Hi Simon, you are right (and I know) that with such a low resolution it is difficult to draw sensefull data. But I want to understand what RRD does. I think the aggregation is wrong:
If I sample the data every 5 minutes (1/12h) and get a single 1kWh step in one of these 5 minute intervals then I get a peak about 0,3kW in the dayly graph. But why? I get headache with these calculation. I would say the formular is 1kWh / (1/12)h but that gives 12kW, which is definitely wrong. Another weird thing is what happens on the weekly graph. I get some "nice" step lines up and down. Shouldn't it be simply a flattened out curve just as you said. I cannot give you a picture right now, because my server is down for implementing the S0 photosensor, just as you suggested. I will implent both. So I can adjust the S0 pulse counter once a day or so to the real counter value. Thanks Thorsten > -----Ursprüngliche Nachricht----- > Von: rrd-users [mailto:rrd-users- > bounces+thorsten=trektech...@lists.oetiker.ch] Im Auftrag von Simon > Hobson > Gesendet: Montag, 30. März 2020 14:09 > An: rrd-users@lists.oetiker.ch rrdtool > Betreff: Re: [rrd-users] How to graph slow changing counters > > Thorsten Erdmann <thors...@trektech.de> wrote: > > > I want to graph the data of my energy meter. But it is measuring only in > 1kWh raster. So with normal power usage I have every 2..4 hours a step of > 1kWh. The meter displays it’s data as kWh, so it gives e.g 600 for the > absolute > counter value of 600kWh. > > I sample the absolute energy every 5 minutes. So I took this as step and > 600s as heartbeat. > > > > What I get is short peaks with a height which is displayed as 330u over a > period of 24h. With longer periods like a week the values get smaller and > smaller and there are weird stepping curves. So how can I measure/graph > such low resolution measures in a senseful way? > > Realistically, there's not a lot you can do with such low resolution data. > You'll > get a spike each time a unit clocks up, then as you zoom out for a longer > scale > view, it will flatten out to (as you've found) a rather low value. If you are > using a unit every (say) 3 hours (taking a mean between your 2 and 4 hours), > then that equates to an average of 333W - or if you are just storing kWH, > 0.333kW. Again depending on how you store and calculate, this then equates > to around 93µJ/s - at least, if my brain is working right this afternoon ! > > > You don't say how you are interrogating the meter - is it via a data source it > provides ? > If the meter is providing you with a counter value when asked, then this will > give you the best long term accuracy - your counter will always match what is > in the meter. > > As an alternative, many meters provide a pulsed output of some sort (even if > it's only an LED flashing). A bit like the old Ferraris disk meters with > their "X > revolutions/kWH", the meter pulses will give you an indication when a much > lower quantity of energy has been used - it should say on the face of the > meter how many pulses/kWH. The downside to counting these pulses is that > if your counter isn't running or otherwise misses them, then you lose sight of > energy consumed and your RRD calculations will show a lower figure than the > meter. > > You could, of course, collect both sources - use the pulses for short term > indication (ie better graphing up to a few days duration) and the register > count for longer term. > _______________________________________________ > rrd-users mailing list > rrd-users@lists.oetiker.ch > https://lists.oetiker.ch/cgi-bin/listinfo/rrd-users _______________________________________________ rrd-users mailing list rrd-users@lists.oetiker.ch https://lists.oetiker.ch/cgi-bin/listinfo/rrd-users
