Benchtop vs. Handheld Digital Multimeters
Digital multimeters (DMMs) come in at least three forms: benchtops with a front-panel display, modular cards (without a front-panel display) that slot into a card cage, and handheld portable devices that are easy to carry around. This blog post focuses on the features and differences between benchtop and handheld DMMs. Their designs and certifications support different functionalities and applications.
Table 1 compares the features and key specifications of some of Keysight’s handheld and benchtop DMMs.
Table 1. Sample selection of Keysight DMM with features and key specifications
The benchtop and handheld DMMs have many commonalities in terms of measurement functions, such as direct current (DC) and alternating current (AC) voltage, DC / AC current, resistance, capacitance, diode check, signal frequency / period, continuity test, and temperature measurements. However, benchtop and handheld DMMs are meant for different applications.
In general, benchtop DMMs have higher resolutions, better accuracy, and faster reading speeds than handheld DMMs. Most product designers and test validation engineers require those capabilities for product characterization and validation work. Handheld DMMs are portable, withstand harsh working conditions, and offer improved safety. Handheld DMMs have good enough resolutions, accuracy, and reading speed for the outdoor environment and quick verifications.
Five Reasons to Choose Benchtop DMMs
Here are five reasons to consider benchtop over handheld DMMs.
1. Precision and accuracy
Benchtop DMMs usually have higher-performance analog-to-digital converter integrated circuits (ICs) and associated precision signal conditioning circuitry. They provide higher precision and accuracy to meet the demands of product characterization and validation work. Table 1 shows Keysight’s benchtop DMMs with resolution starting at 5.5 digits. The top-of-the-range high-performance 3458A DMM has 8.5 digits of resolution. Accuracy can be measured based on voltage, current, or resistance and guaranteed over a certain period. DMM hardware accuracy tends to drift over time. Table 1 uses basic one-year DCV accuracy as a comparison for benchtop and handheld DMMs. The lower the part-per-million (ppm) count, the higher the accuracy. Benchtop DMMs beat handheld DMMs in terms of accuracy hands down. The 3458A is the industry-leading DMM with only 8 ppm, in terms of one-year DCV accuracy.
Most benchtop DMMs have four-wire measurement capability, which ensures a greater level of accuracy than traditional two-wire measurements. Most handheld DMMs perform only two-wire measurements. If you are working with applications requiring that extra level of accuracy, select a benchtop DMM that supports four-wire measurements.
2. Reading speed performance
Benchtop DMMs are not limited by power and usually have higher performance, albeit power-hungry ICs to get at least 100x–1,000x reading speed performances compared with handheld DMMs. R&D product designers and test validation engineers tend to take thousands of test measurements to characterize their products thoroughly. Therefore, making high-speed and reliable measurements is a must using a benchtop DMM.
3. Wide measurement ranges
When you need flexibility in wide measurement ranges — for example, to measure very low current in the 1 µA range and then quickly measure in the 1 mA range or higher — a benchtop DMM is more versatile than a handheld DMM. The Keysight 34420A is a micro-ohm benchtop DMM that measures DCV and resistance measurements at 100 picovolts and 100 nano-ohms, respectively.
4. Programming automation
Most midrange and top-range benchtop DMMs have multiple connectivity interfaces, such as USB, GPIB, LAN, and RS-232, to connect to your computer. Most benchtop DMMs provide SCPI language compatibility for remote language programming. You can use MATLAB or the programming software of your choice to control your benchtop DMM via SCPI commands to automate your test sequences. Most handheld DMMs on the market do not offer this programming automation.
5. Display and analysis
Modern benchtop DMMs come with large graphical screen displays. Keysight Truevolt Series DMMs have advanced graphical features such as trend charts (value vs. time) and histograms. The Keysight 34465A and 34470A DMMs have a built-in mode that can digitize the measured signal and display it on the front-panel screens.
Four Reasons to Choose Handheld DMMs
Here are four reasons to consider a handheld over benchtop DMMs.
1. Ruggedness and portability
Some handheld DMMs are certified to IP67 and tested to withstand a drop of up to 3 m (10 feet) to suit harsh working environments. The IP Code, or Ingress Protection Code, is defined by international standard IEC 60529 and specifies the level of protection equipment provides. IP67-rated devices protect against solid objects such as dust and sand and work for at least 30 minutes while under 15 cm to 1 m of water. Generally, midrange and above handheld DMMs have ruggedized bodies to handle harsh environments. Benchtop DMMs are not meant for use in harsh environments. All handheld DMMs are battery-powered; hence, they are portable and suitable for use in remote places without a power line.
2. High power safety and regulatory compliance
Handheld DMMs are tested and comply with power safety and regulatory standards. All manufacturers of handheld multimeters must mark their products with the rated measurement category (CAT II, CAT III, or CAT IV) under the IEC 61010 standard (see Table 2). This marking is a convenient way for users to identify the maximum transient voltage that the meter can safely withstand. Handheld DMMs measure high-voltage main sources and circuits. They usually have a higher-rated measurement category than benchtop DMMs. Benchtop DMMs do have this category rating, but they typically have CAT II (300 V mains) ratings. In contrast, handheld DMMs usually have CAT III ratings for mains measurements and CAT IV ratings for measurements close to the mains source.
Table 2. The amplitude of transient voltages in different measurement categories
For more information on choosing a handheld multimeter that is designed and tested to protect you against electrical hazards you might encounter, read this application note – Think SAFETY When Selecting a Handheld Multimeter.
3. Isolated from power-line noise
Handheld DMMs are battery-powered and do not plug into power lines for their source of electricity. Hence, power-line noise does not affect them during measurements. Power-line noise can contribute to measurement errors, especially when measuring high-sensitivity DC voltages. A well-designed benchtop DMM has components that filter out the power-line noise.
4. Special troubleshooting features
Some handheld DMMs have useful features for troubleshooting or convenience in a harsh environment, including these:
- A built-in flashlight helps you get around in dark places.
- The OLED display provides better contrast and wide viewing for crystal-clear viewing outdoors and indoors — even in dark, off-angle situations.
- Harmonic ratio function helps you determine the presence of harmonics in AC signals.
- A built-in frequency counter and square wave generator let you conveniently perform more tests with one tool.
- Contactless voltage sense helps you trace the location of live wires.
Summary
A DMM is an essential tool for an engineer or a technician in a car workshop, in a building performing HVAC maintenance, in a hospital setting up medical equipment, or in an IT server room.
If you need accuracy, precision, speed, wide range, programming automation, and a built-in graphical display, you should get a benchtop DMM. If you need a rugged and portable instrument, you need to measure high power lines, or you need to make measurements in harsh and dark environments, it is best to look for a handheld DMM.
For more information about Keysight DMMs, please visit www.keysight.com/find/DMM.
