I. Determining the quality of a solid-state relay
Solid-state relays are widely used in modern industrial equipment, and their functionality is crucial to the safety and quality of the equipment. Therefore, determining the quality of a solid-state relay is of paramount importance.
1. A good solid-state relay will illuminate a red LED indicator when a signal is input, indicating that the main circuit is conducting. Observing the indicator light is a good way to check if the control signal is normal.
2. Use a multimeter to measure whether the main circuit voltage is within the normal range when the solid-state relay indicator light is on. When the indicator light is off, check whether the main circuit voltage is zero.
3. Disconnect the power supply to the solid-state relay, set the multimeter to the automatic ohm setting, and measure the resistance of the solid-state relay's main circuit in forward conduction. The normal resistance is close to infinity.
4. Inspect the solid-state relay for any damage and ensure the surrounding environment is suitable. Check that the terminals are secure and free from oxidation. Use a multimeter to measure the solid-state relay's resistance to ground to ensure it is close to infinity.
5. If necessary, measure the input signal of the solid-state relay. Industrial equipment generally uses a current signal (4-20mA). Use a multimeter or ammeter to measure whether the ampere reading is normal.
6. If the solid-state relay is found to always be in an off or on state regardless of whether there is a signal, it is recommended to replace it with a new one. When replacing the relay, be sure to use thermal paste and anti-static paper.
II. Analysis of Common Relay Problems
When using a relay, please refer to the (relay manufacturer's) instruction manual for common application issues and operational guidelines. Do not exceed the rated voltage or load current. Excessive discharge voltage may cause partial short circuits between the relay coil cores, leading to improper relay operation. It may also cause issues such as incorrect surge protection of the relay's diodes.
Therefore, there are quite a few issues to pay special attention to with relays. Below, we will discuss and analyze some common problems related to relays:
1. Never exceed the rated voltage of the load current during the application of a relay. Excessive voltage may cause a partial short circuit between the relay coil cores and result in poor relay operation. It may also lead to malfunctions such as incorrect surge protection of the relay's diodes.
2. Poor insulation between relay outputs is mainly due to the arcing generated between relay contacts being distorted by external electromagnetic fields or the electromagnetic field generated by the operating coil, reaching the coil terminals and causing a short circuit. However, the carbon or contact powder deposits generated by the arcing between contacts under load are a direct cause of poor insulation, leading to reduced insulation performance or voltage withstand capability.
3. Relays sometimes experience increased loop resistance in power supply circuits. This is mainly due to the damage caused by organic compounds adhering to the surface of the relay contacts. To remove the natural gas emitted from the molded components of the relay beforehand, a baking process (heating under high vacuum) is performed. Molded components that significantly reduce natural gas emissions have also been developed and are gradually being used in various products.
4. Secondly, relays have higher requirements for small and medium-sized, highly sensitive equipment, therefore the coil core wire is becoming increasingly thinner. Because relays are mounted on a printed steel plate, even after cleaning, ultrasonic waves can sometimes concentrate on the coil core wire, causing it to break. The key is that relays generally cannot be cleaned with tap water to remove dust and dirt; otherwise, the use of water will create a strong standing wave, which may cause the coil core wire to break. Therefore, it is essential to determine this beforehand.
5. The current decreases as the coil temperature of the AC-operated relay rises (approximately 0.4% decrease for every 1°C increase). Avoid incorrect diode connections within the relay to prevent misoperation. Otherwise, the relay may vibrate and disconnect, and in severe cases, it could even damage the relay.
