Seeing is Believing! Why the DET2/2 is Simply the Best!

The Megger® DET2/2 is AVO International's high-end Digital Ground Resistance Tester. The DET2/2 offers critical advantages over other models in two key respects: increased noise protection, and extra digital resolution.

The effects, or even existence, of "noise" in the form of voltage transients in the soil, have been the subject of a much-publicized debate in recent years between the utilities and certain sensitive industries, most notably dairy. Whatever the outcome, there is no argument that grounding is an important part of protection. Just like the electrical system itself, the ground tester can be influenced by voltage transients. Megger ground resistance testers have always been the leader in maximum noise protection. First, AVO introduced 40 volts of peak protection, twice the industry standard, in the DET2/2. Later, this capability was extended to all newly-introduced models. But the DET2/2 is still the leader with three additional noise protection features: filter, high/low test currents, and adjustable test frequency.

It is this last feature that enables noise interference in the soil to be visually demonstrated. For instance, set up a typical Fall of Potential test configuration with leads and probes extended to conforming distances, then take a reading. The tester defaults to a test frequency of 128 Hz, and everything should go well. Then, with everything in place, go to the keypad and adjust the frequency downward. Chances are, when you approach the vicinity of 120 Hz, the digits will destabilize, under the influence of the second harmonic from the power grid. It won't always happen, but it may. You will have to make the final decision as to how significant the additional protection is to your situation. If noise is prevalent, the delays or moving of probes which are standard countermeasures can become excessively time-consuming and counter-productive.

And don't forget the other extra feature: additional resolution of the measurement, to 0.001 Í, above 0.010 Í. Design formulas for grounding systems become more precise and accurate as more data is fed into them, including better definition of the resistivity measurements. Increased probe spacing for greater depth in resistivity measurement results in very low resistances. Added resolution is significant in determining critical small changes in low values. But these slight changes in measurement can prove crucial in recognizing changes in rock strata that could result in costly rework if undetected. (Remember, small differences in readings magnify when worked through the Wenner formula [multiplied by large probe spacing] and engineering calculations.) The engineer will appreciate this extra resolution.