Virtual Feed : add values from input

Tags: #<Tag:0x00007f10a7a22948> #<Tag:0x00007f10a7a22718>
(Benoit D) #1


I’m having an hard time figuring out how I should configure my virtual feeds.

Let’s say I have two sensors : A and B. They work together to give a value that interests me : A+B.

In emoncms, I have inputA which gets the data from sensor A and inputB which gets the data from sensor B.

What processes do I need to get a graph that is the sum of the values of the sensors A and B ?

The sensors send the data every 15 minutes.

I have tried a lot of possibilities, none of them gives what I want… That’s why I’m calling for help here…

Thank you in advance,



Unable to Create a Virtual Feed
(Chaveiro) #2

From inputs, you should ‘log to feed’ sensor A and sensor B to another feed.
Then create a new virtual feed and add “source feed” referring to previous created feed A and next “+ source feed” referring feed B.


(Neil Hastings) #3


My software version is 9.9.8.

I have two feeds (A and B) 'Logged to Feed". If I try to create a New Virtual Feed using ‘Source Feed’ and Feed A I get the following error message: ERROR: Could not save processlist. Cannot use virtual feed as source.

Am I missing something or do you think this might be a bug of some kind?

Best wishes


[See Unable to Create a Virtual Feed - Moderator - RW]


(Dan Padure) #4

I’m having the exact same issue!


(Dan Padure) #5

I was able to “add” them using +inp and then specifying input.
the value in feeds is fine, but when viewing it in a graph it is all messed up


(Dan Padure) #6

I edited modules/feed/feed_model.php and commented lines 1093 and 1094, now the script allows me to add the sources

but still it does not work, it calculates zero values

I think the problem is in that php file. But I’m not that good at programming to properly debug it


(Neil Hastings) #7

After messing with this for a while I realized that Virtual Feeds may only be created from physical inputs, as Dan also discovered.

Processes created from a physical input (such as power to kwh/d) can’t [currently] be used in Virtual Inputs. I don’t see any reason why one should not be able to used ‘calculated inputs’ such as kWh/d if they are logged.

A work-around: If I send data from Node-Red to EMONCMS it shows up in the Inputs list and these data can be used in Virtual Inputs -even though they are not real ‘physical inputs’- so, to calculate kwh$/d, I can send kwh/d to Node-Red, calculate kwh$/d and return this value to EMONCMS. This value then shows up on the Inputs list and can be used in Virtual Inputs. I do not recommend this method for critical or robust systems, but it works.

So why not the ability to create a virtual feed from a kwh/d process? I see no reason why Virtual Feeds could not be created from any input, physical or calculated. However my knowledge of EMONCMS programming is essentially zero so I defer to the experts.


(Dan Padure) #8

the best workaround is to install the post processing module


(Neil Hastings) #9

Thanks Dan,

I have been unable to use the Post Processor because of the issue I raised here: Missing Formula Box in Post Processor Emoncms

Is the Post Processing module something that I need to Install?



(netrider) #10

My software is and fresh install of 9.9.8 version.
In this fresh install I can’t make a virtual feed when the source feed is an calculated feed.
This give the following error already report:
ERROR: Could not save processlist. Cannot use virtual feed as source

I have another raspberry with 9.9.8 upgraded version when I have this virtual feed done and work well.

The objective is to add a multi-tarrif cost day to have the total of the cost by day.
Can some one help ?

Thanks in advance