Volt Meters

Tech Net Library

Volt Meters

How to Use a Volt Meter

by Rick Medero s/v C_Language

Get Better Results by Avoiding Common Pitfalls

Volt Meters are also known as MultiMeters

Typically a MultiMeter will include an Ohm (unit of resistance) and Amperage functions. User should take care not to overload the meter especially in the Ohm or Amperage mode. While using these functions, significant current must pass through the meter and if connected to an active power source. It can draw too much current. Most contain low current fuses to protect the meter and some are user replaceable.

Here is one common pitfall with using a voltmeter to verify a voltage supply to a device; measuring the voltage without the device connected or while off. Modern voltmeters draw near zero current and if there is some higher than normal resistance in the conductors, connectors, or switches the meter will still likely read full voltage, but once loaded by the device it may drop to a voltage lower than required. To avoid this pitfall, measure the supply while loaded. That is with the device on and consuming full power. With electronic devices you can not always depend on it to load the supply when there is not adequate current or voltage at the device. In this case the device may fail to turn on and load the supply. When in doubt that the device is providing a load, you can use a light bulb (one that will draw significant current) as a load.

Another pitfall is the use of the Resistance (Ohm) function to verify continuity. It is best to use the lowest Ohm scale as the higher ones may give a false indication. For example when verifying that a switch is good using the KiloOhm it may appear to be good when in fact it is highly resistive. Also, when testing for high resistance make sure your fingers are not touching the probe ends as this could result in measurement of your body's resistance in parallel with the resistance you are trying to measure.

Some Multi Meters are available with Clip-On current measurement probes. While the conventional Amp Meter requires that the probes be in series with the load, the Clip-On type works by measuring the magnetic field produced by current flowing in the conductor. It is important to note that only one conductor should be in the core of the probe. If more than one conductor and the current is flowing in equal magnitude but opposite directions there will be a net of zero magnetic field and the probe will measure zero current. Note that many Clip-On current probes are AC only and will not measure DC current flow.

Thanks to the Sailing Vessel Cat Tales for info on a Multi Meter with Clip-On amp probe that will measure DC current flow: Sears model 82369.

Rick's site s/v C_Language


  • Home
  • Site Map
  • Site Policy
  • © 2000- Bigdumboat.com
    All Rights Reserved.