I/O Modules and converters

The I/O modules and peripherals are connected to serial ports over separating interface converters. The I/O modules are powered by 10 to 30 V DC or 12 to 24 V AC. Inputs and outputs, power part and communication are optically separated from each other which prevents the rest of the bus from damage in case of overvoltage at one module.

Each module is addressed by a configuration software. Analogue inputs are entered with their measuring range: either they are declared as active (0..10 V) or passive for connection of all common temperature sensor types. For special sensor characteristics, each input can be separately linearized with freely defined linearization curve.


Digital outputs with relays can switch directly 230 V AC low voltage, so that for small loads no separate contactors / relays are necessary. Digital inputs and outputs statuses are indicated by LEDs. Some of the digital output modules provide manual intervention buttons.

The modules communicate over a RS485 bus with Modbus RTU and configurable baudrate. Using a standard protocol, they provide an open I/O bus also for 3rd party manufacturers. The other way round, 3rd party devices, such as variable speed drives, IRC controllers, and energy meters using one of the supported protocols can be integrated directly into the process station. Sometimes they can be even connected to the same I/O bus as the I/O modules, providing integration at the I/O level. The process station is usually installed at a place accessible for the maintenance staff. As the I/O bus may reach up to 1000 m, data from the whole building can be linked to one process station, or more panels with I/O modules can be connected together to one process station, which saves cabling costs.

Above the I/O modules in the topology there are interface converters. The mostly deployed devices are level converters, such as R012 (RS232 to RS485), which is used to connect I/O modules to process stations IPCT.1, or R095 and R096 (RS232 to M-Bus) to connect utility meters to PLCs.

To exchange data between systems communicating with different protocols, the protocol converters are used. Usually they also convert physical interfaces, such as R090 (Modbus TCP to DALI), R060 (Modbus TCP / RTU to Belimo MP-Bus), or R085 (Modbus RTU to Landis & Gyr P-Bus). Domat converters with Ethernet interface contain a web server which can be used for configuration and service of the 3rd party bus. No other software and service converters are necessary.

The serial to Ethernet converters are R020, R031 – terminal servers (after a driver is installed on a PC, it has an extra virtual serial port which is mapped over the network to the serial port of the converter), and R025, R035 which can be configured as Modbus TCP/RTU or Modbus RTU/TCP routers.

The complete list of converters incl. data sheets is in the product catalogue.


A process station may have – same as a MiniPLC – a web server enabled, so even without a SCADA system the process data can be accessed, setpoints changed, schedules set, trends monitored etc. in a dynamic vector graphics. A process station can be connected over the Ethernet to other stations and / or MiniPLCs and share data – outside temperature, load shedding signals, energy demand signals, etc. This is possible – thanks to TCP/IP – even in distributed and large networks of a company, city, or in the Internet.