Safety Sensors

Safety sensors and switches are used to construct a safety-related control system that ensures operators are protected from mechanical hazards in the workplace. Safety interlock switches, cable pull switches and limit switches are three common devices used to provide operators with emergency stop functions, as well as automatic safety assurance.

Safety interlock switches are used on guards and covers that are installed around machinery to protect operators. Some covers and guards are fixed into place, while others can be opened and closed. Dangerous machinery should stop when a guard is opened or removed. To ensure that this happens, installing an interlock switch will actively interlock the guard so that it cannot be opened when the machine is in operation. This is accomplished when the door monitoring portion of the interlock switch senses the presence of the interlocking tongue, which proves the guard is closed and closes an electrical contact. The lock monitoring portion makes sure that the lock is energized. The interlock switch must be wired to a safety relay or circuit, which will de-energize and stop the machinery if the guard is opened.

Cable pull switches are used as an emergency stop at any point along a cable run installed around conveyer systems, transfer machines, presses and woodworking equipment. The cable must have appropriate tension applied in order to set or reset the pull switch. Once the cable tension has been set, the pull switch will open the normally closed positive opening contacts if the cable is pulled or breaks. Cable pull switches can be used in place of individual emergency stop push buttons.

Limit switches are devices designed to detect the presence, proximity or absence of an object and to indicate if the movement of the object has exceeded preset limits. Electromechanical limit switches require physical contact to detect the presence of an object, while solid state limit switches   can use electric switches, proximity sensors or light sensors to detect an object. They can be used to control standard operations or used as emergency devices to prevent malfunction.