Safety mats are used to guard a floor area around a machine or robot. A matrix of interlocking safety mats is laid around the hazardous area and any pressure (e.g. an operator's footstep) will cause the controller unit to send a stop signal to the guarded machine.  Mats are also used to protect a point of entry. A 4-wire safety mat operates on a low-power DC or AC signal (depending on the controller). Signal is transmitted through the upper and lower plates separately via the two wires connected to each plate. A controller monitors the signals. Signals are unimpaired when no pressure is applied to surface of the mat. The output relays in the controller are energized permitting the guarded machine to run. When sufficient pressure is applied to the mat, the conductive plates touch causing the output relays in the controller to de-energize and a stop signal is sent to the machine

 

The active safety area of an electrical safety mat is determined by its length and width.  Important performance parameters to consider when specifying a safety mat include minimum actuation force and maximum mechanical life.  The minimum actuation force is the minimum force that must be applied to activate the pressure sensing mat.  The maximum mechanical life is the maximum number of mechanical activations before the reliability of the safety mat comes into question.

 

Safety Mat Switch Configurations

A safety mat can have one of several switch pole and throw specifications.  Single pole, single throw (SPST) is a switch that makes or breaks the connection of a single conductor in a single branch circuit. This switch typically has two terminals. It is commonly referred to as a "Single-Pole" Switch.  Single pole, double throw (SPDT) is a switch that makes or breaks the connection of a single conductor with either of two other single conductors. This switch typically has 3 terminals, and is commonly used in pairs and called a "Three-Way" switch.  A double pole, single throw (DPST) is a switch that makes or breaks the connection of two circuit conductors in a single branch circuit. This switch typically has four terminals.  A double pole, double throw (DPDT) is a switch that makes or breaks the connection of two conductors to two separate circuits. This switch typically has six terminals and is available in both momentary and maintained contact versions.  Special throw types with more than 2 poles, such as switches designed to split loads into separate circuits (e.g., headlamp switch) are also available.

 

Safety mats can have a switch configuration that is normally open or normally closed.  A normally open switch is a switch that when no power is applied the contacts are open.  A normally closed switch is a switch that when no power is applied the contacts are closed.   Common electrical switch specifications include maximum current, maximum AC voltage, maximum DC voltage and maximum power.

 

Safety Mat Categories

 

Safety mats may come with an external controller that is included with the mat.  Multi-tasking controllers are capable of monitoring and controlling more than one safety mat at a time.  Safety mats can have one of three safety category types assigned.  Type 2 safety mats require that the safety function shall be checked at machine start up and periodically by the machine control system. If a fault is detected, safe status shall be initiated or if that is not possible, a warning shall be given. The occurrence of a fault between checking functions can lead to a loss of the safety function between checking intervals.  Type 3 safety mats provide that a single fault in any of the system parts does not lead to a loss of the safety function. Some but not all faults will be detected. An accumulation of undetected faults can lead to a loss of the safety function.  Type 4 specifications state that a single fault does not lead to a loss of the safety function. The faults will be detected in time to prevent the loss of the safety function.

 

Safety mats can have special surface features.  These include chemical or moisture resistant surface and an impact resistant surface.  Non skid safety mats are also available. Commonly safety mats will be either UL or CE certified.


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