Presence-sensing Devices

Presence-sensing devices are triggered when a worker's body part or another object enters a certain field near the hazardous machine parts. Distance from the device to the machine varies based on two factors: how long the machine takes to shut down and how long it takes for an object to travel from the edge of the field to the danger zone. There are three main types of presence-sensing devices:

• Photoelectric (optical) devices use a beam of light that, when interrupted or blocked, shuts down the machine.
• Radiofrequency (capacitance) devices use the same concept as photoelectric devices, but with radio waves instead of light waves.
• Electromechanical devices have an arm that must extend to a certain length or distance for the machine to operate. This ensures that only the correct materials are being used in the machine, as incorrect materials would not possess the same dimensions.

Advantages and Disadvantages of Presence-sensing Devices

Presence-sensing devices (photoelectric, radiofrequency, and electromechanical) are effective because they stop the machine before the object or body part reaches the hazardous parts. They also allow the operator to move more comfortably in the workspace, rather than being tethered to a fixed object. However, one disadvantage is that proper maintenance is required for these devices, and if the machine malfunctions, the device could potentially be overridden.

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