting nut
Main structural elements membrane actuator are a membrane pneumatic chamber with a bracket and a movable part.
The membrane 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 hermetic working cavity, cover 1 is attached to bracket 5. The movable part includes support disk 4, to which the membrane is attached 2, rod 7 with connecting nut 10 and spring 6. The spring rests at one end against the support disk 4, and at the other end 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
To date, there are several types of lamps for. Each of them has its 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 lamps. The advantages of such lamps include its cost, simplicity of the device. The light from such 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 - energy-saving lamps. Such lamps can be found absolutely for any type of socles. They are an elongated tube in which a special gas is located. 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 glow, great choice plinths. The disadvantages of such lamps include the complexity of the design and flicker. The flicker is usually imperceptible, but the eyes will get tired from the light.
28.11.2019
cable assembly- a kind of assembly unit. The cable assembly consists of several local ones, terminated on both sides in the electrical installation shop and tied into a bundle. Installation of the cable route is carried out by laying the cable assembly in the cable route fastening devices (Fig. 1).
Ship cable route- an electric line mounted on a ship from cables (cable bundles), cable route fastening 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 cross-sectional area of the cable route is 780 cm 2. On individual ships with a total cable length of more than 400 km, cable corridors are provided to accommodate the cable route.
Cable routes and cables passing through them are divided into local and trunk, depending on the absence (presence) of sealing devices.
Main cable routes are divided into routes with end and through boxes, depending on the type of application of the cable box. This makes sense for the choice of technological equipment and cable route installation technology.
21.11.2019
In the field of development and production of instrumentation and instrumentation American company Fluke Corporation is one of the world's leading companies. It was founded in 1948 and since that time has been constantly developing and improving technologies in the field of diagnostics, testing, and analysis.
Innovation from an American developer
Professional measuring equipment from a multinational corporation is used in the maintenance of heating, air conditioning and ventilation systems, refrigeration systems, air quality testing, electrical parameter calibration. The Fluke branded store offers certified equipment from an American developer. Full the lineup includes:- thermal imagers, insulation resistance testers;
- digital multimeters;
- power quality analyzers;
- rangefinders, vibration meters, oscilloscopes;
- temperature and pressure calibrators and multifunctional devices;
- visual pyrometers and thermometers.
07.11.2019
Use a level gauge to determine the level different types liquids in open and closed storages, 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 level gauge, microwave (or waveguide), radiation, electrical (or capacitive), mechanical, hydrostatic, acoustic.
Principles and features of operation of radar level gauges
Standard instruments cannot determine the level of chemically aggressive liquids. Only a radar level transmitter is able to measure it, since it does not come into contact with the liquid during operation. In addition, radar level transmitters are more accurate than, for example, ultrasonic or capacitive level transmitters.Whatever machine you assemble, for sure more than once, when testing the machine, you thought: you need a tachometer. But he was at your fingertips all the time, of course, if you have such simple components as a small motor and a voltmeter. Get acquainted with the proposed device, and make sure that in just five minutes you will have a compact and accurate home-made 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 do not 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 components store. If there is no voltmeter, it will cost more than a motor, but on 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 of rotation will be created. Therefore, the readings of the voltmeter will also be proportional to the rotational speed.
You can calibrate such a tachometer in different ways. For example, build a reference graph of the dependence of voltage on the frequency of rotation of the armature or make a new voltmeter scale, on which the number of revolutions is recorded instead of volts.
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 you have access to branded machines, it is easy to get control points by holding a rubber tube put on the motor shaft in a drill chuck or lathe and including the machine in various gears, record the readings of the voltmeter (the spindle speed in each gear is indicated in the machine's passport). Otherwise, you will have to use either a drill or an engine for calibration in an operating mode for which the speed is known. And even if it was possible to measure the voltage at the contacts of the motor for only one speed, the second point is the intersection of the axes (x) and (y) (that is, the number of revolutions and voltage), although the accuracy of measurements 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 goes off scale when measuring high rotation speeds, 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 you make a roller friction adapter with a diameter of 31.8 mm, the tachometer will also allow you to measure the linear speed, expressed in meters per minute. To do this, the number of revolutions per minute determined by the schedule is divided by 10.
The accuracy of the measurement depends practically only on the thoroughness of the plotting and the division value of the voltmeter. Such a simple and very cheap homemade 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 are an iPhone owner, then I strongly advise you to install the best application for measuring revolutions shown below. And don't stop at the strobe from your phone flash, it will just help you understand how the strobe-tachometer works. DIY very simple electronic circuits, You will get 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. Watch a video demonstrating this app below.
