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Tim Wescott
science forum Guru Wannabe
Joined: 03 May 2005
Posts: 292
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 Posted: Fri Jul 01, 2005 8:19 pm Post subject:
Reconstruction
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On the other side of the coin from sampling, do you ever use any kind of
reconstruction filter in a control loop? I have never, ever done so; if
I'm concerned about the edges of my drive samples it means I'm sampling
too slow and I need to correct the problem. The only time that I could
see doing it would be if I were driving some otherwise well-behaved
plant that were somehow sensitive, but that seems to be a rare thing.
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Tim Wescott
Wescott Design Services
http://www.wescottdesign.com |
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Jerry Avins
science forum Guru
Joined: 03 May 2005
Posts: 534
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| Posted: Fri Jul 01, 2005 8:26 pm Post subject:
Re: Reconstruction
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Tim Wescott wrote:
| Quote: | On the other side of the coin from sampling, do you ever use any kind of
reconstruction filter in a control loop? I have never, ever done so; if
I'm concerned about the edges of my drive samples it means I'm sampling
too slow and I need to correct the problem. The only time that I could
see doing it would be if I were driving some otherwise well-behaved
plant that were somehow sensitive, but that seems to be a rare thing.
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A little RC to round the corners sets my mind at ease. I squirm if I can
hear the DAC on the radio.
Jerry
--
Engineering is the art of making what you want from things you can get.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ |
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Guest
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| Posted: Sat Jul 02, 2005 2:55 pm Post subject:
Re: Reconstruction
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On Fri, 01 Jul 2005 15:19:44 -0700, Tim Wescott <tim@seemywebsite.com>
wrote:
| Quote: | On the other side of the coin from sampling, do you ever use any kind of
reconstruction filter in a control loop? I have never, ever done so; if
I'm concerned about the edges of my drive samples it means I'm sampling
too slow and I need to correct the problem. The only time that I could
see doing it would be if I were driving some otherwise well-behaved
plant that were somehow sensitive, but that seems to be a rare thing.
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
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Most actuators provide enough roll-off to filter the output from the
DAC, but I suppose if the control software didn't implement smooth
switching between control modes that might cause a transition from Max
to Min output, then a low pass filter might be needed to prevent the
excitation of high frequencies in the system. |
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Kelvin Hales
science forum beginner
Joined: 03 May 2005
Posts: 45
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| Posted: Sun Jul 03, 2005 7:41 am Post subject:
Re: Reconstruction
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In article <11cbgbsqhnmktbc@corp.supernews.com>, Tim Wescott wrote:
| Quote: | On the other side of the coin from sampling, do you ever use any kind of
reconstruction filter in a control loop? I have never, ever done so; if
I'm concerned about the edges of my drive samples it means I'm sampling
too slow and I need to correct the problem. The only time that I could
see doing it would be if I were driving some otherwise well-behaved
plant that were somehow sensitive, but that seems to be a rare thing.
-------------------------------------------
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
In sampled-data theory (which has similarities with discrete-time digital systems), the |
sample-and-hold device (the DAC in a digital system) is itself a low-pass filter which does the
reconstruction of the signal to produce a continuous-time signal from a discrete-time (sampled)
signal. Of course, the reconstructed signal then still has a stair-case like appearance; but this
is not usually a problem because, as you say, the appropriate choice of sampling frequency as a
function of the plant's frequency bandwidth means that the controlled system itself provides
further low-pass filtering; so that the stair-case like output signal becomes an smoothed
response in the actual controlled system.
Kelvin B. Hales
Kelvin Hales Associates Limited
Consulting Process Control Engineers
Web: www.khace.com |
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RRogers
science forum beginner
Joined: 09 Jun 2005
Posts: 10
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| Posted: Fri Jul 15, 2005 3:20 pm Post subject:
Re: Reconstruction
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I haven't used it; but I would think the design considerations would be
covered in articles/books on microstepping of stepping motors. The
engineering theory must consider both the time and space resolution in
order to do the design.
Never had to do microstepping myself though, so I can say for sure.
Rrogers |
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