Pressure Sensitive Mats
Pressure-Sensitive Mat Relays for Presence-Detection Safety Systems
A pressure-sensitive mat relay is the monitoring and control component that makes a safety mat installation functional as a safety system. Within Galco's safety relays category, pressure-sensitive mat relays serve a distinct function from e-stop relays and other safety relay types, though some configurable safety relays can handle multiple input device types including mats, e-stops, and light curtains in a single unit. The mat itself, as defined by ISO 13856-1, is a presence-sensing device with internal pressure switches that open or close when personnel step onto the active area. The mat alone cannot meet the fault-detection, redundancy, and circuit-integrity requirements for a safety-rated system. The relay monitors the mat's output channels, detects wiring faults including open circuits and short circuits, provides dual-channel redundancy, and controls the safety output that commands the machine to a safe state when presence is detected, or a fault occurs.
Selection of a pressure-sensitive mat relay starts with the required Performance Level (PL) or Safety Integrity Level (SIL) for the safety function, which is determined by a formal risk assessment of the machine and application, not by the relay specification alone. The relay's certified PL or SIL rating, combined with the mat's own rating and the architecture of the overall safety system, determines what the complete safety function can achieve. Most dedicated mat monitoring relays support dual-channel input connections, which are required to achieve higher safety category ratings under ISO 13849-1. The number of mat zones the relay can monitor is also a selection parameter: some relays monitor a single mat or a mat array as a single zone, while others support multiple independently monitored zones, allowing different machine areas to be covered with zone-specific outputs. The relay's output configuration, typically safety-rated relay contacts or solid-state outputs, must be matched to the machine's safety stop circuit, including the number of output contacts needed to control contactors or drives.
Reset behavior is a safety-critical design decision that must be determined by the risk assessment rather than defaulted to convenience. Manual reset requires an operator to deliberately actuate a reset input after the mat is cleared before the machine can restart, preventing automatic restart in situations where personnel may still be present or in the hazard zone. Automatic reset allows the machine to restart as soon as the mat is cleared, which is permissible only when the risk assessment confirms that no hazard exists from automatic restart in that specific application. Selecting automatic reset where the risk assessment requires manual reset compromises the safety function regardless of the relay's rated PL or SIL. For applications requiring multiple safety device types across a machine, Galco's configurable safety relays can combine mat monitoring with e-stop, muting, and two-hand operation functions within a single safety system architecture, with contact expansion relays available where additional output contacts are needed.
Frequently Asked Questions
Why does a safety mat need a dedicated safety relay rather than a standard relay or PLC input?
A standard relay or PLC digital input accepts the mat's signal and acts on it, but provides no fault monitoring of the mat's wiring or internal switches. A wiring fault, such as a short circuit across the mat's output contacts, could prevent the mat from generating a stop signal when stepped on, with no indication that the protection is compromised. A dedicated safety relay actively monitors both channels of the mat connection for open circuits, short circuits, and cross-faults, and holds the safety output in the off state if a fault is detected, preventing the machine from continuing to operate unprotected. This fault-detection capability enables the mat relay system to meet the circuit integrity requirements of ISO 13849-1 and IEC 62061 for higher safety category ratings.
What is the difference between a single-zone and a multi-zone mat relay?
A single-zone relay treats all connected mats as one monitored area, producing a single safety output that de-energizes when presence is detected anywhere in the zone. A multi-zone relay monitors separate mat areas independently, with individual outputs for each zone, allowing different machine motions or hazardous areas to be controlled selectively based on which zone detects presence. Multi-zone configurations are common around robotic cells or machinery with multiple hazardous areas, where stopping the entire machine when only one zone is entered would unnecessarily reduce productivity. The zone boundaries and the safety outputs assigned to each zone must be defined by the machine's risk assessment, not by the relay's capability alone.
Can a pressure-sensitive mat relay be used in combination with other safety devices on the same machine?
Yes, and this is common in practice. Safety mats typically cover floor-level access zones but cannot protect elevated entry points, and are often used alongside light curtains, interlocked guards, or e-stops to cover the full perimeter of a hazardous area. When combining multiple safety device types, each device's output must be appropriately monitored and logically combined so that any single device detecting a hazardous condition produces the required machine stop. Configurable safety relays simplify this by accepting multiple device types on separate inputs with configurable logic, while dedicated mat relays can be cascaded with other safety relay types using single-wire safety connections where the relay family supports it. The overall system PL or SIL achieved depends on the weakest link in the combined architecture, which requires evaluation at the system level rather than per device.