dual impedance digital multimeters

The Dual Impedance of Digital Multimeters

There are numerous digital multimeters that offer several features to make electrical measurement easier, safer, and more reliable. However, there are still factors that need to be considered when measuring electricity and voltages. Most digital multimeters such as the Fluke 114, 116, and 117 series are capable of having a dual impedance in order to solve common electrical measurement complications. To have further understanding, we are here to discuss the basic features and uses of dual impedance.

Impedance Basics


Nowadays, digital multimeters that are being used for testing industrial, electrical, and electronic systems have high impedance input circuits. Basically, 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 is especially important for sensitive electronics or control circuits.


However, older troubleshooting tools such as analog multimeters generally have low impedance input circuitry. This limits their performance and is only used for testing power circuits or other circuits where the low impedance will not negatively impact or alter circuit performance.

What About It?


As a means of safety and accurate results, dual impedance meters provide technicians the ability to safely troubleshoot sensitive electronic or control circuits as well as circuits that may contain ghost voltages, and can more reliably determine whether a voltage is present on a circuit.


On the Fluke 114, 116 and 117 DMMs, the meter’s regular Vac and Vdc switch positions are high impedance. These switch positions are mostly used for troubleshooting scenarios and sensitive electronic loads.


The Fluke low impedance function (Auto-V/LoZ) Auto-V reduces the possibility of false readings due to ghost voltages and improves accuracy when testing to determine the absence or presence of voltage. Use the Auto-V/LoZ switch position on the DMM when readings are suspect (ghost voltages may be present) or when testing for the presence of voltage.

Ghost Voltages


In order to understand more what dual impedance, do to electrical measurement processes, Ghost voltages must be carefully identified and explained. These voltages occur from having energized circuits and non-energized wiring located in close proximity to each other, such as in the same conduit or raceway. This condition forms a capacitor and allows capacitive coupling between the energized wiring and the adjacent unused wiring.


The most common places to encounter ghost voltages are blown fuses in distribution panels, unused cable runs or electrical wiring in existing conduit. Some amount of ghost voltage can be coupled from the hot side to the open side across the blown fuse. When facilities or buildings are built and wired, it’s very common for electricians to pull extra wire through the conduit for future use.

Absence or presence of voltage testing


Traditionally most electricians and plant maintenance professionals used some form of solenoid tester to determine whether circuits were energized or not. Because of their low impedance circuit, solenoid testers are not fooled by ghost voltage.


These testers did their job back in the day but they rarely comply with the current IEC 61010 safety standards and current North American regulatory requirements. But with a dual impedance meter that has Auto-V/LoZ function, leads are placed on an open circuit that contains a ghost voltage. The low input impedance will cause the ghost voltage to dissipate and the meter will display a reading near zero volts indicating no voltage present.


Given the variety and complexity of measurement and testing requirements found in most facilities today, a meter with a dual impedance input offers the troubleshooter or technician more flexibility to cover applications or measurement needs ranging from basic voltage testing to troubleshooting sensitive electronic circuits. Having a trusted voltage detector helps increase efficiency and adds an additional safety check for technicians, Presidium is your top choice to bring you that efficient voltage detector. As the authorized distributor of Fluke products in the country, we are committed to providing the best measurement tools, especially those that are equipped with high-quality dual impedance input.


For more information, you can contact us at +632-464-9339 or visit our website at www.presidium.ph

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