[ RadSafe ] Interlock question

Ted de Castro tdc at xrayted.com
Mon Oct 27 20:11:23 CDT 2014

Specifically - analytical x-ray machine ....

On 10/27/2014 2:27 PM, Ted de Castro wrote:
> I am dealing with an x-ray machine interlock design.
> Of course it will be redundant and failsafe and testable - but the 
> question has come up regarding using semiconductor devices in the 
> interlock circuit.
> When I was the x-ray safety officer at a national laboratory I 
> resolved that issue by simply not accepting semiconductor devices in 
> interlock circuits - problem solved.
> I maintained that when such included logic circuits that showing that 
> its was failsafe with the failure of any single component could not be 
> demonstrated - even disregarding issues with defining what constituted 
> a "component".
> Further testing requires that each component be isolated, exercised 
> and tested - and I maintained that is simply not possible with logic 
> circuits.  ie. - just opening the door and observing that the x-rays 
> turn off is most definitely NOT a test!
> Its not as simple anymore.
> I have heard however that there is a euro standard that prohibits the 
> use of semiconductor devices in interlock circuits.  So - I was hoping 
> someone here might know IF that were in fact so - and if so shat that 
> standard is.
> Thanks
> Ted de Castro
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