How to determine the rotational speed of an electric motor. How many revolutions does an induction motor have? How to measure the speed of an electric motor with a multimeter

Old and used asynchronous machines Soviet production 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 rated 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 drawings to determine the engine speed. The bottom line is that a paper circle with a given pattern glued to the end of the shaft, when 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, this data will be enough to find in the table desired engine and not only determine the rotational 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. If you access such equipment, measure the speed asynchronous motor can be done 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 viscous wax and press the dipstick 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 longitudinal risk of white 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 electric cars and the dependence of the 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 paddle fan for cooling 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 is connected to any of the motherboard connectors, where measurements can be made, while the cooler itself does not need to be supplied with power. An accurate RPM reading can be obtained through the BIOS utility or a diagnostic utility running under the operating system.

Thousands of people around the world are involved in repairs every day. When performing it, everyone begins to think about the subtleties that accompany the repair: in what colors choose wallpaper, how to choose curtains in the color of the wallpaper, arrange furniture correctly 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 exactly 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. 1.

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 shape 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.

Rice. 1. Diagram of a device for measuring the extensibility of hosiery: 1 — guide, 2 — left ruler, 3 — slider, 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, using coupling sleeve 18 is associated with worm gear 17. A helical gear 16 is mounted on the shaft of the gearbox, 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, the mechanisms are diaphragm, piston and bellows. 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 linear-thrust diaphragm 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.

Rice. 1. The design of the direct-acting diaphragm actuator: 1, 3 - covers, 2 - membrane, 4 - support disk, 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 disk 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 has its 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 in which there is 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. Advantages of such lamps: low power consumption compared to incandescent lamps, daylight, large selection plinths. The disadvantages of such lamps include the complexity of the design and flicker. The flickering is usually subtle, but the eyes will get tired 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 into 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 cross-sectional area of the cable route 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 use of the cable box. It makes sense for the choice 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 and 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. Full the lineup includes:

thermal imagers, insulation resistance testers;
digital multimeters;
quality analyzers electrical energy;
rangefinders, vibrometers, oscilloscopes;
calibrators of temperature, pressure and multifunctional apparatus;
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, 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.

Several years ago I urgently needed to measure the engine speed, but there is no tachometer! How to be here? Since I really needed to measure the speed, the option of ordering a tachometer and waiting for it for a month did not suit me. I had to think! And I came up with the idea to use a computer for this purpose, or rather, a sound editor installed on a computer.

I have installed the sound editor "Adobe Audition" for a long time to work with sound. Therefore, it remains to come up with a way to connect the engine to the computer. This issue was resolved literally within 1 minute - IR LED receiver! He reached into the box and took out the LED, as well as the mini-jack plug. I found a piece of microphone cable and in 10 minutes the LED sensor was ready! I glued the diode itself into a bug from a fountain pen.

Cable assembly.

I used a flashlight to illuminate the IR LED sensor. Also LED.

I glued the sensor with a piece of tape on the nose of the model, and just held the flashlight with my hand. The distance between the sensor and the flashlight is 5 ... 7 cm. The light flux from the flashlight illuminates the receiving LED, and the propeller interrupts (modulates) the light flux. As a result, the LED generates pulses. The sensor is connected to the microphone input of the sound card. The voltage required for the operation of the LED is provided by the design of the microphone jack of the sound card. Any sound card is designed to work, including with an electret microphone, since it needs a supply voltage of + 5 Volts. Therefore, this voltage is present at the center contact
the microphone jack and goes to the LED, which ensures its operation. As a result, the impulses arising from the rotation of the propeller go through the microphone input to the sound card, and the "Adobe Audition" editor records all this as a regular sound file.

To measure the engine speed, it is sufficient to record for a few seconds. It's enough. This is what we will see on the screen in the sound editor window.

First of all, I would like to note that at the very bottom of the Editor there is a timeline, and it is from it that the engine speed is determined. In this case, the recording time was 9 seconds. An arrow shows the timeline at the bottom of the Editor window. Now we need to enlarge the scale of the audio file. In order not to count the impulses in one second (they are long to count), we will count them for a time interval of 0.1 seconds, and then multiply by 10. First, along the timeline, select a recording area a little over 0.5 seconds and stretch it to the entire screen.

The selected area ~ 0.5 sec is stretched to fill the entire screen. The timeline is also stretched out.

Now select a period of time on the timeline smooth 0.1 sec - from 3.1 to 3.2 sec.

and also stretch it to full screen. Now you can see clear impulses, which are not difficult to calculate.

We count impulses in a time interval of 0.1 sec. - there are 42 of them.

