Download Chapter 37: Meter Usage and Circuit Diagnosis

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► The digital volt-ohmmeter (DVOM) or digital multimeter (DMM) is electrical measurement tool used to
diagnose and repair electrical faults.
► To properly use a DVOM requires time and effort to learn the parts and how it works.
► The DVOM can measure volts, ohms, and amps in a circuit.
► An advanced DVOM can measure frequency, temperature, and has a dedicated diode test capability.
► A DVOM is the first tool used to take electrical measurements.
► The DVOM allows the technician to see the movement of electrical impulses that cannot be seen without
some type of electrical test equipment.
► The DVOM can measure electrical volts within circuits.
► The DVOM can measure ohms, which is the resistance of a circuit.
► The DVOM can measure amps, which is the current flow of a circuit.
► The main parts of the DVOM is the main body and the two current leads.
► The main body has a function switch, a connection point for the leads, and a digital display to show
values.
► The leads are black for negative and red for positive connections.
► There is a wide selection of leads for the DVOM to enhance the testing capabilities.
► Before you can use a DVOM, the technician needs to know the quantity of the measurement (volt, ohm,
or amp).
► The DVOM can read a wide range of scales depending what position is selected.
► The DVOM can read from low to high values.
► The DVOM in auto range will select the best value for the range being measured.
► The min/max setting gives the technician the ability to measure circuits that are only on momentarily.
► The hold function freezes the value measured.
► There are many different ways to probe a circuit depending on the circuit being tested.
► The probes should never be forced as this could damage the circuit being tested and the probes being
used.
► If the technician uses the back probe method, the holes probed need to be resealed to keep moisture out.
► The most common measurements taken with the DVOM are voltage, current, and resistance.
► Depending on measurements taken, the leads need to be in the correct location on the body of the
DVOM.
► If the leads are connected in the wrong place on the DVOM, it could cause a fuse to blow.
► When voltage is measured, the leads are placed parallel to the circuit being measured.
► When current is measured, the leads are placed in series with the circuit being measured.
► When resistance is measured, the component should be isolated from the circuit so no power is present.
► The meter is very useful in finding opens, shorts, grounds, and high resistance.