08-03-2016, 01:03 PM
Yes, AC is difficult.
Cheap multimeters use an average-responding circuit; the posh ones ("TrueRMS") use what is effectively a miniature analogue computer to calculate RMS. The classic AD536 was the IC of choice for many years: http://www.analog.com/media/en/technical...AD536A.pdf
Detection is separate from AC+DC measurements. The Fluke 187/8 and 287/9 can do this - most don't (I'll check the 87V at the weekend). Bandwidth is important - but knowing the bandwidth of your instrument is the critical thing.
My best AC meter is a Fluke 8920A - this uses a thermal converter, and has a bandwidth of 20MHz. The crest factor is up to 7 - double most good non-thermal DVMs. It does AC+DC, and dBm - so it's ideal for me. It's a complex beast, but most of the complexity is there to prevent the thermal sensor being overloaded. Funnily enough, despite all the goodness, the best accuracy at AC is only 0.5%. It's only a 2000-count meter, but no point having more with that accuracy. BTW, I recommend these. Because they are old and crusty, and a bench meter form factor, they don't seem to fetch huge amounts - I paid just over £30 for mine.
Cheap multimeters use an average-responding circuit; the posh ones ("TrueRMS") use what is effectively a miniature analogue computer to calculate RMS. The classic AD536 was the IC of choice for many years: http://www.analog.com/media/en/technical...AD536A.pdf
Detection is separate from AC+DC measurements. The Fluke 187/8 and 287/9 can do this - most don't (I'll check the 87V at the weekend). Bandwidth is important - but knowing the bandwidth of your instrument is the critical thing.
My best AC meter is a Fluke 8920A - this uses a thermal converter, and has a bandwidth of 20MHz. The crest factor is up to 7 - double most good non-thermal DVMs. It does AC+DC, and dBm - so it's ideal for me. It's a complex beast, but most of the complexity is there to prevent the thermal sensor being overloaded. Funnily enough, despite all the goodness, the best accuracy at AC is only 0.5%. It's only a 2000-count meter, but no point having more with that accuracy. BTW, I recommend these. Because they are old and crusty, and a bench meter form factor, they don't seem to fetch huge amounts - I paid just over £30 for mine.
