An electrical energy is invisible to naked eyes, There are multiple types of electrical parameters such as “voltage“, “ampere “and “resistance “. Electrical work is incomplete without knowing these parameters.
There are multiple types of meters to measure these parameters such as “voltmeter “for “voltage“, “Ammeter” for “current “while “ohm meter” for “resistance “. Some times, All the parameters needed to be monitor at a same time. It is really cumbersome to carry all these devices together.
For the convenience, To measure these parameters at a single point, There is device knows as “MULTIMETER“.
Multimeter
Multimeter as name suggest; a type of meter equipped with multiple functions. Multi-meter is single tool which is utilized to check the parameters such as “voltage“, “ampere “, “resistance” and much more .
Generally, A multi-meter consists of display, Buttons, Selector switch/Knob and testing leads. Multimeter contains microcontroller; the brain; Which monitors the particular parameters with the help of test leads. Measured values reflects on the display.
Generally, Multimeters have 2 terminal points. Also, There are multimeter with multiple terminal points more than 2. In those terminals, One of the terminal is common terminal. Rest of the terminals have different parameters with different ranges.
There are 2 test leads available for multimeter one is red and second one is black. Black test lead should be connected at common point on multimeter. While second; red rest lead should be connected to another function point of multimeter.
Different functions of Multimeter
There are multiple types of multimeter such as analog and digital, having multiple measurable parameters with different ranges and efficiencies. It all depend upon the requirement; which makes the selection of multimeter.
It is quite difficult having a multimeter with all the functions. That’s why we are saying multimeters are been bought on the requirement.
Functions; That multimeters carry; are listed below :
- Voltage AC
- Voltage DC
- Ampere AC
- Ampere DC
- Resistance
- Capacitance
- Continuity/Diode
- Temperature
- Transistor gain testing
Multimeter shared above is “3.5 digits hand held model M-86 by HTC“.
Meter measuring ranges are specified below :
- AC voltage : Ranges from 200mV to 700 Volts
- DC voltage : Ranges from 200mV to 1000 Volts
- AC ampere : 200 μA to 20 Amps
- DC ampere : 200 μA to 20 Amps
- Resistance : up to 20 M ohm
- Continuity/diode testing
- Temperature
- Non-contact voltage function
- HFE (Hybrid parameter function gain common emitter)
Types of multimeter
- Analog
- digital
- AC powered specific (specially designed for alternating current(AC) measurement)
- DC powered specific (specially designed for direct current(DC) measurement)
- general purpose
Method for usage of multimeter
- For particular parameter observation, knob or pointer must be pointed to a parameter. Parameters such as “resistance“, “continuity“, “voltage ” and “current“.
- Parameter range also need to be considered. Some multimeters have specified parameter range selection.
- Higher range more than the multimeter capacity can damage the multimeter or it does not reflect the actual value. It is also harmful for the person who is measuring it.
- Low range lower than the multimeter capacity does not reflect the precise actual value. That’s why measuring must be done in between the range of multimeter.
- Test leads must be connected at right point of multimeter. Current measuring terminals can be different from voltage measuring terminals.
- The terminals of specimen under the test, must be confirmed. Wrong test lead placement can damage the multimeter and it is also dangerous for the person who is measuring it.
- By placing the testing leads across the specimen terminals; parameter can get observed.
- Observed value can be hold through the hold button.
- After measurement, The knob should be placed to off position.
Next, We are going to discuss the method of measurement of different parameters one by one.
Continuity
When conductor length is short or its short length completely visible to eye, We can observe whether conductor is continuous or not. But when it is wounded in coil than it becomes difficult; visibly.
Continuity reflects, 2 terminal ends of a conductor, continuous or not ! there is complete electrical path in between 2 nodes. When 2 nodes are connected than circuit is having continuity(closed). We can say conductor is “continuous “. When 2 nodes are not connected than circuit is discontinuous(open) having no continuity.
