Anerma Research b.v.

Modular power meter with MODBUS-RTU™ interface: concept.

For specialist, we go deeper into the meter details. the schematic is rather complex, to achieve a system that is as simple as possible for the user.

Each module contains, beside the 24V power bus, 3 communication busses.

  • The MODBUS-RTU bus for communication with a master, enabled in the first module
  • A bidirectional broken ring, for address configuration and set-up
  • A high speed bus, that sends the Voltage samples to, and returns the power components from, all the current modules.

    • Modular meter

    While power and MODBUS-RTU A master system or PLC with MODBUS RTU interface is coupled to the first element cascade. The different modules are placed in a chain, to become a cascaded multi channel meter.
    The first module is the Volt1000 which samples the voltages L1,L2,L3 and N and send them to the following modules.
    The following, up-to 15 modules, have 4 current sensors each, (L1,L2,L3,N) are connected by patch cables (RJ45-UTP).
    A mix of RoCo's and, with less required space, then Cube can be used.
    Only one cable should be connected to the master system to measure up-to 60 power lines.
    This modular system consist of a voltage module (Volt1000) that measures L1,L2,L3,N, and one up to fifteen current modules (RoCo or Cube) that measures power and current.
    In other words, for up to fifteen 3-phase+N outgoing power lines, it is possible to measure the voltage, current and power for the 3 phases and the voltage & current in the Neutral.
    Each module contains multiple analog to digital convertors, so all voltages and currents are measured synchronously, without multiplexing.

    The Volt1000 is always connected to the MODBUS-RTU master via a RJ45-in plug that also supports the 24V power for the whole metering system. An internally 120 Ohm MODBUS termination-resistor is fix
    The local meter bus and local power is forwarded with a patch cable from the one to the next module.

    MODBUS communication:

  • The MODBUS master (often a PLC) delivers communication and power to the Volt1000N module, the Volt1000N is always a slave for MODBUS. The MODBUS interface is disabled for the following modules.

    • Broken ring communication:

  • This ring is used to give each module a MODBUS address, and figures out the configuration.
  • In the Volt1000's display the user can enter his MODBUS address, or alternatively the MODBUS master can do this also.
  • The Volt1000 forward the power and is the first member of the local meter-bus.
  • The next RoCo/Cube module gets power and data from the former. And uses the MODBUS address+1 from the former
  • The First and last module of the bus, switches on the termination resistors, for the high speed bus

    • High speed bus:

  • For the interconnection between modules, the robust CAN-FD standard is used.

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