Do-it-yourself homemade stroboscopic tachometer from iPhone
Do-it-yourself homemade laser (optical) tachometer from iPhone
Comparative measurements of engine speed with laser and stroboscopic tachometers
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Sometimes during operation it is necessary to determine the number of revolutions of an asynchronous electric motor on which there is no tag. And not every electrician can cope with this task. But this needs to be figured out. Determining the number of revolutions of the electric motor is very easy and simple.
We determine it by the winding. To do this, remove the engine cover. It is better to do this with the back cover, because the pulley or half-coupling does not need to be removed.
It is enough to remove the cooling casing and the impeller - and the engine cover will be accessible. After removing the cover, the winding can be seen quite well. Find one section and see how much space it takes up around the circumference of the circle (stator). Now remember: if the coil is half a circle (180 degrees), this is a 3000 rpm motor.
If three sections (120 degrees) fit in a circle, this is a 1500 rpm engine. If the stator fits four sections (90 degrees), this motor is 1000 rpm.
This is how you can easily determine the number of revolutions of an "unknown" electric motor. This can be clearly seen in the presented figures.
This method of determination is suitable when the winding coils are wound in sections. And there are windings "pushed", and here this method will not work. But "spill" windings are rare.
There is another method for determining the number of revolutions. There is a residual magnetic field in the rotor of an electric motor, which can induce a small EMF in the stator winding if we rotate the rotor. This EMF can be "caught" by a milliammeter. Our task is as follows: we need to find the winding of one phase, regardless of how the windings are connected, a triangle or a star. We connect a milliammeter to the ends of the winding. By rotating the motor shaft, we look at how many times the milliammeter needle deviates in one revolution of the rotor.
From this table you can see what kind of engine is in front of you:
- (2p) 2 3000 r/min;
- (2p) 4 1500 r/min;
- (2p) 6 1000 r/min;
- (2p) 8 750 r/min.
In the USSR, the TC10-R device was produced, maybe someone has preserved it. For those who have not seen and did not know about such a meter, I am attaching a photo. The kit includes two nozzles: for measuring revolutions along the axis of the shaft and for measuring along the circumference of the shaft.
You can also measure the number of revolutions using a digital laser tachometer.
Specifications:
- Range: 2.5 rpm ~ 99999 rpm.
- Resolution/step: 0.1rpm for 2.5~999.9rpm range, 1rpm 1000rpm and more.
- Accuracy: + / - 0.05%.
- Working distance: 50mm ~ 500mm.
- The minimum and maximum values are also indicated.
The speed of rotation of an asynchronous electric motor is usually understood as the angular frequency of rotation of its rotor, which is given 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 it is 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, then 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 “2760 rpm” on the plate. With regard to an asynchronous electric motor, these are revolutions, taking into account slip s.
The synchronous speed this engine(excluding slip) will be equal to 3000 rpm, since when the stator windings are powered by mains current at a frequency of 50 Hz, every second the magnetic flux will make 50 full cyclic changes, and 50 * 60 = 3000, so it turns out 3000 rpm - synchronous speed of an asynchronous electric motor.
In this article, we will talk about how to determine the synchronous speed of an unknown three-phase asynchronous motor, simply by looking at its stator. By appearance stator, by the location of the windings, by the number of slots - you can easily determine the synchronous speed 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 has two coils connected in series for each phase - in each pair of coils one is located opposite the other. These coils form a pair of poles on the stator.
One of the phases is shown in red for clarity, 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 fed in turn (three-phase current), then for 1 oscillation out of 50 in each of the phases, the stator magnetic flux will turn once to full 360 degrees, that is, it will make one revolution in 1/50 of a second, which means 50 revolutions will turn out in give me a sec. So it goes 3000 rpm.
Thus, it becomes clear that in order to determine the synchronous revolutions of an asynchronous electric motor, it is enough 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. Therefore, 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 per pair of coils (we will not focus on winding methods within this article).
1500 rpm
To obtain a synchronous speed of 1500 revolutions per minute, the number of stator poles is doubled so that for 1 oscillation out of 50 the magnetic flux would make only half a turn - 180 degrees.
To do this, 4 winding sections are made for each phase. Thus, if one coil occupies a quarter of all the slots, then you have a motor with two pairs of poles, formed by four coils per phase.
For example, 6 slots 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 about 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 revolutions per minute, each phase already forms three pairs of poles, so that in one oscillation out of 50 (hertz) the magnetic flux would turn around only 120 degrees, and would turn the rotor accordingly.