And now for some simple arithmetic. Every 0.1 sec. we have 42 impulses, which means in 1 sec. they received 420 from the sensor. And in 1 minute 420 x 60 sec. = 25200 impulses. But since the propeller has 2 blades and interrupts the luminous flux twice, the result must be divided by 2 and we get 12600 rpm. What was required to be determined. In the case of a 3-blade propeller, we divide the result by 3. In the case of a 4-blade propeller, we divide it by 4. Such an unusual tachometer - the synthesis of an IR diode, a computer and a sound editor, quite satisfied me! And the question of purchasing an "iron" tachometer in a store,
I have disappeared by itself. And he refused the purchase.
I don't need a tachometer when flying in the field, but at home a computer and a cable with an LED are always at hand.
I think that not all colleagues at home already have a tachometer, but I want to measure the engine speed! In this case, my experience, I hope, will be useful to my comrades. "Adobe Audition" can be downloaded free of charge from http://www.fayloobmennik.net/2293677. You can use another sound editor, whoever you like. My sound file of this engine test, recorded by the Editor, is here. In this article, I wanted to show that, if necessary, if you really want to, in most cases that arise with us, modelers, you can come up with a worthy replacement for the necessary, but absent, device. I hope the Chinese comrades are not offended by me.

Sometimes, in the process of work, 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 you need to understand this. Determining the number of revolutions of an electric motor is very easy and simple.

We determine it by the winding. To do this, you need to remove the engine cover. It is better to do this with the back cover, since the pulley or half-coupling does not need to be removed.

It is enough to remove the cooling jacket 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 spans half a circle (180 degrees), this is a 3000 rpm motor.

If there are three sections in a circle (120 degrees), this is a 1500 rpm engine. If the stator accommodates four sections (90 degrees), this motor is 1000 rpm.

This is how it is quite simple to determine the number of revolutions of an "unknown" electric motor. This can be clearly seen in the presented figures.

This determination method is suitable when the winding coils are wound in sections. And there are "loose" windings, and here this method will not work. But "loose" windings are rare.

There is another method for determining the number of revolutions. There is a residual magnetic field in the rotor of the electric motor, which can induce a small EMF in the stator winding if we rotate the rotor. This EMF can be "caught" with a milliammeter. Our task is as follows: you need to find the winding of one phase, regardless of how the windings are connected, delta or star. We connect a milliammeter to the ends of the winding. Rotating the motor shaft, we see how many times the milliammeter needle will deviate in one rotor revolution.

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 TCh10-R device was produced, maybe someone has preserved it. For those who did not see and did not know about such a meter, I am attaching a photo. The set includes two attachments: for measuring revolutions along the shaft axis and for measuring along the circumference of the shaft.

You can also measure the number of revolutions using a digital laser tachometer

Specifications:

Range: 2.5rpm ~ 99999rpm.
Resolution / step: 0.1 rpm for the range 2.5 ~ 999.9 rpm, 1 rpm 1000 rpm or more.
Accuracy: +/- 0.05%.
Working distance: 50mm ~ 500mm.
The minimum and maximum values are also indicated.

When buying an electric motor from your hands, you cannot count on the availability of technical documentation for it. 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 honesty is not always their hallmark.

Then there is a problem with determining the number of revolutions. You can solve it, knowing some of the subtleties of the motor device. This will be discussed further.

Determine the speed

There are several ways to measure the speed of an electric motor. 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 motor covers in order to detect 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 is visible, it is necessary 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 method is related to the windings inside the stator. The number of grooves that one section of a coil occupies is counted. The grooves are located on the core, their number indicates the number of pole pairs. 3000 rpm will be in the presence of two pairs of poles, with four - 1500 rpm, with six - 1000.

The answer to the question of what the number of revolutions of the electric motor depends on is the statement: on the number of pole pairs, and this is inversely proportional.

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 complicates the task of determining the number of revolutions a little.

Adjusting the speed

Working with a variety of electrical tools and equipment in everyday life or at work certainly raises the question of how to regulate the speed of an electric motor. For example, it becomes necessary to change the speed of movement of parts in a machine tool or along a conveyor, adjust pump performance, reduce or increase air consumption in ventilation systems.

It is practically pointless to carry out these procedures by lowering the voltage, the revolutions will drop sharply, the power of the device will significantly decrease. Therefore, special devices are used to adjust the engine speed. Let's consider them in more detail.

Frequency converters act as reliable devices capable of drastically changing the current frequency and waveform. They are based on high-power semiconductor triodes (transistors) and a pulse modulator.

The microcontroller controls the entire operation 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 domestic equipment.

All converters are equipped with protection that has several degrees. Some models operate due to a single-phase voltage of 220 V. The question arises, is it possible to make a three-phase motor rotate thanks to one phase? The answer will turn out to be yes if one condition is met.

When a single-phase voltage is applied to the winding, it is required to "push" the rotor, since it itself will not budge. This requires a starting capacitor. After the motor 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 for by including an autotransformer in the circuit. Overall, it is quite complex scheme... The advantage of the frequency converter is the ability to connect asynchronous 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 savings in electrical energy are achieved. Since not all equipment requires high rotational speeds of the motor shaft, it makes sense to reduce it by a quarter.

Reliable protection of all mechanisms is provided. 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.

A pressure sensor is installed in the tank, sends a signal when the proper level is reached, due to which the motor stops.

A smooth start is performed. Thanks to the regulator, the need for additional electronic devices... The frequency converter is easy to tune 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 prove 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.