Fluke Multimeters in Automotive Maintenance
Perhaps the most commonly used automotive electrical repair tool is a multimeter. A typical multimeter can test voltage, current and resistance. Specially developed multimeters such as Fluke's F78/F88/F98 models have many features specifically for automotive testing, such as frequency, duty cycle, diode testing, temperature, latching time (Dwell), and even engine RPM (using accessories).
This information is how to use these high quality specialised multimeters from Fluke and their accessories for automotive repair. The analogue/digital combination of these meters has a completely different advantage to other meters, and their accessories make repairs easier and more convenient. Although multimeters have been used for many years to repair cars, most of them do not have specialised features for car repair. Computers and sensors of all kinds are widely used in today's cars, and a true multifunction multimeter is needed for automotive repair. Early use of analogue (pointer) type multimeter input impedance is too low, the measurement of electronic circuits have too great an impact. This kind of meter tests resistance mostly with 9V voltage, so it is easy to damage those sensitive electronic components. In recent years, the new digital multimeter (DMM) has been adopted in large numbers.
It has a high input impedance and is superior to analogue meters in terms of accuracy and safety. The voltage during resistance measurement is also low (typically 5V, 3.5V for Fluke), so it does not damage per-sense components. But the digital meter also has a problem. It can't display information about changes that increase or decrease the measured reading. This is seen in exhaust emissions testing and engine analysis where a purely digital meter cannot give a steady change in value.
Fluke overcame the shortcomings of digital meters and replaced them with a combined analogue/digital meter. It has the advantages of a digital meter and the dynamic measurements of an analogue meter.
Troubleshooting Considerations
When troubleshooting the electrical parts of a vehicle, the most important aspect is the process of reasoning about the cause of the fault. This process is important. This is because you can't see inside nor can you take a large number of components apart like you can with mechanical parts. Instead, using logic and logical steps you can quickly find the problem. The key tool in this process is the multimeter.
Classification of signals
The main signals tested are voltage, current and resistance. But the most commonly used is voltage. The questions involved are: Is there a voltage? What is the value of the voltage? What should be the normal value? What is the voltage drop across the component or connection point? For example, if a relay has an input voltage of 12.8 V and 9.2 V at the output, the voltage drop is 3.6 V. Note that the connectors of the wires should all be regarded as components and will produce a voltage drop. So it is also possible to cause a fault.
