Data analysis with IoTaWatt Outputs

I’m interested… How did you create that chart showing the imbalance? I mean, I understand how the chart with the two power traces would be created, this is information that is measured by your emon system, stored in a database file and retrieved into the chart. But the imbalance trace? Did you create a virtual feed? Is it necessary to store that information into a database file to plot the trace or is it calculated as needed from the data stored for the other inputs?

These may seem like trivial questions, but I’m at a roadblock right now. I can create a virtual feed that creates a value that updates correctly, this is evident in the feeds panel. But I have no idea of how the setup the system to store the data on an ongoing basis in a database file. I presume this is necessary to plot a virtual feed as you did. If I try to graph the virtual feed I set up, the system throws a series of errors that forces me to deselect the virtual feed to recover.

I have not seen any ‘plain English’ instructions on how to use or set up virtual feeds and use them. Maybe this is obvious to people who have experience using database systems and are familiar with Linux systems. I am neither and it is not obvious how this is to be set up. There is a lot of technical documentation out there and I am sure that the answers I need are there if I could comprehend it all and put the pieces together. But its not gelling for me at the moment.

If you, or anyone else, is willing to help I am appreciative.

I did that with my IoTaWatt in local graph mode. I defined an output that was the difference between the two mains and then just added that to the graph:

Then I ran the local graph app (modified Emoncms graph app) and selected that output along with the mains:

The advantage with using IoTaWatt outputs is that it’s just a script that runs against the selected data, so you can define an output and view it against data from today or last year. The datafile holds all of the raw input data and everything is computed in the query using the internal scrip system. Same goes for uploading to Emoncms or other servers.

I’ve got a number of outputs defined. I define Total_power as the sum of the two mains. Because I don’t have CTs on every circuit in the house, I define an output called Misc that is the sum of the mains minus all of the measured circuits. I have another that tells me my total usage minus the heat-pump.

These outputs can be created on the fly and plotted immediately. No need to restart or wait for data files to be built.

Looks easy enough if I had an IoTaWatt. My questions pertained though to the use of the emonPi hardware. I had not gleaned the fact that you were using an IoTaWatt based on the previous conversations with Duncan.

Thank you for your effort.

7 posts were split to a new topic: Questions about feeds and virtual feeds