Design step by step

The control system is designed so as to make plant design and components specification as simple as possible. It is not necessary to use bus supply modules, external bus terminators, etc. – all functions are settable either by software, or by DIP switches. See data sheets for modules and process stations.

The basic steps when designing are as follows:

Specify the number and types of inputs and outputs (physical data points) in the panels.

Specify which panels have to be autonomous (with their own process stations) and which only are remote I/O islands (with power part and I/O modules connected to a process station in another panel over the I/O bus).

Remote I/O islands are used when:

  • the I/O amount is so small that a separate process station is not worth it
  • the panel is installed in a location where the control panel of the process station (touch screen or LCD display and buttons) would not be accessible.

A certain disadvantage is that the I/O bus is outside of the panel and may be subject to damage or EMC interference.

Based on the I/O amount and types in the panel, the I/O modules are selected and populated.

Usually, analogue inputs and outputs are covered by compact modules RCIO. Then, digital inputs and outputs are assigned, mostly using extra digital modules like R220, R420 etc.

0209_io_bus

Example of connection of I/O modules to the bus incl. bus termination.

To control thermic valves or modulated electrical heaters by a pulse width signal (PWM), triac outputs shall be used: R312 (8 triacs) or RMIO, which contains (among other I/Os) two solid state relays which have unlimited number of switching cycles. Both SoftPLC and Merbon function blocks provide conversion function from 0…100 % signal to PWM.

The modules may be placed on the bus with any combinations and any order. It is not necessary for the control loops to be within one module. However, this may make commissioning more comfortable and easy to overview.

The last module on the bus should be marked as “BUS END ON“. The other end of the bus is usually terminated at the process station or R012 converter.