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What do RMS and True RMS stand for? Here we explain you the differences



RMS stands for Root Mean Square and TRMS (True RMS) for True Root Mean Square. The TRMS instruments are much more accurate than the RMS when measuring AC current. This is why all the multimeters in PROMAX catalog have True RMS measurement capabilities.

TRUE RMS MULTIMETERS

Why the RMS or True RMS measurement are necessary?

Because the voltage of a sine wave varies over time, meaning it is not equal to its peak voltage. The effective voltage of an AC signal is its equivalence in the form of DC voltage and can only be calculated by RMS or True RMS measurement instruments.

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What is RMS?

RMS stands for Root Mean Square which is the mathematical formula internally computed by the RMS-capable instruments to take measurements. This formula is simplified by the instrument to take into account only the positive peak value of the sine wave:

The RMS measurement is reliable when the sine wave is perfect, because this measure only takes into account the peak value of the waveform.

So, what happens when the sine wave is not perfect? This means, what happens in the REAL world?

What is True RMS? The most reliable measurement

RMS measurements cannot be seen as reliable because nowadays any installation has multiple sources of noise causing the AC waveform to never be perfect.

The True RMS measurement (True Root Mean Square) uses more complex mathematical formulas that allow getting a value closer to reality than the RMS. In addition to peak values, they take several samples of values along each cycle.

TRUE RMS MULTIMETERS

All this noise is induced by drives, variable switches, appliances, computers and cheap power supplies of routers, battery chargers, etc.

For this reason, because sine wave is never perfect, the reliable measurements in AC current installations are only those taken by True RMS multimeters.

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A brief overview to PROMAX multimeters

	PD-350, PD-351, PD-352 Digital multimeters with RMS and bluetooth control via Android app Digital multimeters with Bluetooth remote control (via Android app), RMS and voice. Voltage, current, resistance, capacity, frequency, diode, transistors, continuity and temperature measurements. Request a quote
	MD-200C Digital multimeter TRMS Brings together the basic features of a professional instrument such as high accuracy, reliability and a wide range of measurements. Request a quote
	FP-2 True RMS digital multimeter Digital multimeter FP-2 from PROMAX is a measuring instrument designed to go hand in hand with the vocational training students, both during their learning and their later everyday working life. Request a quote
	PD-183 Industrial Series Digital Multimeters Users will find the basic features of a professional instrument, such as high precission, reliability and a wide range of measurements. Their reliability is also an appreciated value for their use in education. Request a quote

PROMAX is a leading manufacturer of test and measurement systems, broadcast and TV signal distribution equipment. Our product lines include measuring instruments for cable TV, satellite TV, broadcast, wireless and fibre optics networks, FTTH and GPON analyzers. DVB-T modulators, IP streamers or IP converters (ASI, DVB-T) are among the company’s latest developments.