A Proposed Wattmeter Using Multielectrode Tubes

FrOR direct measurement of small amounts of power, or for measurement of power over a wide range of frequencies, dynamometer wattmeters are unsatisfactory, and vacuum tube wattmeters are often resorted to. Hitherto vacuum tube wattmeters have depended for their operation on the use of tubes having a square-law characteristic, connected in a push-pull circuit so as to avoid indications caused by current or voltage alone. Such a device was described by H. M. Turner and F. T. MacNamara in 19301 and was patented by E. Peterson in 1926.2 References to this type of wattmeter may also be found in standard works on radio-frequency measurement.',' An attempt to use a multielectrode tube with coplanar grids for the measurement of power was made by T. B. Wagner.5 While the device developed was satisfactory as a voltmeter or ammeter, it must be discounted as a wattmeter, for it is clearly brought out in Wagner's article that readings may be obtained by applying voltage or current alone, a condition of zero power. Moreover, it is stated that the output of the tube used is proportional to the sum of the effects of voltage and current if applied separately. The author wishes to propose a new method of measuring power through the use of multielectrode tubes. It may be shown of some multielectrode tubes that under certain conditions the application of alternating voltage to two controlling elements or grids results in a change in the direct-current component of the plate current proportional to the product of the voltages at the grids and the cosine of their phase angle. Hence such tubes may be used in the construction of a vacuum tube wattmeter.