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MSP430FE4272 - Energy pulse Error variation

Getaneh Alesew
Prodigy 50 points
Other Parts Discussed in Thread: MSP430FE4272Part Number: MSP430FE4272

Application: Electric energy measurment

Question type: Development and troubleshooting

Support topic: /Product/Development and troubleshooting/Search the forums for my problem/

Description of the problem: I am using MSP430FE4272 for single phase electric energy measurement, the active power displayed on the LCD is constant and is not varying ,but the error reading using the LED pulse varies for arround 0.6% ,could any one help me how can I resolve this problem pleas?

  • 0
    TI__Mastermind 49692 points

    Hi Getaneh,

    Are you using the EVM430-FE4272 or a custom board? Are you using one of the Demos or custom code?

    Getaneh Alesew said:
    the error reading using the LED pulse varies for arround 0.6%

    Unfortunately, I'm not sure what your statement above means. Could you please provide more background about what you're measuring and what is expected? The pulse generation seems to indicate a specific energy level, which can be specified in the 'parameter.h' file.

    Regards,

    James

    MSP Customer Applications

  • 0 in reply to James Evans
    Prodigy 50 points
    I am using a custom board with the DEMO 2 software,"the error reading using the LED pulse varies for around 0.6%",I mean the pulse interval is not constant for a constant load,I realize this from the energy error indicator of a test bench equipment, the energy error between the test equipment and my devices pulse varies
  • 0 in reply to Getaneh Alesew
    TI__Mastermind 49692 points

    Hi Getaneh,

    To rule out whether or not this is a hardware-related issue, do you have access to the EVM430-FE4272, so you can compare its results to those observed on your custom board? Did you go through the calibration process described in Section 7.7.2 in the User's Guide?

    Regards,

    James

    MSP Customer Applications

  • 0 in reply to James Evans
    Prodigy 50 points

    Thanks James for your reply,I noticed that it is not a hardware issue after observing the energy displayed on the LCD is constant for a constant load. By the way what is the number of pulse at which energy error is calculated during accuracy test?there are different error result for different number of pulses.the error goes good as i increased the number of pulses from 1 to 2 to 3 to 4...etc.is there any standard on the number of pulses I should set?and what is 'n' on the test document

    shown on  is that the number of pulse?

    Thanks

  • 0 in reply to Getaneh Alesew
    TI__Mastermind 49692 points

    Hi Getaneh,

    I apologize for the delayed response due to the holidays.

    Regarding the energy pulses, typically more pulses means better resolution. Obviously, there's a practical limit that's influenced by the test setup, time spent in interrupt service routines (ISR), etc. Typically, we use 1600 and 6400 pulses per kWh.

    Regarding the "n" in the test document, the maximum current (I_MAX) is a multiple (n) of the nominal current (I_B), not the number of pulses. For the first test scenario, the nominal current is 6A and the max current is 60A. Thus, n=10. In the first table, the single currents/range of currents are just shown as multiples of the nominal current up to I_MAX. For your single-point calibration, it's important to start somewhere in the middle (log scale, not linear) of your expected current range. For example, if we have a range from 1A (I_MIN) to 100A (I_MAX), I'd start my calibration at 10A. Then, depending on your expected nominal current, you could shift your calibration point accordingly to try to achieve better accuracy.

    In Figure 6 in the Implementing An Electronic Watt-Hour Meter With MSP430FE42x(A)/FE42x2 (Rev. C) User's Guide, "n" is just the number of meters, not the number of pulses per kWh. While this looks like a bus that's n-bits wide, this figure is showing you'd need "n" connections for "n" meters to measure the energy pulses from each one.

    Hopefully these explanations help!

    Regards,

    James

    MSP Customer Applications

  • 0 in reply to James Evans
    Prodigy 50 points

    thank you so much james,this is helpfull. But my question was not about pulse constant(pulse frequency). it's about error measurment. when you measure an error a test equipment there are parameters that you need to set (voltage,current,power factor,pulse constant(pulse/KWH)) then to measure the error you need to set the number of pulses after which the error is computed. for example if your pulse constant is 1600 and you want the error to be computed after 4 pulses(after (4*1/1600)KWH) you will set the number of pulses to 4.this number has an effect on testing the error variation. if I set the number of pulse to 1 the error will be computed for every LED(energy indicator ) blink,so here the variation is obviously high. but if I increased the number of pulses to some higher value,lets say 10.the error variation is decreased because the error computer uses averaging. so is there any limit on the "number of pulses after which the error is computed" please?

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