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Multimeter 101

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  • Multimeter 101

    A multimeter is one of the most basic trouble shooting tools you can use to track down an electrical problem in any vehicle. With a good service manual and a cheap digital multimeter trouble codes (DTCs) in newer computer controlled cars can be diagnosed. In the RC world everything is electronically controlled. Below are basic instructions for using your multimeter.

    Turn on multimeter and connect probes (if necessary). The negative probe is black and the positive will be red. For some applications this is important, while for others, it does not matter.
    Use the probes to measure resistance by placing one on each side of the component to be measured. For this function, the probes are interchangeable. The item being repaired should be turned off and the multimeter set to resistance, which may be symbolized by a horseshoe- shaped icon. Note the numbers on the display; this is the resistance measured in ohms. Some multimeters have the ability to check for continuity, or unbroken connections and wiring. This is checked in the same way as resistance except the meter is set to continuity (symbolized by a series of diminishing curved lines). Continuity is indicated with a tone.
    Measuring voltage requires the electricity to be on in the device being measured. To measure DC voltage, set the multimeter to VDC. Touch the negative (black) probe to ground and positive (red) probe to the point in the circuit where DC voltage is to be checked. The voltage reading in volts will register on the display with a - symbol indicating voltage towards ground; a + symbol may or may not be displayed to indicate voltage moving away from ground. To measure AC voltage, set the multimeter to VAC. The reading will also be in volts although there is no direction to AC voltage.
    Checking diodes is accomplished by setting the multimeter to diode check, which may be symbolized with an arrow against a vertical line. Turn the device off, and measure the diode by placing the negative probe on the cathode of the diode (frequently indicated by a stripe around the end of the diode) and the positive probe on the anode (unmarked) side. Most multimeters will first make a tone, like when indicating continuity, and then display the voltage drop across the diode. This varies with the diode type, but it is typically between .5 and .75 voltages.
    Reading capacitance, on meters equipped with this option, requires removing the capacitor from the circuit unless the meter measures "in circuit capacitance." This is almost always a feature only found in meters designed for this purpose. After removing the capacitor, set the meter to capacitance, which is often symbolized by a curved line and a vertical line. Some capacitors have a positive and negative side; others do not. If there is a negative side, it will be indicated by a stripe or even - symbols, and the negative probe should be placed on that lead, positive on the other. If a negative side is not indicated then probe orientation will not matter. Capacitance measurement will take several seconds to register and will display in farads.
    Turn the meter off when not in use and store probes so they will not be damaged.