Low frequency function generator that provides 0.1Hz resolution  - Page 1
Forum section: electronics / testgear

author: e100
author_rank: Frequent Contributor
timestamp: May 17, 2017, 04:48:06 am
content: I'm looking for something that can be used to emulate digital RPM sensors that are used for measuring motors and flow meters that operate in the range of 0.5 to 50 Hz.It needs to be stable to within 0.1 Hz over a period of about an hour.None of the cheap function generators I've seen offer sub 1 Hz resolution. I could send the output from one of these into a series of decade divider chips but that seems like a hack.Mike

author: tautech
author_rank: Super Contributor
timestamp: May 17, 2017, 05:02:48 am
content: Plenty, the whole Siglent SDG range of models.http://siglentamerica.com/prodcut-db.aspx?id=-1&tid=16&T=1

author: KE5FX
author_rank: Super Contributor
timestamp: May 17, 2017, 05:13:49 am
content: Have a look at these guys' Kickstarter, closing May 21:https://www.kickstarter.com/projects/1349373177/universal-logic-frequency-generatorIt may be exactly what you're after. Not sure about the sub-Hz resolution part.Disclosure: I don't have any relationship with the company, but I have a pre-release eval unit that they sent me. I have not put it through any sort of exhaustive evaluation, but I can say that it is nicely built and does what it says on the proverbial tin.

author: Muxr
author_rank: Super Contributor
timestamp: May 17, 2017, 05:18:12 am
content: My Siglent SDG 1025 can. You can input mHz (Millihertz as opposed to MHz = Megahertz). Or even uHz (Microhertz)

author: DaJMasta
author_rank: Super Contributor
timestamp: May 17, 2017, 05:19:17 am
content: +1 for the SGD series, my SDG2082X goes down below miliHertz, and I've actually tested it out... when you get below a certain frequency, it just becomes a step function, even with a fairly high resolution DAC.If you need analog-smooth transitions, you may have to look for a specialty generator of some sort... but there could be another viable way: a PC sound card. A sound card will give you basically as many bits as reasonably possible on a DAC and as long as your DC coupled, the performance at very low frequencies should be fine. Aside from a totally smooth analog generator, the 20ish effective bits of a PC sound card should get you near the smoothest low frequency step function if you've got a simple tone generator running it. If you just want a square wave and logic level drive... hook your favorite micro to a crystal oscillator and be set. Even a crystal oscillator attached to some dividers and some jumpers could do the job.As for stability's sake, if you're going the digital generation route, then the target should be no problem. At 0.5Hz, +-0.1Hz/hour is 10^-5 class frequency performance, which any decent crystal oscillator should be able to manage. That being said, temperature drift could play into your readings, so if you are using a PC sound card that is internal to the PC, I would definitely let the system warm up and let its temperature stabilize before starting your measurement. External devices using external clocks should be much less effected, and anything with temperature compensation should do better than your performance target.

author: egonotto
author_rank: Super Contributor
timestamp: May 17, 2017, 05:48:46 am
content: Quote from: KE5FX on May 17, 2017, 05:13:49 amOutput frequency adjustable in 1 Hz increment from 130 KHz to 225 Mhz??

author: e100
author_rank: Frequent Contributor
timestamp: May 17, 2017, 06:10:59 am
content: Quote from: DaJMasta on May 17, 2017, 05:19:17 amThere seems to be big price steps at the low end of the market.The cheapest function gen with 0.1Hz resolution I could find was the Longwei lw-1641 for $AUD 170. Unfortunately it seems to be an old design that uses an analog oscillator (as far as I can tell).Anything reasonably modern is priced in the hundreds of dollars range and has far more features than I'll ever use.As bizarre as it sounds a DIY solution using the hardware counter in a microcontroller is currently the cheapest option.

author: e100
author_rank: Frequent Contributor
timestamp: May 17, 2017, 06:13:48 am
content: Quote from: KE5FX on May 17, 2017, 05:13:49 amIt only provides 1 Hz resolution, even though the promotional material says that it "generates any frequency".There's a gap in the market and they missed it.

author: KE5FX
author_rank: Super Contributor
timestamp: May 17, 2017, 07:30:47 am
content: Quote from: egonotto on May 17, 2017, 05:48:46 amYeah, that's a bit odd, now that you mention it. It would make more sense for something like this to go all the way down to DC (which I actually thought it did).