Two probe-type capacitance meters

Two types of instrument are described, suitable for the measurement of wiring and component earth capacitances in electronic apparatus. The instruments have a range of 50 pF and consist of a probe and an indicator unit. In the first instrument a substitution method is used. The unknown capacitance can be read on the dial of a small variable capacitor contained in the probe. The accuracy of the instrument depends only on the stability of this capacitor. An estimate of the parallel loss resistance of the unknown capacitance is possible. In the second instrument a moving coil meter gives a direct indication of capacitance and it is suitable for production purposes. The accuracy is ± 5 per cent or ± 1 pF, whichever is greater.