Sunday, August 15, 2010

PLC Programming by Integrators

The complexity of dealing with integrators has been a surprise. Integrator companies in the irrigation market have been quite independent, with little independent review of their work. Their procedures for documentation of programming, their neatness of organizing wiring and panels, their usage of programming languages, and their exposure to PI algorithms for canal automation are quite varied. This means that nothing can be taken for granted – even if an integrator can list numerous completed projects,

Three items are of particular concern:
1. A good integrator will always understand hardware, installation, communications, and programming quite well. But it is rare that an integrator is familiar with modern canal control algorithms, and how they are tuned within a simulation model. This can be a problem if the integrators take unwarranted liberties in the programming of the control algorithms that supply as well as with the tuning constants.

2. Integrators sometimes embed numerous checks into their code with various hidden constants that can shutdown a gate or pump operation. The irrigation district operators (i) do not know these constants exist, (ii) do not know how to access them, (iii) must generally personally visit the PLC to change the constants should be changed. It believes all constants and alarm should be transparent and changeable from within the office via the SCADA system. A portable PC with a copy of the office HMI software can be used in the field to change constants if it is desired t make in-field adjustments.

3. The “control algorithm” for a gate (the algorithms that are published in irrigation literature) may only occupy 10% of the total programming handles numerous checks of equipment and sensors, consideration of gate inertia, and other factors.

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