Profibus Low Node Voltage 1

[Bluff]

I have one Profibus DP network with +- 40 DP nodes including simocodes, vsd's, 2 DP/PA Links and couplers with +- 15 devices on each PA network. I would like to know how to improve the bus voltage at each node? We have used a profibus tester which tells us that some nodes are below 2VDC. When is a voltage too low on a device, what are the standards and what can we do about the problem.We have already installed a repeater at different points on the network but no significant improvement has been noted.

 

[aj180949]

I assume that "2V DC" refers to the amplitude of the differential signal on the RS-485 link.

You should not have more than 31 nodes on any segment (a length of cable), use repeaters to create new segments if the need be. Make sure that the termination resistors are present at both ends of each segment and only there (more is NOT beter). Make sure that each segment length is within the limits as stated in Profibus International Technical Guideline, publ. no 2.112, available from PI.

If you stick to the good book 2.112, the amplitude will be above 4V and all will be fine. If you do not, the proverbial will hit the fan in no time at all.

Good luck!