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Zanduino / INA

Combined Arduino library for reading multiple INA2xx power monitor devices
GNU General Public License v3.0
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Wrong VBUS Reading #45

Closed jobitjoseph closed 5 years ago

jobitjoseph commented 5 years ago

The device gives wrong vbus reading . for example please see the table below DMM reading................... INA226 Reading 2.467.........................................2.60 4.976.........................................5.24 7.64............................................8.05 10.00.........................................10.53 the current reading is correct.

SV-Zanshin commented 5 years ago

Which INA are you using? Are you running an example program or your own code? Have you tested it with another chip?

The reason I am asking is that the bus voltage is read directly from the INA device and not changed in the library at all, and these readings all look like a similar percentage offset.

jobitjoseph commented 5 years ago

Which INA are you using? Are you running an example program or your own code? Have you tested it with another chip?

The reason I am asking is that the bus voltage is read directly from the INA device and not changed in the library at all, and these readings all look like a similar percentage offset.

Hi I'm using INA226 modules, i Have tried The sample program as well as my own. Both gives the same result. And i have tried Multiple module still the same results. And yes its gives around 5-5.3% error

SV-Zanshin commented 5 years ago

I am away from computers at the moment so cannot test this directly. Can you do a small program that uses the following functions and displays the values:

getBusRaw(yourDevice); // This will return that actual bits in the Bus voltage register getBusMilliVolts(yourDevice); // This will return the raw value multiplied by the device LSB

and the value from your multimeter for the actual voltage at the time.

jobitjoseph commented 5 years ago

I am away from computers at the moment so cannot test this directly. Can you do a small program that uses the following functions and displays the values:

getBusRaw(yourDevice); // This will return that actual bits in the Bus voltage register getBusMilliVolts(yourDevice); // This will return the raw value multiplied by the device LSB

and the value from your multimeter for the actual voltage at the time.

Hi sorry for the late reply, was busy with work. please find the reading below DMM...........INA....................raw
2.522.........2.6480................2119
3.309.........3.4760................2781 5.023.........5.2780................4223 7.49 ..........7.8730................6299 10.07.........10.590................8472 12.46.........13.112................10490 14.96.........15.728................12582 17.52.........18.423................14739 20.07.........21.105................16884

SV-Zanshin commented 5 years ago

If you divide INA by RAW you will always get exactly 0.00125. This is what internal LSB value is and therefore the library is indeed returning the correct value for what is being measured.

Thus I believe it is not a bug in the library but a problem in the hardware. At first blush I can think of the following possibilities;

  1. Invalid INA Device. Have you tried using another INA chip?
  2. Incorrect measuring point for voltage. Is the DMM measuring at the same junction that the INA device is measuring?
  3. Could the DMM be incorrect?
jobitjoseph commented 5 years ago

If you divide INA by RAW you will always get exactly 0.00125. This is what internal LSB value is and therefore the library is indeed returning the correct value for what is being measured.

Thus I believe it is not a bug in the library but a problem in the hardware. At first blush I can think of the following possibilities;

  1. Invalid INA Device. Have you tried using another INA chip?
  2. Incorrect measuring point for voltage. Is the DMM measuring at the same junction that the INA device is measuring?
  3. Could the DMM be incorrect?

I have tried 3 different Ina modules. Yes I'm measuring at the same junction. I have tried 4 different multimeters and 2 panel meters. Each meter returns the same valuy. Only difference is the panel meter reading is around 2mV off.

I can't find what's going on. The current reading is spot on. But vbus reading is giving this 5% off reading

SV-Zanshin commented 5 years ago

Even though I can't see a problem in the code, could you try using another INA library to see if that also has the same error?

SV-Zanshin commented 5 years ago

Any luck with another library? It would be nice to know that the error is reproducible regardless of which INA library is used, or that the error only occurs with my library.

jobitjoseph commented 5 years ago

Any luck with another library? It would be nice to know that the error is reproducible regardless of which INA library is used, or that the error only occurs with my library.

Hi, currently I'm out of town. I will get back to you as soon as I return. Thank you.

jobitjoseph commented 5 years ago

Any luck with another library? It would be nice to know that the error is reproducible regardless of which INA library is used, or that the error only occurs with my library.

Hi sorry for the long hold. I have tried other libraries as you suggested and all gives the same ,5% error. I can't pinpoint what's the actual issue. The current reading is extremely accurate , we can assume the shunt voltage too.but when it comes to vbus don't know what is really happening

SV-Zanshin commented 5 years ago

OK, at least we've ruled out Software issues.

You stated that you've tried different INA226 modules so the module itself shouldn't be a defective one. Could you measure the voltage directly from the 2 Pins on the INA226 to make 100% certain that you are measuring the same Thing that the INA is?

jobitjoseph commented 5 years ago

OK, at least we've ruled out Software issues.

You stated that you've tried different INA226 modules so the module itself shouldn't be a defective one. Could you measure the voltage directly from the 2 Pins on the INA226 to make 100% certain that you are measuring the same Thing that the INA is?

Hi I have already done that. If we change the value of LSB to 1.19 in the code, it gives accurate vbus reading. I know the LSB is 1.25 by default, but in this situation it's not. May be these chips at counterfeit ( it's the only explanation I can think of now).thanks for your help. Have a great day.

SV-Zanshin commented 5 years ago

I'll close this out for now as it really doesn't seem to be a library issue and I hope that you get it sorted out. It could have been a bad batch that shouldn't have been sold.