Electronics > Projects, Designs, and Technical Stuff
[Question] Precision Voltage and Current Measurment ways for E-Load
MasterT:
To avoid errors introduced by loading divider, use a buffer OPA, arduino Mega has internal, plus it has optional differential configuration for inputs.
Can't comment on INA226, I played with ACS712 - galvanic isolation great advantage, safe to measure anything AC, DC, high side/ high voltage. There are many kind off, ACS758, with different ranges 5-10-20 Amps, search hall current sensor.
Where did you get ADS1262IPW? I wish to have one, $350 evaluation board from TI ? >:D
IamSynthetiC:
I found it on LCSC as standalone, i planed to copy the Layout Example to the letter, but i do want to have a look at the evaluation board. What does it do?What is it for? Who is it for ? Is it worth it ?
As for the current sensor, i think i am now presented with 2 paths:
1.)Now that i know the INA226 can perhaps be faster, i can use that sensor only. I (again) forgot to mention, this sensor communicates with the arduino through SPI, and reports both Voltage aswell as Current and Power. Therefore i can drop the whole "external ADC" idea and move on to the rest. This is the preferable option as the arduino ADC can handle the temprature sensors (i assume).
2.)I can continue as planned (ADC and all) by using the hall sensor. The ACS lineup seems very intresting, i think i will order one or two regardless of the INA225 results, so i can test their accuracy and stability. My primary concern is whether they will be able to drive to other modes (CV,CP,CR) sufficiently well (with low enough noise and deviations down to a milivolt perhaps). I'll have to do the math.
MasterT:
I'm not advising eval board, 32-bits adc for beginners is wrong choice.
Internal adc with PGA (arduino Mega) brings you close to 18-bits (10-bits adc and 200x PGA). Plus, there is a MUX, for measuring both current - voltage inputs, fast conversion rate - 1000x faster than external module, and switchable reference voltage.
Problem with a library, likely atmega data sheet has to be read thoroughly.
IamSynthetiC:
I took the time to conduct some experiments with the INA226.
The library i used was indead the problem, i used the INA-Master library as it offerede all the possibl configurations for any INA device (though few were tested by the developer, the INA226 fortunately was). I gave it some reasonable seetings (in the middle, beetwing accuracy and speed), and started the expirement.
I had the device measuring the current and voltage going to a small blue LED from my power supply, and had my two multimeters monitoring those two aswell.
The code itsellf was as simple as possible, to not load the arduino with extra code, with only a serial connection to a PC where i would extract the data from.
Right away, the INA226 seems to need 9-10 ms to make a measurment, which i believe it is fast anough for my purposes, but for some loads its should be faster.
The voltages where exremely accurate and consistent. My Keithley gave me a Median of 2.99578V where the INA226 gave a 2.99678, which is a ~0.002V diference.
The standard deviations where too very close, both sitting at ~0.002.
So the INA226 seems to agree with the Keithly so far on my power supply's regulation.
The results for the currents were not as good . It is important to mention that an HP3457A was doing a High-Side current measuring and its results were 13.896322 +- 0.02mA while the INA226 gave 0.16000 +- 0.005A (or 160 +- 5 mA which is about 10-plus times more than expected. This deviates from the HP about ~291 times |O.
I will test this further when i get the chance.
Also the resolution was 1.25mV and 0.2mA which are both good enough.
Any thoughs ?
I have placed the order for an ACS hull sensor and I will test it also when it arrives. I'll post my results then
IamSynthetiC:
Greetings
I experimented again with the INA226, and ultimately decided to drop the module, as with a loaded arduino code it took about ~100ms to report any values. That is too slow for my needs.
I have taken the time to design a PCB to see whether i can fit everything on it. I have fitted almost everything, but i now dont know where to place the ADC (and where to make the voltage measurment), as i am worried about noise from the switching power supply, the coils of the relays, the digital lines of the arduino etc. Where should i place it? Where is the place with the least noise? Any special way to route it? Can i shield or filted the noise somehow ?
I have attached bellow pictures of my PCB.
some details :
The Electronic load is not on this board. It is on another board whitch will be underneath this one.
The Switchin Mosfets for the load will be underneath and along the top of the PCB (inside the green rectangle).
Keep in mind the board is nor ready yet, but feel free to point out any ideas, or mistakes you see (there will probably be alot of them).
Thank you very much and have a good day.
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