I am monitoring the main feeds from the utility and all circuits (22) but one individually including the GEM. I am currently acquiring at 10s intervals and sending data to emoncms (OpenEnergyMonitor) at 30s intervals. I grabbed the monitored values for a single interval from emoncms and dumped them into a spreadsheet and the sum of individual circuits was greater than the main feed value by about 100W. If it was less I'd simply attribute it to the unmonitored circuit. Main feed CTs are installed in opposing directions. All other CTs alternate orientation vertically in the panel on each side. I am wondering if this observation is simply due to sample timing. Presumably there is an AtoD in the GEM somewhere that samples channels serially? Any thoughts?
How many unmonitored circuits and what's the mains vs the sum of all loads? The split CTs have about a 1% error, whereas the micros can be anywhere from 1% to 3%, 100W does seem a bit large though.
One unmonitored circuit - our electric range, 22 of 32 channels used, no pulse, no temp. I just checked again and the mains value was 5914 and the sum of all monitored loads was 6462. I have one 240v circuit w/o a neutral so I subtracted 1 from the range value in setup. It's the A/C circuit which we are not using this time of year
Second, I was thinking about trying to compare cumulative energy usage between the monitor and what is reported by my utility per month. I see two potential issues. 1) Knowing the exact times when the utility read the meter; and 2) I presume my digital meter does something that could be approximated with integration. I might be able to deal with 2) using numerical methods and 1) I could just pick a time like midnight on the dates the meter was read and assume a reasonable amount of error in the result. Maybe I'm in the weeds here.
Does it say on your bill when they read?
Yup. I have a month and day but not a time. I would use that day and then just be consistent with the time on each end. BTW - it also occurred to me that the values are watt-seconds so I guess integration is not required - just sum up the mains values from btmon assuming it stored differences between consecutive values in the db?