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Safety relays must always be designed in such a way that, if wired correctly, neither a fault in the device nor an external fault caused by the sensor or actuator will lead to the loss of the safety function. [8] A normal relay uses a wire coil and the mechanical movement of the metal contacts to switch the load on and off.
A relay Electromechanical relay principle Electromechanical relay schematic showing a control coil, four pairs of normally open and one pair of normally closed contacts An automotive-style miniature relay with the dust cover taken off. A relay is an electrically operated switch. It consists of a set of input terminals for a single or multiple ...
The non-tripped state is typically 24 VDC, and the tripped state (when the safety barrier has been violated) 0 VDC. If a wire were to break between the light curtain and the safety relay, the safety relay would trip to the safe state. The OSSD outputs are self-checked. In the non-tripped state, the outputs periodically pulse low.
Distance relays are actually double actuating quantity relays with one coil energized by voltage and other coil by current. The current element produces a positive or pick up torque while the voltage element produces a negative or reset torque. The relay operates only when the V/I ratio falls below a predetermined value (or set value). During a ...
An SIS performs a safety instrumented function (SIF). The SIS is credited with a certain measure of reliability depending on its safety integrity level (SIL). The required SIL is determined from a quantitative process hazard analysis (PHA), such as a Layers of Protection Analysis (LOPA). The SIL requirements are verified during the design ...
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Switchgear is a combination of electrical disconnect switches, fuses or circuit breakers used to control, protect and isolate electrical equipment. Switches are safe to open under normal load current (some switches are not safe to operate under normal or abnormal conditions), while protective devices are safe to open under fault current.
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