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IC TO PROVIDE HIGH ACCURACY PULSE OUTPUT FOR 0.1 CLASS ENERGY METER

SUMAN BHARTI
Intellectual 555 points
Part Number: MSP430F47127

I am making a energy meter/reference meter with 0.1 class accuracy based on MSP430F47127.

All thing is ok, but i am not able to provide pulse output for its accuracy check. Although i have provided 1600 impulse/Kwh output through an led, but it can't be used to check its proper accuracy at low current.

Even if I provide 128000 impulse/Kwh, it will not provide proper accuracy on low currents.

For its proper calibration and testing i need high frequency pulse output to fed into reference meter with 0.01 class accuracy.

Please suggest me any ic/chip for this purpose.

  • 0
    TI__Mastermind 49692 points

    Hi Suman,

    To confirm, you are getting pulses for higher currents? For low currents, do the pulses slow down, show up randomly, or not at all? What voltage and current ranges (min, max) are you working with here? What values were used during your calibration?

    Depending on how low your currents are, they may be lower than what's specified by the RESIDUAL_POWER_CUTOFF macro definition and could be ignored. This macro appears to be set to 2.5W by default (using a value of 250), according to Section 4.4 in the Implementation of a Three-Phase Electronic Watt-Hour Meter Using the MSP430F471xx app note. I'd suggest lowering this value according to your application.

    In conjunction with this change, it'd also be good to increase your PHASE_ENERGY_PULSES_PER_KW_HOUR macro to 6400 pulses per kWh from 1600. Another important macro is the ENERGY_PULSE_DURATION macro. Here, if the duration of LED on-time is too large, you could experience overlap at higher currents where the pulses merge into a continuously high signal. Since you're working with low currents here, this probably isn't the issue, but I still wanted to point it out.

    Regards,

    James

    MSP Customer Applications

  • 0 in reply to James Evans
    Intellectual 555 points

    Thanks James Evans for reply.

    Voltage under consideration : 80V to 600V

    Current under consideration : 10mA to 90A

    Currently i have made it with 1600 impulse output. But it is not possible to check its accuracy. Plz consider below calculation :

    Running load : 1KWh = 1000 Watt hour  ->  Pulse output : 1600 pulse/hour

    Running load : 1 Watt hour  ->  Pulse output : (1600/1000) pulse/hour

    At 100mA Current, 240V

    Running load : 24 Watt hour  ->  Pulse output : (1600/1000)*24 pulse/hour = 38.4 Pulse/Hour

    If i get 39 pulse :

    Error = (39/38.4)*100 = 101.5625-100 = 1.5 %   ; Calculations are done theoretically, however it is clear we cant receive exactly 38.4 pulse practically for exact in one hour.

    Similarly  consider for 6400 impulse/kwh :

    Running load : 1KWh = 1000 Watt hour  ->  Pulse output : 6400 pulse/hour

    Running load : 1 Watt hour  ->  Pulse output : (6400/1000) pulse/hour = 6.4 Pulse/hour

    At 100mA Current, 240V

    Running load : 24 Watt hour  ->  Pulse output : 6.4*24 pulse/hour = 153.6 Pulse/Hour

    If i get 154 Pulse :

    Error =  ((154/153.6)*100)-100 = 100.26-100 = 0.26 % ; Still not under 0.1%.

    At higher currents it will not be any problem. But  to check error % at low currents we require higher pulse output.

    That is why in reference meters, they provide pulse output in TTL level (as LED cant support at such higher frequency) with constants in more than 10 Million. We too want to provide same.

    So for this purpose please suggest any IC/Chip that can provide pulse output in TTL level with constant more than 10 Million.

    Thanks in Advance.

  • 0 in reply to SUMAN BHARTI
    Guru 12050 points

    Are you asking how to change the software to output pulses that is 2778Hz at 1KWh (10million pulses in a hour)
    so to get better granularity with smaller loads, in software anything is possible.
    Plenty of buffer chips to up translate 3.3 to 5v, TI's: SN74LV1T34DBVR and 3KHz is considered slow in electronics.

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