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This post was last edited by yunrun on 2019-7-11 10:10. A safety relay is composed of several relays and circuits, and it is primarily used in safety control circuits to connect safety sensing elements (such as emergency stop buttons, safety doors, two-hand buttons, safety light curtains, etc.) to the motion controllers of mechanical equipment (such as safety PLCs, contactors, etc.). Safety relays are designed to compensate for each other’s inherent flaws, thereby ensuring the proper and reliable functioning of the relays with minimal false operations. The lower the rate of errors and failures, the higher the safety level. Therefore, various types of safety relays must be developed to protect machinery at different risk levels; the primary objective is to safeguard machine operators who are exposed to varying degrees of danger. Safety relay yunrun.com.cn/product/2608.html 1. What is a safety relay? A safety relay is a module composed of multiple relays and logical circuits; it is a circuit component designed to compensate for each other’s shortcomings in fault conditions, thereby ensuring proper operation with minimal false activations. This helps reduce errors and failures and enhances safety levels. To be precise, it should be called a safety relay module. Currently, there is no unified terminology for safety relays in China; some refer to them directly as safety controllers, while others simply call them relays. Due to the fact that different mechanical equipment and different process stages involve different safety risks and hazard levels. Therefore, during product design, various safety relays were developed to protect mechanical equipment of different risk levels, with the main purpose of safeguarding machine operators exposed to different levels of hazard. 2. What is the difference between safety relays and ordinary relays? ①Larger size: Safety relays and ordinary relays have different dimensions, with safety relays being larger. ②Modules rather than components: A safety relay is a module, not an electronic component like a regular relay. ③Red and yellow: Safety relays have their own distinctive colors, usually yellow or red, or these two colors are used as the main hues (just as in the explosion-proof safety designs of Changhui Instruments, the hazardous side and the intrinsically safe side are typically marked in blue). Of course, these are still just surface phenomena. ④【Core】Safer: Due to differences in design principles, ordinary relays cannot achieve a high diagnostic coverage rate (DC); they can only be used in industries with lower safety requirements, such as Cat.B/1 in the machinery industry and SIL1 in the process control industry. It can be said that ordinary relays are not safe enough. Through the definition of requirements for relays and the aid of logical circuit design, An Ji achieves a high diagnostic coverage rate, which can even reach 99.9% in some cases. Moreover, in applications with high safety requirements, it is stipulated that certified safety relays must be used to meet those safety standards! ⑤Forced guidance structure: A “safety relay” is not a “relay without faults,” but rather one that performs predetermined actions in the event of a fault. Safety relays feature a forced-guided contact structure (or other protection mechanisms) that ensures safety even in the event of contact welding, which is completely different from ordinary relays. ⑥From the perspective of relays, the difference between safety relays and ordinary relays can be seen here: http://yunrun.com.cn/upload/201801/15/201801152348225451.png a. Ordinary relays: When the contacts weld together, it causes both sets of contacts (NO/NC) to become ON at the same time. b. Forced-guidance relay: The most crucial component of a safety relay is the forced-guidance relay; thanks to the action of the internal forced-guidance rod, even if the contacts weld together, it prevents both sets of contacts (NO/NC) from becoming ON at the same time. In short: safety relays are safer and more reliable, making them suitable for industrial safety applications. 3. What are the main standards followed for mechanical safety certification? IEC 61508 / ISO 13849/ IEC 62061. 4. How to select a safety relay? Depending on the input devices of the safety circuit, safety relays are selected based on five factors: the input devices, the number of output channels, the requirements for backend driving capability, the safety level, and the functional requirements. The input devices of mechanical safety circuits are typically safety sensors, including emergency stop buttons, safety doors, safety light curtains, safety mats, interlock devices, two-hand buttons, laser scanners, and so on. 5. Are there **standard requirements that mandate the use of safety relays in SIS systems?