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As such, safety relays monitor a specific function. When connected to other safety relays, they guarantee full monitoring of a plant or machine. [1] They meet the requirements of EN 60947-5-1, EN 60204-1 and VDE 0113-1. [5] Furthermore, there are many variants of safety relays, which are suitable for various machinery applications.
Today, microprocessor-based relays can perform many protective functions in one device. [1] When one device performs several protective functions, it is typically denoted "11" by the standard as a "Multifunction Device", but ANSI Device Numbers are still used in documentation like single-line diagrams or schematics to indicate which specific ...
Relays with calibrated operating characteristics and sometimes multiple operating coils are used to protect electrical circuits from overload or faults; in modern electric power systems these functions are performed by digital instruments still called protective relays or safety relays.
These relays convert voltage and currents to digital form and process the resulting measurements using a microprocessor. The digital relay can emulate functions of many discrete electromechanical relays in one device, [26] simplifying protection design and maintenance. Each digital relay can run self-test routines to confirm its readiness and ...
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.
In a digital/numeric relay, many functions are implemented by the microprocessor programming. Any one numeric relay may implement one or all of these functions. A listing of device numbers is found at ANSI Device Numbers. A summary of some common device numbers seen in digital relays is: 11 – Multi-function Device; 21 – Distance; 24 ...