How Sensing Edges Work

All electrically activated edges operate on the same basic principle referred to as a Normally Open (N.O.) electrical configuration:

1. Miller Edge sensing edge exteriors are typically made of flexible PVC or vinyl and contain conductive elements separated by a gap. These elements run throughout the length of the edge.
2. When an object or person comes into contact with a sensing edge, the flexible exterior compresses and the internal conductive elements come into contact with each other. This contact completes an electrical circuit.
3. When the circuit is completed, it generates an electrical signal. This signal is then transmitted to the control system or motor of the door, gate, or machinery.
4. The control system receives the signal and responds by immediately stopping or reversing the movement of the door, gate, or equipment.

UL 325 Compliance

Effective August 31, 2010, the UL 325 safety standard requires motorized doors installed with momentary contact on the down control to require the installation of a monitored reversing device.

With a monitored device, the motor controls are able to check for the presence and operation of the reversing system.

A 2-wire monitored sensing includes a termination resistor or diode capacitor at the end of the sensing edge. This monitored configuration can be specified at the time of order based on the requirements of the operator. Monitored sensing edges offer an additional layer of safety by providing feedback to the control system about their operational status. This continuous monitoring ensures that the sensing edge is functioning correctly, reducing the risk of false positives or negatives due to edge damage or wear.

Advantages:

• Simplicity: 2-wire non-monitored sensing edges are straightforward and easy to connect to operator controls.
• Monitored Safety: They provide a monitored safety function, continuously checking the circuit for faults or failures. The termination resistors at the end of the edge helps ensure proper operation and signal integrity.

Limitations

• Compatibility: Monitoring methods vary by operator brand. It’s essential to ensure that sensing edge monitoring method is in alignment is alignment with the operator. It’s crucial to verify that the selected monitoring method aligns with your operator. To confirm the edge’s monitoring method matches the operator, consult the operator manufacturer’s manual. For your convenience Miller Edge provides the termination resistor or diode capacitor required by most operator brands.

In summary, 2-wire monitored sensing edges offer a balance between simplified installation and monitored safety. However, monitoring compatibility considerations are important when selecting them for a specific application.

A 4-wire fail-safe sensing edge consists of four wires and is designed to ensure a fail-safe operation, meaning it’s engineered to detect and respond to faults or failures in a way that prioritizes safety. Here are the pros and cons of 4-wire fail-safe sensing edges:

Advantages:

• Enhanced Safety: The primary advantage of a 4-wire fail-safe sensing edge is its ability to detect faults, such as wire breaks or sensor failures, and respond by opening the circuit to stop motion. This ensures that even if there is a problem with the sensing edge, the door or gate will not pose a safety risk.
• Reliability: These sensing edges are known for their reliability. The fail-safe design reduces the likelihood of false readings or malfunctions that could compromise safety.
• Compliance: Many safety regulations and standards, including UL 325, require the use of fail-safe devices in certain applications. Using a 4-wire fail-safe sensing edge helps ensure compliance with these regulations.

Limitations:

• Complexity: Compared to simpler sensing edge designs, 4-wire fail-safe sensing edges can be slightly more complex to install. They require careful wiring and configuration to ensure proper operation.

In summary, 4-wire fail-safe sensing edges are designed with a strong emphasis on safety and reliability, making them suitable for applications where safety is of utmost importance, such as industrial and commercial settings. However, their complexity and cost should be considered when selecting them for a specific project, and proper installation and maintenance are essential to ensure their effectiveness.

Unlike monitored sensing edges, non-monitored sensing edges do not have a feedback mechanism that continuously checks their status or functionality.

Advantages:

• Simplicity: 2-wire non-monitored sensing edges are straightforward and easy to connect to operator controls.
• Reliability: They are generally reliable in detecting obstructions and initiating safety measures, which helps prevent accidents and damage.

Limitations:

• Limited Diagnostic Capability: One of the main drawbacks of non-monitored sensing edges is their lack of diagnostic capability. They cannot provide real-time feedback on their condition or functionality. If a non-monitored sensing edge becomes damaged or fails, there may be no immediate way to know.
• Potential for Unnoticed Failures: Since there is no continuous monitoring, a non-monitored sensing edge may become damaged or malfunction without anyone noticing until an accident occurs or it’s manually inspected.
• Reduced Safety: In situations where the sensing edge may be subject to wear and tear, exposure to harsh conditions, or potential damage, relying solely on a non-monitored sensing edge may not provide the same level of safety assurance as a monitored system.
• Compliance Issues: 2-wire non-monitored sensing edges are not compatible with the current UL 325 safety standard as a primary entrapment device on motorized industrial/commercial doors and automated vehicular gates.