GB579910A - Improvements in or relating to instruments for measuring resistances - Google Patents

Abstract

579,910. Resistance measurements. LOVE, A. May 22, 1944, No. 9858. [Class 37] In a resistance measuring instrument wherein a constant D.C. voltage is applied to the resistance under test and the resulting current flow is a measure of the resistance, the test voltage is derived from a generator 3, 4 of the rotating permanent magnet type giving an alternating output proportional to the speed of rotation. This output is stabilized in amplitude electrically, e.g., by an impedance 5, 6 shunted across the inductance coil 4, and applied to a static rectifier bridge 7-10, the D.C. output of which is applied at terminals 15, 16 to the resistance under test. The generator is preferably hand driven through gearing 2 and a gas discharge lamp 12 in parallel with a part of the shunt resistance 11 lights up when the required test voltage is reached. A current limiting resistance 13 is provided in series with the moving coil milliammeter 14 which may be calibrated to read resistance direct. Any other known means may be used for limiting the generator voltage. For example a flat topped peak resonant circuit may be used, Fig. 2 (not shown), or a saturated iron cored choke or transformer. The rectifiers may be of the metal contact type or thermionic.