Features: Communication through RS232 serial port is convenient to connect to various devices and systems. Support Modbus communication protocol to realize data transmission and control functions. The design is stable, ensuring the reliability of long operating. The module is simple in design and easy to install and configure. It have the interactive relationship between the control systems and the controlled systems. Usually used in automatic control circuits, it is actually "automatic Switches" that use small current to control the operating of large current. Therefore, it plays the role of automatic adjustment and conversion circuit in the circuit. Specifications: Component:PCB Type:1CH/2CH/3CH/4CH 1CH:Approx.59x38mm/2.32x1.49inch 2CH:Approx.71x38mm/2.79x1.49inch 3CH:Approx.77x44mm/3.03x1.73inch 4CH:Approx.77x60mm/3.03x2.36inch Package Includes: 1Pc RS232 Modbus note: 1.Please allow 1-2cm errors due to manual measurement, making sure that you not mind before order. 2.Due to the differences between different monitors, the picture may not reflect the actual of the item.