Configuration Command

The configuration command (“CNF”) is used to configure the metrology library according to the hardware in the input networks as well as the programmable gain of the internal amplifiers.

This command must be sent before the calibration command, to ensure that the proper configuration was applied before calibrating the system. If the programmable gain of the internal amplifiers changes, then the metrology library must be reinitialized to apply the changes. So, the calibration procedure must follow these steps:

  • Send a “CNF” command. If the programmable gain of the internal amplifiers changes, then:
    • Send an “RST” command to apply the new gain.
    • Send the “CNF” command again.
  • Apply the input conditions (voltages, current and angles), then wait until the input stabilizes.
  • Send a “CAL” command.
Warning: The "CNF" command affects to all channels, so it is not valid for meters having different kinds of sensors (for example, a combination of Rogowski coils and CTs, or CTs with different current transformer ratio or different burden resistors).

The configuration command has the following parameters:

  • MC: Meter Constant (amount of energy signified by one output pulse). Units: pulses/kWh (active energy), pulses/kVARh (reactive energy) or pulses/kAmp2-h (amp square)
  • ST: Sensor type:
    • 0: Current Transformer
    • 1: Shunt Resistor
    • 2: Rogowski Coil
  • F: Mains frequency. Units: Hz
  • G: Programmable Gain Amplifier of the AFE (analog front end). Possible values: 1, 2, 4 or 8
  • Tr:
    • In the case of a current transformer, this is the current transformer ratio.
    • In the case of a Rogowski Coil, this is the current sensitivity (units: uV/A) at the main frequency specified in “Frequency” parameter.
  • Rl:
    • In the case of current transformer, this is the resistor load or burden resistor (units: Ω).
    • In the case of shunt resistor, this is the shunt resistor value (units: uΩ).
  • Ku: Voltage divider ratio

The application code receives the parameters and writes the proper metrology control registers.

Examples:

  • The current sensor are 1000:1 Current Transformers. The burden resistor is 3.24Ω, the gain setting for the AFE’s PGA is 1, and the voltage divider is composed of a resistor divider of 1650 kΩ:1 kΩ. The meter constant is 800 pulses/kWh. The command to be sent is:

    “CNF(MC=800,ST=0,F=50.00,G=1,Tr=1000,Rl=3.24,Ku=1651)”

  • The sensor is a 150 uΩ shunt resistor, AFE’s PGA is 4 and the voltage divider is composed of a resistor divider of 1650 kΩ:1 kΩ. The meter constant is 3200 pulses/kWh.The command to be sent is:

    “CNF(MC=3200,ST=1,F=50.00,G=4,Tr=1000,Rl=150,Ku=1651)”

  • The sensor is a Rogowski Coil with current sensitivity equals to 416.667 uV/A when main’s frequency is 50 Hz, AFE’s PGA is 2, and the voltage divider is composed of a resistor divider of 999 kΩ:1 kΩ. The meter constant is 1600 pulses/kWh. The command to be sent is:

    “CNF(MC=1600,ST=2,F=50.00,G=2,Tr=416.667,Rl=3.24,Ku=1000)”