How to check the relay for operation: continuity of the terminals with a multimeter

Although electromechanical devices are considered reliable, they become unusable over time. The relay is no exception. You can check it for performance in several ways. The most convenient and fastest of them is a continuity test using a measuring device - a multimeter. To correctly perform the test, you need not only to be able to use the tester, but also to understand the essence of the relay device.

Switching device design

An electrical relay is a device designed to be used as a switch. It knows how to connect or disconnect an electrical circuit, depending on the control signal coming to it. The line that is connected to the element is called controlled, and the one through which the command is sent to it is called control.

Relays are used to automate various operations. They successfully cope with the management of various kinds of signals, protection of electrical equipment. They are used in security and heating systems, sound engineering, that is, wherever it is necessary to automatically switch operating modes when changing any parameters.

When troubleshooting various faults in technology, one of the repair stages is to test the switching element. This is done using a magnitude meter. But before you check the relay for operation with a multimeter, you should know how it works and understand the principle of its operation.

Principle of operation

A relay is an electromagnet consisting of a contact group, an armature and an inductor. All parts are installed on the base and placed in a closed case. The elements are mounted as follows: an anchor (yoke) is placed on top of the core of the magnetic system. It is held in its initial position by means of a spring and is a movable L-shaped plate.

A group of plates with contacts is attached to the lower arm of the transmission, while the same number of contact bases are installed opposite them. Each plate contact extends outwardly from the housing to form device leads.

The principle of operation of an electronic device lies in the ability of an electromagnetic field to affect conductive objects. When voltage is applied to the terminals of the winding, current begins to flow through it. When its value reaches a certain value, two forces (electromotive and magnetic) arise in the winding, forcing the armature to press against the surface of the coil, overcoming the force of the spring.

At the same time, the arm with the fixed contact plates moves, bending them in such a way that they break contact with the connected group. The result is electrical contact. In the case of connecting to the terminals of these plates, the line is closed.

Depending on the design, the initial position can be either closed or open, therefore, in a relay of the second type, after voltage is applied, the line will open. As soon as the signal of the required amplitude is removed from the terminals of the relay coil, the contacts of the device will return to their original state.

Types and characteristics

Electrical relay elements differ in the number of leads and shape, but their essence remains the same - connecting or disconnecting the load from the signal line. By the type of physical processes that lead to re-commutation, relays are divided into the following types:

• neutral - do not depend on the polarity of the signal applied to the control outputs;
• polarized - in them the position of the contacts depends on the direction of the current;
• magnetoelectric - react only to direct current;
• ferrodynamic - their design uses ferromagnetic cores that enhance the magnetic flux;
• inductive - based on the relationship between the changing magnetic flux and the induced current in the conductor;
• thermal - react to the heat that appears when current passes through the plates and changes their shape;
• electronic - they use the property of the p-n junction to conduct current only in one direction (diode).

Also, devices are divided by the type of contacts, which can be of three types: normally closed, normally open and changeover. Like any electromechanical device, the relay is characterized by its technical parameters that determine the operation and purpose of the device. Of course, it will be impossible to check all the parameters of the relay with a multimeter, but with its help you can accurately determine the operability of the switch. The main characteristics of the device include:

• winding voltage is the value of the signal amplitude at which the relay goes from one stable state of connecting contacts to another;
• switching current denotes the highest current value that a relay can pass through itself without changing its parameters;
• the rated voltage is divided into values ​​corresponding to the alternating and constant signal level, indicates the maximum potential difference, the occurrence of which is permissible on the connected load conclusions;
• operating frequency is the number of switchings that the device can perform per unit of time;
• wear resistance is determined by the mechanical reliability of contact groups, measured in cycles;
• the response time is characterized by the interval during which the position of the contact groups changes after the arrival of the control signal.

Preparing for verification

Before proceeding with the diagnosis, it is important to decide on the purpose of the conclusions of the element under test. To do this, you can use the datasheet for the device, that is, the documentation issued by the manufacturer. It always describes the characteristics and diagram of the device.

