warning of Kepware

[GL_12704921]

it's a warning in the log of Kepware ,It says "Write request timeout on device'FP_A_U4_Pester.Overwrapper' and 'FP_A_U4_Pester.Overwrapper Unable to write to address on device .Address ='PLC1:.fold_TuT_AlarmInterlock' I use OPC -DA protocol establish communication between Kepware and FP_A_U4_Pester.Overwrapper , and I use Advance tag to write a boolean to PLC ( "PLC1:FP_A_U4_Pester.Overwrapper.fold_TuT_AlarmInterlock") ,I check from the PLC of machine , it's successful sent the boolean from Kepware to PLC1:FP_A_U4_Pester.Overwrapper.fold_TuT_AlarmInterlock ,my question is why I have a warning message when Kepware have a successful sending ? if you want get any further information ,please contact me any time when you are free .thanks a lot.

[pshashipreetham · Accepted solution]

Hi,

It looks like what’s happening is that KEPServerEX is trying to write to your PLC tag, but the write request is timing out before the PLC acknowledges it. Even though you see the boolean value eventually get set in the PLC, the communication layer is still throwing a timeout warning because it doesn’t get a proper confirmation from the device within the expected response time.

A few things to check:

1. Tag Addressing
   Make sure the output tag path is correct. In your Link Tag configuration, the Output is set as
   FP_A_U4_Pester.Overwrapper.PLC1:Fold_TuT_PLC_AlarmInterlock.
   Verify this matches the actual PLC address format used by your device driver. Wrong or extra node references can cause the driver to send the write to the wrong location, leading to timeouts.

2. Write Permissions
   Confirm the PLC tag is actually writable from external clients. Some tags are read-only or require the PLC to be in run mode with write access enabled. Double-check the controller logic or security settings.

3. Communication Timing
   If the PLC is slow to respond or the network has latency, the default write timeout in Kepware might be too short. You can try increasing the write timeout in the device channel settings in Kepware.

4. OPC DA Acknowledgement Behavior
   With OPC DA, Kepware expects a quick acknowledgment. If the PLC logic takes time to process and confirm the write, Kepware will report a timeout, even if the value is eventually written. This can cause the false “unable to write” warnings.

5. Triggering Logic
   Your link tag is set to write “On Data Change of Input Tag”. If the trigger fires repeatedly or very quickly, you can get overlapping writes. Try increasing the scan rate or using “While Trigger True” mode carefully to avoid hammering the PLC with too many writes.

In short, the warning doesn’t mean the write totally failed, it means Kepware didn’t get a proper timely confirmation. Fixing the address, checking permissions, and tuning the timeout usually clears it up.

If the value is still being set correctly in the PLC, the issue is likely just the timing/acknowledgment and not actual communication failure.

Thanks,