Inhibiting a Modbus object's Commfail alarms from inidicating on the alarm panel

[Big Dog]

I have an Lookout v5.0 application that runs under W2K, SP2. This application has 65 modbus objects that have individual pots that are tied to the poll rate for their respective modbus object. When there is a failure of a modbus object, usually vandalism at the remote RTU site bring down the PLC, I would like to inhibit the modbus object from indicating commfail in the alarm window. I know about setting the poll rate to zero or some large number, but this still does not remove the alarm. Even blanking the poll rate field does nothing to remove the alarm. I would like to remove the existing alarm and prevent any further alarms from indicating on the alarm window. Visualize like a modbus alarm enab
le/disable switch. Any suggestions?

[Ken_S]

Hello,

Thank you for contacting National Instruments.

I looked into your questions about disabling the Modbus Comm alarms. The easiest way I�ve found to disable these alarms is to set the Alarm Priority for the Modbus objects to �0�. This should make the alarms not ever appear in the Alarms Window. The only downside to this is that the Alarm Priority cannot be set programmatically so once you set it to 0 you will never see the alarm until you set it to a value grater than 0.

A second option that may or may not work for you is to use a Pulse object to continually acknowledge the alarm area where the Modbus Comm Alarms appear (this defaults to the �comm� area). To do this just create a Pulse object and then create a connection from the $Alarm.comm.ack to the Pu
lse object�s output (the expression might look like �$Alarm.comm.ack=Timer1�). The downside to this approach is that this will only acknowledge the alarms from that area, so if the alarm is still active (for instance if the communications to the RTU is still failing) then the alarm will still appear in the Alarms window in an acknowledged state. The alarm won�t disappear until the fault condition goes away.

I hope this helps. Let me know if there is anything I can help with or clarify.

Ken S.
Applications Engineering
National Instruments

[jpss]

If you're trying just not to display alarms, you could set a lower alarm level to modbus object(instead of default level 😎 and filter them (In edit mode, choose Alarms, Filter Options..., in filter criteria check Priority and enter your settings).

JSS

[Big Dog]

Thanks Ken, Yes I would like to perform this operation while the process is running. I'm going to try the second option with the pulse object. It does not give me what I'm really looking for, but I can turn it on/off programmatically and it is closer than anything I currently have. Thanks!

[Big Dog]

Thanks JSS. Can I set the filter while running programmatically? Not sure, but I'll look into!

[jpss]

I read what Ken S answered. I think that a posible solution to your issue is to set Modbus object's alarm priority to 0 and use an ALARM OBJECT with the expression "Modbus1.CommFail&Switch1" as the condition. This way, the alarm will become active only if Switch1 is True(Runtime).

JSS

[Big Dog]

There is a knowledgebase article on this topic, try the link

URL: http://digital.ni.com/public.nsf/allkb/D270ECBC444F1D3E86256D10004EC2CB