130
The Tektronix Type 130 is a self-contained instrument that measures inductance and capacitance. When measuring inductance, the 130 makes an LC oscillator using the device (inductance) under test and a capacitor internal to the 130. When measuring capacitance, the 130 makes an LC oscillator using the device (capacitance) under test and an inductor internal to the 130. The frequency of the resulting LC oscillator is measured by mixing it down using a fixed reference frequency, generating a pulse at each zero-crossing, and integrating (low-pass filtering) the pulse train. This produces a voltage that is proportional to the frequency difference between the LC oscillator and the reference oscillator. This voltage is displayed on a d'Arsonval meter on the front panel of the 130.