Table of Contents Electrical Measuring Equipment and Procedures Subject Page Introducing the DVOM.3 Choosing a DVOM.3 The Functions .5 Function Selector Rotary Switch .5 Push Button Functions .7 Input Terminals .9 Display.9 Infinity Display.10 Using the DVOM .11 Voltage Testing.11 Amperage Testing.12 Resistance Testing.13 Continuity Testing .14 Voltage Drop Testing.15 Initial Print Date: 03/06 Revision Date: 10/10 Electrical Measuring Equipment and Procedures Model: All Production: All After completion of this module you will be able to: • Understand DVOM/IMIB settings. • Correctly install the DVOM/IMIB to test different circuits. • Understand the use of the DVOM/IMIB for the different type of electrical measurements. • Correctly utilize IMIB to test circuits on a vehicle. 2 Electrical Measuring Equipment and Procedures The ability to measure voltage, current flow, and resistance is important in the diagnosing of electrical problems. Without the results of these measurements troubleshooting in an electrical system is a futile process. The instrument most commonly used to make electrical measurements is called the Digital Voltage-Ohm Meter (DVOM). Basic DVOM’s are capable of measuring: • AC Voltage • Millivolts • Conductance • Continuity • Amps/Milliamps Advanced DVOM’s add: • Frequency • Duty Cycle DC Voltage Resistance Capacitance Diode Test Microamps RPM Pulse Width The DVOM provides for a method of accurate measure¬ ments. Even though accurate measurements are the key to electrical diagnosis, the following four factors determine the effectiveness of the measurements: • Accuracy of the measuring instrument. • Correct installation in the circuit of the measuring instrument. • Ability of the Technician to read the instrument. • Skill of the Technician in interpreting the results. As it is clearly seen, only one of the factors depends on the DVOM (e.g. accuracy), the rest will always depend the ability of the technician to read and interpret the results. Choosing a DVOM A good choice of a DVOM is the IMIB, as the measuring system of each contains a high¬ ly accurate DVOM. Choosing a handheld DVOM from a reputable manufacturer, however, leaves the shop IMIB free to perform other tasks that a DVOM can not do (e.g. Retrieval of fault codes). 3 Electrical Measuring Equipment and Procedures In choosing a DVOM several factors need to be considered, one of which is Impedance. Impedance is the combined resistance to current created by the resistance, capacitance and inductance of the meter. Impedance is measured in ‘Ohms per Volt’. Meters with the highest ‘Ohms per Volt’ impedance are the most accurate. More importantly using a meter with high impedance will not cause damage to sensitive electronic circuitry. When a Meter is connected across a circuit to measure voltage, it must be connected in parallel. This adds parallel resistance. The total resistance in a parallel circuit is less than the lowest resistance in that circuit (Ohms Law). Using a Meter with low impedance will reduce the total resistance of the circuit and allow more current to flow. A meter with low impedance can draw enough current to cause inaccurate measurement, voltage drops or damage sensitive electronic circuit boards. A high impedance meter will draw little current and insure accurate readings. Using older type meters with low impedance values (20,000 to 30,000 ohms-per-volt) can damage modern electronic circuits and components or give inaccurate readings. Test lights should be avoided for the same reason. They lower the total resistance of the circuit and cause increased current flow. Other factors in choosing the proper DVOM are: • Cost • Features Basic DVOM’s are available reasonably priced. These basic models may be more than sufficient for use in BMW Centers, given the availability of the IMIB for advanced mea¬ surement and scope functions. Advanced features and price go hand in hand. The more features added the higher the cost. Some of those features may be worth the increase in cost (e.g. frequency, duty cycle and pulse width). Other features may not (e.g. oscilloscope, graphing). Choose a DVOM wisely based on personal preference and cost. Like many other tools it is valuable in the diagnosis and repair of BMW’s. Experience has shown if the technician is not comfortable with the DVOM or confident in the results of the measurements, the DVOM will not be used. Considering the technology in BMW automobiles, diagnosing with a quality DVOM cer¬ tainly makes repairing the problem correctly and expediently a more manageable task. 4 Electrical Measuring Equipment and Procedures The Functions Function Selector Rotary Switch turned off. — mV Qn^,)))) "- — v/ \ mA RPM / — L—r -mA I A ^ ofX y Volts AC Measures AC Voltage Ranges: 400mV,4V,400V, 1000V Measures DC Voltage Measures DC Millivolts Ranges: 4V, 40V, 400V, 1000V Range: 400mV 5 Electrical Measuring Equipment and Procedures Measures Continuity and Ohms. Test diode operation. Ranges: 400Q ,4kQ , 400kn , 4MQ, Range: 3.000V 40MQ Milliamp or Amps DC Milliamps or Amps AC Measures DC Milliamps or amps. Measures AC Milliamp or amps Ranges: 40mA or 400mA for mA input Ranges: 40mA or 400mA for rmA input 4000mA or 10 A for A input 4000mA or 10 A for A input 6 Electrical Measuring Equipment and Procedures Push Button Functions (zero A) JmIN MAX ^RANGEJ | HOLD h) O i r RPM ^ (Vo DUTY^ [alert:!]) SMOOTH HZ ms-PULSE +TRIGGER Zero (Relative Reading) Function Displays difference between the measured value and the stored value. Minimum (Min), Maximum (Max), Average (AVG) Recording Records minimum, maximum and calculates the true aver¬ age. Manual Range or Auto Range In Manual Range user selects fixed range. Meter stays in that range until user changes it, selects Auto Range or turns meter off. In Auto Range meter selects range automatically. Touch Hold Touch Hold holds last stable reading on display. A new stable reading causes beeper to sound and display to update. If meter is in MIN MAX Recording, RPM, Duty Cycle, Pulse Width or Hz, Touch Hold interrupts the function. The display is frozen, but recorded readings are not erased. 