What is the working principle of safety relay?

This article describes how the safety relay works:

The working principle of safety relays is generally composed of iron core, coil, armature, and contact spring. As long as a certain voltage is applied to both ends of the coil, a certain current flows in the coil, thereby generating an electromagnetic effect, and the armature will absorb the pulling force of the return spring against the iron core under the action of the electromagnetic force attraction, thereby driving the armature. The moving contact is in contact with the stationary contact (normally open contact). When the coil is de-energized, the electromagnetic suction force also disappears, and the armature returns to the original position in the reaction force of the spring, so that the movable contact and the original static contact (normally closed contact) are attracted. In this way, the suction and release are achieved, thereby achieving the purpose of turning on and off in the circuit. For the "normally open, normally closed" contacts of the relay, it can be distinguished as follows: a static contact that is in an open state when the relay coil is not energized, called a "normally open contact"; a static contact that is in an on state It is a "normally closed contact".

Pilz safety relays have two main functions: one is isolation; the other is to add auxiliary contacts. In practical applications, there are fewer contacts, because the current contactor can add a lot of auxiliary contacts, and the action is also reliable, so it is not necessary to add auxiliary relays in the general control day. The isolation function is used more in the current control. The author thinks that there are two main aspects of isolation: one is to divide one control loop into two or more relatively independent loops; the other is to convert the analog signal of strong power into the switching source or passive through the intermediate relay) . What is emphasized here is not the role of these relays, but through the engineering examples, the technical problems in the application of intermediate relays are analyzed and the countermeasures are proposed.

Pilz safety relay works: The Peltz safety relay works by turning an input signal into one or more output signals. Its input signal is the energization or de-energization of the coil. Its output is the action of the contact (with the normally open point closed, the normally closed point is open), its contact is connected in other control loops, and the control loop changes (such as turn on or off) through the change of the contact. To achieve the purpose of established control or protection. In this process, the relay mainly plays the role of transmitting signals.

The working principle of the safety relay is a control device that realizes the delay control by using the electromagnetic principle or the mechanical principle. It has many types, including air damping type, electric type and electronic type.

Air-damped time relays are often used in AC circuits, which use the principle of air throttling through small holes to obtain delayed action. It consists of three parts: the electromagnetic system, the delay mechanism and the contacts.

The time relay can be divided into two types: power-on delay type and power-off delay type.

The air damping type time relay has a large delay range (both 0.4 to 60 s and 0.4 to 180 s), and has a simple structure but low accuracy. When the coil is energized (voltage specifications are ac380v, ac220v or dc220v, dc24v, etc.), the armature and the pallet are attracted by the core and instantaneously moved down, so that the instantaneous action contact is turned on or off. However, the piston rod and the lever cannot fall together with the armature because the upper end of the piston rod is connected to the rubber film in the air chamber. When the piston rod starts to move downward under the action of the release spring, the rubber film is then concave downward. The air in the air chamber becomes thin and the piston rod is dampened and slowly descends. After a certain period of time, the piston rod is lowered to a certain position, and the delay contact is actuated by the lever, so that the breaking contact is opened and the moving contact is closed. From the energization of the coil to the completion of the delay contact, this time is the delay time of the relay. The length of the delay time can be changed by adjusting the size of the air inlet of the air chamber with a screw.

After the attracting coil is de-energized, the relay is restored by the action of the return spring. Air is quickly expelled through the vent.

The relay is an automatic switching element with isolation function. It is widely used in remote control, telemetry, communication, automatic control, mechatronics and power electronics. It is one of the most important control components.

Relays generally have an inductive mechanism (input section) that reflects certain input variables (such as current, voltage, power, impedance, frequency, temperature, pressure, speed, light, etc.); it has the ability to "pass" and "control" the controlled circuit. The actuator (output portion) of the control unit is disconnected; between the input portion and the output portion of the relay, there is also an intermediate mechanism (drive portion) that couples the input amount, functions, and drives the output portion.