** Given the current state of functional safety technology development in China and the existing standards related to functional safety in the process control industry, there are currently no mandatory standards. There are indeed some mandatory standards regarding mechanical safety. Some of the principles and specifications regarding the design of safety-related systems, as stated in the \"Design Specifications for Safety Instrumented Systems in the Petrochemical Industry,\" state that: ① The logic operators of a safety instrumented system can be composed of relay systems or programmable electronic systems, or a combination of both. ②For Safety Instrumented Systems of SIL 2 and SIL 3, redundant or fault-tolerant logic solvers should be used. ③Process interfaces include associated devices such as input/output cards, sequential event input cards, power distributors, safety barriers, switches, relays, etc. ④The safety integrity level represents an overall assessment of the entire safety circuit; obviously, even the connected devices within this circuit, such as relays, also require fail-safe design requirements. Meanwhile, in the reports shared by experts from various design institutes, among the SIS design principles outlined, it was also stated that the [SIS logic controllers] should obtain functional safety certification from **authoritative certification bodies**. For relays used in the safety circuits of safety-related systems, whether they are applied in relay systems or in the associated devices of process interfaces within those circuits, from the perspective of design reliability and safety assurance, safety relays that possess self-diagnosis capabilities, a high diagnostic coverage rate, a low failure probability, and authoritative certifications represent a better choice. 6. Can ordinary relays be used in the SIS system? Ordinary relays have a relatively low diagnostic coverage; they lack design features related to fail-safe operations and no self-diagnosis function. Therefore, they may be used in some safety systems where the required safety level is low, such as SIL1. However, for safety levels of SIL2 and above, safety relays with high diagnostic coverage and self-diagnosis functions are typically used. 7. What are the common faults of safety relays and how to deal with them? When a safety relay is used to disconnect the circuit, it is necessary to determine accurately whether the relay is damaged or has detected an unsafe condition and therefore disconnected the circuit. ①If there is a safety hazard in the circuit, after eliminating that hazard, restart the safety relay to restore normal operation of the circuit. For example: The pulse detection in the SIS system causes the safety relay to shut off and turn on frequently; adjust the duration of the low level detected by the SIS system’s pulse detection mechanism so that this period is not recognized by the safety relay. ②If the safety relay fails, the following actions are usually taken: a) The output contacts of the safety relay are generally protected by contact fuses; during operation, these fuses may blow due to short circuits or overcurrents, preventing the relay from enabling the on-site equipment. Solution: Replace the fuse. b. The overvoltage caused damage to the internal components of the safety relay in its control circuit. Solution: Replace the safety relay, contact the manufacturer for repair or replacement. 8. Is it necessary to use safety relays on mechanical equipment? Domestic equipment does not have strict mandatory standards regarding safety, or it has not undergone the corresponding standard certifications, such as CE in the European Union. Safety relays are used when there is a risk of personal injury or property damage to equipment. It does not use a PLC; instead, a hardware-based method is employed to cut off the power supply, bringing the device to a completely stopped state ； Moreover, the safety relay itself has several contacts to ensure it can be effectively disconnected in the event of a fault. If your device wants to enter other **, it must at least have CE certification; otherwise, there will be issues in this regard. Therefore, in equipment designed for export, especially to the EU and Japan, safety relays are usually included. Of course, as there is an increasing emphasis on safety in the country, some technical standards and their implementation are also gradually being brought in line with international standards. The 13th Five-Year Plan for standards-related work in the field of safety mentions the updating and upgrading of standards related to mechanical safety, as well as stricter enforcement of these standards; the requirements regarding the design of safety circuits will also become increasingly stringent. At this point, for forward-thinking equipment manufacturers, is it necessary to use safety relays? Is there any need to elaborate on this? 9. What is the automatic start of a safety relay? It starts automatically; as long as the conditions for activation are met (the sensors and feedback circuits are closed), the device will automatically activate the start circuit. 10. Safety Relay | What is a monitored start? Before starting, the startup conditions must be met (the sensor and feedback circuit are closed). Additionally, the device requires an ON button as a start signal, and the safety relay activates the equipment by detecting the falling edge (pulse) of the ON signal. 