21-11-2012, 12:32 PM
Hi Keith,
Glad you found your way here - welcome
I'm just reading through your notes, which are most excellent - just right.
You mention that you suspect that your Fluke uses reciprocal counting, and you're dead right. Indeed, many frequency counters do this - especially the ones that use a microprocessor to control the count (as opposed to using a microprocessor to just manage the user interface). Indeed, some switch between reciprocal and gated depending on frequency. Obviously, the reciprocal calculation is done by the microprocessor. Counter that do this normally have a period mode as well.
I've spotted an minor error on page 8: when discussing the -3dB point of a 'scope, you say that's when the amplitude has fallen by 50%. It would be 50% if discussing power, but when considering voltage, it's 70.7% (1 over the square root of 2). As a handy tip, when finding the -3dB points of a circuit, I adjust the amplitude in the pass-band to give 8 divisions of height, and adjust the frequency until I see 5.6 divisions (2.8 from the centre line).
I know from my day job that putting together something like that isn't easy, and it's clear that a lot of prep went into it - perhaps a lot more than most people might realise! Just building up the demo circuit boards takes time, and being sure it'll all work on the day is exciting to say the least. But I bet you enjoyed it
Thanks for making the notes available - they are an excellent resource.
All the best,
Mark
Glad you found your way here - welcome
I'm just reading through your notes, which are most excellent - just right.
You mention that you suspect that your Fluke uses reciprocal counting, and you're dead right. Indeed, many frequency counters do this - especially the ones that use a microprocessor to control the count (as opposed to using a microprocessor to just manage the user interface). Indeed, some switch between reciprocal and gated depending on frequency. Obviously, the reciprocal calculation is done by the microprocessor. Counter that do this normally have a period mode as well.
I've spotted an minor error on page 8: when discussing the -3dB point of a 'scope, you say that's when the amplitude has fallen by 50%. It would be 50% if discussing power, but when considering voltage, it's 70.7% (1 over the square root of 2). As a handy tip, when finding the -3dB points of a circuit, I adjust the amplitude in the pass-band to give 8 divisions of height, and adjust the frequency until I see 5.6 divisions (2.8 from the centre line).
I know from my day job that putting together something like that isn't easy, and it's clear that a lot of prep went into it - perhaps a lot more than most people might realise! Just building up the demo circuit boards takes time, and being sure it'll all work on the day is exciting to say the least. But I bet you enjoyed it
Thanks for making the notes available - they are an excellent resource.
All the best,
Mark
