176 Auto Electricity and Electronics Copyright by Goodheart-Willcox Co., Inc. amps. An inductive pickup is a handy meter attachment for analyzing charging systems and hybrid power system opera- tion. Most meters connected in series will not read more than a few amps without an inductive pickup. Meter Controls Most digital and digital-analog multimeters have a large function knob that can be rotated to select the type of electrical reading to be taken. Th e function knob can select a reading in volts DC or AC, amps DC or AC, and ohms. It may also have other settings, such as rpm and diode testing. See Figure 9-17. Meter control buttons are usually provided to allow you to select other function variables: zero meter, minimum/maximum readings during the test, range, hold, duty cycle (percent on and off ), and sound alert. Most multimeters also have diff erent test lead sockets or holes, as shown in Figure 9-17. Each socket is for a diff erent type or range of measurement. Most digital meters are auto ranging—they automati- cally change to the correct scale. All you have to do is set the meter knob for volts, amps, or ohms, and the meter adjusts itself automatically to the correct range. For example, a digital meter might display a “k” next to the number read- out when you are measuring a high resistance, as shown in Figure 9-18. Th is means the meter is displaying the value in kilohms. A reading of 9.27 k Ω equals 9270 Ω. An “M” next to the readout means the value is displayed in megohms. If no prefi x is shown, the reading is in ohms. Note: To read a meter correctly, you must understand the electrical multipliers shown on the meter display. The prefixes used on digital multimeters are standard for electrical units. Refer to Figure 3-21 if you need help remembering the prefixes for electrical units. Figure 9-19 shows a few voltmeter readings. Th is meter has function settings for DC volts and AC volts. DC volts are used for most measurements in a vehicle’s electrical systems. AC volts might be used to check the signals from speed or position sensors that generate a small AC signal indicating engine or drive line speed. Figure 9-20 shows some ohmmeter readings from a digital multimeter. Note the multiplier shown on the far right of the display screen. Some ohmmeters must be calibrated to zero before you can make accurate resistance measurements. Th e calibrate function compensates for bat- tery condition and provides accurate measurements. To calibrate the ohmmeter, touch the two meter leads together. Th e meter should display a reading of zero ohms. If it does not, press the Zero button to recalibrate the meter to zero. See Figure 9-21. Figure 9-22 shows a multimeter set to make amp read- ings. To avoid blowing a fuse in the ammeter, make sure the possible amp reading is below the rating of the ammeter. Meter damage can occur if you accidentally send too much current through a meter connected in series. Use an induc- tive pickup for higher amp readings. Th e bar graph on a digital-analog multimeter serves as an analog display that can show rapid changes in readings. Th e bar graph functions much like the needle on an analog meter. If a circuit or component has an intermittent open or bad connection, the bar graph display moves back and forth to display this rapid change in the reading. Th e digital display changes as well, but it may not be able to keep up with the changes. See Figure 9-23. Figure 9-17. Study the basic parts of this digital-analog multimeter. Digital Display Control Buttons Test Lead Sockets Analog Bar Graph Function Knob Figure 9-18. Auto ranging meters automatically adjust to the cor- rect value range. This value is being displayed in kilohms (kΩ). Value is displayed in Kilohms