February 16, 2006 -- If you had the option, you probably wouldn't use high-Z (high-impedance) sensors. Their sensitivity to external noise, solder-flux residue, particle tracking, bias currents, and distant charges can make repeatable measurements difficult. High-Z sensors have an upside, though: They don't self-load, and they inherently use little power. For certain variables, such as pH, light, acceleration, and humidity, the most practical sensors are high-Z devices. Because nature offers them, expediency urges their use. Careful attention to design can minimize the devices' tendency to receive adverse effects from the world around them. As an interesting note, with the advent of practical superconduction, impedance values have achieved an infinite range.

By Glen Brisebois. (Brisebois is an applications engineer responsible for customer support for op amps, comparators, references, and rms-to-dc converters at Linear Technology Corp.)