Continuity of a conductor can be checked by multimeter which is having the option; known as “Continuity“.
Insulators have high resistance value. On the other hand, Even it is less, but conductors also have some resistance value. That means there should be some resistance range, under that range we can say, circuit is having continuity. While above the range, circuits have no continuity.
A conductor length with resistance value lower than 50 ohm, in continuity checking, Multimeter produces a beep sound or shows a value 0 or below 50 ohm. Above 50 ohm, meter do not produce the beep sound rather it only shows the resistance value.
Method of checking the continuity
- Place the multimeter knob to continuity.
- Place the test lead across specimen under test.
Diode testing
A diode is an electronic element made with semi-conductor. It is unidirectional element and allows current flow from only one direction acting like a NRV (non-return valve) for electrical current.
Through a continuity option, A diode can be checked. Some times special diode symbol is also been made on multimeter. Diode is having continuity in one particular direction. If polarity supply get reversed, It produces the heavy resistance in mega ohm; ideally it is infinite.
Through the option continuity, We can rectify the terminal ends of diode.
Method of checking the diode
- Place the knob at continuity or diode
- Place the test probes across the diode.
- Common test lead should be connected to cathode of diode while function test lead should be connected to anode of diode. If diode is fine, than beep will sound.
- In reverse testing across diode, multimeter does not reflect any value or it shows higher resistance .
Resistance
Resistance is a opposition to the flow of electrical current under the influence of applied pressure. Resistance is the property of a material. According to resistance; material is divided in three categories;
- Conductor : Having low resistance.
- Semi-conductor : having intermediate resistance level.
- Insulator : having very high resistance level.
The range of Resistance is also important which is going to be measure. Range selection should be done accordingly. Normally, An ohm symbol is marked on multimeter for Resistance measurement.
An image of Clamp-meter is shown below which shows the different Resistance ranges from 200 ohm to 200M ohm.
Method of checking the Resistance
- Select the Resistance range first.
- Place the test terminals across the test specimen.
- hold or note down the value.
Voltage AC
AC stands for “alternating current“. Voltage is a type of pressure which causes the current flow across the closed circuit. Voltage AC changes its magnitude with respect to time, It also changes its direction in alternate pattern at fixed interval, that’s why known as “alternating“.
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Method of checking the Voltage AC
- Place the knob at AC voltage sign.
- Voltage range should also be considered.
- Place the test probe across the 2 nodes to detect the potential difference.
- A potential of single node can also be observed by placing one of the test lead on neutral or earthing.
- Hold or note down the AC Voltage reading.
Voltage DC
DC stands for “direct current“. DC as name suggest, its magnitude remains constant throughout the time and it does not change the direction like wise; in AC.
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Method of checking the voltage DC
- Place the knob at DC voltage sign.
- Place the test probe across 2 nodes to detect the potential difference.
- A potential of single node can also be observed by placing one of the test lead on negative.
- Black common test lead should be placed at neutral otherwise a reading always shows negative sign value.
- Hold or note down the DC voltage reading.
Ampere DC
Multimeter has low ampere range, normally up to 10Amps. For that purpose multimeter needed to be inserted in between the circuit, in a series manner.
Method of checking the ampere DC
- Disconnect the circuit. Make sure circuit is completely discontinue, No power supply.
- The wire whose ampere needed to observed, must be disconnected in between so that multimeter can get inserted in between the circuit; in a series manner.
- Make sure connections are right and tight.
- Place the knob at DC ampere measurement. Select the ampere range.
- Start the circuit and observe the current.
- Hold or note down the value.
Ampere AC
for AC ampere also, multimeter needed to be inserted in between the circuit.
Method of checking the ampere AC
- Disconnect the circuit. Make sure circuit is completely disconnected.
- The wire whose ampere needed to observed, must be disconnected in between so that multimeter can get inserted in a circuit in a series manner.
- Make sure connection are right and tight.
