The safety tester is used for high-voltage component withstand voltage measurement tests (using AC and DC withstand voltage testers), such as silicon stacks. It is mainly used as a specialized instrument to detect whether a product leaks electricity, whether it is well grounded, and whether it will harm personal safety. The main testing items include voltage, leakage current, insulation resistance, and grounding resistance.
Note that the DC high voltage output is negative voltage, while the ground is positive. When testing capacitors, there is a charging process when voltage is applied across the capacitor. At this time, there is a charging current in the testing circuit. When the current is greater than the set leakage current value, the voltage tester will alarm, interrupting the test and preventing it from proceeding. Therefore, when testing with a safety tester, the voltage should be slowly increased and the charging current should be less than the set leakage current value until the specified test voltage is reached for testing. And fixed voltage, reset start mode cannot be used for testing In the AC circuit, it is equivalent to the resistance in the DC circuit. Therefore, the safety tester generates a current in the AC circuit. When the current exceeds the set leakage current value, the voltage tester will alarm, causing the test to be interrupted and unable to proceed. Therefore, before the test, the capacitance reactance (Xc) of the capacitor should be calculated first, then the circuit current value under the test voltage should be calculated, and then the preset value of the leakage current of the withstand voltage tester should be adjusted so that it is slightly greater than the circuit current value before the test. Testing components (equipment) with high distributed capacitance such as cables should be equivalent to capacitor testing.
Test project:
1. High voltage test:
Dielectric Voltage with Stand Test is a mandatory test required by international safety certification bodies. Products must undergo percentage testing before leaving the factory. It is a quality assurance and electrical safety indicator for products. The testing method is to apply an abnormal voltage higher than the normal operating voltage to the product for a period of time. Finally, as long as there is no insulation breakdown, it can be considered as passing this test
2. Insulation impedance test
Insulation resistance test applies a direct current voltage to the relevant two points, with a maximum of 1000 volts, usually measured in ohms, to determine good and defective products
3. Grounding impedance test
Ground bond test is used to test the grounding point of a product. A constant current power supply is applied to the outer shell or metal part of the product to test the impedance between two points. Generally, products are required to test 25 amperes, and the impedance should not exceed 0.1 ohms. However, CSA requires measuring 40 amperes for testing, which can detect problems such as loose grounding screws, small grounding wire diameter, and open grounding lines
4. Leakage current test
Touch current test refers to the current that flows through the metal touchable part of the device and through the human body to the grounded or touchable part when the device is supplied with current.
5. Input test:
The purpose of safety input testing is to examine whether the input during product design meets the requirements of the product's normal operation, and whether the input circuit can withstand the current required for product operation. In the product standard, it is stipulated that the input current of MAX power consumption cannot exceed 110% of the nominal value of the product. This nominal value also informs users of the minimum current required for the safe operation of the product, requiring them to prepare for such an electrical environment before using the device.
6. Stability testing of safety signs:
Warning signs for user safety must be stable and reliable, and should not become blurry after a period of use, leading to user error and danger, or directly causing danger to occur. So we need to test this stability. According to the safety standards, it is required to test with water for 15 seconds and then with gasoline for 15 seconds, and the labeling must not be blurred.
7. Capacitor discharge test:
For a device with a power cord that can be plugged in and out, the power cord is often unplugged from the socket, and unplugging the power plug from the socket is often played with or placed arbitrarily. This leads to a problem where the unplugged power plug is charged, and this charge disappears over time. If this time is too long, it can cause electric shock to the person playing with the plug, and damage other devices or the device itself to any placed power plug. Therefore, various overall safety standards have strict regulations on this time, and the product design should consider this time. The product needs to measure this time for safety certification.
8. Circuit stability test:
SELV circuit
SELV circuit is a safe ground voltage circuit, which is safe for users. For example, the DC output terminal of a mobile phone charger to a mobile phone is safe and can be touched freely without any danger.
Note: SELV circuits have different interpretations in different standards, for example, the interpretation in IEC60364 is different from that in IEC60950-1. Therefore, when it comes to SELV, attention should be paid to which standard it belongs to, and its hazards are also different.
SELV circuits need to meet special requirements in order to be considered SELV circuits, which means that even in the event of a single fault, they still meet the requirements of SELV circuits. Therefore, a single fault test is required for each SELV circuit to prove that the SELV circuit is stable. During testing, single faults are introduced one by one to monitor the SELV circuit.
9. Power limited source circuit
Due to the small output power of power limiting source circuits, based on known experience, they do not pose a fire hazard. Therefore, in safety standards, specific requirements have been lowered for the enclosures of such circuits, and their flame retardant rating is UL94V-2. Therefore, all such circuits need to be measured to prove that they are power limited source circuits.
