Error in OPC output pending write Queue max Exceeded

[suresh.r]

Hi When my application is running the follwoing error msg is displayed . " Error Server Error from Server National. OPC Lookout drivers. Server Msg Output pending write queue max length has been exceeded output data has been discarded. After ack the error i find that there is an certain amount ( Varies from 4 seconds to 25 sec) of delay in communicating with the PLC. Iam communicating via ethernet protocol with Allen bradley plc via lookout 4.5.1. using labview express 7.0 . How do i solve this.

[rem]

Do you communicate to the PLC at a constant rate, or in bursts?

[suresh.r]

Communication with PLC is at constant rate .Poll rate is set at 5 sec

[Kriha]

Did you ever get this error resolved? I am coming across the same issue.

[Khalid]

Hello Kriha,

Are you using the same setup -- Lookout OPC Server? What PLC/RTU? What's the poll-rate?

How many tags do you have in your SCF file? Did you try modifying the Engine queue lengths?

Khalid

[Kriha]

No I am using DSData Server with a DL205 PLC. Update rate has been set to different values right now .2s seems to give the most reponsive results. There are 55 tags in the .scf file. We have changed the queue length from 2000 to 4000 to 10000, that just seems to increase the length of time before the error shows up.