The Carel pCO2 and pCO3 controllers can be equipped by a Modbus communication card. It enables reading and writing variables prepared in the Carel controller. Some vars can be read only, some can be written – this is up to the Carel engineer. The output of the Carel delivery should be a table with three types of variables, which is used as source for SoftPLC IDE enfineering.
Carel uses three variable types: Analog, Integer, and Boolean. Analog is so called HVAC integer, i.e. signed integer with one decimal position: 201 actually means 20,1.
Analog: read Modbus function F03, write F06. All is Hi-Lo, Signed.
Addressing starts at 2, 3, 4, 5… up to 127 (?). Quantity of inputs (bytes): 2.
Set the KP parameter to 0.1, which gives the decimal point.
Integer: read Modbus function F03, write F06. All is Hi-Lo, Signed.
Addressing starts at 130, 131, 132, 133… Quantity of inputs (bytes): 2.
Boolean: read Modbus function F01, write F05.
Addressing starts at 2, 3, 4, 5… Quantity of inputs (bytes): 1.
Comm line parameters: at the Carel controller set the BMS address (Modbus slave address), Modbus protocol, and comm speed. Tested at 19200, 8, N, 1, no flow control.
The Carel controllers are used by Lennox, labeled as Climatic 50.