Explanation of IBM Three Wire Correction System.

[ibm clock]

These scans are via Jim Lane. Here is an explanation of the IBM Three Wire Correction System.

 

[Toughtool]

This is the first schematic I have seen where the system voltage polarity is reversed, i.e. - on C and + on A and A. Most apply +24 volts to the contacts and the master relay grounds (-) to A and B. What publication is this document from?

Here is Page 16 from the ITR Service Instructions No. 230, April 1, 1938

 

[ibm clock]

You would have to ask Jim where they are from. My guess is they are from a 1950s IBM or maybe even Simplex Service Manual built around the 090 movement found on the 91 series masters. That is what Jim gave me when I had questions on my 91 series master. I also think the print you are showing is from clocks that use a seperate relay to transfer between the A and B wire, rather than use the stop contact on the clock. I called it the Duplex Relay, but some masters were wired to run 3 and 2 wire systems of impulse correction and had to accomplish the polarity reversal of the two wire systems vi a reversing relay, and the stop contact on the master controlled that relays coil. My 25 master has such a set up. I do have a diagram from the same 1950s manual that shows the Duplex Relay set up, id just have to get it off a disk and upload it.