This invention relates to electronic test equipment for determining the number of turns of a coil wound on a magnetic core. More particularly, this invention relates to such apparatus for checking the number of coil turns quickly and accurately, and which is operable by relatively unskilled personnel.
Manufacture of transformers and related wound-coil elements commonly requires close control over the number of turns on the core. Coils are wound both manually and by machine, but in either procedure it is not readily possible to be precisely certain that the exact number of turns specified has been wound. This becomes a problem not only for the manufacturer of the coil or transformer, but also for the purchaser of the device, especially for applications where the number of turns must be exactly as specified or else the apparatus incorporating the coil will be rejected. Thus it is important to be able to perform a test on the completed device to determine the exact number of turns, so that if the number is not in accordance with the specifications, the winding can be augmented or reduced to reach the required number of turns. In additiion, it often is desirable to have means for continuously monitoring the number of turns applied as the winding operation proceeds, in order to be able to stop the operation when the specified number has been reached.
Various different kinds of apparatus have been proposed and used heretofore for determining the number of turns on a wound core. Such prior apparatus generally has not been satisfactory. For example, simple devices to measure the output voltage for a given excitation of the core suffered from inacuracies resulting from the effects of changeable resistances (contact resistances, etc.) in series with the excitation circuit. In an effort to solve such problems, one prior coil turns checker required that two separate, relatively heavy rigid bars be passed through the core being tested. Such arrangement is unsatisfactory for several reasons, including the fact that it is not suited for making measurements of the very small-sized coils used in many modern electronic components.