Modbus TCP¶

The modbus probe polls Modbus TCP Holding Registers on PLCs, industrial sensors, and smart-building controllers. Each configured register becomes one metric with a name and unit you define. Supports uint16, int16, uint32, int32, float32_abcd and float32_cdab register types.

Quick start¶

probes:
  - name: modbus-plc
    type: modbus
    params:
      host: 192.168.1.100
      registers:
        - name: temperature
          address: 40001
          type: float32_abcd
          scale: 0.1
          unit: Cel
          description: Room temperature

Parameters¶

Parameter	Default	Description
`host`	required	IP address or hostname of the Modbus TCP device
`port`	`502`	Modbus TCP port
`unit_id`	`1`	Modbus unit (slave) ID
`registers`	required	List of register definitions (see below)

Register definition¶

Field	Description
`name`	Register name — becomes the `register.name` tag and PRTG channel name
`address`	Modicon 1-based holding-register address (e.g. 40001)
`type`	Data type: `uint16`, `int16`, `uint32`, `int32`, `float32_abcd`, `float32_cdab`
`scale`	Multiplier applied after decoding (default `1.0`)
`unit`	OTel unit string for the value (e.g. `Cel`, `%`, `1`)
`description`	Human-readable label

Metrics¶

Metric	Unit	Description
`modbus.register.value`	configurable	Decoded register value, tagged with `register.name` and `register.address`
`modbus.up`	1	1 when the Modbus TCP device answered all register reads this cycle

Operational notes¶

host is required; the probe will fail to start without it.
Address numbering follows the Modicon 1-based convention (40001 = holding register 0). Subtract 40001 to get the 0-based Modbus Protocol Data Unit address if needed.
For float32_abcd vs float32_cdab, check your device manual for the byte-word order it uses.