I am now the proud owner of a shiny new true RMS multi meter I've seen revues of it on YouTube and it gets very good reviews on all aspects of its accuracy and construction and of course safety not sure if I'm aloud to say which one it is maybe someone will tell me if its ok. Anyhow it reads the same as 2 of my other meters which are also true RMS although I didn't know they where. Any how I've found out that the 2 LED meters I bought that I posted about some time ago are both telling lies although one of them is occasionally telling the truth. It's interesting that the voltage is never still but is usually around 240 and also if I look at around 23:30 it drops off by 3 to 4 volts which must be when local economy 7 kicks in
If you really want accuracy some of the 24 bit A/D converters on the market are quite good, on DC of course. Try Analogue Devices website. Reading True RMS AC is a bit more difficult, and the RMS calculation needs a bit of computer power. 24 bits give a resolution of about 1 part in 1.5 Million and an accuracy of about 2 bits is available. The best digital meters can have at least 12 decimal places of resolution and very high accuracy of perhaps 10 - 11 decimal digits but are a bit £££ for general use. It is interesting that Frequency is probably the most accurate physical phenomenon we can measure to extreme accuracy, with voltage not too far behind. Things like temperature are some way behind, but there are not so many requirements for that to ultra accuracy either.
If you really want accuracy some of the 24 bit A/D converters on the market are quite good, on DC of course. Try Analogue Devices website. Reading True RMS AC is a bit more difficult, and the RMS calculation needs a bit of computer power. 24 bits give a resolution of about 1 part in 1.5 Million and an accuracy of about 2 bits is available. The best digital meters can have at least 12 decimal places of resolution and very high accuracy of perhaps 10 - 11 decimal digits but are a bit £££ for general use. It is interesting that Frequency is probably the most accurate physical phenomenon we can measure to extreme accuracy, with voltage not too far behind. Things like temperature are some way behind, but there are not so many requirements for that to ultra accuracy either.
