GB918004A - Improvements in electrical insulation testers - Google Patents

Abstract

918,004. Resistance measurement. EVERETT, EDGCUMBE & CO. Ltd. Sept. 20, 1961, No. 33707/61. Addition to 874,672. Class 37. In the insulation tester claimed and described in the parent Specification the resistance calibrated current-measuring instrument is replaced by a ratiometer whose voltage coil is energized proportionally to the output voltage of the oscillatory voltage converter, and whose current coil is energized by the output current of the converter when connected across the insulation to be tested. The voltage coil may be energized from an intermediate tap of the secondary of the converter transformer over a half-wave rectifier, smoothing capacitance, and series resistance (Fig. 1, not shown). For initial adjustment of the converter voltage ganged switches S 1 , S 2 (Fig. 2) in position b apply a known voltage coil Cv from a further intermediate tapping of the secondary through rectifier D 3 , resistance R 2 and stabilizing Zener diode D z while connecting a known resistance R 4 to the output terminals, to read which the calibrated meter may be adjusted, while in position a the voltage coil is directly energized over rectifier D 2 .