Hello,
I would like to be able to show my line voltage with greater resolution so I can see it's relatively small fluctuations but which are sometimes bigger. I've tried to do it in the Inputs / Feeds area of Emoncms but haven't worked out how to do it - or if it can be done (I'm sure it can!). I would also like to be able to use the centre green voltage dial to show that the voltage is within the acceptable / statutory range.
I've had a VPhase 220Vac voltage optimiser for a couple of years and in due course plan to monitor its voltage too so I can see when it goes in to bypass mode - when demand is 8A or more.
FYI http://www.allecoenergy.co.uk/newsletter/images/Files/Website_Updates/VPhase/VPhase_Tech_Spec.pdf
Please could someone point me in the right direction?
My dashboard is at the link below.
Thank you
Steve
EmonTx v2 & RasPi user
Re: Increasing Vrms Resolution in Emoncms
The limitation is the data in to emoncms.org is a signed integer, -32768 - +32767. You can scale the voltage measured by your emonTx so that it uses all of that range, if you so wish; but it's probably more convenient to multiply by 100 so that the number you are sending is round about 24000. Inside emoncms, you then divide by 100 - eventually. If you want to graph with higher resolution, you could take one of several (similar) approaches. Subtract 200, and display what's left - about 40.00 V; alternatively, subtract 240 and display the deviation from nominal, +13.00 V to - 23.8 V; etc. Leaving the value in centivolts ( ! ) and applying the scaling at the dial widget will allow you to show 2 decimal places. You'll probably end up with several voltage feeds having different offsets and scaling, being used for different purposes.
Just one caveat - that's a phantom accuracy because the calibration accuracy and the stability of your emonTx is probably nowhere near that.
Re: Increasing Vrms Resolution in Emoncms
I've done something similar and here's how I display it:
http://emoncms.org/dBCC/ermvolts
One of the neat things about emoncms is that it auto-scales the y-axis to be just slightly wider than the data it's trying to display, so it effectively auto-zooms the y-axis for you. I can't remember which visualisation I used for that now, maybe "rawdata".
As Robert says, it's only as good as the source data. My front-end is a calibrated precision 3-phase monitor that reports Vrms in mV. But in my house I only have one phase, so effectively I have 3 precision voltmeters all reading the one signal. You can see they're usually within about 10-20mV of each other. The 3 voltmeters' sampling interval aren't particularly time-sync'd, although chances are they'll end up that way. But it gives me a good escape clause as to why they don't give the exact same reading. They do when they're in the lab connected to the calibrator.
Re: Increasing Vrms Resolution in Emoncms
Thank you both for your responses. I need to make some time before I can get on to this in a week or two and will report back.
Regards,
Steve