The analysers

Analyser requirements

Analyser design

The basic design of the system revolves around a Linux box supervising a series of embedded controllers on an RS-485 network, as shown in the diagram below.

[Analyser schematic]

Each node on the network is responsible for either sample pretreatment or analysis and has:

Each of these nodes is contructed as rack mounting 'module' for a standard industrial rack that is located next to one of the tanks in pilot plant.

The embedded controller software handles the real-time requirements of the sample pretreatment or chemical analysis, while the Linux box controls the RS-485 network, initiating pretreatment (and then analyses) every N minutes, archiving data, accepting client connections to the server for monitoring the system, etc.

This design has a number of advantages, including:

  1. The supervising computer is located in the control room rather than the pilot plant, eliminating the expense of an industrial computer system
  2. Each node is a stand-alone system, allowing easy expansion or customisation of the overall analysis system
  3. The RS-485 network is a simple (and inexpensive) way of easily distributing an analysis system
  4. The real-time requirements of the system are at the lowest level (ie. in the embedded controllers). As long as the Linux box can schedule analyses to commence with accuracy in the timescale of seconds, the system will function easily within specs.
The analyser features include:

[The 68HC11F1 embedded controller]

The 68HC11F1 embedded controller

[The phosphate analyser]

Phosphate analyser module

Current status

  1. Sample pretreatment module is ready
  2. First analyser (soluble reactive phosphate) module is ready
  3. Software is in place and tested
  4. Nitrate and ammonia analysers are in design/construction stages
  5. Final testing is currently underway before installation this month

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