Ghost 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. What are ghost voltages and where are they encountered? 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.
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This reduces the possibility of false readings due to ghost voltages and improves accuracy when testing to determine absence or presence of voltage. This feature presents a low impedance input to the circuit under test. This feature automatically, determines whether the measured signal is ac voltage or dc voltage, selects the correct function and range, and displays the correct information. The Fluke low impedance function is called Auto-V/LoZ. Use these switch positions for most troubleshooting scenarios and especially on sensitive electronic loads. On the Fluke 114, 116 and 117 DMMs, the meter's regular Vac and Vdc switch positions are high impedance. With dual impedance meters, technicians can safely trouble shoot sensitive electronic or control circuits as well as circuits that may contain ghost voltages, and can more reliably determine whether voltage is present on a circuit. While these tools aren't fooled by ghost voltages, they should only be used for testing power circuits or other circuits where the low impedance will not negatively impact or alter circuit performance. Older troubleshooting tools such as analog multimeters and solenoid testers generally have low impedance input circuitry around 10 kilohms or less. This is the desired effect for most voltage measurement applications, and is especially important for sensitive electronics or control circuits. 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. Most digital multimeters sold today for testing industrial, electrical, and electronic systems have high impedance input circuits greater than 1 megohm. This application note describes what dual impedance and voltage detection are and why it helps to have them built in to your multimeter.
#Multisim 12 impedance meter series#
The Fluke 114, 116 and 117 Digital Multimeter (DMM) series offer several features designed to make electrical measurement easier, safer, and more reliable.