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NORA Oilheat Technicians Manual

Chapter 8 Basic Electricity Figure 8-20 L1 Volts, Open Switch L2 Volts, Closed Switch 8-18 Basic Electricity Voltage Drop L1 L2 with the different functions based on the symbols marked on your meter. • Be careful how you treat your meter • Protect it from moisture and high temperatures • Replace worn or cracked test leads • When not in use store it in its case • Check the battery for corrosion • Remove the batteries for long storage periods • Do calibration checks against known volts, amps, and ohms regularly Measuring voltage A voltmeter is used to measure the difference in electric pressure between two points. Since a load creates a difference in electric pressure (or force) as it does work, the pressure is relative; that is, one point must be measured against another. Electrical charge flowing from any power source is at a high energy level; when it returns from the circuit, its energy is low. The power source’s job is to boost the energy level of the charge. The voltmeter measures this change in charge (the difference in energy level) through the circuit. Somewhere in the circuit, the energy of the flowing charge is converted into other forms by the load. When a light bulb is lit, the electric energy becomes heat and light. To measure this conversion of energy (change in charge), use a voltmeter. Figure 8-20. Remember, “Voltage applied is voltage used.” Whatever voltage is applied to a circuit will be used up by that circuit. This is why measuring voltage is the best way to find out if a circuit is working properly. A voltmeter allows very little current to go through it. It has very high resistance, so it has almost no effect on the circuit being measured. When you connect the leads from the voltmeter to two different points in the circuit, it measures the difference in potential (volts) between those points. It tells you how much energy is being used between the points where the two leads are touching the circuit. To measure voltage, touch the one of the voltmeter’s leads to each of the two wires on either side of the load. This will measure the voltage drop of that load. Voltage drop is the amount of electrical energy that is being converted by that load. If you touched the meter leads to L1 and L2, you would measure the voltage step-up from the energy source. There will be no voltage drop across a closed switch. The pressure drop across an


NORA Oilheat Technicians Manual
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