telegraf/plugins/inputs/modbus/sample_request.conf

  ## --- "request" configuration style ---

  ## Per request definition
  ##

  ## Define a request sent to the device
  ## Multiple of those requests can be defined. Data will be collated into metrics at the end of data collection.
  [[inputs.modbus.request]]
    ## ID of the modbus slave device to query.
    ## If you need to query multiple slave-devices, create several "request" definitions.
    slave_id = 1

    ## Byte order of the data.
    ##  |---ABCD -- Big Endian (Motorola)
    ##  |---DCBA -- Little Endian (Intel)
    ##  |---BADC -- Big Endian with byte swap
    ##  |---CDAB -- Little Endian with byte swap
    byte_order = "ABCD"

    ## Type of the register for the request
    ## Can be "coil", "discrete", "holding" or "input"
    register = "coil"

    ## Name of the measurement.
    ## Can be overridden by the individual field definitions. Defaults to "modbus"
    # measurement = "modbus"

    ## Request optimization algorithm.
    ##  |---none       -- Do not perform any optimization and use the given layout(default)
    ##  |---shrink     -- Shrink requests to actually requested fields
    ##  |                 by stripping leading and trailing omits
    ##  |---rearrange  -- Rearrange request boundaries within consecutive address ranges
    ##  |                 to reduce the number of requested registers by keeping
    ##  |                 the number of requests.
    ##  |---max_insert -- Rearrange request keeping the number of extra fields below the value
    ##                    provided in "optimization_max_register_fill". It is not necessary to define 'omitted'
    ##                    fields as the optimisation will add such field only where needed.
    # optimization = "none"

    ## Maximum number register the optimizer is allowed to insert between two fields to
    ## save requests.
    ## This option is only used for the 'max_insert' optimization strategy.
    ## NOTE: All omitted fields are ignored, so this option denotes the effective hole
    ## size to fill.
    # optimization_max_register_fill = 50

    ## Field definitions
    ## Analog Variables, Input Registers and Holding Registers
    ## address        - address of the register to query. For coil and discrete inputs this is the bit address.
    ## name *1        - field name
    ## type *1,2      - type of the modbus field, can be
    ##                  BIT (single bit of a register)
    ##                  INT8L, INT8H, UINT8L, UINT8H (low and high byte variants)
    ##                  INT16, UINT16, INT32, UINT32, INT64, UINT64 and
    ##                  FLOAT16, FLOAT32, FLOAT64 (IEEE 754 binary representation)
    ##                  STRING (byte-sequence converted to string)
    ## length *1,2    - (optional) number of registers, ONLY valid for STRING type
    ## bit *1,2       - (optional) bit of the register, ONLY valid for BIT type
    ## scale *1,2,4   - (optional) factor to scale the variable with
    ## output *1,3,4  - (optional) type of resulting field, can be INT64, UINT64 or FLOAT64.
    ##                  Defaults to FLOAT64 for numeric fields if "scale" is provided.
    ##                  Otherwise the input "type" class is used (e.g. INT* -> INT64).
    ## measurement *1 - (optional) measurement name, defaults to the setting of the request
    ## omit           - (optional) omit this field. Useful to leave out single values when querying many registers
    ##                  with a single request. Defaults to "false".
    ##
    ## *1: These fields are ignored if field is omitted ("omit"=true)
    ## *2: These fields are ignored for both "coil" and "discrete"-input type of registers.
    ## *3: This field can only be "UINT16" or "BOOL" if specified for both "coil"
    ##     and "discrete"-input type of registers. By default the fields are
    ##     output as zero or one in UINT16 format unless "BOOL" is used.
    ## *4: These fields cannot be used with "STRING"-type fields.

    ## Coil / discrete input example
    fields = [
      { address=0, name="motor1_run" },
      { address=1, name="jog", measurement="motor" },
      { address=2, name="motor1_stop", omit=true },
      { address=3, name="motor1_overheating", output="BOOL" },
      { address=4, name="firmware", type="STRING", length=8 },
    ]

    [inputs.modbus.request.tags]
      machine = "impresser"
      location = "main building"

  [[inputs.modbus.request]]
    ## Holding example
    ## All of those examples will result in FLOAT64 field outputs
    slave_id = 1
    byte_order = "DCBA"
    register = "holding"
    fields = [
      { address=0, name="voltage",      type="INT16",   scale=0.1   },
      { address=1, name="current",      type="INT32",   scale=0.001 },
      { address=3, name="power",        type="UINT32",  omit=true   },
      { address=5, name="energy",       type="FLOAT32", scale=0.001, measurement="W" },
      { address=7, name="frequency",    type="UINT32",  scale=0.1   },
      { address=8, name="power_factor", type="INT64",   scale=0.01  },
    ]

    [inputs.modbus.request.tags]
      machine = "impresser"
      location = "main building"

  [[inputs.modbus.request]]
    ## Input example with type conversions
    slave_id = 1
    byte_order = "ABCD"
    register = "input"
    fields = [
      { address=0, name="rpm",         type="INT16"                   },  # will result in INT64 field
      { address=1, name="temperature", type="INT16", scale=0.1        },  # will result in FLOAT64 field
      { address=2, name="force",       type="INT32", output="FLOAT64" },  # will result in FLOAT64 field
      { address=4, name="hours",       type="UINT32"                  },  # will result in UIN64 field
    ]

    [inputs.modbus.request.tags]
      machine = "impresser"
      location = "main building"