How to Select a Handheld DMM That is RIGHT for You Application Note Introduction Handheld digital multimeters (DMMs) are among the most widely used instruments for installation, test, and repair of electrical equipment. However, the variety of brands and DMM features can make it difficult to determine which handheld DMM is best suited to your application needs.
Table of Contents Introduction ............................................................................................... 1 Things to Consider When Selecting a Multimeter ............................. 3 Resolution, digit, and accuracy ....................................................... 3 True RMS versus average responding DMMs ............................. 4 Multimeter input impedance ........................................................... 4 Multimeter Basic Features ...........................
Things to Consider When Selecting a Multimeter To choose the handheld DMM that is best suited to your requirements, first consider the following: Resolution, digit, and accuracy Resolution is defined as the smallest change in an input signal that produces a change in the output signal. Resolution of a DMM is expressed in the number of digits the unit can display.
Things to Consider When Selecting a Multimeter True RMS versus averageresponding DMMs Basically, there are two types of multimeters available: “average-responding” and “true RMS” (root mean square). True RMS is the measurement of AC voltage or current that reflects the amount of power dissipated by a resistive load driven by the equivalent DC value. This power is proportional to the square of the measured true RMS voltage, independent of wave shape.
Multimeter Basic Features A basic DMM measures AC voltage, DC voltage, AC current, DC current, resistance, continuity, and diodes. More expensive DMMs also measure capacitance, frequency, temperature, and pressure. Before purchasing a handheld DMM, you should first identify the type of testing you will need to perform, establish which features are important, and determine the anticipated tolerance range for those tests.
Multimeter Basic Features Temperature measurement The maximum temperature range measurement capability of a DMM is limited by the type of thermocouples that can be used with the unit. Check which types of thermocouples are supported by the DMM to ensure compatibility with your application needs. For example, for maintenance of an air conditioner’s compressor, it is sometimes necessary to obtain the temperature difference at the inlet and the outlet of the compressor.
Advanced DMM Features Besides the basic multimeter measurement functions such as AC voltage, DC voltage, AC current, DC current, resistance, continuity, and diodes check; consider looking for a DMM that offers advanced capabilities to suit your application needs. These advanced DMM functions save you time when performing troubleshooting tasks. Here are some of the advanced capabilities designed to ease the job of engineers and technicians.
Advanced DMM Features LPF (low pass filter) While the trend to replace mechanical systems with electronic systems is growing, troubleshooting motor drives can be difficult. This is especially true when taking voltage, frequency, and current measurements on the output side of the motor drive. A regular true RMS multimeter cannot measure the output from a motor drive because the variable frequency drive (VFD) applies pulse width modulated, non-sinusoidal voltage to the motor terminals.
Think Safety When Selecting a Handheld DMM Safety is frequently not given much consideration when selecting a multimeter. However, different handheld DMMs are designed with different levels of protection against common electrical hazards. For that reason, one of the most important considerations in selecting a handheld DMM centers on thoroughly understanding the test environment and test requirements. Using this knowledge you can choose the appropriate device.
Think Safety When Selecting a Handheld DMM Energy capacity In addition to the transient voltage ratings of circuits, you need to consider the energy capacity of the circuit. To protect yourself, you should know the energy capacity of the circuit before you start taking measurements. Circuits with higher energy capacity can deliver more current and energy into faults than lowenergy circuits.
Think Safety When Selecting a Handheld DMM Safety indicators Safety certification is important. Responsible manufacturers of handheld DMMs, like Agilent, obtain safety certifications from third-party independent testing agencies such as the Canadian Standard Association (CSA), which evaluate products or systems for compliance with specific requirements. Before you purchase a new handheld DMM, remember to check for the symbol of a recognized testing organization.
Agilent Solutions Agilent offers many DMMs with different combinations of features to enable you to make fast, safe, and accurate measurements at an affordable price. Each delivers superior performance and provides a wealth of functionality while maintaining portability, ruggedness, and safety compliance. All handhelds come in vivid orange cases to provide greater visibility, and all Agilent handheld products highlight investment protection through feature sets that go beyond those of typical handhelds.
Agilent Solutions U1250 Series The U1250 Series is a 4½-digit DMM with a high-resolution display of 50,000 counts. The U1250 Series lets you achieve greater confidence in your measurements with accurate true RMS AC measurements and a low DC voltage rate up to 0.025%. Agilent U1251A/B and U1252A/B handheld DMMs expand your capabilities beyond typical DMM measurements to include data logging.
Conclusion Choosing a proper handheld product for electrical service, repair, and installation needs has become more complex. In addition to the product’s electrical specifications and features, the product safety features and safety specifications should be important purchasing considerations when you deal with main power or high-voltage measurements.
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