LC meter - with moving-coil instrument

with moving-coil instrument An LC meter is undoubtedly in- dispensable to anyone involved in h.f. techniques. The present design accepts the unknown inductance, Lx, or capacitance, Cx, in a two- transistor oscillator circuit, of which the output voltage is kept constant between 30 and 40 mV by a regu- lator. When, in the oscillator circuit, Cx is connected in parallel with capacitor Co, or Lx in series with inductor Lo, 1 2 3 4 5 6 7 8 9 100 pF 1 nF 10 nF 100 nF 10 pH 100 IAN 1 mH 10 mH 100 mH 7-36 the frequency of the circuit diminishes. This diminution is measured by a frequency-to-voltage converter, T3/T4. The consequent output voltage of emitter follower T5 frequency-determining capacitor CL in the frequency-to-voltage converter is balanced out by P1. It is therefore necessary to switch in a different 10 k preset for each measuring meter f.s.d. range Lo Co mH nF 1 0.1 1 1 10 10 10 100 0.01 10 0.1 10 1 10 10 10 100 10 CL fo nF kHz 0.1 502 0.33 158 3.3 15.8 10 5.02 0.1 502 0.33 ...