Thus, a minimum of 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, then you have an asynchronous motor with a synchronous speed of 750 (or about 730, taking into account slip).
500 rpm
Finally, to get induction motor with a synchronous speed of 500 rpm, 6 pairs of poles are needed - 12 coils (poles) per phase, so that for each oscillation of the network the magnetic flux would turn 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 including slip).
When buying an electric motor from hand, count on the presence technical documentation does not belong to him. Then the question arises of how to find out the number of revolutions of the purchased device. You can trust the words of the seller, but conscientiousness is not always their hallmark.
Then there is a problem with determining the number of revolutions. You can solve it by knowing some of the subtleties of the motor device. This will be discussed further.
Determine the turnover
There are several ways to measure motor speed. The most reliable is to use a tachometer - a device designed specifically for this purpose. However, not every person has such a device, especially if he does not professionally deal with electric motors. Therefore, there are several other options that allow you to cope with the task "by eye".
The first involves removing one of the engine covers in order to locate the winding coil. There may be several of the latter. The one that is more accessible and located in the visibility zone is selected. The main thing is to prevent violation of the integrity of the device during operation.
When the coil opened up, you need to carefully examine it and try to compare the size with the stator ring. The latter is a fixed element of the electric motor, and the rotor, being inside it, rotates.
When the ring is half closed by the coil, the number of revolutions per minute reaches 3000. If the third part of the ring is closed, the number of revolutions is approximately 1500. At a quarter, the number of revolutions is 1000.
The second way is connected with the windings inside the stator. The number of slots occupied by one section of any coil is considered. The grooves are located on the core, their number indicates the number of pairs of poles. 3000 rpm will be in the presence of two pairs of poles, with four - 1500 revolutions, with six - 1000.
The answer to the question of what the number of revolutions of the electric motor depends on will be the statement: on the number of pairs of poles, and this is an inversely proportional relationship.
On the body of any factory engine there is a metal tag on which all the characteristics are indicated. In practice, such a tag may be missing or erased, which slightly complicates the task of determining the number of revolutions.
We adjust the speed
Working with a variety of electrical tools and equipment at home or at work will certainly raise the question of how to regulate the speed of the electric motor. For example, it becomes necessary to change the speed of movement of parts in the machine or along the conveyor, adjust the performance of pumps, reduce or increase the air flow in ventilation systems.
It is almost pointless to carry out these procedures by lowering the voltage, the revolutions will drop sharply, and the power of the device will significantly decrease. Therefore, they are used special devices to adjust engine speed. Let's consider them in more detail.
Frequency converters act as reliable devices that can radically change the frequency of the current and the shape of the signal. They are based on high power semiconductor triodes (transistors) and a pulse modulator.
The microcontroller controls the entire process of the converter. Thanks to this approach, it becomes possible to achieve a smooth increase in engine speed, which is extremely important in mechanisms with a large load. Slow acceleration reduces loads, positively affecting the service life of industrial and household equipment.
All converters are equipped with protection having several degrees. Some of the models operate at the expense of a single-phase voltage of 220 V. The question arises, is it possible to make a three-phase motor rotate due to one phase? The answer will be positive if one condition is met.
When a single-phase voltage is applied to the winding, it is required to “push” the rotor, since it will not budge on its own. This requires a start capacitor. After the engine starts rotating, the remaining windings will provide the missing voltage.
A significant disadvantage of such a scheme is a strong phase imbalance. However, it is easily compensated by the inclusion of an autotransformer in the circuit. In general, this is a rather complex scheme. The advantage of the frequency converter is the ability to connect asynchronous type motors without the use of complex circuits.
What does the converter give?
The need to use an electric motor speed controller in the case of asynchronous models is as follows:
Significant energy savings are achieved. Since not all equipment requires high speeds of rotation of the motor shaft, it makes sense to reduce it by a quarter.
Provided reliable protection all mechanisms. The frequency converter allows you to control not only the temperature, but also the pressure and other parameters of the system. This fact is especially important if a pump is driven by a motor.
The pressure sensor is installed in the tank, sends a signal when the proper level is reached, due to which the motor stops.
A soft start is in progress. Thanks to the regulator, the need for additional electronic devices is eliminated. The frequency converter is easy to set up and get the desired effect.
Maintenance costs are reduced as the regulator minimizes the risk of damage to the drive and other mechanisms.
Thus, electric motors with a speed controller turn out to be reliable devices with a wide range of applications.
It is important to remember that the operation of any equipment based on an electric motor will only be correct and safe when the speed parameter is adequate to the conditions of use.
Photo of motor speed
