The SDM-CVO4 allows most Campbell Scientific data loggers to produce a value by whatever means measured or derived as a scaled 0 to 20 or 4 to 20 mA signal (four terminals).
The data logger sends an instruction to the SDM-CVO4 with the voltage or current to be transmitted to the other device. The SDM-CVO4 does not itself convert a voltage to a current. A data logger is needed to make a measurement and instruct the SDM-CVO4 as to what the output should be.