Often, the relay device diagram is presented on the element itself. In this case, the control contacts are depicted by dots connected by an inductor, and the switching contacts are represented by straight lines with a dotted line indicating their possible position. True, the pins for supplying power can also be drawn in the form of a rectangle with straight segments extending from the middle of its lateral sides, controlled like a conventional mechanical switch.

But even if there is no such scheme, then you can try to evaluate the contacts visually (the control outputs are made a little lighter in color). If the relay is soldered into the circuit, then it will be easy to track the common bus and power paths on the board. At the same time, contacts are often signed on the textolite, and according to the schematic diagram, it will be possible to determine their purpose.

To test the relay with a tester, you can use both a digital and an analog instrument. But due to ease of use, it is better to give preference to the first one. No setup or special preparation of the instruments is required. The only thing you should pay attention to is the state of the multimeter's battery. In the digital tester, the battery replacement icon should not light up on the screen, but in the analog version when shorting two test leads to each other, the arrow must be set opposite scratch.

In addition to the tester, you will need an adjustable power supply to carry out a set of measurements. In order to obtain correct test results, the relay must be removed from the circuit. This is due to the possible shunting of its terminals with both active and passive radioelements, therefore, with the help of the power supply, voltage is supplied to the outputs in an autonomous mode. The relay is checked in several stages, during which it is tested:

• winding;
• normally closed state;
• normally open position.

Winding diagnostics

The winding of an electromechanical relay is an inductor, that is, a wire wound in a spiral around a core. It has a certain resistance, which can be calculated using Ohm's law: R = U / I, where the current and voltage are taken as high as possible to supply to the device. In any case, the value of the coil resistance should be in the range from tens to hundreds of ohms. But for a solid-state relay, this figure can be as high as a few kilo-ohms.

This position is used to check the integrity of the coil. Testing it can be represented as the following sequence of actions:

1. The multimeter switches to resistance dialing mode. To do this, the switch of the device is moved to the area marked on the device with the symbol Ω, and the range is set to about two kilo-ohms.
2. One test lead connects to the jack labeled V / Ω and the other to COM.
3. The wire probes touch the relay terminals corresponding to the control contacts.
4. By the deviation of the arrow or the number that appears, the winding resistance is recognized.

It should be noted that the coil of an electromechanical relay can be protected by a diode, therefore, depending on the polarity of the applied probes, the resistance value can change. A large resistance between the control pins will correspond to an open coil or indicate degradation of the wire-to-pin connection.

Contact group testing

To ring the relay with a multimeter, the changeover contacts are checked in 2 stages. On the first, their resistance is measured in an autonomous mode, and on the second - when voltage is applied to the relay winding, therefore, to diagnose the device, you will additionally need a power source. In accordance with the technical characteristics of the relay on the voltage block, the amplitude and shape of the signal are set close to those required for the switching element to operate.

For example, if the device is designed to operate from a constant voltage of 36 volts, then the source can be set to any value in the range from 30 to 40 volts. In theory, switching can work even from 12 volts, but such a contact will be unreliable, although this is purely individual for each relay model. But it is necessary to exceed the values ​​with caution, since there is always a risk of burning the winding of the device.

If the tester is digital, then it switches to the diode continuity mode. This area is indicated on the meter by the icon - |> | -))). The analog device is a pointer device, it is set to the ohm limit of resistance measurement.

The test leads are plugged into the V / Ω and COM sockets of the tester. They must be closed with each other or open. In the first case, the digital multimeter will emit a signal, and on the analog device, the arrow will deviate towards zero. When open, the dial gauge will show infinity, and the number 1 will light up on the digital screen.

Then the control contacts are supplied with voltage from the signal source. At the same time, a characteristic click can be heard on the electromechanical switch. As soon as the power is applied, the situation with a working relay should change to the opposite: when the voltages are at there is no winding, normally open groups should not be connected to each other, but normally closed, on the contrary, connected. This checks the status of each contact group.

To test the solid state relay, the multimeter also switches to diode continuity mode. When the tester probes are touched, the device will apply a small voltage to the device. If the relay is damaged, then zero will be displayed on the multimeter screen, in case of serviceability - the number 0.7 or 0.5, corresponding to the value of the p-n transition.