Sample Rate - Page 1
Forum section: electronics / beginners

author: metrologist
author_rank: Super Contributor
timestamp: August 29, 2019, 07:26:46 pm
content: Is it incorrect to specify sample rate in terms of Hz?Sampling Techniques: Real-time / Equivalent Time / Statistical SamplingContinuous Sample Rate: 100 MHzEffective Sample Rate: 10 GHzOr is MS/s and GS/s a more correct way to specify this? Can any supporting discussion around that also be provided?Context:https://boonton.com/Portals/0/Products/Real%20Time%20Power%20Sensors/RTP5000/RTP_8PG_2019.pdfThank you.

author: magic
author_rank: Super Contributor
timestamp: August 29, 2019, 07:45:41 pm
content: 1Hz = 1/s so technically correctAlso common in audio, but S/s is more common in scopes to avoid confusion with bandwidth.BTW, what the fuck is one megasiemens per second?

author: TheHolyHorse
author_rank: Regular Contributor
timestamp: August 29, 2019, 09:16:26 pm
content: Quote from: magic on August 29, 2019, 07:45:41 pmNever heard it before but it doesn't sound to comfortable

author: Benta
author_rank: Super Contributor
timestamp: August 29, 2019, 09:33:27 pm
content: There's no convention for samples/second in the SI system, but both S (siemens) and s (seconds) are already reserved.My favourite would be to write it in full: Gsamples/second. That way, there's no ambiguity, and that's what communication is about

author: metrologist
author_rank: Super Contributor
timestamp: August 29, 2019, 10:20:21 pm
content: Yes, I meant Sa/sBut there was a question on if there could be two samples per Hz due to rising/falling edge sampling.

author: fourfathom
author_rank: Super Contributor
timestamp: August 29, 2019, 11:16:46 pm
content: Quote from: metrologist on August 29, 2019, 10:20:21 pmI see no ambiquity. If the sampling was done on the rising and falling edge of a 1MHz clock, then the sample rate would be 2MHz, or 2M samples per second.

author: metrologist
author_rank: Super Contributor
timestamp: August 29, 2019, 11:39:28 pm
content: The ambiguity is whether the 100 MHz sample rate specified in the datasheet could mean 200 MSa/s. I play more in O-Scope land and generally see samples per second. There is the following mention in the user guide:QuoteI appreciate the dialog. Thanks

author: Jwillis
author_rank: Super Contributor
timestamp: August 30, 2019, 04:39:57 am
content: Quote from: magic on August 29, 2019, 07:45:41 pmI sort off get the joke . A Siemen is a measurement of electric conductance, electric susceptance, and electric admittance.The reciprocal of resistance, reactance, and impedance.Also called a mho.

author: radiolistener
author_rank: Super Contributor
timestamp: August 30, 2019, 07:30:31 pm
content: Quote from: metrologist on August 29, 2019, 11:39:28 pmThere is no ambiguity, because 100 MHz sample rate equals to 100 MSa/s and equals to 100 M cycles, which is equals to 100 MHz.200 MSa/s is 200 MHz sample rate and means 200 M cycles per seconds, which means 200 MHz.

author: metrologist
author_rank: Super Contributor
timestamp: September 03, 2019, 02:36:09 pm
content: Quote from: radiolistener on August 30, 2019, 07:30:31 pmWhat if a sample is taken on both the rising and falling edge? I guess your 50 MHz sampling clock would produce a 100 MHz sample rate, which would still be 100 MSa/s. It was more of a semantic question of whether sample rates are properly specified in Hz.

author: TimFox
author_rank: Super Contributor
timestamp: September 03, 2019, 02:51:56 pm
content: When the re-naming of cps = cycles/second to Hz was first proposed, a conservative German scientist objected “One might as well name the liter/minute the Falstaff.”

author: magic
author_rank: Super Contributor
timestamp: September 03, 2019, 07:02:48 pm
content: Funnily enough, there is becquerel - the count of decays per second in a radioactive material.

author: Mechatrommer
author_rank: Super Contributor
timestamp: September 03, 2019, 07:27:48 pm
content: Quote from: Jwillis on August 30, 2019, 04:39:57 ami dont get the joke, but i'm not too serious either. if unitless (count or cycles) per sec is Hz, any unit per sec, is the rate of change, such as m/s, kmph, dT/dt (temperature), V/us. hence anything that change conductivity with delta 1Meg in one sec is one megasiemens per second. i'm not sure if such material exists though.

author: taydin
author_rank: Frequent Contributor
timestamp: September 03, 2019, 08:25:12 pm
content: I often see Msps or Gsps in oscilloscope specs. Not a standard, but conveys the meaning.

author: SparkyFX
author_rank: Frequent Contributor
timestamp: September 03, 2019, 08:44:10 pm
content: Quote from: metrologist on September 03, 2019, 02:36:09 pmYou only know if you are on a falling or rising edge when sampling more often than the signal changes (Nyquist-Shannon) and what causes the sample to be taken is the elapse of time, without regard for the signal.Triggering requires either software with enough samples to be taken or separate hardware.

author: radiolistener
author_rank: Super Contributor
timestamp: September 03, 2019, 09:46:16 pm
content: Quote from: metrologist on September 03, 2019, 02:36:09 pmif sample is taken on both rising and falling edge, then sample rate Sa/s and sample frequency Hz will be still equals.For example if you use clock source 50 MHz and use rise and fall edges to produce samples, then you will get 100 MSa/s = 100 MHz = 100 M cycles per second sample rate. Nothing confusingSample rate means how many samples per second is produced. If you put strobe for each sample, you will get square wave with frequency which is exactly equals to sample count per second. And it doesn't matter what is source oscillator frequency.

author: macboy
author_rank: Super Contributor
timestamp: September 04, 2019, 02:21:22 pm
content: Quote from: radiolistener on September 03, 2019, 09:46:16 pmI agree with radiolistener. No ambiguity exists unless the reader chooses to add unnecessary confusion to a simple topic. Sampling at 100 MHz means sampling at "100 Million per second" since the "Hz" unit is literally "per second". Whether or not a DDR clock is used internally is moot. I am absolutely certain that my oscilloscope, which can sample at 16 GHz real time, does not have any 16 GHz clock internally. It actually samples on multiple phases of a slower clock.In other words: Hz, MHz, GHz, can specify rate of anything, not just a clock signal.