How to test relays with a voltmeter?
In the field of testing electronic components, it is crucial to accurately test the performance of relays. A voltmeter is a common and useful tool that can help us to test relays efficiently. Today, MobikeChip will give you a detailed introduction on how to test relays with voltmeter, so that you can easily master this key skill.
1. Preparation work before testing
(I) Choose a suitable voltmeter
The choice of voltmeter is directly related to the accuracy of the test results. Priority should be given to selecting a voltmeter with high accuracy and suitable range. For relay testing, the voltage value to be measured is usually between a few volts and tens of volts, so make sure that the range of the voltmeter can cover this range, and at the same time, its accuracy should meet the demand for detecting small changes in the operating voltage of the relay. For example, if you want to test a relay with a rated voltage of 12V, it is more appropriate to choose a voltmeter with a range of 0 - 20V and an accuracy of 0.01V.
(ii) Checking the status of the voltmeter
Before using the voltmeter, be sure to check its status carefully. Confirm that the display of the voltmeter is clear and undamaged, the meter plug is connected tightly with the voltmeter jack, and the meter pen is not broken, fractured and so on. At the same time, check whether the battery power of the voltmeter is sufficient to ensure that it can work normally. In addition, the voltmeter will be zeroing operation, so that the measurement value is more accurate and reliable.
(iii) Prepare relays and related circuits
Prepare the relay to be tested and a simple test circuit. The test circuit should contain a power supply, a switch and a power supply unit that matches the rated voltage of the relay. Ensure that the circuit is connected correctly and the components work properly to provide a stable test environment for the subsequent relay test.
2. Relay coil voltage test
(i) Connect the test circuit
Connect the pens of the voltmeter with the two ends of the relay coil. When connecting, note that the polarity of the meter pen is the same as the polarity of the voltage at both ends of the coil, with the red pen connected to the positive pole and the black pen connected to the negative pole. Next, close the switch in the test circuit so that the current passes through the relay coil.
(ii) Read the voltage value
Observe the display of the voltmeter and read the voltage value at both ends of the coil. Under normal circumstances, the voltage value should be close to the rated operating voltage of the relay. For example, if the rated voltage of the relay is 24V, the voltage value measured by the voltmeter should be between 23V and 25V under normal operation (taking into account the internal resistance of the power supply and line loss). If the difference between the measured value and the rated voltage is too large, for example, lower than 20V or higher than 28V, it may mean that there is a problem with the coil of the relay, such as the internal resistance of the coil is too large, or the power supply is abnormal.
(iii) Analyzing the test results
If the voltage value is normal, it means that the relay coil is able to obtain the required voltage when energized, and the preliminary judgment is that the electromagnetic performance of the coil is good. However, if the voltage value is abnormal, it is necessary to further investigate the cause. Firstly, check whether the power supply is working normally and whether the output voltage is stable; secondly, check whether there is poor contact or short circuit in the connection line. If the voltage value is still abnormal after eliminating these external factors, it is likely that the relay coil itself is faulty, such as local short circuit or disconnection of the coil, etc., which requires further testing or replacement of the relay.
3. Contact on-off voltage test
(i) Setting up the test scenario
Connect the relay into a circuit containing a load (e.g., light bulb, resistor, etc.) and make sure that the contacts of the relay can control the on-off of the load. At the same time, connect a voltmeter across the load (for normally open contacts, measure when the relay is not energized; for normally closed contacts, measure when the relay is energized).
(ii) Operate the relay and measure
For normally open contacts, close the switch controlling the relay coil in the test circuit to energize the relay, and observe the voltmeter reading at this time. Under normal circumstances, the relay is energized after the normally open contacts closed, the load should be the voltage on both sides, the voltmeter should show a voltage value consistent with the normal operation of the load. For normally closed contacts, the first closed control relay coil switch, so that the relay is energized, this time the normally closed contacts are open, the load should be no voltage on both sides, the voltmeter should read zero.
(iii) judgment contact state
If the measurement result is consistent with the expected, it means that the contacts of the relay can normally control the circuit on and off, and its function is normal. For example, in the normally open contact test, if the voltmeter shows a voltage value similar to the rated operating voltage of the load, it indicates that the normally open contact is closed well; if it is zero, it may be that the contact is not closed or poor contact. Similarly, for normally closed contacts, if the voltmeter reads zero, indicating that the normally closed contacts are disconnected normally; if there is an abnormal voltage display, the normally closed contacts may be sticky and other problems, the need for overhaul or replacement of the relay contacts.
4. After the test, organize and summarize
(i) organize the test equipment
After the test is completed, turn off the power of the test circuit, remove the voltmeter's pen from the circuit, and organize the voltmeter and other test equipment. Store the voltmeter properly to avoid collision and damage for next use.
(ii) Record the test results
Record in detail the various data of this relay test, including the coil voltage measurement, the voltage value of the load terminals when the contacts are on and off, and the problems found during the test. These records not only help to evaluate the performance of the relay in this test, but also provide reference for similar subsequent tests and accumulate valuable testing experience.
At MobikeChip, we specialize in providing you with professional electronic component testing knowledge and high quality products. Mastering how to test relays with voltmeter can make you more comfortable in the maintenance and troubleshooting of electronic circuits. If you have any questions about relay testing, selection or other electronic components, please feel free to visit MobikeChip website, our professional team will be happy to serve you.
Category page: Safety Relays
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