I/O Modules and Converters

The Domat Control System input and output modules provide standardized interfaces between the process and the control system.

They are used for process controls and for data acquisition in metering systems as well. Standard modules (4/8 DO, 8/16 DI, 8 AI, 8 AO, counters), and compact modules with HVAC-optimized I/O mix are available. Communicative room controllers are also integrated at this system level.

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.

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.

A small module MW240-B is designed for control of two lighting groups or one blinds actuator. Its internal logic features pushbutton or switch control of lights with remote override over bus. A modified device, MW241, provides triac outputs rather than relays, so that LED power supplies with capacitive characteristics can be switched safely. To control blind actuators, the module contains internal memory with estimated slat position. It is possible to set the blinds position and slat angle and override the blinds remotely from a PLC using data from weather station, time schedulers, security system etc. Both modules can also be used as standard I/O modules with 2 inputs and 2 independent relay outputs with installation into a flush-mount box.

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 R091 (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 R025 with RS232 interface, and R035 with a RS485 interface. Both are able to work as 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), or can be configured as Modbus TCP/RTU or Modbus RTU/TCP routers.