Digital Multimeters 101
Multimeters offer a range of capabilities to tackle everything from basic DIY electrical repairs to heavy-duty industrial predictive maintenance.
What are multimeters?
The digital multimeter (DMM) is the go-to, front-line diagnostic test tool to find and fix electrical and electronic issues. Electrical troubleshooting begins with testing and measuring using a multimeter.
How are multimeters used?
Multimeters connect to electrical circuits to measure voltage, current, frequency, capacitance, temperature and resistance. DMMs also test for continuity in a circuit, to see if something failed or if there is an open circuit. For added safety, some meters check for voltage without electrical contact by using non-contact voltage (NCV) technology.
Advanced multimeters offer more accuracy even in challenging jobs. “True RMS” (Root Mean Square) meters ensure accuracy even when electrical waveform isn’t a clean sine wave. When wires are bundled close together coupling can cause stray (or “ghost”) voltages leading to inaccurate readings. A “LoZ mode” can eliminate the error. Select models measure temperature with a point-andshoot, no-contact infrared thermometer built in. Multimeters with wireless datalogging stream readings to a mobile device with productivity apps to further expand versatility.
Lo-Pass filter ensures accurate readings from variable frequency drives.
Where are multimeters used?
Check a meter’s overvoltage category rating (“CAT” for short) to see where it can be used. CAT II can be used indoors on electrical equipment or appliance wiring while the most robust, CAT IV, is for outside wiring coming from the utility to the service entrance. For safety, always factor in potential work needs and go with the best CAT rating. Multimeters are used on circuit wiring and equipment like motors, pumps, lighting, sensors and switches. They are found everywhere from DIY toolboxes to industrial maintenance tool carts.
Who uses multimeters?
Basic DMMs are used by do-it-yourselfers to fix appliances, lighting and wiring around the house. Electrical contractors use them for new installations and repairs. Similarly, HVAC and refrigeration technicians use them to test electrical components in their systems. Telecom, alarm/security, smart-home and audiovideo techs use them to troubleshoot their equipment installations. In industrial plants, DMMs are used by predictive maintenance technicians to ensure equipment keeps working.
Which multimeter is right for me?
Choose a multimeter with capabilities matched to your job’s needs. Professionals should opt for True RMS meters. Think about typical sites and equipment you work on, and look for the features listed above that match your needs. Consider adding new features you hadn’t considered that might make your job easier including VFD mode, LoZ, waterproof/drop-proof, or wireless readings that display on your mobile device – so you can step away from energized equipment.