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What is a Digital Multimeter?
A multimeter is also known as multitester or volt-ohm-milliammeter is mainly an electronic measuring instrument that combines various measurement functions in a single unit. A digital multimeter comprises a numeric display in addition to a graphical bar that represents the measuring value.
Digital multimeters are known for rendering analog multimeters obsolescent as they have low cost, have higher precision, and are comparatively more physically robust. A multimeter is a hand-held device that is useful for finding basic faults and doing field service work. It may also be defined as an instrument that measures a very high degree of accuracy.
A test instrument, a digital multimeter is used for measuring various electrical values which include resistance, current, and voltage. However, modern digital multimeters are known for making many more measurements. It measures various electrical characteristics which is why it is termed as “multi”.
A multimeter is used for measuring AC voltages and currents, DC voltages and currents, resistances or temperatures, and capacities that depend on the functionality and design. A test may be performed for operating the diodes, transistors, or the electrical continuity with the device.
For stationary use in a workshop or laboratory, a digital multimeter in contrast to the mobile multimeter is designed in a specific way. Typically, the dimension of a tabletop device is generally 25 cm in width, 10 cm in height, and 30 cm in width. A digital multimeter is usually secured by its users in the front of the bench on an elevated and small stand which makes it easy to read and use.
Parts of Digital Multimeter
A multimeter is a useful and simple device, there are three parts of a digital multimeter that are display screen, ports, and a selection knob. A display screen of a digital multimeter helps in better visualization through illumination. A digital multimeter has a five-digit display screen – where one represents the sign value, the other four represents the number.
The selection knob helps the user in selecting various jobs which a single multimeter performs such as reading resistance, voltage, and current. It has two ports on the front, while one is mAVΩ that allows the measurement of three units voltage, resistance, and current up to 200 mA.
The red probe is generally found to be plugged in the port while the other COM port which refers to common is connected to -ve of a circuit with a black probe plugged in it. There is only one specific port which is 10A, the use of it is to measure the large current flowing in the circuit.
Operations of Digital Multimeter
The display screen of a digital multimeter shows measured values including the resistance or voltage. The multimeters generally have an illuminated and digital version which is known for having the highest readability. Generally, the multimeter operates with the main voltage of 230 V which is essential for it. Let’s read more about the operations of a digital multimeter.
There are various devices that are capable of operating in an alternated mode of battery. Majorly, the digital multimeters may be connected by using a USB or RS-232 cable to a computer. The long-term measurements of various readings may be easily recorded and the values can be displayed graphically by utilizing the visualization software.
Additionally, it can be printed out with a possibility of measuring values and time series which may be exported to the other devices using interfaces. It has been seen that the multimeters may differ significantly in their performance ratings. This is the reason that various values are to be studied and accurately compared while selecting the correct functionality for specific unit needs.
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The ranges which are possible for the individual sizes normally hold particular importance. When the multimeter is used for DC voltage measurement, the values are found to be typically present between 400mV to 1000 V comprising resistance up to 40 megohms. This is generally measured in the range of 400 ohms. There are frequencies of the order of 50 Hz to 100 kHz which can be easily measured.
The tolerance limits must be considered which indicates the reliability of measurement in the ranges. Many devices are known for offering automatic range selection, the unit of which automatically turns the possible ranges on. The less convenient devices comprise this choice to be done manually with the help of a switch.
However, this may be an uncomfortable position in which both hands are required for maintaining the stability of measuring points. The measurement process is a simple one comprising a digital multimeter and in which the cables are connected to the front panel jacks.
The measurement points of the component or the circuits which are to be tested (diode or transistor) may be shown as a measurement on the display screen. There are many multimeters that have a “HOLD” button that may freeze the measured value in the last. This happens so that the display screen doesn’t immediately have a zero value after the wire disconnection.
Features of Digital Multimeter
There is a wide range of digital multimeters which are present in the market. The features that a particular multimeter possesses make it a good multimeter. A few features of a digital multimeter that are highly useful and must be present in every multimeter are:
Auto-Rang – This is one of the features that enable a multimeter to change its internal range as per the need for detecting the correct current, resistance, and voltage of the circuit. It possesses the ability to stop the meter at a particular range along with the prevention of overloading when the meter is in volt range. These multimeters are generally of high quality and are full of numerous features.
A Back-Lit LCD – This one is considered as a fancy feature of a digital multimeter which has proved itself in dark situations when there was no light source for watching the reading multimeter.
Auto-Off – This is one of the features which is found in the higher-end version and facilitates users in forgetting to turn the meter off when not in use.
Decent Probes – These probes are considered as a bonus above all as in the multimeters leads are used for getting damage at the flex point. Therefore, it is considered better to use probes that make the work easier and easy for replacement whenever damaged.
Auto Polarity – This is an important feature that is known for showing the polarity of the current. The voltage of the current is measured which either shows positive reading (same polarity to meter connections) or negative reading (opposite polarity to meter connections). These types of facilities were not available in the analog multimeter. However, the meter deflects backward to reverse back for taking the readings accurately.
Working principle of Digital Multimeter
A digital multimeter or DMM may be defined as a multifunctional meter that is known for displaying electrical quantitative values on the LCD screen. Similar to the analog meter, a digital multimeter is capable of reading current, voltage, and resistance. Let’s read about the working principle of a digital multimeter.
