K1 and K2 on a safety relay represent the two internal output relays that work together to ensure safe and reliable machine shutdown. These relays are part of a dual-channel system designed for redundancy, meaning both channels (K1 and K2) must operate correctly for the safety relay to allow the machine to run. When a safety device such as an emergency stop button, safety gate, or light curtain is activated, both K1 and K2 open their contacts to cut off power to the machine actuators. This immediate disconnection stops the machinery safely and prevents it from restarting until the safety condition is cleared. The dual-relay design ensures that even if one contact fails or gets welded shut, the other relay still functions to stop the system, maintaining a fail-safe condition.
The safety relay continuously monitors the state of both K1 and K2 during operation. If it detects a mismatch — for example, K1 is closed while K2 remains open — it recognizes this as a fault and prevents the system from restarting. This mechanism helps identify problems like contact failure, wiring faults, or welded contacts early, reducing the risk of unsafe operation. In simple terms, K1 and K2 provide redundancy and fault detection, which are key principles of industrial safety circuits. This dual-channel setup ensures that any single fault won’t compromise the entire safety function. You’ll find K1 and K2 used in most safety relays, including popular models like Pilz PNOZ, Siemens 3TK, or Omron G9SA. In summary, K1 and K2 are the core safety outputs of a safety relay, working in synchronization to achieve reliable machine shutdown, continuous monitoring, and high fault tolerance in safety-critical automation systems.