Hello Frends...:-).. Eager to know how a "True RMS is calculated inside multimeter"

[ramshkrish]

Hello Frends..... Eager to know how a "True RMS is calculated inside multimeter"

Hello frends....
I have a fair idea of what a " TRUE Rms " is.. But can someone tell me how it is calculated inside a multimeter.. Some say they can be found by calculating the heating potential of a resistor. So how its done inside the multimeter.. Is the temperature being measured accross the resistor when the voltage is applied..?????? or is there any formula to find out..:!::!::!:

Thanks in advance..

 

[wa1kij]

Re: Hello Frends..... Eager to know how a "True RMS is calculated inside multimete

What the multimeter is giving you is probably an approximation. I'm sure there are instruments that will give you an exact value, but that involves sampling a time period, then performing the calculation. Analog VTVM's gave a good approximation, too, thanks to the hysteresis of the meter movement.

 

[kak111]

Re: Hello Frends..... Eager to know how a "True RMS is calculated inside multimete

Here is the principle.......

True RMS converter - Wikipedia, the free encyclopedia

Microcontroller for better live: Calculate True RMS Value

 

[shaiko]

Re: Hello Frends..... Eager to know how a "True RMS is calculated inside multimete

Simple Flukes also gives a true RMS measurement (try the Fluke 115)

 

[antedeluvian]

Re: Hello Frends..... Eager to know how a "True RMS is calculated inside multimete

I am sure that it will depend on the DVM. I seem to remember the old Flukes (like 8060 type) used an external True RMS chip.

I suggest the following article as a good starting point:
**broken link removed**

 

[ark5230]

Re: Hello Frends..... Eager to know how a "True RMS is calculated inside multimete

It is interesting that all analogue measurement devices are RMS value reading devices because of the working principle with a moving coil in a magnetic field.

 

[ramshkrish]

Re: Hello Frends..... Eager to know how a "True RMS is calculated inside multimete

Thank your guys.. This really helped me a lot.. The two articles link posted in this thread is much useful.. .. Thanks..

 

[Eric Best]

Re: Hello Frends..... Eager to know how a "True RMS is calculated inside multimete

...all analogue measurement devices are RMS value reading devices because of the working principle with a moving coil in a magnetic field.

I am sorry, but you are not right - for instance the 'Deprez D'Arsonval' systems (exactly a moving coil in a magnetic field, imho the most common analogue measuring instrument) measure the mean value, not rms, i.e. ac (sine) without rectifying gives zero reading.
If intended for ac, these instruments use rectifier, so they measure the mean value of a rectified waveform in fact then (without other remedies); provided the intended measured waveform is sine the relation between the mean value and rms is constant and the scales of such devices are adjusted to read (but not measure) rms (this case is very often).
So... if you try to measure a waveform noticeably different from sine (for instance using a phase controlled scr) with such an instrument then you come to grief (you can get a more accurate result when you make it out of whole cloth