Multimeters are widely used in measurement technology. The multimeter can measure various electrical quantities like resistance, AC and DC voltage, current, capacitance, etc. at one go. Voltmeter, ammeter, and millimeter are combined in a multimeter, which is also called VOM (Volt-Ohm Millimeter). Multimeters may also have different capabilities, for example, diode testing, coherence testing, transistor testing, TTL logic testing, and repetition testing. This device plays an important role in finding the problems present in the circuit so that those problems can be easily rectified.
It is a handheld device with positive and negative indicator needles on a numerical LCD digital display. Multimeters can be used to test batteries, household wiring, electric motors, and power supplies.
The essential parts of a multimeter mainly consist of a display, power source, probe and control.
Functions of Multimeters
These devices are capable of doing different readings depending on the model. So basic types of multimeters are mainly used to measure amperage, resistance, voltage, check continuity, and a complete circuit can be tested like the following.
- Resistance in Ohms.
- Capacity in Farads.
- The temperature is Fahrenheit/ Celsius.
- AC Voltage & Amperage.
- Inductance Henrys.
- DC Voltage & Amperage.
- Frequency in Hz.
- Conductance in Siemens.
- Duty Cycle.
In some types of multimeters, special sensors or accessories may be attached for additional readings such as acidity, light level, alkalinity, wind speed, and relative humidity.
How to use a Multimeter?
The multimeter has a rotary switch on the front panel, which is used to select various electrical parameters to measure electrical properties. The multimeter consists of three parts display, knob, and port. Typically, the display on a multimeter has 4 digits indicating positive and negative signs. Some types of meters have illuminated displays so that they are clearly visible even in low light conditions. Using the selection knob allows the operator to adjust the multimeter to check a number of parameters such as current, voltage, and resistance.
The function and operation of a multimeter are the same for both analog and digital types. It has two leads or probes red and black and three ports. The black-colored probes are used to connect the GND of a circuit to a common COM port, while the red-colored probes are plugged into other ports as needed.
In a multimeter, a special port such as 10A is mainly used if there is a need to measure large currents above 200mA. As a port, mAVΩ is used to measure current, resistance, and voltage up to 200 mA into which the red probe is inserted. These probes have a banana-shaped connector on the end-user for plugging into the multimeter.
Once the probes are plugged in, the knob can be turned in the center of the appliance to perform the appropriate function for the specific component tested.
To get a reading from the meter, the end of each probe needs to touch the end of the terminals of the components. The types of multimeter devices are very safe to use on instruments and circuits to provide current or voltage that does not go above the meter’s highest rating. Great care must be taken while making measurements.
Types of Multimeters
There are main types of multimeters like Analog and Digital.
An analog multimeter or VOM (volt-ohm-millimeter) measures readings indicated on a scale using a moving coil meter and a pointer. A moving coil meter consists of a coil wound around a drum placed between two permanent magnets.
When current passes through the coil, a magnetic field is induced in the coil, which reacts with the magnetic field of the permanent magnets and the resultant force causes the pointer attached to the drum to deflect on the scale, thereby displaying the current reading. Is. It also has springs attached to the drum which provide an opposing force to the movement of the drum by which the deflection of the pointer is controlled.
For the measurement of DC, the de Arsonval movement described above can be used directly. However, the current to be measured must be less than the meter’s full-scale deflection current. For high currents, the current divider rule is applied. The meter can also be used for multi-range current measurement, using different values of the shunt resistors. For current measurement, the instrument is connected in series with an unknown current source.
For DC voltage measurement, a resistor is connected in series with the meter, and the current passing through the resistor remains the current passing through the meter and the full reading is indicated by the voltage reading. For voltage measurement, the instrument is connected in parallel with an unknown voltage source. Multirange measurements use different resistors of different values, which are connected in series with the meter.
For the measurement of resistance, the unknown resistance is connected in series with the meter and with a battery. The current passing through the meter is proportional to the unknown resistance. For AC voltage or current measurement, the same principle is applied, the AC parameter being measured is first rectified and filtered to obtain the DC parameter and the meter displays the RMS value of the AC signal.
Advantages of Analog Multimeter It is cheap, has no battery required, and can measure fluctuations in readings. The two main factors affecting measurement are sensitivity and accuracy. Sensitivity refers to the reciprocal of the full-scale deflection current and is measured in its unit ohms per volt.
A digital multimeter has a digital display which is a liquid crystal display (LCD). It displays the values of the quantity measured as numerical values. This display works on the principle of Seven Segment Display and its seven-segment display has a total of seven displays and any number between 0-9 can be represented on the screen by these seven displays. It has two probes positive and negative which are represented by black and red colors.
