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Digital multimeters are without a doubt the most frequently used measuring tools in the fields of electrical engineering and electronics. In keeping with their popularity, the selection of models is vast. This guide will help you make the right choice for your application.
A multimeter is used to measure the basic electrical quantities of current, voltage (AC+DC) and resistance. This versatility is what earned them their name: ‘multi’ (=many) ‘meter’ (=measuring). Most multimeters also enable you to measure additional quantities, such as capacitance, frequency or temperature. At its core, a multimeter is a compact and versatile tool.
The customary term “digital multimeter” is derived from the tool’s method of measurement rather than its digital display. Almost all multimeters use a digital measurement method, meaning that the initial analogue data collected is converted into digital signals and further processed by an A-D converter that’s integrated into the multimeter. Features such as autoranging or controlling the digital display establish a requirement for digital information. Even so, digital multimeters with an analogue display are also an option – these devices display readings in analogue bar graphs or by imitating a gauge.
A multimeter’s measurement accuracy can be the deciding factor when picking between different models. Matching a circuit’s voltage exactly, for instance, requires a higher voltage accuracy than general electric testing.
Accuracy can be measured as a percentage, taken either from the final value of the set measuring range or from the measured value. The difference between these two is sizable, and it is wise to consult the data sheet to determine what value your multimeter is advertising. As a rule of thumb, AC measurements are much less precise than DC measurements.
Resolution is defined as the smallest measurement differential a multimeter can recognise. A multimeter will have different resolutions for different measurement ranges. Usually, the resolution is high enough to deliver good results within the basic accuracy range.
There is an extensive range of multimeters available for purchase, and hence the price range can differ as well. A hobbyist might be looking for limited functionality available in basic multimeters, ranging from EUR 10-100 in price. Cheaper multimeters have a sampling speed of two times per second, which generally is not high enough for professional applications. The low price range for professionals starts at EUR 100. Mid-range professional products cost between EUR 200-500, and high-end multimeters can cost from EUR 500-1500 – a high price tag that is justified by their high specifications.
The real differences between multimeters that go beyond the most basic functionality of measuring current, voltage and resistance start to show when we get into the list of additional features that can be provided. With some multimeters, capacitance, frequency, continuity, diode and duty cycle can also be tested.
We have compiled a few additional features that multimeters can offer and might influence your purchasing decision:| Feature | Function | Benefits |
|---|---|---|
| Autoranging | Adjusts multimeter automatically to the measurement range for inputs | Saves time and minimizes the measurement error |
| Transistor testing circuits | Checks whether transistor is functioning | Useful in testing digital logic circuits and integrated circuits |
| Display rate | Represents speed at which digital display refreshes | Faster display rates mean more accurate readings |
| "Hold" function | Keeps the display from changing | Useful when noting readings |
| Display with large digits and backlight | Designed for ease of use | Easy to read, even in dark crawl spaces and basements where electrical systems may run |
| ISO or NIST calibration | Indicate compliance for certified companies | Ensures highest levels of accuracy in reading |
| Calibration | Multimeter comes calibrated | Calibrated parameter’s measuring tolerance is guaranteed |
| Graphic representation | Quantity under test shown i.e. as a bar graph | Allows spotting of fast-moving trends |
| Adjustable sample rating | Represents speed at which samples are taken | Faster sample rates mean more accurate readings |
| Removable data storage | Measured data stored in removable component | Ability to access data on different devices |
| Data acquisition | Sampled signals values are saved into device’s memory | Records readings over given period, takes number of samples at fixed intervals |
| Low pass filter | Only allows signals up to a frequency limit of f(x) | For measuring variable frequency drives (VFD) |
Measuring non-sinusoidal alternating currents requires a multimeter with the true-RMS feature. Some examples of environments in which true-RMS meters are needed are variable-speed motor drives, electronic ballasts, computers, HVAC and solid-state environments. Inhomogeneous alternating voltages or currents can only be measured correctly by a TRMS multimeters. Simple RMS multimeters always assume that the AC voltage under test is a sine wave – the reading is calculated via the mathematical average value of this perceived sine wave. This approach does not work for amplitude- or frequency-modulated alternating currents and a TRMS multimeter is necessary to take an accurate reading.
A multimeter’s safety is an important factor that will undoubtedly influence your decision on which one to get. Each multimeter will fall into one of four safety ratings:
Keeping the intended use of your multimeter in mind, it is easy to determine which safety rating your device needs. If you suspect you may be using your multimeter to measure higher voltages in the future, it may be advisable to select a higher category safety rating.
We hope that with all of these points in mind, your choice of which multimeter to buy will be an easier one. If you’d like some product examples, feel free to check out our recommendations below, or have a browse in our online shop.
If you’d like to go one step further than a multimeter can take you, why not check out our Step-by-step guide to choosing the right oscilloscope? Or discover the special functionality some Fluke multimeters can offer – discover Fluke Connect.
The Fluke 179 True RMS Digital Multimeter is the industry standard for troubleshooting and repair of electrical and electronic systems.
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The Fluke 287 with quickly documents design performance and graphically displays what happened. Its unique logging and graphing capabilities mean you no longer need to download logged readings to a PC to detect a trend.
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The RND 355-00002 industrial multimeter has a 6000 count digital display, 62 segment bar graph, Extra large scale display and white backlight, Smart data hold feature, VoltSeek (non-contact voltage detection), CAT IV 600V / CAT III 1000V high safety rating
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Automatic illuminated functions keys and rotary switch, Integrated powerful LED Flashlight, Continuity with buzzer and diode-test, Data-Hold, Min, Max, Peak functions and Duty Cycle
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