Hello everyone. I am Rose. Today I will introduce safety relay to you. The so-called "safety relay" is a combination of numerous relays and circuits that complement each other's abnormal defects in order to create accurate and low malfunction relay complete performance, with the lower the error and failure value, the higher the safety factor.

Ⅰ. What is safety relay?

1. Definition

The so-called "safety relay" is a combination of numerous relays and circuits that complement each other's abnormal defects in order to create accurate and low malfunction relay complete performance, with the lower the error and failure value, the higher the safety factor. The "safety relay" becomes a "faultless relay" as the height increases, rather than a regular action when a failure occurs. It has a contact structure that is forced-oriented, ensuring safety in the event of contact fusion. It differs significantly from standard relays. Figure 1 illustrates this.

In a safety circuit, a safety relay is an essential control component. It accepts safety inputs and, based on the internal circuit's judgment, outputs a switch signal deterministically to the device's control circuit. Safety relays are all dual-channel signal types, to put it simply. The safety relay can only work normally when both channels' signals are normal; during the working process, if any of the channels' signals is disconnected, the safety relay will stop outputting. All of the channels' signals are normal, and they can function correctly after being reset.

2. Requirement

(1). The machine cannot resume abruptly after the emergency stop is released.

(2). In the event that the machine's safety circuit fails, the machine's power supply can be turned off.

(3). The machine cannot be restarted if the safety circuit fails.

Dualization by itself will not suffice.

Duplication is required, but it must also meet certain conditions, such as mutual inspection of the duplex circuit, confirmation that all safety circuits have been severed once, and the operator's ability to initiate the operation if necessary. In addition, when the input switch wiring is short-circuited or the wire sheath is damaged and grounding is conceivable, it is important to prevent the machine from starting unexpectedly.

In fact, the safety relay is integrated with other components to simplify the design of the safety circuit, and the basic emergency stop circuit and the safety circuit constitute the circuit module known as the safety relay module.

3. Usage

It's utilized in the construction of a safety circuit with input to confirm the machine's safety, and then it's used to control the input of the contactor, etc.

Ⅱ. How does safety relay works?

1. Electromagnetic

Iron cores, coils, armatures, contact reeds, and other components make up electromagnetic relays. A particular current will flow through the coil as long as a certain voltage is given to both ends of the coil, resulting in electromagnetic phenomena. The armature will overcome the return spring's draw force and attract to the core, thus driving the armature, thanks to electromagnetic force. The moving contact (usually open contact) is brought together with the static contact (typically closed contact). The electromagnetic attraction will vanish when the coil is de-energized, and the armature will return to its original position under the reaction force of the spring, releasing the moving contact and the original static contact. This pulls in and releases to meet the circuit's goal of conducting and switching off. The relay contacts that are "usually open" and "typically closed" can be identified as follows: The "normally open contact" is the static contact that is in the off state when the relay coil is not activated; the "normally closed contact" is the static contact that is in the on state when the relay coil is energized. It's what's known as a "typically closed contact."

2. Thermal dry

Reed Thermal Reed Relay is a novel type of thermal switch that detects and controls temperature using thermal magnetic materials. A temperature-sensitive magnetic ring, a constant magnetic ring, a dry reed tube, a thermally conductive mounting sheet, a plastic substrate, and various other components make up the device. The magnetic force generated by the constant magnetic ring powers the switching action of the thermal reed relay, rather than coil excitation. The temperature control properties of the temperature-sensitive magnetic ring decide whether the constant magnetic ring can give magnetic force to the reed tube.

3. Solid state

A solid-state relay has four terminals, two of which are used as input terminals and the other two as output terminals. To provide electrical isolation between the input and output, an isolation device is utilized in the middle.

Ⅲ. Safety relay wiring diagram

The safety relay's internal circuit is as follows:

The following are the wiring schematics for the two applications of safety relays:

Ⅳ. How to use safety relay？

Such relays are widely found in electrical equipment control systems in our daily work, particularly imported equipment from other countries. The equipment cannot operate normally until the failure is eliminated or the failure is not confirmed, which is especially true when the equipment fails suddenly. This is to avoid the device's sudden activity from endangering the person or the equipment when it fails.

As an example, consider the PNOZ V safety relay. The internal control circuit of the device is depicted in the diagram below:

The following are the main features of the safety relay:

What is the best way to connect the power supply? A1 and A2 are power terminals in the diagram; A1 is linked to 24V+, while A2 is connected to 0V.

During normal operation, the requisite switching conditions between S11 and S12 and S11 and S22 must be connected in the control input circuit. It's usually a contact or a button contact.

A matching reset condition must be connected between S33 and S34 in the reset circuit. The condition between Y1 and Y2 is also part of the reset circuit, and both conditions must be established simultaneously.

So how do they work

A. It is pointless to ensure that the input circuit is energized if the safety relay needs to be closed (that is, K1, K2, K4, and K5) (that is, terminals S12 and S22 are energized). It must also meet the standards for K3 to close, in addition to S12 and S22 with electricity.

B. K1, K2, K4, and K5 are all de-activated, and the reset circuit is energized, if K3 is satisfied to be closed (that is, the terminal Y2 is energized). That is, S33 to S34 are both switched on at the same time, as are Y1 and Y2.

2. Example: The control loop is shown in the control circuit drawing of a certain piece of equipment as follows:

Connect the upper and lower diagrams as follows: The input circuit is already energized if the external emergency stop button is pressed and the K11 loses power, even if the external emergency stop switch is reset, however the fault confirmation button on the control box 190SP1 must be pressed. The internal relay on the K11 will then be activated.

In conclusion, the PNOZ safety relay is capable of meeting the requirements. To safeguard personal and other safety, when the emergency stop is released, the machine cannot resume abruptly (you must click on the fault confirmation, that is, the fault reset can be re-powered).