influxdata/telegraf

Modbus: Unsigned float

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#15,909 opened on Sep 17, 2024

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Description

Use Case

I am using power meters that provide measurement values using a Non-IEEE floating point formats:

Unsigned Measurement (32 bit):

  • Decade Exponent(Signed 8 bit)
  • Binary Unsigned Value (24 bit) Example: 123456*10–3 stored as FD01 E240(16)

Signed Measurement (32 bit)

  • Decade Exponent (Signed 8 bit)
  • Binary Signed value (24 bit) Example: - 123456*10–3 stored as FDFE 1DC0(16)

I am looking for a way to configure/extend the modbus input plugin to handle these values.

Am I right that currently, only IEEE (signed) float values are supported? Can I just come up with new data_types like UFLOAT32 and MSIGN_FLOAT32 (as the mantissa holds the sign)?

I'd be able to implement it on my own, just checking what a sane convention would be.

Kind regards

nischu

Expected behavior

I would like the Modbus input plugin to generate correct floating point values

Actual behavior

I cannot really specify this custom data type

Additional info

https://cdn.findernet.com/app/uploads/Benutzerhandbuch_Typ_7M38_DE.pdf page 52

Contributor guide

Tech stack
go
Domain
backend
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
mostly clear
Prerequisites
Modbus protocolGo programming
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
50
Research direction
Examine the Modbus input plugin source code to understand how existing data types are defined and processed. The new data types UFLOAT32 and MSIGN FLOAT32 should follow the same pattern. Confirm with maintainers the naming convention. Implement conversion logic for the custom float format described in the issue.