A selection guide for digital multimeters
Digital Multimeters (DMMs) are useful when it comes to measuring different electrical parameters across various applications.
Different types of DMMs are available, from the immensely portable handheld meters to the common benchtops and the highly useful clamp meters. Whatever the model, it is important to understand vital factors like accuracy, resolution, and safety features, which help to choose the appropriate tool for the job. This guide covers the various DMMs and the important factors that should be considered when making any informed decision.
Types of DMM
DMMs can be classified into different categories, with each category catering to a specific purpose and measurement. The popular categories come in various models and form factors.
- General-purpose DMM: These are preferred by hobbyists who prefer quick readings over accuracy. General-purpose DMMs are easy to use and extremely affordable. They are almost exclusively used for simple applications where they measure voltage, continuity, current, and resistance in simple electrical circuits.
Handheld DMM: These are battery powered devices preferred by electricians, maintenance engineers, HVAC specialists or any professional who need precision and flexibility coupled with mobility in the field. Handheld DMMs are reliable when it comes to current and resistance measurements, making these devices perfect for troubleshooting hazardous systems when and where mishaps occur. Professionals can choose from a wide range of options, beginning with the basic, most affordable model to advanced, premium units. Advanced models like MULTICOMP PRO MP730678 and MP730026 come with features such as temperature measurement that use a K-type thermocouple and NCV detection functions.
Figure 1: MULTICOMP PRO 72-7730ADigital Multimeter, USB Interface, 20000 Count, True RMS, Auto Range, 4.5 Digit (Source)
Benchtop DMM:Benchtop digital multimeters are best for industrial and laboratory settings. These devices are more advanced than general-purpose models. Benchtops have improved measuring capabilities such as automation programming, diode testing, and frequency measurement. Large, high-detached digit counts allow for detailed readings. These mains-powered instruments are typically integrated into workbenches and industrial processes. Benchtop multimeters assure accuracy in complex designs because they can interact with computers for data transfer and sophisticated computations.
Figure 2: KEITHLEY DMM7510 Bench Digital Multimeter, DMM7500 Series, 7.5 Digit, 10 A, 1 KV (Source)
Clamp type DMM: Also known as a clamp multimeter or digital clamp meter, this specialised instrument quickly measures electrical flow without direct contact. This multimeter is clamped around insulated cables. This adaptable instrument is perfect for professionals who need to measure current in high-power applications since it excels at reading amperage flowing through wires while measuring voltage using probes. The integrated jaws of the clamp meter allow for in-line current measurements, in contrast to typical multimeters that need the circuit to be disconnected. These DMMs provide power consumption and analysis of electrical performance by multiplying the current values and voltage.
Figure 3: FLUKE 376 FC Clamp Meter, True RMS, Wireless, 1 kA AC, 1 kV DC, 34 mm Jaw Opening Max (Source)
Modular DMM: This advanced measuring tool is fitted into automated test equipment (ATE). These flexible instruments have dual-play functionality and fast USB 2.0 connectivity, allowing them to function separately and as a modular unit.
Figure 4: KEYSIGHT TECHNOLOGIES U2741A , Modular Digital Multimeter, U2700A Series, True RMS, Auto, Manual Range, 300 V, 2 A, 5.5 Digit (Source)
True RMS DMM: A true RMS meter is the only device capable of accurately measuring both sinusoidal and non-sinusoidal AC waveforms. It is also always effective on power lines where the AC characteristics are unknown. Advanced models like FLUKE 3000 FC come with features like wireless connectivity.
Figure 5: FLUKE 287/EUR, Electronics Logging Multimeter, 50000 Count, True RMS, Auto, Manual Range, 4.5 Digit (Source)
Key selection criteria
- Accuracy and precision: Accuracy is vital in DMM selection. For standard activities, a ±3% accuracy is just about enough. However, greater accuracy is needed for applications that require precise readings, such as calibrating medical or automotive equipment. The accuracy must also be consistent. Accuracy is commonly expressed as a percentage plus a count (e.g., ±2%).
Digits, resolution, and sensitivity: Digits and resolution in a DMM describe how precisely the given instrument can measure and also display electrical values. The more the digits, the better the resolution. This is because a greater number of digits corresponds to the ability of the multimeter to identify a given signal's minute variations. For example, a ½ digit DMM provides more accurate measurements at ±20,000 counts, whereas a 3½ digit DMM may show readings up to ±2,000 counts.
3½ digits +/- 1999 2000 counts 4½ digits +/- 19999 20000 counts 5½ digits +/- 199999 200000 counts 6½ digits +/- 1999999 2000000 counts Figure 6: Digits and count calculation (Source)
Sensitivity is the tiniest change that can be observed in a measured signal. For example, a 5½-digit DMM in the 200 range can detect fractional changes in the signal due to its 1µV sensitivity.
Advanced analysis through visualisation: Higher-priced DMMs have sophisticated features not available in standard, lower-priced multimeters. Users can take advantage of histograms and trend charts to identify abnormal patterns and monitor values over a period of time. A few premium DMMs even offer digitised output via I/O ports. Whatever the price, a good DMM will always show clear and readable visualisations that make for better productivity and making the best decisions based on real-time data analysis.
Figure 7: Trend chart display (Source)
Figure 8: Histogram chart display (Source)
- Measuring range capabilities: These determine the range of tasks a digital multimeter can possibly perform, and it is thus critical to choose the correct one. Ensure the DMM can correctly measure typical voltage and current levels for simple electrical work. Diagnosing circuit problems also requires resistance measurement, and True RMS capability permits accurate readings of complicated AC waveforms. The multimeter must fit the precise measurement ranges and functions. There should be extra capabilities like capacitance measuring and testing diodes, transistors, and inductors of various sizes and shapes, depending on your needs.
