How to Use Pilz Safety Relays?(Includes Wiring Diagram)
A robust control system must first and foremost be a secure system—capable of ensuring the safety of individuals and equipment in the event of system failures or emergency shutdowns. When it comes to safety automation systems, the mention of Germany's Pilz company is inevitable. Pilz has been deeply rooted in the field of safety automation for decades, offering a range of safety products, including safety PLCs, safety switches, and safety relays.
Notably, Pilz pioneered the development of the first safety relay (PNOZ) for emergency stops, gaining widespread recognition worldwide. Since then, PNOZ has become synonymous with safety relays. Today, Pilz offers a variety of PNOZ safety relay series, such as PNOZsigma, PNOZ X, PNOZcompact, PNOZelog, each with different models. In this article, we will take PNOZ X3 as an example to discuss the usage of safety relays for emergency stop buttons.
The appearance of PNOZ X3 is depicted in the image below:
PNOZ X3 features three sets of safety contacts, namely 13-14, 23-24, and 33-34, all of which are normally open contacts and can be used for safety circuits. There is also one auxiliary contact, specifically 41-42, which is a normally closed contact. The auxiliary contact cannot be used for safety circuits. Additionally, PNOZ X3 includes one transistor output contact: Y31-Y32.
PNOZ X3 has ten safety circuit terminal connections, all designated with an "S" (Safe) prefix, including S11, S12, S13, S14, S21, S22, S31, S32, S33, and S34. Among these, S11 and S13 are internally connected to the positive pole of the power supply, while S21 is internally connected to the negative pole of the power supply. The S terminals internally connect two safety channels (CH1 and CH2) and a start/reset channel (Start Unit). The diagram below illustrates the internal wiring diagram of PNOZ X3:
PNOZ X3 can be powered by either 230V AC or 24V DC. When connecting to 230V AC, A1 is connected to L1, A2 is connected to N, and B2 is connected to ground. In the case of a 24V DC connection, B1 is connected to the positive pole (+24V), and B2 is connected to the negative pole. The diagram below illustrates the connections:
PNOZ X3 has three LED indicator lights on the front, representing Power (POWER), Channel 1 (CH.1), and Channel 2 (CH.2). When the power is on, the Power (POWER) LED is illuminated in green. When the power is on, and the safety channel S13-S14 is in a closed loop, PNOZ X3 is ready for operation.
In this state, if both Channel 1 (CH1) and Channel 2 (CH2) are in closed loops (for example, if safety devices are functioning properly), the safety normally open contacts 13-14, 23-24, and 33-34 are closed, and the auxiliary normally closed contacts 41-42 are open. Both channel LED lights are illuminated in green, and the transistor output Y31-Y32 is closed.
However, if either Channel 1 (CH1) or Channel 2 (CH2) is open (for example, if an emergency stop button is pressed), the safety normally open contacts 13-14, 23-24, and 33-34 are open, and the auxiliary normally closed contacts 41-42 are closed. Both channel LED lights are extinguished, and the transistor output Y31-Y32 is open.
Now, let's take a look at how PNOZ X3 is connected to an emergency stop button:
When using a single-channel emergency stop button, connect S21-S22, connect S32-S31, and then connect the normally closed contacts of the emergency stop button between S12-S11.
When using a dual-channel emergency stop button, connect S11-S12, and connect the two normally closed contacts of the emergency stop button to S21-S22 and S31-S32, respectively.
When the safety relay is powered on or the emergency stop button is restored, a signal needs to be given to the Start Unit of PNOZ X3 to activate it. PNOZ X3 can be started in two ways: Automatic Start and Monitored Start.
Automatic Start involves connecting S13-S14 in a closed loop. In this scenario, when both safety channels (CH1 and CH2) close again (e.g., after the emergency stop button is restored), the safety relay will automatically return to the operational state.
Monitored Start, also known as Manual Start or Controlled Start, involves connecting S33-S34 in a circuit with a normally open contact. In this case, even if both safety channels (CH1 and CH2) close again (e.g., after the emergency stop button is restored), the safety relay will not automatically return to the operational state. It must be manually closed (represented by S3 in the diagram) for a period of time (typical value 35ms), and then the safety relay will resume its operational state.
The wiring diagrams for Automatic Start and Monitored Start are as follows:
When PNOZ X3 is in the Active state, Y31-Y32 is closed. You can use the following wiring diagram to transmit the status of the safety relay to the PLC:
The discussion on the internal principles and relevant wiring diagrams of PNOZ X3 will conclude at this point.