MC Miller High Impedance Adapter #5615

When structure-to-soil readings are taken across highly resistive materials such as dry soil, sand, rock, and concrete, readings can appear lower than their actual values. Relying on such low readings can lead to overcompensation of the rectifier's output, overprotection of the structure, and wasted resources.

No longer is it necessary to rely on the fixed 10 MΩ input impedance of standard voltmeters and data loggers for dependable readings. The solution to this common difficulty is the Selectable High Impedance Adapter. The adapter enables any standard impedance voltmeter or data logger to vary its input impedance, thereby eliminating contact resistance errors from readings.

General Information:

Due to the limitations of standard voltmeters, an error can be realized while performing readings with high impedance sources (e.g., structure-to-soil readings at the point where a copper/copper sulfate reference electrode makes contact with the earth). This error is a result of a current loop created by the voltmeter, which causes a drop across the source resistance. The Selectable High Impedance Adapter varies this current loop, allowing the user to determine when the error has been made insignificant. However, with higher impedance there is an increase in noise pickup. Therefore, when two adjacent ranges give the same readings, select the lower of the two ranges to limit pickup while maintaining the most precise reading.