Settings modbus_tcp_source

• type: producer
• output: integer, float or boolean messages

This is a producer block that generates messages by polling a Modbus device over TCP.

It works by specifying a host (optionally with a port), a slave_id and a list of targets to be polled. Data read from registers is converted to well defined formats before generating a Flow Message.

Note: currently polling_interval_ms must be the same for all targets. This limitation will be removed in a future release.

Properties

• host: The IP adress of the Modbus device. (required, string)
• slave_id: The Modbus slave id of the target. (required, integer)
• targets: The array of targets to be polled. (required, array of objects)
• port: The TCP port of the target Modbus device, defaults to 502. (optional, integer)

host

host

A string representing an IP address to reach the Modbus device (e.g. "192.168.1.2").

port

port

The TCP port for the Modbus connection, defaults to 502 (the standard Modbus TCP port).

slave_id

slave_id

The slave id of the target Modbus device. This should be an integer between 1 and 247.

targets

targets

An array of objects representing the targets. Each of these objects should have these keys:

• name: The name of the target. This will be used as key in the generated messages. (required, string)
• base_address: The Modbus address of the target. One or more registers starting from this address will be read when polling this target, depending on the format. (required, integer)
• format: The format of the data. Must be one of these strings: "int16", "uint16", "float32be", "float32le", "boolean". The format will also determine how many registers are read for this target. (required, string)
• modbus_type: The modbus type of the target register. Must be one of these strings: "coil", "discrete_input", "input_register", "holding_register". (required, string)
• polling_interval_ms: The interval between to consecutive polling requests, expressed in milliseconds. Caveat: right now all targets must have the same polling interval, this limitation will be removed in a future release. (required, integer)
• static_metadata: A string -> string object of metadata that will be added as metadata to all messages produced for this target.

Output message

If the polling succeeds, for each target modbus_tcp_source produces a message containing these fields:

• key: contains the name of the target
• data: contains the data converted with the chosen format
• type: depends on the chosen format
• metadata: contains the static_metadata of the target, if present
• timestamp contains the timestamp (in microseconds) the response was received.

Examples

The following example uses modbus_tcp_source to poll every 30 seconds a Modbus device at IP 192.168.1.42 at port 2000, with a slave id value of 3. The only target is a voltage value stored as float with a little endian format in the holding registers 42 and 43.

modbus_tcp_source
    .host("192.168.1.42")
    .port(2000)
    .slave_id(3)
    .targets([
      {
        base_address: 42,
        name: "sensor-V_RMS",
        format: "float32le",
        static_metadata: {
          units: "V"
        }
        polling_interval_ms: 30000,
        modbus_type: "holding_register"
      }
    ])
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