7 Electrical Measuring Equipment and Procedures RPM/HZ RPM 2, RPM 1, or frequency RPM 2, 4-cycle engines RPM 1,2-cycle engines Hz. counts frequency between 0.5 Hz and 200 kHz. Duty Cycle or Pulse Width Duty Cycle between 0.0 and 99.9% displayed. Pulse Width between 0.002 and 1999.9 ms displayed. ms-PULSE fTRIGGER Change Alert, Continuity Beeper or +/- Trigger. In voltage or current functions selects Change Alert. In W function selects Continuity Tests. In Duty Cycle or Pulse Width selects trigger slope. O SMOOTH // V v ' x Smoothing Function and Back-light display (advance model only). Smooth displays average of last eight readings. Press Yellow button to turn on or off back-light. 8 Electrical Measuring Equipment and Procedures Input Terminals mA (1/1000 A) Common For inputs to 400mA Return for all Terminals A Amperes (Current) Inputs to 10A continuous (20A for 30 second) p c UOOmA MAX Fused Volts, Ohms, RPM Diode Testing 10A MAX- FUSED Display 9 Electrical Measuring Equipment and Procedures Infinity Display While most displays of DVOMs are standard (i.e. mV means millivolt, mA means mil- liamp) the display or symbol for infinity or open circuit can be confusing. A display of indicates no or little resistance. It means the circuit or portion of the circuit being mea¬ sured has continuity or is complete. A reading of OL means the circuit is open or not complete, the resistance is said to be “INFINITY”. Some meters may use the symbol B for Infinity. Be aware of which reading the meter being used will give for infinity or open circuit. Meter 1 10 Electrical Measuring Equipment and Procedures Using the DVOM Voltage Testing The voltmeter (DVOM) must be connected in parallel with the load or circuit. The DVOM has a high resistance and taps off a small amount of current. A voltmeter must be used with the current on and with the correct polarity. The red lead should be connected to the B+ side of the circuit and the black lead to the B- side of the circuit. If the leads are reversed the reading will be a negative number. • Select proper function and range of DVOM. • Connect (-) lead of meter to battery B- or known good ground. • Connect (+) lead of meter to test circuit. DVOM will indicate supply or available voltage at that point. 11 Electrical Measuring Equipment and Procedures Amperage Testing To measure amperage the meter must be installed in series in the circuit. The current flow of the circuit must flow through the meter itself. Current must be flowing in the circuit. Installing the meter in parallel with the circuit may cause damage to the meter, because of the increased current flow in the circuit, due to the low resistance in the meter. Caution: Most ampere meters or DVOMs are rated for no more than 10 amps. Current flow above 10 amps will damage the internal fuse of the DVOM and render it unable to measure amperage. • Select proper function of DVOM and move leads to proper position. • Connect meter in series with (+) lead on the B+ side of the circuit. • Connect (-) lead of meter to complete circuit. DVOM will indicate current flow (Amps) through circuit. Typical Application of Amperage Testing • Proper Component Operation (Correct Current Draw). • Parasitic Draw Testing. Ensure meter is capable of handling current flow. £ 12 Electrical Measuring Equipment and Procedures Resistance Testing When set for resistance testing (Ohms) the DVOM must never be connected in a live circuit. The component or portion of a circuit being measured, must be isolated from the power source. Most modern day DVOM’s are self ranging when set to measure resistance, so the meter can not be damaged by out of range measurements. The test leads may be used without regard for polarity, unless the circuit contains a diode. The DVOM functions by placing a very small amount of current on the circuit being test¬ ed, the red lead must be placed on the anode side of the diode. • Select correct function and range (Most meters are self ranging in this function). • Disconnect power to circuit. • Disconnect any circuit wired in parallel with circuit being tested. • Connect test leads. DVOM will indicate resistance (Ohms) of component or circuit being tested. 13 Electrical Measuring Equipment and Procedures Continuity Testing The DVOM uses its own internal power supply to test the continuity of the circuit. The DVOM must never be connected in a live circuit. Any circuits wired in parallel with the cir¬ cuit being tested must also be disconnected. Continuity testing verifies that circuit connections are intact. The continuity mode is extremely fast and is used to detect either shorts or opens that last as little as 1 ms. When a change is detected the beeper tone is stretched to last at least 1/4 second so both shorts and opens can be audibly detected. This is a valuable troubleshooting aid when diagnosing intermittent faults associated with wiring, connections, switches and other components of the circuit. • Select correct function and range of DVOM. • Disconnect power to the circuit. • Disconnect any circuits wired in parallel. • Connect DVOM leads to the circuit to be tested. DVOM display will indicate continuity of circuit. 14 Electrical Measuring Equipment and Procedures Voltage Drop Testing Voltage Drop Tests determine the resistance of an active circuit, a circuit with current flowing. Voltage drop tests are preferred over simple resistance measurements because the power source is not removed from the circuit. By measuring the voltage on both sides of a load, the amount of voltage consumed by the load is measured. The voltage drops of each part of a series circuit added together must equal the power supply for that circuit while it is active. • Select proper function and range of DVOM. • Connect (+) lead to the B+ side of the circuit or component being tested. • Connect (-) lead to the B- side of the circuit or component. DVOM display will indicate the voltage drop in the circuit tested between the DVOM leads. Typical Application of Voltage Drop Testing • Determine proper component operation. • Active circuit continuity • Active circuit resistance. As a “Dynamic” test with the circuit operational, a voltage drop in any non-resistive part of the circuit indicates a fault in the circuit. 15 Electrical Measuring Equipment and Procedures 16 Electrical Measuring Equipment and Procedures