V20 USS communication error

Dear All,

I am using 10 nos. V20 VFD communicating over USS with S7-1200 PLC. 9 of them is communicating ok. Only one is having problem of communication. Parameters are all the same. Parameter r2025 (rejected telegrams) is continuously increasing and r2026(character frame errors) is also increasing with it. What can be the issue?

I don't suspect issue with communication related parameters as they are same for all drives and other drives are communicating. similarly, PLC program is same for all drives. I suspect hardware related issue. anyone faced similar situation?

Thanks

Kbv

What size terminating resistor is used on the last VFD?

Kbv

Dear All,

I am using 10 nos. V20 VFD communicating over USS with S7-1200 PLC. 9 of them is communicating ok. Only one is having problem of communication. Parameters are all the same. Parameter r2025 (rejected telegrams) is continuously increasing and r2026(character frame errors) is also increasing with it. What can be the issue?

I don't suspect issue with communication related parameters as they are same for all drives and other drives are communicating. similarly, PLC program is same for all drives. I suspect hardware related issue. anyone faced similar situation?

Thanks

Kbv

Hello,

No termination resistor is used. because all VFDs are inside single cabinet with PLC. There is very less distance. It is mentioned somewhere in forum that distance upto 50m is ok without resistor. Also VFD I am facing problem is right next to PLC, I mean it is 2nd node in the bus. It is not the last node. Can this problem be due to lack of termination? On PLC side also I am not using termination.

Thanks,

Kbv.

Kbv

Hello,

No termination resistor is used. because all VFDs are inside single cabinet with PLC. There is very less distance. It is mentioned somewhere in forum that distance upto 50m is ok without resistor. Also VFD I am facing problem is right next to PLC, I mean it is 2nd node in the bus. It is not the last node. Can this problem be due to lack of termination? On PLC side also I am not using termination.

Thanks,

Kbv.

Hello.

What you described as a symptom sounds like the type problem you will get from a missing terminating resistor. There is such a thing as too short device-to-device cable length. This depends on the baud rate. You can use the Profibus specification.

Not to say that this is the cause.

A nice application example which I have used on the V20 drive:
https://support.industry.siemens.com/cs/document/109480894/

The example explains everything.

~

Are you using prefabricating cabling, or self-terminated (screw, solder or crimp) connections?

Is it possible the connector for the problem VFD is the root cause?

You can test that idea by connecting up VFD #1 (1st node) using VFD #2's connector and leaving the 1st connector dangling.  You may need to disconnect connections for the remaining VFDs to test if it's the connector.

Or, disconnect them all and put a cable tester on it from the PLC to the 2nd node connector while wiggling it around to check for a bad connection *inside* the connector.  Obviously it is passing data fine for the 3rd node and beyond to work ok.

Kbv

Hello,

No termination resistor is used. because all VFDs are inside single cabinet with PLC. There is very less distance. It is mentioned somewhere in forum that distance upto 50m is ok without resistor. Also VFD I am facing problem is right next to PLC, I mean it is 2nd node in the bus. It is not the last node. Can this problem be due to lack of termination? On PLC side also I am not using termination.

Thanks,

Kbv.