How to Buy the Best DMM

What do you need to know to buy the best digital multimeter – key hints tips and inside knowledge.

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Digital multimeters are available to buy from many sources. Also digital multimeters can be bought for very competitive prices.

Purchasing digital multimeter these days enables very high performance instruments to be bought for comparatively little money

That said, it is still necessary to have a good look at what is needed and what the real requirements for the digital multimeter are before buying one.

There is a very wide price range between those at the bottom of the price scale and those at the top. One may ask what is the difference and we hope to provide some guidance on selecting the right digital multimeter to purchase.

Analysing the requirements for a DMM purchase

Before setting out to buy a digital multimeter, it is first necessary to look at its usage. Will it be used for occasional use, or is it required for a full time professional use. Is it going to require high levels of accuracy and reliability? What measurement capability is needed. These and many more questions may be asked.

... apart from amps, volts, and ohms, many DMMs can measure parameters including frequency, capacitance, continuity, and temperature....

Typical digital multimeter

It is also necessary to look at other requirements including the type of measurements that will need to be made and other requirements. A careful analysis if these against the estimated cost is always useful: a careful analysis of the measurements to be made, the conditions under which they will be made and any safety / regulatory requirements.

Buying a DMM – key issues

There are several specific points to consider when buying a digital multimeter. There is no single answer and no single best digital multimeter. It is necessary to work out what is required and then choose the best DMM before purchasing the item.

Some of the key points include:

  • General usage:   Consider if the digital multimeter is to be used for home / hobby use. If so, it is unlikely to need the same level of robustness and reliability as one used for industrial or professional use. There is a considerable difference between the cost of the entry levels meters and those used for professional use.
  • Amps, Volts and Ohms:   All digital multimeters will be able to offer the basic measurements of amps volts and ohms. These are the basic measurements that are included in any multimeter that you will want to buy.
  • Additional ranges:   Today, digital multimeters are able to provide a number of ranges beyond the basic Amps, Volts and Ohms. Ranges may include a buzzer for continuity, temperature, capacitance, diode and transistor measurements, as well as frequency and several other measurements. As different DMMs will offer different capabilities, it is necessary to consider what might be needed when buying a digital mutimeter.

  • True RMS:   Many digital multimeters only provide an average reading of an AC waveform that may be calibrated as RMS. This will not provide an accurate reading of the waveform differs from a sine wave. If a true RMS reading is needed, this should be checked so that the correct digital multimeter is bought. Typically DMMs that are able to provide true RMS readings are more expensive than those that do not. If this is required then check that it says ‘True RMS’ and not just RMS.
  • Accuracy and resolution:   Accuracy and resolution are two key aspects associated with any digital test instrument. When choosing a digital multimeter it is necessary to distinguish between the two aspects and determine whether the performance is adequate.
  • Autoranging:   One useful facility that is available, typically on higher end digital multimeters is the autorange facility. It is worth considering whether it is a requirement when buying digital multimeter. Using this it is only necessary to select whether volts, amps, ohms, etc are being measured. The meter will detect the level of the measurement and select the required range. This is particularly useful for applications like field service where it may not be convenient to keep selecting a range to obtain the optimum reading.
  • Safety ratings:   When measuring voltages, particularly on electrical installations it is necessary to ensure that the digital multimeter has an adequate safety rating. IEC 1010 categorises meters according to their safety ratings. These not only take into account the working voltage, but also the resilience to peak transients that often occur on the lines. It is necessary to ensure that any meter being used for these applications is suitably rated. This may result in needing to buy a more expensive meter.

DMM purchase decisions

Whilst a low cost digital multimeter may fit the bill for many hobby or home applications, when considering a digital multimeter purchase for a professional or commercial application, it is often far more cost effective to buy a more expensive one that is better specified, has the required safety ratings and is robustly built.

Essentially, you get what you pay for, so any purchasing decisions should take into account the overall performance and requirement, and not just the basic ranges and cost.

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