Question on Calibration - Voltage energy meter

[FreshmanNewbie]

I have this ATM90E26AS - Energy metering IC and this is the application note that decribes the process of calibration. (https://ww1.microchip.com/downloads...tes/Atmel-46102-SE-M90E26-ApplicationNote.pdf)

In this application note, on page 14, we see the steps they mention to calibrate the voltage.

Ugain = ((24600 x Un)/(Vol_mea))

So, as far as I understand, Ugain is a register and Urms is another register.

As far as I understand, when the ATM90E26 is initially powered, there's some default value in the Urms register.
Now, based on the input voltage that is given (220.024V, as given as an example in the application note), there will be a different value provided by the Urms register.

Converting this Hex value from the Urms register to Voltage (as described in the app note), I can obtain a value which can be converted into Hex. And this is the final Hex value that needs to be written into the Ugain register for calibration. Please correct me if I am wrong.

My question is,

1. How can this approach be termed as calibration? I am given some voltage (220.024V) and just writing that in a register. I am not comparing or validating this 220.024V voltage value against any standard reference. I am also not conveying to the IC that this final Hex value which is being written into the UGain register corressponds to 220V. In that case, how is the calibration process termed as correct? Am I missing something to understand?

 

[KlausST]

As far as I understand, when the ATM90E26 is initially powered, there's some default value in the Urms register.

U_RMS is the result of the RMS measurement and calcualtion. There is no default value in the U_RMS register.

But there should be a valid value in the U_Gain register. This is the factor that is needed to get the U_RMS result to the right magnitude.

So the approach is:
* apply an useful reference voltage U_n. Let´s say 100.0 V RMS sine
* read out the U_RMS value: let´s say it is 87.6 V (= measured voltage, = Vol_mea). Obviously it is not the expected 100.0V
Thus you need to correct the U_Gain

Use the above formula to calculate U_Gain.

program U_Gain into the chip. Wait a little for the values to settle (Not sure if needed. It won´t hurt)
Then verify U_RMS, now it should be very close to 100.0V.

If not: repeate the calibration. Use yor actual V_Gain instead of 26400.

Klaus

 

[FreshmanNewbie]

U_RMS is the result of the RMS measurement and calcualtion. There is no default value in the U_RMS register.

But there should be a valid value in the U_Gain register. This is the factor that is needed to get the U_RMS result to the right magnitude.

So the approach is:
* apply an useful reference voltage U_n. Let´s say 100.0 V RMS sine
* read out the U_RMS value: let´s say it is 87.6 V (= measured voltage, = Vol_mea). Obviously it is not the expected 100.0V
Thus you need to correct the U_Gain

Use the above formula to calculate U_Gain.

program U_Gain into the chip. Wait a little for the values to settle (Not sure if needed. It won´t hurt)
Then verify U_RMS, now it should be very close to 100.0V.

If not: repeate the calibration. Use yor actual V_Gain instead of 26400.

Klaus

Thank you for your clarification.

I have a few follow up questions.

1. How do you confirm that there is a valid value in the UGain register and not in the Urms register? And not the other way round? Do you infer from anywhere in the datasheet/application note?

2. Also, just curious. Any idea on why there will be a default value in the UGain register and not in the Urms register?

3. Even if the Urms is measured as 87.6V and I correct the U_Gain using the given formula in the application note to 100V. After this, any idea on how the UGain understands that if you give U_n = 100V, it will ensure that the voltage given is 100V?

4. Finally, I couldn't understand when you mention "V_Gain". What is it?

 

[KlausST]

1. How do you confirm that there is a valid value in the UGain register and not in the Urms register? And not the other way round? Do you infer from anywhere in the datasheet/application note?

What about readig the datasheet?
It says:
"and 26400 is the decimal of 6720H which is the power-on value of the voltage rms gain register (Ugain, 31H)."
If you write nonsense into it ... you are responsible.

U_RMS .. again: is the measurement result.....

****

2. Also, just curious. Any idea on why there will be a default value in the UGain register and not in the Urms register?

U_Gain: Just think by yourself ... what happened if the Gain register would be 0.

U_RMS: Again it is the measurement result.

3. Even if the Urms is measured as 87.6V and I correct the U_Gain using the given formula in the application note to 100V. After this, any idea on how the UGain understands that if you give U_n = 100V, it will ensure that the voltage given is 100V?

UGain is just a factor for multiplication.
Any reason why "multiplication math" should not be true anymore?

4. Finally, I couldn't understand when you mention "V_Gain". What is it?

My mistake. In the US (maybe other countries, too) "V" is the abbreviation for voltage (I´m not talking about "V" as unit for volts)
In other countries "U" is the abbreviation of voltage.
Years ago I used "U" .. Through the forum I learned to use "V" instead... now I did ... while the datasheet uses "U".
--> just replace my "V_gain" with "U_Gain"


Klaus

 

[FreshmanNewbie]

What about readig the datasheet?
It says:
"and 26400 is the decimal of 6720H which is the power-on value of the voltage rms gain register (Ugain, 31H)."
If you write nonsense into it ... you are responsible.

U_RMS .. again: is the measurement result.....

****

U_Gain: Just think by yourself ... what happened if the Gain register would be 0.

U_RMS: Again it is the measurement result.


UGain is just a factor for multiplication.
Any reason why "multiplication math" should not be true anymore?


My mistake. In the US (maybe other countries, too) "V" is the abbreviation for voltage (I´m not talking about "V" as unit for volts)
In other countries "U" is the abbreviation of voltage.
Years ago I used "U" .. Through the forum I learned to use "V" instead... now I did ... while the datasheet uses "U".
--> just replace my "V_gain" with "U_Gain"


Klaus

Thank you for your clarification