Pilz 774340 PNOZ X Safety Relay for Two-Hand Monitoring

The Pilz 774340 is a safety relay from the PNOZ X product range, designed for two-hand monitoring applications conforming to Type III C requirements per EN 574. This safety relay ensures that an operator must actuate both pushbuttons of a two-hand control device within a specified time window to initiate a hazardous machine motion, thereby requiring both hands to be occupied during the hazardous portion of the machine cycle. The two-hand monitoring function is widely used in press control, punch press operations, assembly station safeguarding, and any machinery where operator hand placement must be restricted during operation.

Safety Relay Functionality and Two-Hand Monitoring

The 774340 safety relay monitors two separate input pushbuttons that must be actuated simultaneously for the safety outputs to energize. The relay implements Type III C operation according to EN 574, which requires that both pushbuttons must be pressed within 500 milliseconds of each other for the outputs to close. If one pushbutton is pressed before the other, the outputs remain de-energized until both pushbuttons are released and then pressed again within the time window. This requirement prevents operators from defeating the two-hand function by holding one pushbutton closed while using the other hand for other actions. The relay also monitors the external wiring for cross-shorts between the two input channels, detecting and preventing faults that could bypass the safety function.

Output Contact Configuration

The 774340 safety relay provides three normally open (N/O) safety output contacts and one normally closed (N/C) auxiliary output contact. The three N/O contacts are used to control the power circuit of the hazardous machine, typically connected in series with the main contactor or safety contactor coils. When the two-hand inputs are satisfied and the relay energizes, the N/O safety contacts close, allowing the contactors to pull in. The N/C auxiliary contact provides a signal output for status indication to a PLC or control system, indicating whether the relay is energized or de-energized. The contact ratings are suitable for switching AC and DC control circuits.

Feedback Control Loop for External Device Monitoring

The relay includes a feedback control loop (EDM) for monitoring external contactors or relays controlled by the safety outputs. The feedback loop input expects a closed circuit condition when the external contactors are de-energized and opened when the contactors are energized. If the feedback loop does not change state correctly within the expected time after the safety outputs are de-energized, the relay detects a fault and locks out, preventing restart until the fault is cleared. This EDM feature ensures that welded contacts on external contactors cannot go undetected, maintaining the integrity of the safety circuit even if a contactor fails.

Supply Voltage and Power Requirements

The 774340 operates on a wide-range power supply accepting both 24 V AC and 24 V DC input, providing flexibility for different control system voltages. The relay includes power supply monitoring to detect undervoltage conditions that could affect correct operation. The power consumption is moderate, allowing the relay to be powered from the same 24 V supply used for other control devices. The power supply inputs are protected against reverse polarity and transient overvoltages.

LED Status Indication

The front panel of the 774340 includes LED indicators for power status and input channel status. The POWER LED illuminates when the proper supply voltage is applied and the internal circuits are energized. Channel 1 and Channel 2 LEDs indicate the state of the two input pushbuttons, lighting when the pushbutton connected to that channel is pressed. These LEDs assist in troubleshooting by immediately showing whether the relay is seeing each input correctly. If the safety outputs are de-energized and the channel LEDs indicate both pushbuttons are pressed, the likely cause is a timing violation or a feedback loop fault.

DIN Rail Mounting and Connection

The 774340 mounts on a standard 35 mm DIN rail, making installation simple in control cabinets already equipped with DIN rails. The housing width is optimized for rail mounting, allowing multiple safety relays and other control components to be placed side-by-side. Connections to the relay are made via screw terminals on the front of the unit, which accept standard industrial wiring sizes. The terminals are clearly labeled for power supply, input connections, feedback loop connections, and safety output contacts. The relay housing is constructed from insulating material with appropriate creepage and clearance distances for industrial voltages.

Safety Certifications and Performance Levels

The Pilz 774340 is certified to multiple safety standards, achieving high safety integrity levels. The safety relay meets EN 954-1 Safety Category 4, prEN ISO 13849-1 Performance Level e, and IEC 62061 Safety Integrity Level SIL CL 3. These certifications indicate that the relay is suitable for use in safety-related control systems where failure could result in serious injury or fatality. The relay is tested and approved by recognized certification bodies, including BG (Berufsgenossenschaft) and other notified bodies. The device carries CE marking for the European market.

Compliance with Two-Hand Control Standards

The 774340 two-hand monitor complies with EN 574 Safety of machinery - Two-hand control devices, and specifically meets the requirements for Type III C two-hand controls. Type III C requires that the two control actuators must be pressed within 500 milliseconds of each other for the safety outputs to close. The relay also satisfies the requirement that the two-hand control function must be designed such that the two actuators cannot be operated using only one hand or one arm. The relay inputs accept signals from standard industrial pushbuttons with normally open contacts, which must be installed such that they cannot be mechanically or electrically defeated.

Typical Applications and Integration

The 774340 is used in applications requiring the operator's hands to be occupied during hazardous machine motion. Typical examples include press brake operation, where the operator must hold both pushbuttons during the bending stroke; punch press controls, where the punching cycle requires both hands to be on the actuation buttons; riveting and staking machines, where the stroke must be initiated only when hands are safely away from the tooling; and assembly stations with closing or clamping motions. The safety outputs of the 774340 typically control the main contactor or safety contactor of the machine, interrupting power to the hazardous motion when the two-hand conditions are not satisfied.