Product Overview

The Allen-Bradley 440R-S07139 Guardmaster CU2 Safety Relay is an industrial safety control device designed for monitoring machine motion and supporting safety-related stopping functions. Manufactured by Rockwell Automation, it belongs to the Guardmaster safety product family and is intended for applications where machine movement must be monitored as part of a defined safety control strategy.

Unlike a general-purpose control relay, the CU2 is designed for safety-related machine applications. It monitors connected sensing devices and controls its safety outputs according to the configured operating conditions. When the monitored condition indicates that the required safety state has not been achieved, the relay responds through its output circuits.

The 440R-S07139 operates with a 24 V AC/DC supply and supports automatic or manual reset. Its output arrangement includes two normally open safety outputs and one normally closed auxiliary output. The unit uses fixed terminals and is designed for DIN-35 rail mounting, making it suitable for installation in industrial electrical control cabinets.

The CU2 is associated with stop-motion monitoring applications. It can be used with appropriate motion-sensing devices to monitor whether a machine has reached the required stopped condition. This is particularly relevant where access to a hazardous area depends on confirming that dangerous movement has ceased.

The device’s documented safety performance includes Stop Category 1, Performance Level PL c, and SILCL 1 under the standards and editions identified in its technical documentation. These ratings should be interpreted within the context of the complete safety system, including sensors, wiring, logic, final switching devices, and validation.

The 440R-S07139 is a discontinued product. It remains relevant to maintenance teams responsible for existing machinery using the Guardmaster CU2 control unit. When sourcing a replacement, the complete catalog number and safety-system configuration should be checked carefully.

Technical Specifications

Note: Safety ratings and switching specifications must be interpreted according to the applicable product documentation and installation standards. The dimensions and weight are the supplied listing values.

Function and Working Principle

The 440R-S07139 is designed to monitor machine motion as part of a safety-related control arrangement. Its function is to evaluate signals from compatible motion-sensing devices and control its output contacts according to the detected machine condition.

1. Stop Motion Monitoring

In machinery with rotating or moving components, removing a motor command does not necessarily mean that the equipment has stopped. Motors, shafts, fans, and other mechanical assemblies may continue moving because of inertia.

A stop-motion monitoring system helps determine whether the monitored equipment has reached the required stopped condition. The CU2 control unit is designed for applications using appropriate proximity sensors to detect machine movement.

The sensor arrangement and wiring must follow the device’s intended application. Incorrect sensor selection or installation can prevent reliable motion monitoring.

2. Safety Output Control

The unit provides two normally open safety outputs and one normally closed auxiliary output. These contacts allow the CU2 to interact with external control circuits.

The safety outputs can be incorporated into an appropriately designed safety circuit, while the auxiliary output may provide additional status information to a machine-control system.

The actual safety function depends on the complete circuit design. The relay should not be treated as an independent guarantee of machine safety.

3. Automatic and Manual Reset

The 440R-S07139 supports automatic and manual reset arrangements.

In a manual-reset application, the system requires an appropriate reset action after the monitored condition has returned to the required state. This can help prevent unexpected machine restart after a safety-related event.

Automatic reset may be used where the machine risk assessment and safety design permit it. Reset behavior must be selected according to the application and applicable safety requirements.

4. Stop Category 1 Operation

The CU2 is documented for Stop Category 1 applications. This refers to a controlled stop in which power remains available during the stopping process and is removed after the machine has reached the required stopping condition.

This approach can be relevant to machinery that requires a controlled deceleration before power isolation. The stopping sequence must be engineered according to the machine’s hazards and risk assessment.

5. LED Status Indication

The relay includes LED indication to assist with checking operating status. During commissioning and maintenance, status indicators can help technicians identify whether the unit is powered and whether its operating conditions are satisfied.

LED indications should be interpreted using the applicable product instructions rather than relying on assumptions based only on indicator color.

Role in Industrial Control Systems

The 440R-S07139 can serve as part of a machine safety architecture, working alongside sensors, contactors, motor-control equipment, and PLC-based automation systems.

Machine Safety Monitoring

In applications involving rotating equipment, the CU2 can monitor signals from suitable proximity sensors. The monitoring arrangement is designed to establish whether the machine has reached the required stopped condition before a related safety action is permitted.

This function may be relevant to equipment with rotating shafts, mechanical drives, or other components that require monitored stopping.

Integration with PLC Systems

A PLC can coordinate normal machine operation, production sequencing, alarms, and process monitoring. The CU2 has a separate safety-related role within the machine’s control architecture.

Its auxiliary output may be used to communicate a status condition to a standard control system where appropriate. Safety functions, however, must be implemented through a properly designed and validated safety circuit.

A standard PLC input or software status bit should not automatically be considered a safety-rated replacement for the relay’s safety outputs.

