Investigation on current comparator with electrical shielding to improve the measured values

Generally, resistance measurements at high accuracy and precision using current comparator bridge system uses the comparison of resistors by measuring the current ratio corresponding to voltage drop equality. When adjusting the circuit until the bridge is balanced, the voltage between resistors is null and the voltage drop across resistors is equal with opposite polarity. This can be used to calculate the resistance value. This null voltage can be detected by Null detector. In Some case, measuring system must be connected terminally to Null detector, whose external connections may generate some electrical effects in the measuring circuit. This paper studies on the size of the electrical shielding box installed on the junction between Null detector and the other equipments. The differences between using a normal cable and a low thermoelectric EMF cable in measuring systems, which may affect the voltage accuracy, are also discussed. Finally, it has been found that the applications of the low thermoelectric cable and the shielding box can decrease voltage error. The size of the shielding box is related with the voltage error on the Null detector at balance condition of the bridge.