The ability of the digital multimeter to display the measured electrical values without many computations is what makes it different from the analog multimeter. The design of the digital multimeter creates a way for building the processor allowing the user for taking measurements of the capacitance of a capacitor, a host of various high functional electrical measurements, and the inductance of a coil.
There are two types of digital multimeters or DMM which are scalable digital multimeter and auto-ranging digital multimeter. You need an idea of the value of current, resistance, or voltage which is to be measured when work is being done with the scalable digital multimeter.
Any failure in observing the values generally results in meter damage and inaccurate readings. Due to the high functionality, quick display readings which are achieved in the absence of any user completing calculations and ease, the auto-ranging digital multimeter is used widely.
An auto-ranging digital multimeter needs the selection of the electrical quantity which is being attempted to be measured. It is to be ensured that the leads are properly placed in the correct terminals before the readings are made from the LCD display. These types of digital multimeters permit the technicians to spend more time finding the root cause of the problem instead of calculating and switching.
Voltage testing is carried out for ensuring the electrical system’s effectiveness. Loads such as motors or lights are designed in such a way that they need nominal voltage for operation. The overvoltage generally results in the failure of equipment and not enough voltage which further results in the load that is not turned on.
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While voltage testing, the voltage reading is expected to be looked out for. In case the load is rated at 120 volts, there arises a requirement from the outlet to be more than 120 volts or minus 10%. If it is found that the voltage reading in outside the specifications then the issue may be found by using the voltmeter for isolating the load and by finding the problem with the lead or the source.
If you are willing to use a multimeter for testing voltage then the following steps are to be followed. The first step is figuring out whether the application used for testing uses AC or DC voltage. After this, the meter dial is to be adjusted to function suitably to AC or DC voltage.
It is all about adjusting the range to a number that is a bit higher than the value predicted. If the measured value is unknown, the range may be set to the maximum number available. Further, plug in the test lead in the voltage (red) and common (black) terminals. Once this happens, the leads are to be applied to the test circuit.
The test is to be positioned and repositioned till a dependable reading becomes visible on the LCD of the meter. Variations may take place in the reading while the measurement of the AC voltage is going on. It has been observed that the measurements become steady as and when the test continues.
When there is no particular physical way to find out if the job is being performed by the load or not as there may be no indicators or the load present in a hazardous area, this is when the testing is used for current. When it is found that the voltage is being tested or found to be available at the load, the whole story isn’t told until the current is being measured.
It is necessary that the load consumption power is understood which is measured in watts. Watt is calculated by multiplying volts by the amps. A digital multimeter is used for the purpose of measuring and giving an indication regarding the current flowing. The current may be tested in numerous ways out of which the reliable procedure is the one performed using the clamp meter.
Resistance may be tested using a digital multimeter. The procedure includes turning the power off in the circuit board which is to be tested. Once this happens, the meter dial is adjusted to the resistance mode. Choose the required range on the dial and plug in your test lead in the terminals which are suitable for you. Lastly, connect the leads to the component which are to be tested and note the reading.
Use of Digital Multimeter
A digital multimeter is a test tool that has many uses. It is used for measuring two or more electrical values consisting of principal voltage (volts), resistance (ohms), and current (amps). It may be said that a digital multimeter is a standard diagnostic tool used by technicians in the electronic or electrical industries.
Long ago, digital multimeters were replaced by needle-based analog meters because of their ability to measure with higher accuracy, impedance, and reliability. These multimeters are known for combining the testing capabilities of single-task meters including the ohmmeter (ohms), the voltmeter (volts), and ammeter (amps). They often include numerous additional advanced features or options.
Digital multimeters are much more accurate when compared to analog multimeters. They are known for reducing interpolation and reading errors. It has an auto-polarity function which is known to assist in preventing problems that arise during connection creation of meter to the test circuit having the wrong polarity.
It is known for eliminating parallax errors. In case the pointer of the analog multimeter is viewed from a diverse angle, a different value is shown. This is what is known as a parallax error. This digital multimeter is known for its numerical display which solves the problem. Its display doesn’t have any moving parts which makes them free from any kind of shock failures.
It has a high reading speed which makes it easier to read. It doesn’t require zero adjustments, unlike analog multimeters. The digital output is considered suitable for processing and recording further as it has been found to be useful in rapidly increasing the computer-controlled applications range.
The advent of integrated circuits has reduced the size, cost, and power need of digital multimeters to a great extent. Its accuracy is increased as a result of the digital readout. Generally speaking, there may be a mistake in reading the scale of the analog multimeter but the digital ones with LCD display show accurate readings.
They are used for maintaining the testing continuity, diodes, capacitors, transistors. Advanced multimeters are used for measuring the frequency. It has a portable size which makes it very easy to carry anywhere anytime.
The auto-ranging feature for this multimeter is helpful in selecting various measurement ranges which prevent the damage that might be caused if the wrong range is selected. Also, these have very high input impedance.
Yet some of its other uses of digital multimeter include having microprocessors that are capable of storing the reading for future processing. Additionally, these cause fewer effects that arise from meter loading on the circuit which being tested.
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