Integration with Contactors

Safety outputs may be used in a circuit controlling suitable contactors or other final switching devices. These devices can disconnect or control power to machinery according to the safety design.

The contactor arrangement, feedback monitoring, and required fault response must be evaluated as part of the complete system.

Integration with Motion Sensors

The CU2 is intended for use with suitable motion-sensing devices. Its documented conversion guidance describes a sensor arrangement involving NPN and PNP proximity sensor outputs.

Sensor type is especially important when replacing the CU2 with another safety relay. A replacement with different input requirements may require changes to sensors, wiring, or the control architecture.

Industrial Applications

The Guardmaster CU2 is intended for machine safety applications involving motion monitoring and controlled stopping.

1. Rotating Machinery

Rotating machinery may continue moving after a stop command because of mechanical inertia. A stop-motion monitoring arrangement can help determine when the monitored component has reached the required stopped state.

Potential applications include rotating shafts, mechanical drives, and selected production machines.

2. Industrial Processing Equipment

Processing machinery may contain moving parts that require a verified stopping condition before maintenance or access operations can proceed.

The CU2 can be incorporated into a suitable safety circuit where its monitoring function matches the machine’s risk assessment and stopping sequence.

3. Conveyor and Material-Handling Equipment

Conveyor systems may include rollers, shafts, belts, and other moving components. In selected applications, motion monitoring can support controlled access or maintenance procedures.

The safety design must account for all relevant moving components, including sections that may continue moving after the main drive has been switched off.

4. Packaging Machinery

Packaging machines often combine motors, rotating mechanisms, feeding systems, and mechanical actuators. A monitored stopping arrangement can be useful where access to a hazardous area depends on confirming that movement has ceased.

The CU2 should only be selected when its sensor arrangement and safety performance are suitable for the specific machine.

5. Industrial Maintenance Systems

Maintenance teams may encounter the 440R-S07139 in older machinery where the original safety architecture was designed around the CU2 control unit.

For these installations, identifying the exact model and understanding the original sensor arrangement are important steps when repairing or replacing the safety device.

Installation and System Integration

Correct installation is essential because the 440R-S07139 is used in safety-related control applications.

1. Verify the Supply Voltage

The CU2 is designed for a 24 V AC/DC supply. Confirm the available supply voltage and polarity requirements before connecting the unit.

Use an appropriate industrial control power supply and ensure that the supply arrangement meets the requirements of the complete safety circuit.

2. Install on a DIN Rail

The unit is designed for DIN-35 rail mounting. Install it securely inside a suitable electrical enclosure and provide sufficient room for wiring, inspection, and maintenance.

The supplied dimensions are 120 × 45.5 × 73 mm. Confirm the physical dimensions and terminal access requirements before designing or modifying a control panel.

3. Connect Compatible Motion Sensors

The CU2 requires an appropriate sensor arrangement for its stop-motion monitoring function. Verify sensor output types, supply requirements, sensing distance, mechanical alignment, and wiring.

The manufacturer’s conversion documentation highlights an important distinction: the CU2 uses one NPN-output proximity sensor and one PNP-output proximity sensor in the documented arrangement. A replacement relay may require a different sensor configuration.

4. Wire the Safety Outputs

Connect the two normally open safety outputs and the normally closed auxiliary output according to the approved circuit diagram.

The output contacts must be used within their rated electrical limits. Confirm the connected load type, operating voltage, current, and switching category.

Do not use the auxiliary output as a substitute for a safety output unless the system design and applicable documentation explicitly permit the intended function.

5. Select the Reset Method

Choose automatic or manual reset according to the machine’s safety requirements.

Manual reset should be arranged so that the reset action does not itself initiate unexpected hazardous movement. The reset device should be positioned and implemented according to the machine risk assessment and relevant safety standards.

6. Validate the Safety Function

After installation, verify the sensor signals, relay response, output switching, reset behavior, and interaction with the final switching devices.

The complete safety function should be validated by qualified personnel. Testing should include relevant fault conditions and the expected response to loss of sensor signals or supply power.

Compatible System Components

The 440R-S07139 is generally used with components that form part of a machine safety and motion-monitoring arrangement.

The components listed are examples of equipment that may be used in a complete installation. They are not necessarily supplied with the 440R-S07139.

Alternative Models and Replacement Considerations

The 440R-S07139 Guardmaster CU2 is discontinued. Rockwell Automation’s migration documentation identifies the 440R-GL2S2P Guardmaster GLP safety relay as a functional replacement direction for the CU2.

However, a functional replacement is not necessarily a direct wiring replacement.

