Direct-Reading Frequency Meter

The frequency meter described functions over the whole scale of acoustic frequencies from 20 to 10,000 cycles per second, and in addition constitutes a static equivalent of the vibrating reed apparatus used for precise comparisons of a capacity with a resistance and a time. A condenser is charged at a given voltage E0across a triode in a half period and discharged across another triode in the successive half period; for this two grid circuits are controlled by opposite phases of the periodic voltage variations obtained from the two secondaries of a single transformer whose primary is supplied with the frequency to be measured. If the continuous voltage supply E0is kept constant, the frequency may be read directly on the calibrated scale of a milliammeter. It is possible to attain an almost complete independence of the triode characteristics and of the form and value of the voltage of the applied oscillation, within very wide limits. The frequency meter may also serve for the measurement of very small capacities.