Algorithm and voltage monitoring
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From: Martin Brown on 27 Jul 2010 03:01 On 26/07/2010 22:37, john1987 wrote: > Hi, > > I am monitoring the voltage across the resistor and needs to maintain > it steady at set point value. Let�s suppose if the set point value is > 100 volts peak to peak and if the voltage goes below this value or > above this value than I have to make MOSFETS turn ON and OFF using > pulse width modulation to keep the voltage steady. > > Right now, I am reading the voltage across the coil and doing �if > else� statements to see whether the voltage is right and make > adjustments accordingly. > What coil? And this is AC so you can only sample around the peaks. > > My question is > > Is this algorithm of using �if else� algorithm is enough or should I > be controlling the voltage using like control algorithm like PID > controller etc. It depends critically on the load. If the load current is likely to vary suddenly or is non-linear with applied voltage like a filament then you are probably better off with a PID using control based on whatever it is you actually want controlled out of the other end. Until you decide how closely you *need* the thing regulated your question is impossible to answer. How noisy is the line? etc. Regards, Martin Brown
From: Robert Baer on 27 Jul 2010 05:26 john1987 wrote: > Hi, > > I am monitoring the voltage across the resistor and needs to maintain > it steady at set point value. Let�s suppose if the set point value is > 100 volts peak to peak and if the voltage goes below this value or > above this value than I have to make MOSFETS turn ON and OFF using > pulse width modulation to keep the voltage steady. > > Right now, I am reading the voltage across the coil and doing �if > else� statements to see whether the voltage is right and make > adjustments accordingly. > > > My question is > > Is this algorithm of using �if else� algorithm is enough or should I > be controlling the voltage using like control algorithm like PID > controller etc. > > Regards, > > john Isn't this bass-ackwards? Constant voltage power supplies are almost as common as dirt. "Peak-to-peak"??? That hints of AC. Well, a constant AC voltage can also be had; not exactly as common as a DC constant voltage as one might presume at the start of the question. In either event, turning a supply on and off certainly does not lend to a result that could, by any stretch of imagination, as being "constant".
From: john1987 on 27 Jul 2010 13:08 Hi, The other important question that I have is that how can I calculate that how fast my digital system can response to the input. What I meant to say that the ADC on the micro. detects the voltage across the ressitor or coil and then increase or decrease the current accordingly. I just do need to know that what parameters I need to take into account to keep the feed back loop reacts as fast as possible while designing it. I want to calculate it before I start building the system. Thanks John
From: JosephKK on 31 Jul 2010 11:30
On Mon, 26 Jul 2010 22:44:35 -0400, ehsjr <ehsjr(a)nospamverizon.net> wrote: >Tim Wescott wrote: >> On 07/26/2010 02:37 PM, john1987 wrote: >> >>> Hi, >>> >>> I am monitoring the voltage across the resistor and needs to maintain >>> it steady at set point value. Let�s suppose if the set point value is >>> 100 volts peak to peak and if the voltage goes below this value or >>> above this value than I have to make MOSFETS turn ON and OFF using >>> pulse width modulation to keep the voltage steady. >>> >>> Right now, I am reading the voltage across the coil and doing �if >>> else� statements to see whether the voltage is right and make >>> adjustments accordingly. >>> >>> >>> My question is >>> >>> Is this algorithm of using �if else� algorithm is enough or should I >>> be controlling the voltage using like control algorithm like PID >>> controller etc. >> >> >> Depending on what "make adjustments accordingly" translates to, you're >> working on something that might work. >> >> Do a PID, get it right, and you'll be working on something that _will_ >> work. Assuming, of course, that all the rest of the system is right -- >> but if the rest of the system is screwed up, then some oddball hybrid >> bang-bang controller is going to have less of a chance at it than even a >> simple PID controller. >> >> While it lasts: dpm1480.pbworks.com/f/PID%20without%20a%20PhD.pdf. >> >> eetimes.com has moved things around; they've put all the interesting >> stuff behind an email harvester. Dang!! >> > >Nice article. Repeating your link: > >http://dpm1480.pbworks.com/f/PID%20without%20a%20PhD.pdf > >Ed Days later and it works for me. Sasved a copy. |