The multimeter is the most important tool used in electrical diagnostic and testing. For any electrical circuit or system to function electric charge must flow through it. Due to these facts the following electrical quantities are important in electrical science, these are;
Current (Amperage)
Voltage
Resistance
Also another important test done using the alternator is the Test for CONTINUITY.
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In this course we would be using the common digital multimeter as the reference tool for this course.
Figure: Multimeter.
The multimeter indicating switch knob divided into eight (8) parts which signifies the eight different quantities that the multimeter can test, they are;
Voltage (DC)
Voltage (AC)
Current (DC)
Current (AC)
Resistance
Continuity
Frequency
HFE
This course would carefully cover all these various testing for this various quantities in cases where they are needed. Before we proceed on how we can test using the multimeter we would firstly consider these quantities.
Voltage (DC): This means voltage from a DC powered circuit, (NB; DC stands for alternating current) this is the usually voltage found in automobile electrical systems as the primary source of electrical power is from the battery which supplies DC voltage.
Voltage (AC): this means voltage from an AC powered circuit, (NB: AC stands for alternating circuit) this is hardly found in vehicle’s electrical systems and circuits. It can be found in rare occasion especially with old vehicles that has alternator which generates AC before they are converted to DC converters.
Current (DC): this means the current from a DC powered circuit it is also known as DC amperage, this is the usually current found in automobile electrical systems as the primary source of electrical power is from the battery which supplies DC.
Current (AC): this means the current from a AC powered circuit it is also known as AC amperage, It can be found in rare occasion especially with old vehicles that has alternator which generates AC before they are converted to DC converters.
Resistance: Resistance is the opposition to the flow of current, when electric charge flow through any electrical component it experience some resistance from that component, the level of resistance depends on the voltage/current rating of that component.
Continuity: continuity is to test electrical circuit if the connection is complete, it is also used to test a conductor (especially a long conductor) if current/voltage can flow through it.
Frequency
HFE
The last two quantities are hardly used in general automobile electrical diagnostics and testing except for more advance repairs jobs like ECU repairing.
The multimeter usually has a digital display screen, the control knob which can be used to test any of the eight quantities listed above.
There are different types of multimeters but basically the various types of multimeter works with the same principles, they usually have different numbers of ports for connecting lids and different kind of buttons or settings for taking various types of test.
Multimeter usually has two testing lid which are the positive and the negative testing lid. The positive lid is usually coloured red, while the negative lid is coloured black. The multimeter may have two, three or four ports for connecting the testing lids depending on the test being carried out.
Firstly, we would talk about the multimeter with four ports for connecting testing lids, these four ports which are to plug in the two testing lids. These four ports may be three depending on the type of multimeter, but on this course we use the multimeter with four ports as our reference tool. These four ports are
Voltage port
COM port
Milli-Ampere port (below 20 ampere)
20 ampere and above port
Voltage port: the positive testing lid (the red lid) is usually fixe here when testing for AC voltage, DC voltage, Resistance and continuity.
COM port: the negative testing lid is usually connected here for all tests.
Milli-Ampere port (below 20 ampere): the positive testing lid (the red lid) is usually fixe here when testing for AC current and DC current for amperage less than 20 ampere.
20 ampere and above port: the positive testing lid (the red lid) is usually fixe here when testing for AC current and DC current for amperage greater than 20 ampere.
Each of the various quantities that can be tested by the multimeter usually have various categories of values that it can be used to tested, these feature is available for the Voltage, Resistance, Amperage and Capacitances section of the multimeter. The control knob is used to activate any of the desired quantity to be tested.
There is also the HOLD button on the multimeter that helps to hold the figure recorded from the last test on the screen until when the button is pushed to stop it. Depending on the type of multimeter the power button may differs.
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