- Place the knob at AC ampere measurement.
- Select the ampere range.
- Start the circuit and observe the current.
- Hold or note down the value.
Capacitance
Capacitance is the capacity of a capacitor to store an electrical charge under the influence of applied “potential difference”.
Method of checking the capacitance
- Before measurement make sure capacitor must be discharged.
- Place the knob across the capacitor testing.
- Place the test lead across the test capacitor.
- hold the capacitance value.
Common Mistakes While Using a Multimeter
Multimeter should be operated safely. One wrong step can not only damage the multimeter but it can be harmful too for the person who is testing it.
Next, Some of the common mistakes are discussed one by one.
- Wrong knob selection. Measuring voltage but knob is placed at continuity.
- Wrong range selection.
- Wrong leads placement such as red test lead at common side
- loose lead connections
- Not checking the condition of testing leads whether properly insulated or not ?
Advantages and Limitations
Advantages of multimeter
- Compact and handy
- multiple function at point single device
- no auxiliary power supply required mostly battery operated
Limitations of multimeter
- For current measurment we need to stop the running circuit so that multimeter can be place in between.
- low current range
- Physical contact with test point
Frequently Asked Questions About Multimeters
1. What is a multimeter and what is it used for?
A multimeter is an electrical test instrument used to measure different electrical quantities such as voltage, current, resistance, and continuity. Depending on the model, it may also measure capacitance, frequency, temperature, diode characteristics, and other electrical parameters. It is widely used for electrical testing, troubleshooting, maintenance, and repair.
2. How does a multimeter work?
A multimeter works by using its internal electronic measuring circuit to detect an electrical quantity and display the measured value. Depending on the selected function, the meter measures voltage, current, resistance, or another parameter and converts the measurement into a readable digital value. The test leads provide the electrical connection between the circuit and the multimeter.
3. What can a multimeter measure?
A typical digital multimeter can measure AC voltage, DC voltage, resistance, current, and continuity. Many advanced multimeters can also measure capacitance, frequency, diode voltage drop, temperature, and other electrical parameters. The exact functions depend on the particular multimeter model.
4. How do you measure AC voltage with a multimeter?
To measure AC voltage, select the AC voltage (V~) function and choose an appropriate voltage range if the meter is not autoranging. Connect the black test lead to COM and the red lead to the V/Ω terminal. Place the probes across the two points where the voltage is to be measured. The voltage should be measured in parallel with the circuit, and proper electrical safety precautions must be followed.
5. How do you measure DC voltage with a multimeter?
Set the multimeter to the DC voltage (V⎓) function. Connect the black probe to COM and the red probe to the V/Ω terminal. Touch the probes across the positive and negative points of the circuit. If the probes are connected with reversed polarity, a digital multimeter will normally display a negative value.
6. How do you check continuity using a multimeter?
Set the multimeter to the continuity test mode, usually identified by a sound or diode/continuity symbol. First, make sure the circuit is de-energized. Touch the probes to the two ends of the conductor or component being tested. A beep or a very low resistance reading generally indicates a continuous electrical path, while no beep or a very high/OL reading indicates an open circuit.
7. What do COM, VΩ and A terminals mean on a multimeter?
COM is the common terminal and is normally connected to the black test lead. V/Ω is used for measuring voltage, resistance, continuity, and commonly diode tests. The A or mA/µA terminals are used for measuring current, depending on the meter’s design. The red lead must be connected to the correct terminal for the selected measurement to avoid damaging the meter or creating a short circuit.
8. What safety precautions should be followed when using a multimeter?
Always select the correct measurement function and terminal before testing. Never measure resistance or continuity on a live circuit, and never connect a multimeter configured for current measurement directly across a voltage source. Use test leads and a meter with an appropriate CAT safety rating and voltage rating for the installation. Inspect the probes and leads for damage, keep fingers behind the probe guards, and follow the manufacturer’s instructions.