The Design, Construction, and Performance of a Wide Range of DC Conductance Bridge

A dc conductance bridge for laboratory use is described which embodies a combination of features not found in any other bridge. The range of measurement extends from 10-15 mho to 1 mho, and the minimum detectable change in conductance is 4X10-16 mho. Bridge voltages of 6, 45, and 135 volts may be applied. Since the highest resistance arm is only 107 ohms, the time constant of the bridge is small and the effect of leakage in shunting an arm is very small. By virtue of a specially designed terminal block, guarded and shilded measurements can be made at, or remotely from, the bridge terminals. Provision has been made for performing both grounded and direct conductance measurements. For high conductance measurements, a zero balance circuit has been incorporated to compensate for lead resistance. The resolution is ten parts per million from 1 mho to 10-9 mho. The bridge performance was studied employing individual calibrated resistances, and low conductance wye networks fabricated from these components. The accuracy is better than 0.05 percent from 1 mho to 10-8 mho, about 1 percent at 10-12 mho, and 5 percent at 10-14 mho.