Precision in AC, low dynamic current, and triggered measurements: The crest factor of a DMM is vital for measuring complex AC signals. This factor establishes the ratio of peak value to RMS value and ensures reliable readings, especially for pulsed signals. For low current and dynamic current measurement, accuracy is essential, especially in sensitive semiconductor applications where load voltage can skew the results. Dynamic current measurements are exceedingly difficult, especially when varying ranges are involved. For example, a portable radio transceiver in Figure 9 may switch between sleep, standby, and active modes; its standby draw ranges from 1-10 µA to its operating draw of 30-40 mA. Precise measurement techniques are necessary to accurately capture the complete current profile or any huge dynamic range.
Figure 9: Dynamic current measurements (Source)
Advanced triggering features allow precise timing and sampling in modern DMMs, ideal for capturing intermittent signals in wireless or power-sensitive devices.
- Compliance with safety standards: Safety is foremost when it comes to choosing a particular digital multimeter. Select models with overload protection to guard against accidental high-voltage exposure and those that comply with AS 61010.1-2003 safety standards. Choose the correct CAT safety rating (CAT I to CAT IV) depending on your application—CAT II for household use or higher for professional and high-energy environments. Higher CAT rating corresponds to better insulation and protection, and ensures that the instrument last longer and user safety not compromised.
Secondary measurement: Users can track several parameters all at once by unlocking the versatility of secondary measurements obtained by using digital multimeters. This makes for easier interpretation of complex data. For example, engineers can effortlessly verify the resistance for sensor accuracy when they use a thermistor to monitor the temperature. Similarly, a clearer understanding of the signal’s behavior can be obtained when AC and DC components are viewed simultaneously.
Primary measurement functions 34460A secondary measurement functions 34465A/70A secondary measurement function DCV ACV ACV. peak, pre-math ACV Frequency OCV, frequency, pre-math 2-wire,4-wire resistance Pre-math DCI ACI ACI, peak, pre-math ACI Frequency DCI, frequency, pre-math Frequency Period Period. ACV, pre-math Period Frequency Frequency, ACV, pre-math Temperature Sensor Sensor, pre-math Ratio Input/Ref Input/ref. pre-math Capacitance Pre-math Continuity None Diode None Figure 10: This table lists the secondary measurement functions available on the Keysight Truevolt series of DMMs (Source)
- Temperature variations and auto-calibration: When choosing a digital multimeter, it’s essential to consider temperature variations and auto-calibration features. The temperature difference between the calibration point and operating temperature can introduce measurement errors. For example, a temperature coefficient error is inevitable if a 22°C-calibrated DMM is used in a hot 40°C environment. This is why premium DMMs have auto-calibration (ACAL) features. These multimeters automatically adjust for any temperature drift. Such automatic adjustments ensure accurate measurements in fluctuating conditions. High-end DMMs are thus preferred for challenging, dynamic environments.
Advance interfacing: Interfacing allows an instrument and its external systems to seamlessly communicate with each other and is an important feature in DMMs. It is a mandatory feature in benchtop and modular models. Programmable interfaces (such as USB and Ethernet) are found in applications that require automated testing, complex measurements, or long-term monitoring where manual intervention is not a feasible solution. Efficient interfacing improves productivity, enhances accuracy, and facilitates complex post-processing. For instance, Keysight Benchvue allows users to synchronously measure multiple signals, quickly set up and gather data, and visualise or export results to Excel, Word or other tools. It not only simplifies and speeds up the measurement process but also—through real-time monitoring and graphical or numerical analysis—makes for more efficient measurements.
Figure 11: Diagram of PathWave BenchVue software remotely controlling and capturing test signals from a device under test (Source)
Figure 12: PathWave BenchVue’s data logger function screen (Source)
Application of digital multimeters
Industry professionals use DMMs for evaluating components and to diagnose electrical circuits. They are versatile and find use across several industries, from automotive to electrical maintenance. DMMs are needed to ensure that complex systems run reliably with minimum downtime. Various DMMs along with their respective applications are:
Types | Applications | Industries |
---|---|---|
Handheld DMM | General electrical tasks, troubleshooting, field testing, and basic circuit checks. | Electrical maintenance, HVAC, construction, basic electronics. |
Benchtop DMM | Precision measurements in R&D, laboratories, automated test systems, and calibration. | Research and development, laboratories, education, manufacturing, and calibration services. |
Modular DMM | Automated testing in industrial settings, integration into ATE (Automated Test Equipment) systems. | Manufacturing, aerospace, automotive, telecommunications, defence, industrial automation. |
Automotive DMM | Diagnostics of automotive electrical systems, measuring voltage, current, and resistance in vehicles. | Automotive, heavy machinery, transport, repair shops, electric vehicle testing. |
Wireless DMM | Remote measurements, data logging in hard-to-access locations, and wireless monitoring. | Construction, utilities, remote monitoring, smart infrastructure, wireless communication. |
Conclusion
As a user, you should choose a DMM most responsive to your needs. Consider important parameters like resolution, interfacing capabilities, and safety ratings before arriving at a decision. There should be a fine balance between accuracy, functionality, and safety. The appropriate multimeter improves measurement precision and productivity. The following are the variety range of instruments available with .