[ARC5] ARC5 CW Question

[Mike Hanz]

On 6/23/2014 11:46 AM, w4thq at cox.net wrote:
> The Apollo program during the 1960's and 1970's had complex relay logic in the control systems of both the launch vehicle and ground support equipment.  Because of RFI-EMI problems, NASA required double-anode zeners across all 28 volt crystal-can relays.  We found this approach was effective.  We also discovered that the back-emf would "ring" and was not just one spike.  The drop out time was not significant in our application so I don't remember what it was exactly.

Yup, we also used them on the relays that were installed in nuclear 
weapons back in the 1960s, and for the same reason.  Like your Apollo 
app, they were not used in circuits where drop-out time was critical 
either, and cost was no object.  I designed a couple of automated relay 
testers for the nuke folks that examined every aspect of a relay - coil 
inductance, coil and contact resistance, pull-in time, drop out time, 
contact bounce time of every pair of contacts, etc.  They found that 
once these relays had been hermetically sealed, variations of more than 
5% indicated higher probability of failure in life testing, so those 
were rejected.  I still have a couple of those around here somewhere - 
they worked fine in my little home projects for years, but there are 
some places where you don't want to gamble.

  - Mike  KC4TOS