How to choose a multimeter? Types of multimeters and their characteristics
A multimeter, combining 3 basic ones (voltmeter, ammeter and ohmmeter), allows you to measure voltage, amperage and resistance. It is used to test items such as batteries, radio components, cables, electrical circuits, switches, power supplies, motors, etc. Electricians, car repair shop employees, laboratories, etc. use instruments to diagnose and troubleshoot electrical systems.
Multimeters can be digital or analog and differ in the range of values for the measurement of which they are calculated. The latter determines which devices can be tested with a specific model and which ones cannot.
Measuring instruments may have special functions that make them more useful for certain tasks. For example, the best multimeters with an oscilloscope allow you to read the change in the measured parameter over time. The temperature sensor is useful when measuring the temperature-sensitive components of a computer.
Customers who take into account the additional functionality of multimeters will definitely find a model that meets their needs.
Multimeters are used to measure the three basic parameters of electrical circuits, components and systems - voltage, resistance and current.
In the voltmeter mode, the device determines the potential difference, that is, the voltage (constant or alternating) between two points of the electrical circuit. This is the most common type of measurement of electrical circuits, which is made by simply touching the test leads to two different points in the system. The device determines the potential difference, without requiring changes in the circuit.
As an ohmmeter, a multimeter measures the resistance that a particular element provides to electric current. In this case, the part must be removed from the chain for individual testing. Attempting to measure the resistance of an element connected to a power source may damage the instrument.
Also in the mode of an ohmmeter is produced and a dial with a multimeter electrical circuit. Unclosed contours have infinite resistance, and closed - small. In the latter case, the device gives either a sound or a light signal.
The ammeter measures the amperage (constant or alternating) when the multimeter becomes part of an electrical circuit. That is, the measuring device itself must be included in the circuit, breaking it in such a way that the current passes through it.
Digital or analog?
One of the first decisions that should be made before choosing a multimeter is to decide between a digital and an analog model. In addition, it is necessary to clarify a number of issues related to the power of the device and its intended use.
Digital multimeters differ from traditional analog ones in several ways, including the way indications are indicated, the level of accuracy and the ability to download data to a computer. The measurement results are displayed on the LCD screen in the form of specific decimal numeric values. Accuracy is generally considered equal to 1% for direct current and within 2% for alternating current. The readings of digital multimeters can sometimes be downloaded to a computer for later viewing and analysis. And devices with oscilloscopes allow you to get a lot of data associated with the timeline.
The result of the measurement of analogue multimeters is more difficult to count, since it is displayed by a pointer on a numerical scale with discrete values. The user must interpolate intermediate readings, therefore the accuracy of such measurements does not exceed 2.5%.
Multimeters for different purposes
The sensitivity range is the maximum and minimum values that the meter can read. Generally speaking, this determines the scope of each specific model. The characteristics of a multimeter designed for a car battery voltage are insufficient to measure low-voltage sources. This means that the buyer must know exactly the purpose of using the meter. For example, the most popular objects of inspection are fuses, batteries, incandescent lamps, lighting switches, boilers, transistors, integrated circuits, automotive electronics.
Different applications require different sensitivity ranges. Low voltages in integrated circuits cannot be tested with a multimeter designed for testing automotive systems.
Resolution and numbers
Resolution is defined as the smallest change in input signal that produces a change in output. The resolution of a digital multimeter is expressed by the number of digits it can display. For example, a 3½-bit indicator consists of 3 digits, taking values from 0 to 9, and one position with values of 0 or 1. Thus, the resolution is ± 1999, because the device can display positive and negative numbers from 0 to 1999 Most of the instruments on the market are 3½ or 4½-bits with a range of values of ± 1999 or ± 19999, respectively. Sometimes in the instructions for the multimeter resolution is indicated as a number that the device can display without changing the measurement range. In this case, a 4½-bit display is indicated by a score of 19999 or 20000.
Multimeters with a graphic display allow you to read and display readings that change over time. This function is useful when it is important to know how the characteristics of a particular equipment change over a specific period. Oscilloscopes can be equipped with both digital and analog measuring devices, but only digital models allow you to download data to a computer for storage and viewing.
How to choose a multimeter: functionality
Below are some additional features that are important when choosing a meter. Some of them, such as the range of sensitivity, are common to all measuring instruments.
- Automatic selection of the measurement limit adjusts the multimeter to the required input range without user intervention. This saves time when performing a large number of tests.
