On 01/05/2013 13:54, whisky-dave wrote:
Measuring low frequecies accuratly is more difficult than you think.
What you have to do is count cycles in one second yuod get perhaps 47 or 53 so you need to average it out especailly in times of high or low demand.
So you need to sample it for at least 10 seconds to giove you 0.1 resoultion and in that time the situation can change.

You ought to measure the time for 50 (or something) cycles instead. If
you time it at the zero crossing that doesn't move about much.

Even so - yes, it's hard, especially with a noisy waveform.

Andy