>From: Chris Dupres[SMTP:[email protected]] >Sent: Monday, June 23, 1997 11:04 PM >... >Wow, you are using semiconductors for an interlock system! Maybe I >misunderstand what you are doing. >>Surely an interlock system for a system with hazards as you describe >requires a level of intrinsic safety way ahead of board level >electronics...
Chris, It's been a long time since the days of everything being interlocked with wide switch and relay contacts. Everything from traffic and elevator controls to robotics, air traffic control and nuclear power has graduated to electronic protection and operation. It is possible to get much more reliability and safety out of electronic controls these days than the old electromechanical ways in many applications. Some applications such as motion detection or laser scan detection are impossible to implement otherwise. Some of the best machinery protection devices are proximity detectors. This doesn't mean its easy. You need lots of careful engineering work, robust designs and extensive testing and analysis. For help I would refer to (among others): IEC 812 "Analysis Techniques for System Reliability - Procedures for Failure Mode and Effects Analysis" UL 991 "Tests for Safety Related Controls Employing Solid-State Devices" CSA C22.2 No. 0.8 "Safety Functions Incorporating Electronic Technology Requirements for Safety of Electrical Products" UL 244A, "Solid State Controls for Appliances" None of these guarantee safety. They just help you analyze your problems. But like everything else, its a cost-benefit tradeoff. Spend the appropriate time and effort till you have been appropriately careful considering the risks. Its possible to come up with a pacemaker you can bet your life on. Bob
