Cal Enterprises Ltd

Construction and testing of a 50Hz ratio decade

During my work at B.Ae calibration centre there were many times that we were called upon to calibrate 50Hz syncro alignment test sets.
The recognised method of calibration is nulling against a ratio transformer. The input limitations of the 1011 Tegam ratio box are 0.35X f(Hz) or 350v whichever is smaller. Since most calibrations are required at the user level of 115v/90v the Tegam ratio box will not satisfy the requirement and some other (less accurate) method has to be used.

Yet it is only the first ratio decade which is overloaded by 100v,50Hz.
I came up with the idea of constructing a separate 50Hz decade which can be used in-front-of the 1011.

This is a picture of the set-up to check the "depth-of-null" which could be obtained when comparing the newly constructed 50Hz decade against the 1011 at 10v input. The decade was checked for freedom of magnetic saturation and possible loading due to connection of the 1011against a DVM. The accuracy in use calibrating syncro-alignment sets is related to the depth-of-null which can be obtained and this information has been used in the calculation of the uncertainties given in measurement capabilities. The ratio/simulated angle relationship being well known to the author.

50Hz/60Hz High Voltage Decade details