Many Atonometrics products use RS485 communication and support Modbus RTU protocol.

RS485 has two signal lines. We typically document these signals as A and B. However some manufacturers refer to these signals as + and -.

Unfortunately the exact assignment of A and B or + and - signals, and the correspondence between these, can be confusing. The RS485 standard is not clear and many manufacturers are using different definitions.

Below are some of the RS485 transceivers used in Atonometrics products, with links to the data sheets for these transceivers. The data sheets define the exact meaning of the A and B signals and Atonometrics follows these designations:

Because of the potential for different vendors to use different signal definitions, if you connect our sensors' A/B wiring to your communication device and communication does not work, try reversing the signals.