[GreenKeys] [Milsurplus] Another Whats-it ???

[Keith Lueck]

Hi John -

I see that others have identified this device...  I 
thought I could add some details.  You might google the "McCulloh" 
system for signalling if you're curious.  I believe that is what this 
box used. It was a current loop system with reversing polarity that made
 it "fail safe."   The monitoring station (much like a telco CO) had a battery room to power all the loops.  The pulses were sent to an array of recording machines that recorded the pulses on 
paper tape.  Multiple transmitters shared a dedicated line to each receiver.  The receivers had status lights to indicate an open or 
shorted line.  When pulses started being received, the receiver would start a motor driven paper tape recorder and a pen would mark each pulse on the tape.  The pulses recorded on the tape were easily read by a human operator, but, 
since the pulse wheel was driven by a spring-loaded clockwork mechanism,
 the pulse timing was highly variable, even from "round" to "round" ( a 
round being one revolution of the wheel).  In the units I worked
 with, there were 3 decimal digits per round.  As the clockwork spring 
unwound the pulse rate would slow.  

About 20 years ago, I worked
 on a system to read these pulses with a pc.  At that time, the central 
station I was working for still had a hundred or so customers using 
these boxes.  They were trying to phase them out and upgrade to modern 
equipment.  They had trouble getting the pens and narrow paper tape for 
the recorders (which looked to date from the 50's or early 60's), and of course they wanted the benefits of recording the event with a pc and immediately identifying the source of the alarm.  

Cheers,

Keith


-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://mailman.qth.net/pipermail/greenkeys/attachments/20121109/cb25a5e0/attachment.html