How to measure the quality of the relay_How to measure the quality of the relay with a multimeter
1. What is a relay
A relay is an electrical control device, which is an electrical appliance that makes a predetermined step change in the controlled quantity in the electrical output circuit when the change of the input quantity (excitation quantity) meets the specified requirements. It has an interactive relationship between the control system (also known as the input loop) and the controlled system (also known as the output loop). Usually used in automated control circuits, it is actually an "automatic switch" that uses a small current to control the operation of a large current. Therefore, it plays the role of automatic adjustment, safety protection, and conversion circuit in the circuit.
Second, the relay contact form
There are three basic forms of relay contacts:
1. The two contacts of the moving type (normally open) (H type) coil are disconnected when the coil is not energized, and the two contacts are closed when the coil is energized. It is represented by the pinyin prefix "H" of the ligature.
2. The two contacts are closed when the coil is not energized, and the two contacts are disconnected when the coil is energized. It is represented by the hyphenated Pinyin prefix "D".
3. Conversion type (Z type) This is a contact group type. This kind of contact group has three contacts in total, that is, the middle is a moving contact, and the upper and lower are a static contact. When the coil is not energized, the moving contact and one of the static contacts are disconnected and the other is closed. After the coil is energized, the moving contact will move, so that the original open is closed, and the original closed is open, and the conversion is achieved. Purpose. Such contact groups are called changeover contacts. It is represented by the pinyin prefix "z" of the word "zhuan".
3. Working principle of relay
The changeover contact of the relay is a moving contact and two static contacts of the relay. Among them, the moving contact and the static contact 1 are in a closed state, which is called a normally closed contact, and the moving contact and the static contact 2 are in a disconnected state, which is called a normally open contact.
When the coil is energized, its moving contact is immediately disconnected from the static contact 1 and closed with the static contact 2, cutting off the control circuit of the static contact 1 and contacting the control circuit of the static contact 2.
When the coil loses power, the moving contact is reset, that is, the moving contact and the static contact 2 are reset and disconnected and are reset and closed with the static contact 1, and the control circuit of the static contact 2 is cut off and the control circuit of the static contact 1 is connected.
It can be seen from the above figure that when the relay K coil is connected between the non-blocking normally open button and the battery; the normally closed contact K-1 is connected between the battery and the bulb EL1z, which is used to control the lighting and extinguishing of the bulb EL1; The normally open contact k-2 is connected between the battery and the bulb EL2, and is used to control the lighting and extinguishing of the bulb EL2. When the line is not connected, the bulb EL2 is off.
When the button SB is pressed, the circuit is connected, the coil of the relay K is energized, the normally closed contact K-1 is disconnected, the power supply of the bulb EL1 is cut off, and the bulb EL1 is turned off; at the same time, the normally open contact K-2 is closed, and the bulb is turned on. The power supply of EL2, the bulb EL2 lights up.
When the button SB is released, the line is disconnected, the relay K coil is de-energized, the normally closed contact K-1 is reset and closed, the power supply of the bulb EL1 is turned on, and the bulb EL1 is lit; at the same time, the normally open contact K-2 is reset and disconnected , cut off the power supply of the bulb EL2, the bulb EL2 goes out.
Fourth, the main function of the relay
Relay is an automatic switching element with isolation function. It is widely used in remote control, telemetry, communication, automatic control, mechatronics and power electronic equipment. It is one of the most important control elements.
Relays generally have induction mechanisms (input parts) that can reflect certain input variables (such as current, voltage, power, impedance, frequency, temperature, pressure, speed, light, etc.); Between the input part and the output part of the relay, there is an intermediate mechanism (drive part) that couples and isolates the input quantity, processes the function and drives the output part.
As a control element, to sum up, the relay has the following functions:
1) Expand the control range: For example, when the control signal of a multi-contact relay reaches a certain value, it can switch, break, and connect multiple circuits at the same time according to different forms of contact groups.
2) Amplification: For example, sensitive relays, intermediate relays, etc., can control high-power circuits with a very small amount of control.
3) Integrated signal: For example, when multiple control signals are input to the multi-winding relay in a specified form, the predetermined control effect is achieved after comparison and synthesis.
4) Automatic, remote control, monitoring: For example, the relay on the automatic device can form a program control circuit together with other electrical appliances to realize automatic operation.
5. How does a multimeter measure the quality of a relay?
The relay is the key device in the smart prepaid electric energy meter. The life of the relay determines the life of the electric meter to some extent. The performance of the device is very important to the operation of the intelligent prepaid electric energy meter. So how is the relay tested?
The relay is divided into two parts, the coil and the electric shock. The resistance of the coil can be simply measured by electricity blocking. Generally, it is tens to thousands of ohms. Depending on the AC or DC, the power is different. If it is a short circuit or a short circuit, it is basically burned. coil. Then normally open contacts, measured with electrical blocking, are basically infinite, and normally closed contacts, measured with electrical blocking, are shorts. If the contact has a certain resistance, it can also be judged that the relay is broken.
1. Measure the DC resistance of the relay coil
The method of measuring the DC resistance value of the relay with a digital multimeter is similar to that of a pointer multimeter. According to the nominal DC resistance value of the relay, place the multimeter in an appropriate electrical barrier, and connect the two test leads to the pins of the relay coil arbitrarily for measurement, as shown in the figure. Compare the test result with the nominal value, if the error is within ±10%, it is normal; if the resistance value is obviously too small, the coil has a local short-circuit fault; if the resistance value is zero, the coil is short-circuited; if the multimeter shows The overflow symbol "1" indicates that the coil is open circuit.
2. Measure pickup current
The method of measuring the pull-in current is the same as that of the pointer multimeter. Put the digital multimeter in the DC current 200mA block, connect it in series with the relay coil, 5.1kΩ potentiometer, and 200Ω resistor, and connect it to both ends of the 20V DC power supply.
Before measuring, first adjust the potentiometer to the maximum resistance value, then turn on the DC power switch, and slowly adjust the potentiometer to reduce the resistance value. When the relay just produces a pull-in action, the current value displayed by the multimeter is the pull-in current.
3. Measure the release current
After measuring the pull-in current in the previous step, the circuit remains unchanged and continues to measure the release current. During measurement, slowly adjust the potentiometer to increase the resistance value when the relay is in the pull-in state. When the relay just releases the action, the current value displayed by the multimeter is the release current of the relay.
4. Measure the contact resistance of the contacts
Use the 200Ω electrical barrier of the multimeter to measure the resistance value between the two closed contacts, usually showing a few tenths of ohms, as shown in Figure 4.97. If the display shows the overflow symbol "1", it means that the two contacts under test are disconnected.
If the buzzer is used for detection, the multimeter should not only display the resistance value between the two closed contacts, but also beep at the same time. If the multimeter displays the overflow symbol "1", the buzzer does not sound, indicating that there is no connection between the two contacts under test.
