what is true rms

True-RMS in calibration industry: Explained

A True-RMS device can be classified as one of three tools that can measure either alternating current (ac) or ac voltage. They can be classified as: True-RMS digital multimeters (or clamp meter), Average-responding digital (or clamp meter), and oscilloscope.


The first two classifications are commonly used, and both of them can accurately measure standard, pure alternating current waveform. A waveform is a representation of how alternating current (AC) varies with time. There are many types of waveforms but the most familiar is the Sinusoidal (sine) waveforms. Other forms of AC waves are grouped and classified as Non-sinusoidal waveforms. To further differentiate the two, below is each of the waveform’s distinct definition and structure.


  • Sinusoidal (sine) Waves: Pure, without distortion, and has symmetrical transitions between peaks and valleys.


  • Non-sinusoidal Waves: Waves with distorted and irregular patterns, waveforms such as spikes, pulse trains, squares, triangles, and any other ragged or angular waves are classified as Non-sinusoidal waves.


A true-RMS meter is widely preferred because it is the only device that can accurately measure both sinusoidal and non-sinusoidal waveforms. See illustrations below for reference.


It is essential to have an understanding about true-RMS devices. Its formula is based on RMS = root mean square. Though it is challenging to grasp, RMS essentially calculates the equivalent direct (dc) value of an ac waveform. Technically, it determines the “effective”, or dc heating value of any ac wave shape.


It is important to know that a sophisticated true-RMS meter can accurately measure both pure waves and complex non-sinusoidal waves. Factors such as variable speed drives or computers can potentially distort the structure of waveforms. Thus, averaging true-RMS multimeters attempt to measure these distorted waveforms with these standard calculations below:

The need for true-RMS meters has grown due to the increase of non-sinusoidal wave possibilities in circuits from the following apparatuses below:


  • Variable-speed motor drives
  • Electronic ballasts
  • Computers
  • HVAC


The environments from these devices produces current that occurs in short pulses rather than the smooth sine wave from a standard induction motor. Hence, true-RMS meter is the best choice for taking measurements on power lines where ac characteristics are unknown.


A legitimate true-RMS meter is needed for every electrical and AC voltage measurements. There are many companies who have promised this type of product that is dependable and reliable. Fluke Industrial Group is the world leader in the manufacture, distribution and service of electronic test tools. It is your number one choice for your True-RMS meters, and if you are looking for any Fluke Calibration instruments in the countr, Presidium.ph Corporation could help you with that! We assure you that our products our straight from Fluke Industrial group themselves. Expect to have accurate results with your True-RMS meter. Let us be your reliable partner for your reliable test instruments!


For more info, you can contact us at +632-464-9339 or visit our website at www.presidium.ph.



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