There are two jacks present on the multimeter one is a COM JACK to which the black-colored probe is connected and the other is a positive JACK to which the red-colored probe is connected as per the user’s requirement for measurement.
The jacks marked VΩ and COM jacks on the multimeter are used to measure voltage, resistance, current, and test diodes. For measurement and testing, the unit and range have to be selected which is done by the rotary switch or sector present on the meter. It is also used to turn on/off the multimeter. A multimeter has a continuity test point, which is used to test the continuity between two terminals in electrical and electronic circuits. This overload protection prevents damage to the meter and circuit and protects the user.
The digital multimeter consists of an LCD, a knob for selecting different ranges of three electrical characteristics, an internal circuitry that houses the signal conditioning circuitry, and an analog to digital converter. The PCB consists of concentric rings that are connected or disconnected depending on the position of the knob. Thus, the required parameters and limits are selected and the section of the PCB is activated for the respective measurement.
To measure resistance, current flows from a constant current source through the unknown resistor, and the voltage across the resistor is amplified and inserted into an analog to digital converter, and the resulting output as resistance is represented on a digital display. Is. To measure unknown AC voltage, the voltage is first downregulated to obtain the appropriate range and then rectified and filtered into the DC signal and the analog DC signal is fed to the A/D converter to receive the display, Which will display the RMS value of the AC signal.
To measure an AC or DC, one converts the unknown input into a voltage signal and then inputs an analog to a digital converter to obtain the desired output (with correction in the case of AC signals). Advantages of a digital multimeter It provides the output to directly display the measurement value, high accuracy, and the ability to read both positive and negative values.
Types of Digital Multimeters
Digital multimeter types are available in three types.
Fluke Digital Multimeter
The Fluke Digital Multimeter is designed with several different collaboration functions. It has a large display and is used to measure voltage and electrical resistance. There are some instruments available including many facilities to measure humidity, duty cycle, pressure, frequency temperature etc. This meter is used a lot.
This multimeter is primarily used for calibration efforts and for calibrating currents, volts and other power units. Temporary multimeter can be protected with floating voltage. It is a portable meter which is also used to measure voltage, current and test diode. The multimeter has a multi selector to select the desired function. The temp multimeter is meant to select most measurements automatically. This means that the magnitude of the signal no longer needs to be determined in order to obtain an accurate reading, it is sent directly to the appropriate port for the desired measurement. This multimeter is protected to avoid damage if it is connected to the wrong port.
Clamp Digital Multimeter
Clamps use a digital multimeter to measure the flow of electricity. This multimeter includes a clamp feature that measures amps while the probe measures volts. Adjustment of power usage can otherwise be done by multiplying the reading of the voltage with the amps watts. One feature of this multimeter is the variety of settings that are used at the time of measurement.
This multimeter includes fixed instruments to measure the flow of current. This device is different from the floating type. In a floating multimeter, a clamp is used to measure the flow of current. This tool is recommended for professionals only.
The auto-ranging multimeter is a simple multimeter. This multimeter has a knob in the middle and has a low position. It is unable to automatically switch to measure. This tool is used in simple projects. For beginners and home electricians, this tool is highly recommended. This instrument can measure only one component at a time.
Advantages of Multimeter
The multimeter has the following advantages:
- Provides high accuracy of measurement quantities.
- It is found to have high input impedance so there is no effect of loading.
- In this a clear reading can be obtained at high viewing distance.
- Power generation can be used to interface with additional equipment.
- These are less expensive due to the integrated technology.
- In this the output display can be provided automatically.
- It has auto polarity function.
Disadvantages of Multimeter
The multimeter has the following disadvantages:
- It is costlier as compared to other meters.
- There are issues of power supply requirement and isolation.
- It does not perform well through fluctuations in measurement.
- This LCD display mainly relies on an external power source such as a battery.
- The range of this meter is 1V. If the range is exceeded, the multimeter may be damaged.
- The meter should be used as per the manufacturer’s specified measurement as well as the grade rating otherwise the meter may be damaged.
Applications of Multimeter
The multimeter has the following applications:
- It is used for AC/DC voltage and current measurement.
- Used in resistance and continuity measurement.
- Used in Diode Testing.
- Used in measuring capacitance.
- Used in the measurement of time and frequency.
- To test the battery.
- A broken power cable can be fixed by this.
- Switches can be tested using this.
- It can test an outlet.
- Older incandescent type light bulbs can be tested.
- It can be used in environmental and temperature applications.