Pulsar Process Measurement What to check if your RS485 is not communicating. If you’re using a Pulsar controller with RS485 communications… …Modbus or Profibus DP… … and can’t receive signals… …you can check that the RS485 hardware is functioning correctly using a Digital Volt Meter (DVM). First, however, you should check the Modbus or Profibus settings in your Pulsar device. These are found in the ‘Device Comm’ menu of your Pulsar device. (Check the ‘Menu system and parameter guide’ of your product manual) RS485 terminations (The position of these may vary depending upon the controller used) A- (RS485 negative) B+ (RS485 positive) SCR/GND (RS485 0V) First, disconnect the RS485 cable from its terminals. Set your DVM to d.c. volts and place the negative probe on the GND/SCR terminal. Then place the positive probe on the B+ terminal… … and then the A- terminal, noting the voltages. B+ terminal should be between 3.1 to 3.5Vdc A- terminal should be between 1.5 to 1.75Vdc If the voltages measured are outside the ranges stated please contact Pulsar or one of our representatives. If they are OK, re-connect the RS485 cable and test the communication again. If you have any questions, please contact Pulsar or one of our representatives.