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| Measuring sub 2Hz frequency with high accuracy |
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| max_torque:
The answer depends on how quickly / often you need to know the frequency? If you can afford to measure lots of pulses, and wait a while, then you can simply calculate the time for say 1000 pulses, by counting say the rising edges, and using a stopwatch. Your edge count has a max error of 1 (either an edge has happened or it hasn't) and even a hand held stop watch is good to around 1 sec resolution (mainly the latency in the wetware jelly (<< you!) pressing the stop button) At a true 2.000000 Hz 1000 pulses takes 500 seconds, so you pulse counting worstcase error is 1/1000 and your time counting 1/500. So the longer you time for, the better your resolution! Of course, this tells you nothing about jitter and repeatability, just about the average frequency over the counting time period |
| Benta:
Universal frequency counters always have a "Period" function. That's the one to use. |
| bob91343:
If the reading is unstable, it indicates noise - including phase noise. An unsteady frequency won't give steady readings. |
| AndyC_772:
--- Quote from: ricko_uk on June 05, 2020, 07:40:48 pm ---1) I tried using the digital oscilloscope Rigol MSO1104 but unless the whole signal fits in the display it does not measure it and if I set the scope's timescale to fit the whole period in the display then the accuracy is not there. Any suggestion to doing such measurement with a scope? --- End quote --- The built in measurements on a scope are quick and easy to use but are never the right way to measure time as accurately as possible. The way to measure the period of a wave with a scope is to start by capturing a single period using as much of the scope's horizontal memory as possible. Zoom in on one edge and position a cursor, then zoom out, scroll to the other edge, then zoom in on that one and position the other cursor as accurately as you can. The distance between the two cursors is your answer. If your scope won't let you capture, freeze and zoom in this way, then the other option is to trigger one one edge but move the trigger point one whole cycle off to the left of the screen, then measure the time between the trigger event and the next rising edge. Any scope should let you zoom right in on the second edge so you can position a cursor accurately. This is also the way to measure cycle to cycle jitter. |
| mino-fm:
Using a reciprocal counter it is no problem to get 5-6 digits resolution. Accuracy can be the same, if a calibrated quarz or TCXO is used. Are you able to programm AVR8 devices like ATtiny4313, ATmega48, ...? Here you can find examples in C for AVR and even for Arduino Uno (Fmeter_UNOR3.ino) or Bascom (fm48_bas): http://www.mino-elektronik.de/fmeter/fm_software.htm Examples for ATtiny44 or ATtiny45/85 with 4-digit LCD are shown here: http://www.mino-elektronik.de/7-Segment-Variationen/LCD.htm |
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