1. What is a safety relay
Safety relay is a module composed of multiple relays and logic circuits. It is a circuit composition unit. Its purpose is to learn from each other's strong points to complement each other's weak points in the fault state, achieve the function of correct and low misoperation, reduce its error and failure value, and improve the safety factor. In its entirety, it should be called a safety relay module. At present, the title of safety relay in China is not unified, some are called safety controller, some are called relay.
Different mechanical equipment and different process links have different safety risks and different risk levels. Therefore, in the product design, various safety relays are designed to protect mechanical equipment at different levels, mainly to protect mechanical operators exposed to different levels of risk.
2. What is the difference between safety relay and general relay?
(1) Larger appearance: the safety relay is different from the ordinary relay in appearance and size, and the safety relay is larger.
(2) Module rather than component: safety relay is a module, not an electronic component like ordinary relay.
(3) Red and yellow: the safety relay has its own color, usually yellow or red, or these two colors are the main color (just like Changhui instrument has blue identification in explosion-proof safety design, dangerous side and intrinsically safe end). Of course, these are only superficial phenomena.
(4) "Core" is safer: due to different design principles, ordinary relays cannot achieve high diagnostic coverage (DC), and can only be used in the machinery industry with low safety level, such as cat B/1 and process control industry sil1, so it can be considered that ordinary relays are not safe enough. Through the requirements of relays and the auxiliary design of logic circuits, the diagnostic coverage of safety relays is high, and some can even reach 99.9%. Moreover, in some occasions with high safety requirements, certified safety relays must be used to meet the safety requirements.
(5) Forced guiding structure: "safety relay" is not a "fault free relay", but a regular action when a fault occurs. The safety relay has a forced contact structure (or other protection methods), which can ensure safety even if the contact is welded, which is completely different from the general relay.
(6) From the perspective of relays, we can see the difference between safety relays and ordinary relays:
a. Ordinary relay: when the contact is fused, two pairs of contacts (no/nc) will be on at the same time.
b. Forced pilot relay: the core component of safety relay is forced pilot relay. Under the action of the internal forced guide rod, even if the contact is fused, the two pairs of contacts (no/nc) will not be on at the same time.
In short, the safety relay is more safe and reliable, which is suitable for industrial safety occasions.