Early history of shunt diode safety barriers



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Figure 6 Instructions card for 10V 47Ω barrier Figure 6 Instructions card for 10V 47ohm barrier

The following years

After 1971 barriers became an accepted technology and the original BIMCAM agreements fell into disuse. Within the UK a number of manufacturers emerged. Included in these were Safety Technology Ltd who emerged from Gresham Transformers Ltd and Measurement Technology Ltd [MTL] who were created by a redundancy purge at Kent Instruments Ltd. BASEEFA became the certifying authority and CENELEC standards began to be created and applicable. In Europe several manufacturers, notably Stahl and Georgin, were very active. This increased activity led to standards and codes of practice being developed and the usual interaction between users, manufacturers and certifying authorities created a lively market. Later ATEX and IEC Ex became major factors in the market development.

 
 

Galvanic isolators with switch inputs and relay outputs were available earlier than 1961. However the introduction of isolators for analogue signals in the early 1970's increased their acceptability and they became the preferred solution for some applications.

If the relevant information covering the period from 1971 onwards from all the possible sources could be collated this would be an interesting account of the further development of a particular product in this field. Perhaps the most useful account would be of the projects which failed or just fizzled out, since these probably contain the most significant lessons. The commercial interests involved make it difficult to gain access to accurate information and therefore probably this part of the history will not be written.

 

Conclusion

This document records the first ten years of the development of shunt diode safety barriers in the UK . This was only the beginning; the following years were equally interesting as the design and applications developed. This history illustrates the lengthy timescales for any new concept in the field of safety in explosive atmospheres to develop and become acceptable. Inevitably the surrounding circumstances change, but the time for development of any slightly different approach taken today will meet different but similar obstacles and the time to overcome them will be similar if not longer.

Acknowledgements
The author wishes to acknowledge the valuable contributions of Robin Garside [Hexagon Technology] and Robin Hingley [BEKA associates] to this document.

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