- A temperature sensor is required to test temperature sensitive hardware such as computer processors.
- Capacity measurement allows you to determine the ability of a part to store an electric charge.
- The dialer with a multimeter diode and transistor is useful when testing digital logic and integrated circuits.
- A low-pass filter is used when troubleshooting motor drives in which the frequency converter sends pulsed modulated non-sinusoidal voltages to the motor terminals. The filter blocks unwanted voltages above 1 kHz, which improves the accuracy of composite waves.
- The low impedance mode is designed to block interference or induced voltages resulting from capacitive coupling between wires. This improves the accuracy of measurements.
- Compensation offset in certain situations also helps to achieve greater accuracy of the instrument. Produced by determining resistance using two different currents used to determine the presence of biased voltages in the input circuit. This eliminates unexpected constant voltages and displays the corrected measurement, bias voltage, or leakage current.
- The speed of displaying information on the display (the frequency of its update) is important for obtaining more accurate readings.
- The "Hold" function allows you to save the contents of the screen to record the readings.
- Large numbers and the presence of screen illumination facilitate the use of a multimeter, since in this case readings can easily be read even in dark rooms and basements, where sometimes electrical systems may be required to be checked.
- Calibration according to ISO or GOST indicates compliance with standards, which ensures the maximum level of accuracy of readings.This is especially important for companies that have the appropriate certificates that ensure that their products comply with strict quality standards. Therefore, the presence of measuring devices that meet the standards, in these cases is of great importance.
How to choose a multimeter on the expected load?
Maintaining the right balance between current and expected needs and financial capabilities is often problematic. The cost of a multimeter increases as its rated load increases. In this case, it may be tempting to save money and opt for a model designed for a smaller load. This significantly reduces the life of the multimeters and leads to additional costs. Calculation for many years to come will allow you to make a choice based on achieving the most efficient life cycle, and not just the purchase price.
The topic of safety of work with electrical equipment is extensive and requires careful familiarization with the instructions for the multimeter. We should also mention the following.
First, is it worth it to plug a multimeter into the socket in order to measure the voltage of the network? If the buyer has no experience in handling electricity, then this is not worth it.Before trying to figure out how to use your measuring device, it’s better to spend some time learning from a more experienced user. And there is a good reason for this.
It seems incredible that a seemingly innocuous device could explode or cause serious harm. But it is so. This phenomenon is called “arc explosion”, and it has many potential causes. For example, high voltage can ionize the air between the multimeter's probes and make it a conductor. As a result, an electric arc arises, which can cause a fire or even the death of the user.
In addition, the arc explosion has a volume of 140 dB, which corresponds to the strength of the sound of a jet plane taking off. This means that the least damage that can be expected is damage to the user's hearing and those around them. Again, those who do not have experience with electricity, before using multimeters to test circuits connected to the network, must be trained by an experienced user.
Multimeter probes should be well insulated and have plugs corresponding to the instrument connectors.Models with built-in fuses are available. Probes not equipped with them, connected to a low-impedance voltage source, often fail when the multimeter is mistakenly set to measure current or resistance.
Well-known brands and where to buy them.
According to user feedback, there are many companies on the market that offer high quality products. The leading global brands include such manufacturers of the best multimeters as Fluke, Agilent HP, Gossen, Sealey, Wavetek, Sanwa, Kyoritsu.
Various online stores (for example, eBay) offer a large number of measuring instruments. Buyers who need multimeters calibrated in accordance with ISO or GOST requirements should include the name of the standard in the search box of the site (for example, “ISO multimeter”). Similarly, measuring instruments with the desired functionality can be found.
A properly selected electrical multimeter capable of withstanding the intended load is a useful tool for household and industrial applications. It allows you to measure voltage, current and resistance in printed circuit boards, batteries, lamps, fuses and other electrical components.You can choose between digital and analog multimeters, which have their own advantages and disadvantages. Digital models allow you to download data to computers for analysis, and oscilloscopes can view changes in values over time.
The next most important issue that needs to be addressed before choosing a multimeter is its sensitivity range. The device, designed to work with high voltage, is not designed for low potential of household batteries or typical printed circuit boards. Similarly, a multimeter designed for domestic use has a very low upper measurement limit for testing high-power devices.
Acquaintance with reviews of multimeters with advanced functionality, including additional sensors or the availability of verification for certified industrial use, will allow the user to make the right choice and facilitate the search for the required model.