Can you trust your meter reading ?
Why True RMS?
Measuring current accurately is a difficult job in today’s industrial plants and offices. More and more personal computers, adjustable speeddrives and other types of equipment that draw current in short pulses rather than at a steady level come on line every day. Equipment like this can cause the readings of conventional average-respondingmeters to be at least inaccurate. If you have ever experienced blown fuses without any clear cause, then maybe your meter is to blame.
verage-responding When people talk about values of AC currents,they normally mean the effective heating or RMS (Root Mean Square) value of the current. This value is equivalent to a DC current with the
However, if the waveform is not a perfect sinewave,this relationship no longer applies. This is why average responding meters often give incorrect readings when measuring currents in today’s power systems. Linear and non-linear loads Linear loads -consisting purely of resistors, coils and capacitors - always draw a sinewave current, so there is no measurement problem (see fig.1). But non-linear loads like adjustable frequency drives and officeequipment power supplies, draw distorted current waveforms (see fig 2). Measuring the RMS value of these distorted currents with an average-responding meter could give you readings which are up to 50%too low (see fig. 3), leaving you wondering why your 14A fuse blows continuously while the current according to your meter is only 10A. True RMS To measure such distorted current waveforms, you couldfirst check the waveform with a waveform capturing device, and only use an average responding meter if the waveform is a perfect sine-wave. Or alternatively you could take no chances by always using atrue RMS meter. A modern true RMS meter uses an electronic measurement technique to provide you with the real effective value of an AC current, no matter if the waveform of the current is a perfect...