MSP430I2041: Accuracy of AC frequency measurement with energy meter design.

huy pham

Prodigy 100 points

Part Number: MSP430I2041
Other Parts Discussed in Thread: EVM430-I2040S,

Tool/software:

Hi all,

I design my 220V/50Hz energy metter using MSP430i2041 based on EVM430-I2040S reference design.

I can measure all AC parameters like current, voltage, frequency..., but the frequency is not accurate.

The AC frequency is about 49.9-50.1Hz at my location (measured by another meter), but my design alway shows 50.4 to 50.9 Hz.

I tried replacing the MSP430i2041 MCU with another MCU, but the accuracy is still not improved.

Please help me solve this problem.

1 month ago

0 Eason Zhou 1 month ago

TI__Mastermind 35720 points

Can you use a multimeter to double check?

Is there any high freq noise on your current and voltage signal?

0 huy pham 1 month ago in reply to Eason Zhou

Prodigy 100 points

Yes, as I comment, I measure chroma 66202 power metter and my oscilloscope, and multimeter, all show frequency 50Hz +/- 0.01 Hz,

0 huy pham 1 month ago in reply to Eason Zhou

Prodigy 100 points

No, I think this because it's only an desktop computer near my place.

0 Eason Zhou 1 month ago in reply to huy pham

TI__Mastermind 35720 points

OK, another possibility is that the MCU clock is not accuracy. Its DCO frequency has about 1% error at room temperature. which will can't be overcomed.

+1 David Schultz 1 month ago in reply to Eason Zhou

Guru 20325 points

Accuracy is a bit better using an external resistor and there is an option to provide an external clock. Presumably from a nice crystal controlled oscillator if you need that sort of accuracy.

0 huy pham 1 month ago in reply to Eason Zhou

Prodigy 100 points

is it possible to adjust DCO manually in the code?

+1 Eason Zhou 1 month ago in reply to huy pham

TI__Mastermind 35720 points

You can do that but you need an accurate reference. If you very care about the Freq accuracy. I would suggest you to use F6736. However, it will be much much more expensive.

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MSP430I2041: Accuracy of AC frequency measurement with energy meter design.