Measurement of multimegohm resistors
A.H. Scott · Journal of research of the National Bureau of Standards · 1953
The method by which multi megohm resisto rs are measured at the National Bureau of Standards is a null method using an electromete r as the null detector.The charge flowing t hrough the resistor during t he time of measurement is obtained from a variable a ir capacitor maintained at a fixed potential.The potentials across t he variable air capacitor and thus across the specimen are maintained constant as indicated by the n ull reading of the elecLrometer by decreasing the capacitance of the air capacitor at just the ri ght rate .The capaci tance of t he capacitor is varied by a small direct-current motor geared to the shaft of the capacitor and whose speed can be controlled.Several mu ltimegohm resistors of t wo d ifferent makes have been studied over a period of abou t th ree years.Although t h ese are t he most sta ble multimegohm resis tors available, i t was found th at they had erratic fluctuation s of 0.5 to 1 percent and were generally voltage sensiti ve.' With the impressed voltage varied from 1.5 to 180 volts, various resistors showed resistance changes ranging from 0.4 to 26.9 per cent.