03DelcoRemy Diagnostic Manual130004222020

Page 4 DIGITAL VOLTMETER CONNECTED CORRECTLY IN RELATIONSHIP TO POLARITY DIGITAL VOLTMETER CONNECTED INCORRECTLY IN RELATIONSHIP TO POLARITY (VALUE CORRECT BUT MINUS SIGN WILL SHOW TO ALERT OPERATOR THAT LEADS ARE REVERSED) DP-1008 12.5 V1 -12.5 V1 FIGURE 1-3. Correct and Incorrect Polarity Readings 1-17. MEASURING CURRENT FLOWWITH THE AMMETER. The ammeter is used to measure current flow. The unit of measure is the ampere or amp. Unless the induction pickup (clamp-on) ammeter is used, the circuit must be opened and the ammeter connected in series in order to take measurements. 1-18. AMMETER SELECTION. With but a few exceptions (See Figure 1-10), it is desirable to make ammeter readings without opening up the circuit and thus disturbing a circuit defect and preventing it from being discovered. Therefore, the use of a clamp-on induction-type ammeter is recommended for most of the measurements described in this manual. This type is easy to use, cannot be damaged by misconnection, and will not damage the vehicle wiring. A clamp-on ammeter operates by measuring the magnetic flux produced by current flow through a conductor and translating that into amperes, which are displayed on the meter readout. 1-19. AMMETER USE. Figures 1-4 through 1-6 illustrate the use of various types of ammeters. 1. Figure 1-4 illustrates the use of an in-line digital ammeter. Note that the circuit must be disconnected in order to use this type of meter. The type of unit shown is an internal shunt and generally used for loads of 10 amps or less. Care must be taken to not measure current greater than the meter rating. This type of ammeter is not recommended for most of the measurements described in this manual. However, if this is the only type available, be sure to follow the meter manufacturer’s instructions for connection and use. FIGURE 1-4. In-Line Digital Ammeter 2. Figure 1-5 shows an in-line digital ammeter used to measure an unknown current draw. An example of this might be the result of a parasitic load. On the 10 amp scale, the current would be too low to be measurable. However, with the meter on the 300 mA scale, the current draw in milliamps can be read. FIGURE 1-5. In-Line Ammeter 3. Figure 1-6 shows a clamp-on ammeter, the most common type of current measurement described in this manual. Zero out the meter before using and make sure the jaws are completely closed during use. Place the meter jaws around the cable, with the arrow points in the direction of current flow, to measure all the current. 10A 10 AMPS OR LESS LOAD DP-1009 UNKNOWN CURRENT DRAW DP-1010