Parts and Function of a Multimeter

• Needle Pointer - The needle-shaped rod  that moves over the  scale of a meter. It is mechanically  connected to the  moving coil. It indicates the  measured values on  the multimeter scale.

• Scale -  A series of markings used for reading the value of a quantity. It can have different types of scale; For Voltage and Current Reading, the scales have mostly linear values which means equal divisions. For Resistance Reading, the scale have logarithmic values whicn means unequal divisions.

• Dial/Infinity Knob - Sometimes known as Zero Corrector Screw. Makes it possible to adjust the pointer to the zero position of the scale.

• Zero Ohm Adjuster - Is used to zero-in the pointer before measuring resistances.

• Range - Allows more accurate measurement for small values. 

• Range Selector - Makes it possible to select different functions and range of the meter.

• Test Probes - Is used to connect the circuit to the electronic components being tested. Serves as the input portion of the multimeter. Red test probe becomes positive in some instances, while the black one is negative. 

One of the functions of a multimeter is being an OHMMETER. An ohmmeter is used to measure resistances in a specific component or in a circuit. An example scale of an ohmmeter is shown below. 

The scale can be divided into eight areas where individual treatment has to be made. The areas involved are 0- 2, 2-10, 10 -20, 20-50, 50 – 100, 100- 200, 200 – 300, 300 – 500, 1K, 2K and infinite. 

Several mathematical computations will be involved to show the manner how values of individual lines are resolved. 

Formula: 

Value of 1calibration = line distance / total calibrations involved 

OHMMETER READING EXAMPLE:

Ohmmeter reading can be performed by taking note of the range selected and the areas where the needle pointer rested. And then identify the value of every calibration in that area. 

Consider the figure below.

Looking at the needle pointer of the multimeter, it rested at the areas inside 0-2 which means that every calibration is equal to 0.2 ohms (Ω). In calculating the measured resistance, we need to consider the range selected. 

For the ranges, we can use the group of color yellow ranges shown in the picture below.

Therefore we can use this formula in solving for resistances using an Ohmmeter.

Resistance Reading = no. of calibration x value per calibration x range selected

Let say we start setting our range selector at X1. So;

Resistance Reading = 8 x 0.2 x 1 = 1.6 ohms or 1.6 Ω

If we set our range selector at X10. So;

Resistance Reading = 8 x 0.2 x 10 = 16 ohms or 16 Ω

If we set our range selector at X100. So;

Resistance Reading = 8 x 0.2 x 100 = 160 ohms or 160 Ω

If we set our range selector at X1000 or 1K. So;

Resistance Reading = 8 x 0.2 x 1000 = 1600 ohms or 1.6 KΩ

Another function of a multimeter is being a VOLTMETER. A voltmeter is used to measure alternating current voltages (ACV) and direct current voltages (DCV) in a circuit. An example scale of a voltmeter is shown below. 

There are rules to consider in measuring voltages using a voltmeter, including the formula in getting the value per graduated line in every range.

1.  Range to 10v AC/DC, every graduated line is 0.2 volt. 

2.  Range to 50v AC/DC, every graduated line is 1 volt.

3.  Range to 250v AC/DC, every graduated line is 5 volts.

4.  Range to 750v AC/DC, every graduated line is 15 volts.

5.  Range to 1000v AC/DC, every graduated line is 20 volts. 

6.  Every graduated line  = range/50 

VOLTMETER READING EXAMPLE:

Voltmeter reading can be performed by taking note of the range selected and the area where the needle pointer rested. And then identify the value of every graduated line in that selected range. 

One important consideration needed in performing voltmeter reading is to always set/select a range higher than the expected value to be measured. 

Consider the figure below.

We can identify the number of graduated line where the needle pointer rested by counting it from zero position at the right. Looking at the needle pointer of the multimeter, we can see that it rested in 44th graduated line of the voltmeter scale.

For the ranges, we can use the ranges identified in the picture below.

Therefore we can use this formula in solving for voltages using a voltmeter.

Voltage Reading = no. of graduated lines x value per graduated lines

Let say, we start setting our range selector at 10 ACV. So;

Voltage Reading = 44 x    0.2  =   8.8 volts or 8.8V

If we set our range selector at 50 ACV. So;

Voltage Reading = 44 x    1  =   44 volts or 44V

If we set our range selector at 250 ACV. So;

Voltage Reading = 44 x    5  =   220 volts or 220V

If we set our range selector at 750 ACV. So;

Voltage Reading = 44 x    15  =   660 volts or 660V

If we set our range selector at 1000 ACV. So;

Voltage Reading = 44 x    20  =   880 volts or 880V

• To accomplish this, insert the red probe of the multimeter to one of the current measuring sockets: 

• mA (to measure low level of current) or 

• 20 A (to measure larger current)

• Connect the meter along the line through which the current is to be measured (nothing but series connection).

• Next set an approximate range around which we expect the current to be in the ammeter section. In this state, if we switch on the power supply, then the meter will read the current flowing through the circuit.

• To start with, one has to insert the red and the black probes of the multimeter to the sockets marked as ‘V’ and ‘COM’, respectively.

• Then we have to select the expected range in which our voltage would be. Simultaneously, even AC or DC should also be selected in the voltmeter section.

• On doing so, the meter reads the value of the voltage, provided one connects the leads across the component (in parallel fashion) or at the point at which the voltage needs to be measured.

• Here the red and the black probes of the multimeter are inserted into the sockets marked as ‘V’ and ‘COM’, respectively while the selection switch is set to an expected range in ohmmeter region.

• Now, the leads need to be connected across the component whose resistance is to be known. On doing so, we get a reading in the display part of the multimeter which reads the value of the resistance.

• Insert the probes into the sockets as that in the case of voltage measurement and set the selection switch to point towards diode check position.

• Now when the red lead of the multimeter is connected to positive terminal of the diode while its negative lead is connected to the negative terminal of the diode, then we have to get a low reading on the multimeter.

• On the other hand, if we connect the red lead to the negative terminal of the diode and the black to the positive terminal, then we have to get a high value. If the readings obtained are as per our expectation, then we say that the diode is working properly; else no. 

• Continuity check is used to know whether there exists any low resistance path via two points i.e. to check whether the points are short or not.

• To accomplish this task, the probes are inserted into the sockets as that in the case of voltage measurement and selector switch is made to point towards continuity check position.

• Then, the points to be tested are touched with the leads of the probes. Now, if the multimeter beeps out, then it means that the points are shorted or else the resistance between them can be read out from the display.