[volt-nuts] Wavetek 1281 - Selfcal Module

[Frank Stellmach]

Todd,

you already have sent me the appropriate SelfCAL circuitry, but I did 
not recognize (understand) it as such!

I also received a hint from another volt-nuts, John, about the complete 
documents for the DATRON 1271 on the KO4BB site, which is very similar, 
and also contains a SelfCAL module, being a bit different than the one 
inside the 1281.

The schematics for the 1271, anhow reveal how the transformer inside 
this module provides different voltage ratios. The transformer there is 
labelled +9.93V, +/-7.23V (that's the main references value), 1.83V, 
1.00V and 0.19V.

These ratios were generated with a precision switch mode / chopper 
circuit, and as the ratios on a transformer are very stable, you only 
have to measure them once during initial calibration.

Obviously that is good for ppm ratio accuracy in the SelfCAL procedure.

So thanks again

Frank