I require a multimeter measuring RMS but unfortunately know little on the subject and am unable to tell which method one uses from it's description.
Its states:
MAX. Voltage between terminals & earth ground: 700V AC rms or 1000V DC Fuse Protection: µA and mA: F 750mA / 250V Ø5x20; A: F 10A/250V Ø6.35 x 31.8
I appreciate it says rms in the above, however would like to ask for confirmation and also if possible help understating the other values it specifies.
Thanks
True RMS measurements is a property the manufacturer will be very proud about to share with you as customer. It is usually printed in bold on the meter itself. True RMS isn't printed on the meter in your example, so it won't be one.
Also I own a more expensive brother of this meter and on that one it says 'True RMS' (in bold print).
Third way to tell is from the specifications. Again the manufacturer will be proud to be able to share True RMS properties and I expect it listed high in the 'key features' and next to the 'ACV' and 'ACA' table headers.
In conclusion: No this is not a True RMS meter.
If you are dealing only with sine waves the conversion from average to RMS is constant and meters are corrected assuming a sine wave. So it will be ok for sine waves such as AC power to the home.
But there are other options with digital scopes (DSO) and others.
If you need to measure current and voltage at the same time for RMS, that is different matter for a wattmeter.
However if it is distorted significantly, then you lose accuracy on the conversion. True RMS AC measurements are equivalent to the DC equivalent power. They are measured using precise thermal heat sensor methods of the energy in the signal.
You can expect to pay $350 for a used portable DMM with true RMS such a Fluke 87 II for complex waveforms. There are many other solutions. I prefer DSO's with multiply.
If the leads of a meter are connected to a constant DC voltage, the average DC voltage and RMS voltage will be identical. The rectified average and rectified peak voltages will also be identical, but the because RMS voltage of an AC waveform will be substantially less than the peak voltage, a non-RMS meter which is set for AC may read a much lower voltage than it should. Some meters may have AC-coupled inputs, in which case trying to read a DC voltage on the AC setting would yield a reading briefly when connected but it would fall to zero. Note that an AC-coupled input would likely not improve accuracy when measuring AC, but its behavior when measuring DC would alert the operator that it was necessary to use the DC setting.
