Light barriers with test facility

Status:

completed 05/1994

Aims:

In the past protective devices used for machinery safety purposes always met the highest safety level "self-control" without taking account of the actual risk to be prevented. In cases where the risk of an injury was low and the protective device costly, no protection at all was chosen. The example of light barriers is given to illustrate how a start-up testing can contribute to a safety-technical design of light barriers so that these guards are usable at moderate costs especially in the case of low-risk applications.

Activities/Methods:

Circuit examples for the use of light barriers to protect dangerous areas were developed in cooperation with manufacturers of machinery and machinery components. The circuit examples allow the cascade connection of two to three light barriers. Contact technology or a standard PLC (programmable logic controller) make sure the operability of the individual light barriers is tested at each machine start. Time-line diagrams, instruction lists, contact plan presentations and typical hardware circuit diagrams are provided to document the examples. A fault analysis was conducted for each of the examples, which can thus be considered validated in accordance with EN 954, Part 1, category 2.

Results:

The circuit concepts were used to advise manufacturers and users of machinery and protective devices. In the context of European standardisation they serve to illustrate the control categories (see EN 954-1 "Safety of machinery. Safety- related parts of control systems - General principles for design", EN 61496-1 "Safety of machinery. Electro-sensitive protective equipment - General requirements and tests" and IEC 61496-2 "Safety of machinery. Electro-sensitive protective equipment - Particular requirements for equipment using active opto-electronic protective devices") and estimate practicability and cost.

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