What is true rms Multimeter

What is true rms multimeter. Without the right tools, troubleshooting electrical equipment and circuits can be complex. Multimeters can measure various conductivity, resistance, inductance, and frequency. Many engineers and technicians familiar with all areas of electronics know the value of multimeters.

What is true rms multimeter


Multimeters save a lot of time by detecting electrical failures. There’s a lot to know about these devices. One of those features is RMS. The Efficient Multimeter (RMS) is a tool for measuring the adequate alternating current or voltage level.

The root means square is a mathematical word that describes the practical level. A true RMS multimeter provides a suitable current or voltage level for all power measurements. Other multimeters currently on the market are designed to measure only average levels.

Principles of true RMS multimeter

  • As mentioned earlier, RMS refers to the root mean square value obtained from the “effective” value of an AC waveform or a formula that measures calorific value. Technically, the RMS AC value equals the DC calorific value (current or voltage) for a particular waveform. For example, suppose the value of a resistance heating element in an electric furnace is 15 kW of heat and 240 volts of ACrms. If you apply 240 volt DC instead of AC, you will get the same heat.
  • As you can see, electrical system components such as circuit breaker thermocouples, busbars, conductors, and fuses are rated at RMS current. This is because the main limitation is related to heat dissipation.
  • Specific low-cost current clamps with no actual RMS circuit usually use shortcut tactics to get the RMS value. Such measuring instruments are marked as “indicating an average response RMS.” These multimeters also take the rectified average of the AC waveform, scale that amount by 1.1, and measure the RMS value.

The displayed value is not the actual value. Instead, it is a measurement based on the waveform hypothesis. The standard response method works for pure sine waves but can result in a significant read error of about 40%.

Why should we prefer the use of a true RMS multimeter?

Note that a standard multimeter can measure current and voltage. These multimeters also provide accurate readings for linear loads. Such linear loads, for those that don’t know, are made up of:

incandescent lamps,

induction motors: heater

The linear load draws a current in phase with the applied voltage. Therefore, the current drawn by the nonlinear load increases in proportion to the voltage. The current detected by the linear load is a sine wave.

  • For linear loads, accurate RMS multimeters can measure current or voltage. Still, there is one thing to keep in mind the multimeter’s average response is relatively low. I use an accurate RMS multimeter to measure currents in nonlinear loads, including electronic equipment, variable frequency drives, and DC drives.
  • Semiconductor devices such as IGBTs, SCRs, and diodes have nonlinear characteristics. The current drawn by these devices is independent of the applied voltage. So the current waveform is unidirectional.
  • Semiconductor devices generate harmonic currents in electrical networks. Average multimeters cannot accurately measure non-sinusoidal currents. As a result, nonlinear loads require an RMS or True RMS multimeter to determine voltage and current. This method provides accurate and realistic measurements regardless of the current waveform.


A true RMS multimeter provides accurate readings of any waveform. This is especially true whether it is a triangular, square, or sine wave. So this is it! We hope we have explained all the necessary information you need about the true RMS multimeter.

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