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Download Chapter 37: Meter Usage and Circuit Diagnosis
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Ready for Review ► 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.