ModbusRTU Write Coil with Pulse output


Thread Starter


We have Honeywell EPKS DCS at our site. We have Terminal server for all the Modbus communication. And we are using 485 to RS232 converter in order to get long distance. The problem here is we could establish communication and everything is fine. But once if I write to the Coil, we have the readback at DCS, it says Control failed at sometime but all the time it is writing as desired. After that we are getting alarm for Control Failed. We need Pulse output with 4 secs duration. Sometimes it is working as a Pulse output but sometimes it holds at Logic 1 and is not coming back to 0.

If anyone came across this problem, could you please help in this regard.

Prakashkumar N

Abhilash Ponoli

Hi Prasanth,
You can disable the control failed alarm in DCS. The reason might be because your PLC is overwriting the register before EPKS does a read back from the same register.