PLCs and SCADA
==============
  Generally automation control systems, a PLC (Programmable Logic Controller) system would be used 
  as the main hardware device that connects to electrical equipment required to be controlled or monitored. 
  Electrical equipment may be motors, actuators, lights or relays as outputs from the PLC and also PLC 
  inputs such as switch inputs, temperatures, pressures, voltages or currents as analogue inputs. 
  PLCs will have specifically designed program for the task required, typically, where it will monitor 
  equipment inputs as well as user input to then control equipment according to the stored PLC program.
  
  
  PLCs are designed to be rugged and withstand the more extreme environments of industrial situations, 
  where there may be high levels of electrical noise, thermal stress or other environmental contaminants. 
  Essentially, a PLC is a small computer that has been programmed for a specific task, which requires 
  little or no attention for many years or operation.
  
  To be able to know what is going on in a PLC system at any given moment, we could connect to the PLC 
  system a typical computer system via a communications channel based on a standard protocol, such as 
  Modbus for example. Being connected to the PLC system can then provide a means to remotely have control 
  of the process from the computer system that may provide visual displays representing the control 
  process or status held within the PLC.
  
  The computer system must therefore have an application that can communicate with the PLC system to 
  facilitate this. The computer system may be physically located close by or far away from the PLC which 
  is generally located in an electrical switchboard where equipment is electrically terminated. 
  The communications between the PLC and computer system is often over a hard-wire cable and is typically 
  one of a few standards, such as Ethernet or optical fibre or asynchronous serial like RS-232 or TIA-485.
  
  As mentioned, the computer system must have appropriate software installed which itself must be 
  configured for the specified process and also for communications to function to connected PLC equipment. 
  This is the aim of QuadlogSCADA.

  WARNING - DISCLAIMER
  
  PLCs control many kinds of equipment and loss of property, production or even life can happen 
  if mistakes in programming or access are made. Always use caution when accessing or 
  programming PLCs.
  
  | The author make no claims or warrants about the suitability of this code for any purpose. 
  | Be careful.