11. What size capacitor should be installed in the control circuit of the safety relay? A capacitor is connected in parallel with the coil of a regular relay to prevent high voltages from developing across the relay coil, which could otherwise damage the relay contacts and cause arcing. However, the addition of a capacitor increases the relay’s operating delay. Therefore, nowadays, most relay applications utilize a freewheeling diode to eliminate arcing. A safety relay is an electronic module that uses a freewheeling diode inside to eliminate arcing. In actual use, there is no need to install a capacitor. 12. Does the safety relay have a service life or lifespan? Is it necessary to replace it regularly? When first put into use, the SIS system has a high security level. But over time, the likelihood of security failures may increase, and the values of security-related parameters might gradually grow larger. If used for an extended period without testing, the safety level will decrease to SIL3-2-1. Moreover, the key factor for a safety relay is the performance of the relay selected for use, and relays have a certain mechanical lifespan. Therefore, it is necessary to perform fault diagnosis on the system regularly. It is also stated that a maintenance management plan is necessary throughout the entire lifecycle of safety-related systems. During a PROOF TEST, it is to check whether there have been any safety failures in the safety system. If there is no fault, its safety level remains within the original range. If a fault is detected, corresponding actions are required, including replacement. Therefore, it is recommended to conduct inspection and testing every 5 years, or even more frequently. Relevant information is usually provided in the product’s “Safety Manual”. Specifically, the maintenance and inspection plan and scheme can be determined by taking into account the characteristics of the safety system, the overall maintenance management plan, as well as the relevant circuits and components. Note: The above are application suggestions for the process control industry. For applications in the machinery industry, mechanical equipment is often used in human-machine collaboration, which increases the risk to personal safety; therefore, testing is required fairly frequently, with the Safety Manual specifying that tests should be carried out at least once a month. 13. How to diagnose safety relay contacts? The safety relay contacts can be checked manually and by the system. Some safety relays provide normally closed contacts. By removing the power supply to the relay, namely the power supply at A1, when there is no power supply, the normally open contact of the relay will open while the normally closed contact will close. Due to the mechanical interlock of the safety relay, the normally open and normally closed contacts cannot be activated simultaneously. If the system detects that the normally closed contact is already connected, it can be safely assumed that the normally open contact of the relay can be disconnected, indicating that the relay is intact. 14. Why is it important to pay attention to the power-on start current of safety relays? The power-on start current refers to the phenomenon where industrial electronic instruments exhibit a current that is much higher than the normal operating current at the moment of power-up. There are two performance indicators for the power-on start current: the maximum power-on current and its duration. Industrial electronic instruments contain capacitors or sensing capacitors. At the moment of power-up, these capacitors need to be charged; during this process, they exhibit a temporary short-circuit behavior, causing the inrush current to increase abruptly. Therefore, when designing industrial electronic instruments, engineers must minimize the starting current in order to reduce its adverse effects on the system. However, since type testing of industrial electronic instruments is often carried out on a single instrument, or the test power supply is relatively ideal, this hazard is often overlooked; as a result, when multiple instruments are used together in the field, the system may fail to operate reliably. In industrial settings, the danger of excessively high inrush current is that multiple instruments often share a single power supply. If the inrush current is too high, it may cause the current peak to exceed the specified limit of the power supply at the moment of power-up. This reduces the power supply’s load-carrying capacity, resulting in incomplete power delivery to industrial electronic instruments and preventing the entire system from functioning reliably. Therefore, industrial electronic instruments must minimize their starting current in order to reduce the adverse effects on the system. In Safety Instrumented Systems (SIS), the parameter of power-up startup current is particularly important. Every circuit in the safety instrumented system comes equipped with diagnostic functions. For example, the power supply circuit for field instruments has short-circuit detection and overload detection capabilities; by measuring the current in this circuit, it is possible to determine whether there is a short circuit or an overload. If it is determined that this current exceeds the internal set value, a fault signal is sent to the system, which then enters fault mode and disconnects the power supply circuit to ensure the safety of the entire system. If the startup current upon power-up is too high, it may cause the system to fail to operate properly. yunrun.com.cn/news/1387.html