Source: Powerful
The so-called "safety relay" is a combination of several relays and circuits, in order to complement each other's abnormal defects and achieve the complete function of the relay with correct and low malfunctions. The lower the error and failure values, the higher the safety factor. A "safety relay" is not a "fault-free relay", but a regular action when a fault occurs. It has a forced guide contact structure, in case it occurs. Safety can also be ensured even when the contacts are welded, which is completely different from ordinary relays.
safety relay is a necessary control part in the safety circuit . It accepts safety input, and through the judgment of the internal circuit, deterministically outputs the switch signal to the control loop of the device. Simply put, safety relays are all dual-channel signal types. The safety relay can work normally only when the signals of both channels are normal; during the working process, as long as the signal of any one of the channels is disconnected, the safety relay will stop outputting until both channels All channel signals are normal and can work normally only after reset.
1. Working principle of safety relay
1. Electromagnetic
electromagnetic relay is generally composed of iron core , coil , armature, contact reed, etc. As long as a certain voltage is applied to both ends of the coil, a certain current will flow through the coil, resulting in electromagnetic effect . The armature will overcome the pulling force of the return spring and attract to the iron core under the action of electromagnetic attraction, thus driving the The moving contact (normally open contact) and the static contact (normally closed contact) of the armature are attracted together. When the coil is powered off, the electromagnetic attraction also disappears, and the armature will return to its original position under the reaction force of the spring, releasing the moving contact from the original static contact. In this way, it is attracted and released to achieve the purpose of conducting and cutting off in the circuit. For the "normally open and normally closed" contacts of the relay, they can be distinguished as follows: The static contact in the disconnected state when the relay coil is not energized is called the "normally open contact"; the static contact in the connected state point is called a "normally closed contact".
2, thermal dry
reed thermal dry reed relay is a new type of thermal switch that uses thermal magnetic materials to detect and control temperature. It consists of a temperature-sensing magnetic ring, a constant magnetic ring, a reed switch, a thermally conductive mounting sheet, a plastic substrate and some other accessories. The thermal reed relay does not use coil to excite , but the magnetic force generated by the constant magnetic ring drives the switch action. Whether the constant magnetic ring can provide magnetic force to the reed switch is determined by the temperature control characteristics of the temperature-sensitive magnetic ring.
3, solid-state
solid-state relay is a four-terminal device with two terminals as input terminals and the other two terminals as output terminals. An isolation device is used in the middle to achieve electrical isolation of input and output.
2. Safety relay wiring diagram
The internal circuit principle of the safety relay:
The corresponding wiring diagram for the two applications of the safety relay As follows:
3. How to use safety relays
In our daily work, this type of relay is commonly found in electrical equipment control systems, especially in imported equipment from abroad. Especially when the equipment suddenly fails, the equipment cannot operate normally until the fault is eliminated or the fault is not confirmed. This prevents sudden operation of the equipment from causing danger to people or equipment after a malfunction.
We take the PNOZ V safety relay as an example. Its internal control circuit is as shown in the figure below:
The key points for using the safety relay are as follows:
How to connect the power supply. In the figure, A1 and A2 are power terminals. A1 is connected to 24V+; A2 is connected to 0V.
In the control input circuit, during normal use, the required switching conditions need to be connected between S11 and S12 and S11 and S22. Usually it is a contact or button contact.
In the reset circuit , corresponding reset conditions need to be connected between S33 and S34. At the same time, the conditions between Y1 and Y2 are also part of the reset circuit, and both conditions must be established at the same time.
So, how do they work?
A. If the safety relay needs to be closed (i.e. K1, K2, K4, K5 are energized), it is useless only if the input circuit is energized (i.e. terminals S12, S22 are energized). If you want K1, K2, K4, K5 is all closed. In addition to S12 and S22 having power, the conditions for K3 to be closed also need to be met.
B. If K3 is closed, the condition is that K1, K2, K4, and K5 are all de-energized, and the reset circuit is energized (that is, terminal Y2 is energized). That is, S33 to S34 are turned on, and Y1 and Y2 are also turned on at the same time.
2. Example: In the control circuit drawing of a certain equipment, the control loop has the following figure:
press the upper and lower diagrams to show the connection method: if the external emergency stop button is pressed and K11 loses power, then even after the external emergency stop switch is reset, the input circuit has power, but the control box 190SP1 must still be pressed After the fault confirmation button is pressed, the internal relay of K11 is closed and energized.
In summary, PNOZ safety relay can satisfy. When the emergency stop is released, the machine cannot restart suddenly (you must click on the fault confirmation, that is, reset the fault before power can be restored), so as to ensure personal and other safety.