10. Current limiting source circuit
People who have worked as electricians know that after passing through a certain resistance, the AC220V circuit is no longer dangerous to people. So what is the actual resistance and what are the requirements for resistance. Maybe everyone doesn't know. There is a regulation in the safety standards, which is the current limiting source circuit. The current of the current limiting source requires that the current flowing out should be below the safe limit under normal and single fault conditions, and should not pose a danger to people. The current should be less than 0.25mA. For isolating primary and secondary circuits, the resistance should meet specific standards for shock resistance.
11. Grounding continuous test:
People who have experience in electrical installation know that some equipment must be grounded, otherwise there will be dangerous voltage on the surfaces it can touch. These dangerous voltages must be released through grounding. According to safety testing regulations, the required current, duration, and measured resistance must be less than 0.1 ohms or the voltage drop must be less than 2.5V (if possible, use this value).
12. Moisture test:
Moisture testing simulates the safety performance of equipment in extreme environments. After manufacturing, the equipment can operate safely under any humidity, and users should not be told that the equipment cannot be used just because it is in the rainy season and the humidity is high. Therefore, when designing, it is necessary to consider that the equipment meets safety requirements under foreseeable humidity, so humidity testing is necessary. The testing requirements vary slightly depending on the standards.
13. Torque test:
Torque testing refers to the bending and deformation of external wires of equipment that are often subjected to external forces during use. This test is to test the number of bends that the wire can withstand, and it will not break or expose AC220V wires due to external forces during the product lifecycle.
14. Stability testing:
In normal use, devices often have different external forces acting on them, such as people leaning against taller devices or climbing them during maintenance; A relatively short device with a stool like appearance, some people may stand on it and wait. Due to the external forces acting on the equipment, the design did not take into account the risk of equipment collapse, flipping, and other hazards that may occur during the week. Therefore, these tests need to be conducted after the equipment design is completed. Check that they meet safety requirements.
15. Shell stress test:
During the use of the equipment, it may be subjected to various external forces, which may cause deformation of the equipment casing. These deformations may lead to internal hazards or failure to meet requirements. Therefore, these impacts must be considered when designing equipment, and these indicators must be tested during safety certification.
16. Drop test:
Small devices or desktop devices may fall from the hand or workbench to the ground during normal use. These drops may result in the internal safety indicators of the equipment not meeting the requirements. Therefore, this impact must be considered when designing equipment, and these indicators need to be tested during safety certification. The requirement is that after the device falls, its function can be lost, but it cannot pose a danger to the user.
17. Stress release test:
If there are hazardous circuits inside the equipment, it is not allowed for the outer shell to deform during normal use, causing the danger to be exposed. These impacts must be considered when designing equipment, and these indicators must be tested during safety certification.
18. Battery charging and discharging test:
If there is a rechargeable battery inside the device, it is necessary to conduct charge and discharge tests, as well as charge and overcharge tests under a single fault. This is because during normal use, the device is charged and discharged, and if there is a malfunction, but the main function has not been lost, the user will not notice the equipment failure. In this case, the charging and discharging requirements are safe and cannot cause danger such as explosion.
19. Equipment temperature rise test:
(Temperature of internal and external surfaces under normal working conditions)
In safety testing, temperature rise testing is the most important. Although the testing equipment and instruments used are the same as those used in artificial climate environment testing, there are significant differences in the testing items, testing devices, and purposes. The artificial climate environment mainly tests the adaptability and reliability of equipment. And safety regulations examine whether the equipment can work safely. Here is an example to illustrate their differences: Safety testing mainly tests the temperature of safety devices, such as the operating temperature of insulation materials under normal conditions, which is lower than the MAX allowable temperature of insulation materials at MAX equipment operating temperature. If the insulation material is tested at a temperature of 100 ℃ in a 25 ℃ environment, and the insulation material can only operate safely below 130 ℃, it is crucial to define the maximum operating temperature allowed by the equipment. If the equipment is tested at an ambient temperature of 50 ℃, the insulation material should be converted to an ambient temperature of 50 ℃ and the test temperature should be 125 ℃, which meets the requirement of less than 130 ℃ and passes the test. If the device operates at an ambient temperature of 60 ℃, the test temperature converted to 60 ℃ should be 135 ℃. If it exceeds the requirement of 130 ℃, the test will not pass. Similarly, other safety devices also need to be tested for operating temperature. To determine whether the requirements are met.
20. Ball pressure test:
As insulation materials or plastic parts supporting hazardous voltage, ball pressure testing is required to ensure that the plastic parts have sufficient support strength when the hazardous voltage components work at high temperatures. The test temperature is MAX temperature plus 15 ℃, but not less than 125 ℃. The ball pressure time is maintained for 1 hour at the required temperature.