On Jul 14, 6:34�am, Jerry Avins <j...@ieee.org> wrote:> On 7/14/2010 5:55 AM, Greg Heath wrote: > > �> ... what's, I& �I? > > Infiltration and inflow, which force sewage plants to process rainwater. > Infiltration occurs when leaky mains are lower than the water table. > Inflow is often illegal pump connections to the sanitary sewer. When > streets become submerged, rainwater can pour in through manhole covers. > > Jerry > -- > Engineering is the art of making what you want from things you can get. > �����������������������������������������������������������������������I think the answer to the OPs questions are in the details of this statment made by the OP: "We measure flow continuously to get the volume and concentration once or twice a week." What does that means exactly,.... Does it mean you measure __FLOW__ continuously and integrate flow continously and once or twice a week you read the integrated value to calculate __VOLUME__ during the last measurment period (integration period) and then rest the integrator? Mark
Analyzing an "undersampled" sequence
Started by ●July 13, 2010
Reply by ●July 14, 20102010-07-14
Reply by ●July 14, 20102010-07-14
On 7/14/2010 1:30 PM, Mark wrote:> On Jul 14, 6:34 am, Jerry Avins<j...@ieee.org> wrote: >> On 7/14/2010 5:55 AM, Greg Heath wrote: >> >> > ... what's, I& I? >> >> Infiltration and inflow, which force sewage plants to process rainwater. >> Infiltration occurs when leaky mains are lower than the water table. >> Inflow is often illegal pump connections to the sanitary sewer. When >> streets become submerged, rainwater can pour in through manhole covers. >> >> Jerry >> -- >> Engineering is the art of making what you want from things you can get. >> ����������������������������������������������������������������������� > > I think the answer to the OPs questions are in the details of this > statment made by the OP: > > "We measure flow continuously to get the volume and concentration once > or > twice a week." > > What does that means exactly,.... > > Does it mean you measure __FLOW__ continuously and integrate flow > continously and once or twice a week you read the integrated value to > calculate __VOLUME__ during the last measurment period (integration > period) and then rest the integrator?I start knowing that he is eminently rational, so that an interpretation that makes no sense is the wrong interpretation. His utility measures flow continuously to get volume by integration (as does mine) and samples the flow once or twice a week to assess its average concentration. (Higher concentration of components that create biological oxygen demand --a.k.a BOD-- increase processing cost. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●July 15, 20102010-07-15
Fred Marshall wrote:> > Jerry Avins wrote: > > > > > Other things being equal, clustering should follow a Poisson > > distribution. If you measure flow -- a quantity that can be heavily > > influenced by rainfall -- only twice a week, how do you bill equitably? > > > > Jerry > > Jerry, > > I don't imagine that we bill entirely "equitably" - more like "agreeably". > > We measure flow continuously to get the volume and concentration once or > twice a week. > > The concentration is assumed to apply for the entire measured volume > between concentration samples. So, one may say that we sample loading > in that fashion. > > I think I answered my own question to the point where I can deal with it: > > We have the weekly or twice-weekly samples and have computer monthly > averages - as the latter have some regulatory importance. > You might consider these monthly averages to be lowpassed versions of > the samples. > Then, one can compute the distribution of outcomes and infer(?) the > amount of loading.The volume measurement is accurate and the accuracy of the load measurement is unknown due to aliasing. And your question appears to be -> what method to use to determine the inaccuracy that aliasing might be introducing to the Load measurement? Seems like the only solution is to either sample at a higher rate or filter out higher frequencies before taking a sample. For instance, would it be possible for a valve controlled by a timer be set up so that it diverted a quart of flow into a holding tank every 6 hours? Then at the end of a week you would have 7 gallons in the tank that could be thoroughly mixed and then a sample taken from that. That would be a crude anti-alias filter in front of the sampler. -jim> > My "backwards" sort of reasoning goes like this: > We take a set of samples. > We determine the distribution of those sample values over a suitably > long time such that daily and even annual variations are included in the > distribution. > The caution here is that trends get wiped out - so a suitable time frame > or set of them needs to be selected that has some meaning where gross > trends are concerned. > If we assume that the distribution represents a reasonable estimate of > ground truth, then we can infer in quantitative terms what's happening - > such as over-loading (i.e. loading that's above some determined threshold). > It's surely not "perfect" but it's better than nothing ... I think. > > Fred