Before replacing the 440R-S07139, check:

• Whether the existing proximity sensors use NPN or PNP outputs.
• Whether the replacement accepts the existing sensor arrangement.
• Supply voltage and terminal requirements.
• Safety output configuration and contact ratings.
• Reset behavior and operating logic.
• Stop category and required safety performance.
• Available panel space and terminal layout.
• Required modifications to wiring and control logic.

The original CU2 arrangement uses different sensor output types for its two proximity sensor inputs. Rockwell’s migration documentation notes that the GLP replacement requires PNP outputs for both proximity sensors. Therefore, sensor compatibility must be addressed during a replacement project.

Key Advantages

Dedicated Motion Monitoring

The CU2 is designed for stop-motion monitoring applications rather than general-purpose switching. This makes it relevant to machinery where the stopped condition must be monitored.

24 V AC/DC Supply

The dual AC/DC supply specification provides flexibility for suitable industrial control power arrangements.

Automatic and Manual Reset

The available reset modes allow the safety system to be configured according to the application and risk assessment.

Two Normally Open Safety Outputs

The two safety outputs provide switching contacts for integration into an appropriately designed safety circuit.

Auxiliary Status Contact

The normally closed auxiliary output can support additional status signaling within the wider machine-control architecture.

DIN-Rail Installation

The DIN-35 mounting arrangement supports installation in standard industrial control cabinets.

Established Guardmaster Design

The product belongs to Rockwell Automation’s Guardmaster safety portfolio and may be found in legacy machinery that requires maintenance or spare-part replacement.

Technical FAQs

1. What is the Allen-Bradley 440R-S07139?

The 440R-S07139 is a Guardmaster CU2 Stop Motion Control Unit designed for monitoring machine movement as part of a safety-related control system.

2. What supply voltage does the 440R-S07139 require?

It operates with a 24 V AC/DC supply. Confirm the supply arrangement and wiring requirements before installation.

3. How many safety outputs does it provide?

The unit provides two normally open safety outputs and one normally closed auxiliary output.

4. Does the CU2 support automatic reset?

Yes. The 440R-S07139 supports automatic and manual reset. The appropriate reset method must be selected according to the machine’s safety design.

5. What is the function of the CU2?

Its primary function is stop-motion monitoring. It is designed to work with suitable proximity sensors to monitor whether the machine has reached the required stopped condition.

6. What safety performance ratings are associated with this model?

Its documented ratings include Stop Category 1, PL c, and SILCL 1 under the standards and editions referenced in its technical documentation. The achieved performance of an installed safety function depends on the complete system design and validation.

7. How is the 440R-S07139 mounted?

It is designed for DIN-35 rail mounting and uses fixed terminal blocks.

8. Is the 440R-S07139 still manufactured?

No. Rockwell Automation announced its discontinuation effective December 31, 2020. Buyers should verify the availability and condition of existing stock.

9. What is the recommended functional replacement?

Rockwell Automation’s CU2 migration documentation identifies the 440R-GL2S2P GLP safety relay as a functional replacement direction. Sensor output compatibility and wiring changes must be reviewed before substitution.

10. Can the 440R-S07139 be replaced without changing the sensors?

Not necessarily. The documented CU2 arrangement uses one NPN-output and one PNP-output proximity sensor, while the identified GLP replacement requires PNP outputs for both sensors. The existing sensor arrangement must be checked before replacement.

Procurement and Maintenance Recommendations

The 440R-S07139 is a discontinued safety control device, so procurement should begin with verification of the complete catalog number and the condition of the available unit.

For existing machinery, compare the replacement with the original device’s supply voltage, output arrangement, reset method, sensor requirements, and safety function. Confirm whether the unit is new surplus, refurbished, or used, and request clear photographs of the product label and terminals.

Because the device is part of a safety-related system, a replacement should not be treated as a simple component swap. Review the machine’s electrical drawings, risk assessment, safety logic, and validation requirements before making changes.

During maintenance, inspect the terminal connections, sensor wiring, DIN-rail mounting, enclosure condition, and supply voltage. Test the motion-monitoring function and reset behavior according to the approved maintenance procedure.

Any modification to the safety circuit should be performed and validated by qualified personnel. Do not bypass safety inputs or force relay outputs to restore production without resolving the underlying fault.

Conclusion

The Allen-Bradley 440R-S07139 Guardmaster CU2 Safety Relay is a 24 V AC/DC stop-motion monitoring control unit designed for industrial machine safety applications. It provides two normally open safety outputs, one normally closed auxiliary output, automatic or manual reset, and DIN-35 rail mounting.

Its role in a safety system is to monitor machine motion through a compatible sensor arrangement and control outputs according to the required operating conditions. Since the model was discontinued in 2020, maintenance teams should verify product condition and carefully assess functional replacement options.

For existing installations, the most important considerations are sensor compatibility, output configuration, reset behavior, and validation of the complete safety function.