Jerry Avins wrote: ...> Control loops need at least 5X oversampling ...That may be too strong an assertion. Suffice it to say that -- with the exception of a toy system -- I never made on work satisfactorily with less than that. 10X is better if one can manage it. Jerry -- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
Sampling rate required to resolve separate sonar echoes
Started by ●January 20, 2009
Reply by ●January 22, 20092009-01-22
Reply by ●January 22, 20092009-01-22
On Wed, 21 Jan 2009 23:20:29 -0500, Jerry Avins wrote:> Jerry Avins wrote: > > ... > >> Control loops need at least 5X oversampling ... > > That may be too strong an assertion. Suffice it to say that -- with the > exception of a toy system -- I never made on work satisfactorily with > less than that. 10X is better if one can manage it. > > JerryAnd if you need precision out to the bandwidth of the loop, even more than that. Anything less than 5X requires an extraordinarily well-behaved plant. -- http://www.wescottdesign.com
Reply by ●January 22, 20092009-01-22
Jerry Avins wrote:> Jerry Avins wrote: > > ... > >> Control loops need at least 5X oversampling ... > > That may be too strong an assertion. Suffice it to say that -- with the > exception of a toy system -- I never made on work satisfactorily with > less than that. 10X is better if one can manage it. > > JerryThanks, Jerry. It's very good to know that 10X oversampling is best for a control system. Nicholas
Reply by ●January 22, 20092009-01-22
Tim Wescott wrote:> And if you need precision out to the bandwidth of the loop, even more > than that. > > Anything less than 5X requires an extraordinarily well-behaved plant. >I'm going to have to take a look at your most recent book on control systems. Thanks, Tim.
Reply by ●January 22, 20092009-01-22
Nicholas Kinar wrote:> > Jerry Avins wrote: >> Jerry Avins wrote: >> >> ... >> >>> Control loops need at least 5X oversampling ... >> >> That may be too strong an assertion. Suffice it to say that -- with >> the exception of a toy system -- I never made one work satisfactorily >> with less than that. 10X is better if one can manage it. >> >> Jerry > > Thanks, Jerry. It's very good to know that 10X oversampling is best for > a control system.I didn't mean "best". I meant better than 5X. :-) Filters introduce delay. Delay destabilizes servos. Often, the best filter isn't the one with sharpest cutoff or least ripple in the passband, it is the one which delivers the signal earliest. Minimum-phase filters are the archetype. Linear-phase filters are probably the worst ever applied, although maximum-phase filters exist. Look at the filter's impulse response and where the bulk of the energy is relative to the impulse. A filter that is nearly minimum phase can sometimes be much simpler than one that is exactly so. In audio work, we freely shift the time origin to simplify the way we represent signals. Servo work is more demanding. Constant delays can't be ignored. Good luck! Jerry -- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
Reply by ●January 22, 20092009-01-22
> > I didn't mean "best". I meant better than 5X. :-) > > Filters introduce delay. Delay destabilizes servos. Often, the best > filter isn't the one with sharpest cutoff or least ripple in the > passband, it is the one which delivers the signal earliest. > Minimum-phase filters are the archetype. Linear-phase filters are > probably the worst ever applied, although maximum-phase filters exist. > > Look at the filter's impulse response and where the bulk of the energy > is relative to the impulse. A filter that is nearly minimum phase can > sometimes be much simpler than one that is exactly so. > > In audio work, we freely shift the time origin to simplify the way we > represent signals. Servo work is more demanding. Constant delays can't > be ignored. > > Good luck! > > JerryThanks, Jerry. This really helps to clarify things. Nicholas
Reply by ●January 22, 20092009-01-22
On Thu, 22 Jan 2009 09:43:31 -0600, Nicholas Kinar wrote:> Jerry Avins wrote: >> Jerry Avins wrote: >> >> ... >> >>> Control loops need at least 5X oversampling ... >> >> That may be too strong an assertion. Suffice it to say that -- with the >> exception of a toy system -- I never made on work satisfactorily with >> less than that. 10X is better if one can manage it. >> >> Jerry > > Thanks, Jerry. It's very good to know that 10X oversampling is best for > a control system. > > NicholasThat's no hard and fast rule! There are many factors that go into determining the sampling rate, primarily having to do with desired performance, sensor/actuator bandwidth, and the amount of money you have lying around to buy processors with. 10X is a good starting point for many systems, but you can often shade it down a bit. OTOH, you often need to speed it up significantly if performance and precision are paramount. -- http://www.wescottdesign.com
Reply by ●January 23, 20092009-01-23
> > That's no hard and fast rule! There are many factors that go into > determining the sampling rate, primarily having to do with desired > performance, sensor/actuator bandwidth, and the amount of money you have > lying around to buy processors with. > > 10X is a good starting point for many systems, but you can often shade it > down a bit. OTOH, you often need to speed it up significantly if > performance and precision are paramount. >...which is precisely why I am proceeding to model the system first to determine the sampling rate. After creating a model of what I what to measure, I can then test my algorithms and find the sampling rate. I agree that 10X is a good starting point. Thanks, Tim. Nicholas
