A series of application notes from Fluke Corp., Everett, Wash., should help electricians and electronics professionals perform advanced electrical testing with their Fluke digital multimeters (DMMs).

Advanced DMMs incorporate a number of sophisticated test and measurement capabilities, and some users may be unsure of how to use them or why the tools are designed as they are. The application notes, available at www.fluke.com, are written and illustrated to take the mystery out of DMMs.

One new feature is the dual-impedance capability built into the Fluke 289 DMM. Most such units sold today for testing industrial, electrical and electronic systems have high impedance input circuits greater than 1 MΩ. In simple terms, this means that when the DMM is placed across a circuit for a measurement, it will have little impact on circuit performance. This is the desired effect for most voltage measurement applications, and it is especially important for sensitive electronics or control circuits.

Older troubleshooting tools generally have low impedance input circuitry around 10 kΩ or less. While these tools are not fooled by ghost voltages, they only should be used for testing circuits where the low impedance will not negatively impact or alter circuit performance.

With dual impedance meters, technicians can do it all. They can safely troubleshoot sensitive electronic or control circuits as well as circuits that may contain ghost voltages, and they can more reliably determine whether voltage is present on a circuit.