RS485 dual redundant ALR121-Yokogawa modbus communication card(2-Wire) is switching automatically between control and stand-by and it
is recovering back by itself within 7-10 seconds. It is not affecting our communication. The error code is A3B0 (No response, as per manual). It is working fine with single card.

Vnet/IP CS3000 R3.08.50.

Third party system L&T(telvent).

 

WE have the latest Alr121 on a Yokogawa. Serial Modbus connected to a gas panel, and with two lines connected it crashes immediately. It would appear to need a hard switch. The Docs on the dual redundant modules state it only switches between two alr modules on a module fault but both modules are communicating to the end device. That part does not work..

> RS485 dual redundant ALR121-Yokogawa modbus communication card
> (2-Wire) is switching automatically between control and stand-by
and it is recovering back by itself within 7-10 seconds. It is not
> affecting our communication. The error code is A3B0 (No response,
> as per manual). It is working fine with single card.

> Vnet/IP CS3000 R3.08.50.

> Third party system L&T (telvent).

 

Hello Everybody

The following steps are required to conclude the fault.

1. Connect a MODSCAN analyzer with a laptop to the n/w, and see the Frames and any bad CRC.

2. Check the Detailed settings of the ALR121 where we set the No reply time out/No. of retries/ no response time between frames etc.

3. Confirm whether these settings are to be the optimum with L&T telvent.

More over the FC(16 Bit or 32 bit) selected at DCS end to be the most important thing which plays a role on redundancy with such 3rd party MODBUS devices.
Is there any write functions(AO/DO) to tELVENT? In such cases FC selection plays a big role which gives problem only when connected as redundant not on single Link.

Hope with the above tips you'll be able to troubleshoot the issue better.

Good Luck
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WE have the latest Alr121 on a Yokogawa. Serial Modbus
>connected to a gas panel, and with two lines connected it
>crashes immediately. It would appear to need a hard switch.
>The Docs on the dual redundant modules state it only
>switches between two alr modules on a module fault but both
>modules are communicating to the end device. That part does
>not work..
>
>> RS485 dual redundant ALR121-Yokogawa modbus communication
>card
>> (2-Wire) is switching automatically between control and
>stand-by
> and it is recovering back by itself within 7-10 seconds. It
>is not
>> affecting our communication. The error code is A3B0 (No
>response,
>> as per manual). It is working fine with single card.
>
>> Vnet/IP CS3000 R3.08.50.
>
>> Third party system L&T (telvent).