I'd like to help improove that next emontx Shield. Can help with pcb design etc.
A few questions and ideias for forum brainstorming session:
1- Why 4 sensor ports? 2Voltage+ 1Current seems fine for all projects. More than this we have lower sample rate.
- can we do a 3 sensor 2V+1I shield only ?
2- Offer to improove design layout to better shield analog part to reduce noise. Capacitor to AREF. Anti-aliasing caps.
3- Sometimes sensor space is critical. Can we leave some place on the shield to receive a mini arduino like this : http://playground.arduino.cc/Learning/ArduinoMini
Instead of pluging sheild in arduino, we can optionaly plug mini arduino in shield.
4- Other option similar to (3) is to ditch arduino itself and place the atmega and cristal directly on the shield.
5- I've taken other considerations at option (4) like a shield with it's own atmega (with arduino code) but outputs only calculated data on I2C shield pins. The ideia is that each of this shields are stakable on each other and can report different fases data for a master arduino on the bottom of the stack that does not need to process any low level data. Eg. fast samples and different zones, etc.
6- Shield with professional Poli Phase Measurement chip like Analog ADE7758 or ADE7780 with this capabilities out of the box:
- Highly accurate; supports IEC 60687, IEC 61036, IEC 61268, IEC 62053-21, IEC 62053-22, and IEC 62053-23
- Compatible with 3-phase/3-wire, 3-phase/4-wire, and other 3-phase services
- Less than 0.1% active energy error over a dynamic range of 1000 to 1 at 25°C
- Supplies active/reactive/apparent energy, voltage rms, current rms, and sampled waveform data
Requires an arduino library for it. I'd go with ADE7780 and I2C to arduino so we can use SPI for ethernet in arduino if required. Also we could adopt the app note schematic for direct line measuremet with galvanic isolation ics and a protective (Heat-shrink large tube) on the exposed solders. All electrical shock warning included. This way we dont need the voltage transformer and can measure 3 line voltages easily for tri-phases.
I can help with this lib development also.
Please post your comments. I see that much improvement can still be made to this energy mettering aparatus.
Note: My prefered is idea 6.
Re: Emontx Shield SMT with new layout in development
4- Other option similar to (3) is to ditch arduino itself and place the atmega and cristal directly on the shield.
Isn't that an emonTX? Or am I missing something?
P.
Re: Emontx Shield SMT with new layout in development
Nuno,
most of these points have been discussed before, results were roughly as follows (please, forum members, correct me if I am wrong!):
1. You need at least 1 voltage and 1 current for one phase consumption meter. Additionally 1 current sensor for PV feed. And 1 voltage plus 3 current sensors total for the usual three phase systems (standard in Germany). 4 current sensors for 3 phase system plus PV feed. So, 1 voltage and 4 currents is very nice to have. More sensors is very special, less does not cover all 'standard' use cases.
2. I would also prefer to have a decent anti-aliasing filter, yes.
3. This is very near to how the new emonTx is designed (with a Ciseco RFu-328)
4. as Paul already said, that is the current emontx.
5. too expensive (in my opinion), very special. Most of this can be done with the existing emontx.
6. sacrificing strict mains isolation and non-intrusive retrofitting is a no-go (my humble opinion, which seems to be shared by OEM).
BR, Jörg.
Re: Emontx Shield SMT with new layout in development
Jörg - two points: (a) don't forget the American system where phases are centre-tapped to earth and loads can be 110 V (L-N) or 220 V (L-L), i.e. essentially 6 phases; and (b) you're assuming with one voltage measurement that the voltages track each other exactly. That's not necessarily true, and increasing the measurement accuracy makes the imbalance more noticeable.
(5) is surely just the same as MartinR's "Full Fat" 3 phase system?
(6) I understand many kits are sold to schools. Anything not totally packaged, certified and safe is not an option in that market. Splitting sales between the safe low voltage emonTx and an emonTxPro (?) that if sold would need CE certification and marking would inevitably raise costs in the shop and support effort needed in the forums.
Re: Emontx Shield SMT with new layout in development
Robert,
a) yes, true, but three phase systems are (to my knowledge) absolutely unusual for residential use in the US (please correct me) and the industrial three phase systems are usually 270/480V? (Is OEM really meant to be used there?).
b) I am running this arrangement since 4-5 months now with an overall accuracy of better than +/-2% compared to the ferraris meter, not too bad (but you are right, there is no guarantee it works that good under all circumstances).
(5) yes, and it is doable with the standard emontx hardware.
Re: Emontx Shield SMT with new layout in development
Jörg:
(a) I think (without searching the forums to check) we've had the question asked, so even if they're as rare as 3 phase residential systems in the UK (I know of 2, MartinR and Tinbum, plus Noah - but his is a converted industrial building I believe, and I'd never ever heard of one before those) they must be considered at the development stage, even if not progressed.
(b) That must be the network planners' dream! What it probably means is that short-term imbalances cancel in the long term.
Re: Emontx Shield SMT with new layout in development
There Isnt a ade7780 as I can see maybe you meant ade7880. The IC seems a bit expensive (£10) and overspeced.
You could use 6) with jack sockets for V & I then people can use either isolated or not.
I am looking at doing a single phase PCB using two ADE7757ARN chips as they are 60p each. I can do a single phase reading of consumption and IMPORT/(EXPORT). These chips are simple to interface just single pulses per 10 Joules and a Reverse flow indicator. I did look at some maxim chips that give you voltage current reactive power etc but I am really only interested in power in and power out.
Re: Emontx Shield SMT with new layout in development
(b) That must be the network planners' dream! What it probably means is that short-term imbalances cancel in the long term.
Yes, as nearly every house-(hold) in Germany is equipped with three-phase and the loads in the houses are distributed with some reason, this seems to work quite well (even locally). This might have changed a bit lately due to more and more PV systems being installed where most of them are one phase or at least not symmetrically distributed between phases. On a bigger scale this should also average out, but local voltage variations have clearly increased.
Before this becomes too much off-topic:
There is a quite interesting range of ICs from Maxim/Teridian (e.g MAX78700) where the (per phase) ADCs are powered from and communicate with a mains isolated (or earthed) master IC via a simple pulse transormer. Unfortunately the protocol is proprietary and not documented.
Re: Emontx Shield SMT with new layout in development
Ok been digging a little further and found this CS5490-ISZ
Its a single phase meter IC with a uart interface and there is a reference design here
http://www.cirrus.com/en/pubs/rdDatasheet/CRD5490-Z_RD1.pdf
It could easily be modded by removing the PIC uart to converter and using an encapsulated 38v to 3.3v converter to make a rather nifty power monitor device it plug into the emon tx. A little monitor that plugs in and give Line voltage, Load current and Active Reactive & Apparent Power, Power Factor, Line Frequency, Zero Cross Point and Temperature. reading kit cost approximately £15 + cost of a CT. All with an accuracy of 0.1% and with the only overhead on the Emon is reading the 24 bit values through the optically isolated UART port.