modbus_rtu collector¶

modbus_rtu collector performs Modbus RTU requests over the serial line to collect performance data.

Configuration¶

Parameter	Type	Default	Description
`id`	String		Collector's ID. Must be unique per agent instance. Will be returned along with the metrics.
`type`	String		Must be `modbus_rtu`
`service`	String	Equal to `id`	Service id for output metrics
`interval`	Integer		Repetition interval in seconds
`labels`	Array of Strings		List of additional labels. Will be returned along with metrics
`serial_path`	String		Path to the serial port device (i.e. `/dev/ttyS1`)
`slave`	Integer		Modbus RTU slave id
`baud_rate`	Integer		Serial port speed
`data_bits`	Integer		Serial port data bits: 5, 6, 7 or 8
`parity`	String	`none`	Serial port parity, either `none`, `even` or `odd`
`stop_bits`	Integer		Serial port stop bits, either `1` or `2`
`register`	Integer		Starting register of modbus request, zero-based
`register_type`	String	`holding`	Modbus request type. Either `holding`, `input` or `coil`
`format`	String		Expected response format. See Response format for details
`timeout_ms`	Integer	5000	Request timeout, ms.

Check address notation

Take note the starting register address is zero-based, while vendors can document the registers starting from 1. Refer to the vendor documentation and subtract 1 when necessary.

Response Format¶

Modbus' response is as an array of 16-bit integers. Actual data encoding should be set as format parameter. Some encodings may require reading 2 or 4 adjacent registers.

Format	Count	Description
`i16_be`	1	16-bit signed integer, big-endian.
`u16_be`	1	16-bit unsigned integer, big-endian.
`i32_be`	2	32-bit signed integer, big-endian
`i32_le`	2	32-bit signed integer, low-endian
`i32_bs`	2	32-bit signed integer, big-endian, swapped
`i32_ls`	2	32-bit signed integer, low-endian, swapped
`u32_be`	2	32-bit unsigned integer, big-endian
`u32_le`	2	32-bit unsigned integer, low-endian
`u32_bs`	2	32-bit unsigned integer, big-endian, swapped
`u32_ls`	2	32-bit unsigned integer, low-endian, swapped
`f32_be`	2	32-bit floating point, big-endian
`f32_le`	2	32-bit floating point, low-endian
`f32_bs`	2	32-bit floating point, big-endian, swapped
`f32_ls`	2	32-bit floating point, low-endian, swapped

Big/Low/Swapped endian¶

32-bit integer 0x01020304 stored as a sequence of 4 octets. 4 different approaches widely used between modbus devices:

Format	1	2	3	4
Big-endian (be)	01	02	03	04
Low-endian (le)	04	03	02	01
Big-endian, swapped (bs)	02	01	04	03
Low-endian, swapped (ls)	03	04	01	02

Collected Metrics¶

Metric	Platform	Description
`ts`	All	ISO 8601 Timestamp
`collector`	All	Collector Id
`labels`	All	List of labels

`value`	All	Measured value

Compilation Features¶

Enable modbus_rtu feature during compiling the agent (Enabled by default).