MHOS PER SQUARE VERSUS OHMS PER SQUARE AS MEASUREMENT QUANTITIES

(or sheet conductance versus sheet resistance)

"Zero drift," under the condition of no sample, produces a numeric value that is additive to the displayed conductance value obtained with a sample inserted into the sensing head of a DELCOM Conductance Monitor. However, with (a) an x10 instrument operating in the ohms per square mode and (b) with no sample inserted; users should note that, a one count conductance drift from an initial value of zero results in a large ohms per square value. Consider that with no sample, the displayed value should be infinity. Infinity, the reciprocal of zero, is a quantity impossible to represent on a five digit display! Ohms is the reciprocal of Mhos, or equivalently, resistance is the reciprocal of conductance. Thus, one positive count of conductance magnitude displays, when reciprocated, a value of 100,000 ohms/sq. and two counts display 50,000 ohms/sq. Thus a one count increase in conductance results in the rejection of a quantity of potential resistance values equal to "infinity minus 100,000." Which is also a quantity equal to infinity. Hence, an infinite number of resistance values, in which to represent what is essentially nothing in significant conductive material, are disregarded by operating an instrument in the ohms per square mode.

Consequently, for low conductance measurements, it is unwise to use ohms per square for measurement units when such a practice results in the rejection of an infinite number of values for representation and measurement of a quantity that is essentially nothing. Consider that MPH is a more valuable quantity for measuring speed ... as opposed to the reciprocal quantity of: "hours per mile!" Or consider; should paint coatings or concrete thickness, or whatever, be measured in units that represent the reciprocal of the coating thickness? Therefore, and without exception, research and production oriented operators use sheet conductance rather than sheet resistance to quantify their products. These users have discovered that conductance is more intuitive and that the values obtained correlate with all coating processes and all known usage requirements.

Following is a plot showing the hyperbolic relationship between resistance and conductance.