Abstract :
P. L. Hoovers I should like to discuss briefly power-factor measurement in connection with bridge methods. There may be some doubt as to the accuracy of any bridge in measuring power factor, for, as Mr. Lee has pointed out, power factor is the ratio of the total power loss to the product of the voltage and the current. Now if a tuned vibration galvanometer is used for detecting the balance point of the bridge, only the losses due to a single frequency and not the total losses are measured. Fortunately in most cases the error that is introduced in this connection is probably very small and negligible. Nevertheless, most a-c. bridges cannot be regarded as precision power-factor bridges, since the power-factor balance is so critically dependent on an accurate capacity balance. For instance, with the Wien or the Schering bridge, if the capacity balance is off by one per cent the power factor may be off by as much as 50 or 100 per cent. Experimentally this means that the capacity balance must be made to a much greater precision than is required for the power factor. Such an experimental condition is to be avoided if possible.
