I am using an OpenOPC client to talk to RSLinx to read and write PLC tag values.
I'm finding that I occasionally get cached data returned when I do a PLC read. As an example, I have a Boolean tag that I can see on a PLC trace has dropped from 1 to 0, but I still get a 1 when I read via OpenOPC for a period of time before I get the most up to date value of 0 returned.
I’ve noticed my PLC topic configurations in RSLinx have the “Polled Messages (mSec)” parameter (Data Collection tab) set to 1000ms. However, my OpenOPC clients set the update rate argument to 100ms whenever they read anything, which I thought would override the update rate specified in the RSLinx topic configuration, is that correct?
After noticing this I changed the RSLinx Topic configuration so that poll rates match on both Server and Client, but I won’t know for a while whether it has helped or not. However, if my understanding of the client poll rate overriding the server poll rate is correct then I guess it won’t make much difference.
Also, I'm seeing 2 other issues which I guess could be related but I am unsure:
- I am seeing active topics/groups hanging around in RSLinx after I've closed all OPC connections (which looking at the OpenOPC code, should remove all groups: “self.remove(self.groups())”). I'm not really sure what is going on here?
- I'm seeing a few RSLinx communication errors with the description of “Desc: A DDE/OPC Client has passed an invalid server handle while attempting a Remove Item call. Handle value is 0x79ac130.”
i) How can I figure out what is causing this?
ii) Is it logical to think that this could be related to the above issue where some groups aren’t being removed?
iii) Snipped of an RSLinx communication error log below
----------------------------------------------------------------------------------------------------------------
-none- : -none- : 11/29/13 - 01:12:05 : 00h
Items: -none-
Type: READ
Mfg: Allen-Bradley
PlcType:
Desc: A DDE/OPC Client has passed an invalid server handle while attempting an Async IO Read call. Handle value is 0x79ac130.
Number of occurrences: 814
Last Error occurred: 11/29/13 - 07:59:02
-none- : -none- : 11/29/13 - 08:07:00 : 00h
Items: -none-
Type: READ
Mfg: Allen-Bradley
PlcType:
Desc: A DDE/OPC Client has passed an invalid server handle while attempting a Remove Item call. Handle value is 0x79ac130.
Number of occurrences: 1
Last Error occurred: 11/29/13 - 08:07:00
----------------------------------------------------------------------------------------------------------------
Any help would be brilliant.
Thanks.
I'm finding that I occasionally get cached data returned when I do a PLC read. As an example, I have a Boolean tag that I can see on a PLC trace has dropped from 1 to 0, but I still get a 1 when I read via OpenOPC for a period of time before I get the most up to date value of 0 returned.
I’ve noticed my PLC topic configurations in RSLinx have the “Polled Messages (mSec)” parameter (Data Collection tab) set to 1000ms. However, my OpenOPC clients set the update rate argument to 100ms whenever they read anything, which I thought would override the update rate specified in the RSLinx topic configuration, is that correct?
After noticing this I changed the RSLinx Topic configuration so that poll rates match on both Server and Client, but I won’t know for a while whether it has helped or not. However, if my understanding of the client poll rate overriding the server poll rate is correct then I guess it won’t make much difference.
Also, I'm seeing 2 other issues which I guess could be related but I am unsure:
- I am seeing active topics/groups hanging around in RSLinx after I've closed all OPC connections (which looking at the OpenOPC code, should remove all groups: “self.remove(self.groups())”). I'm not really sure what is going on here?
- I'm seeing a few RSLinx communication errors with the description of “Desc: A DDE/OPC Client has passed an invalid server handle while attempting a Remove Item call. Handle value is 0x79ac130.”
i) How can I figure out what is causing this?
ii) Is it logical to think that this could be related to the above issue where some groups aren’t being removed?
iii) Snipped of an RSLinx communication error log below
----------------------------------------------------------------------------------------------------------------
-none- : -none- : 11/29/13 - 01:12:05 : 00h
Items: -none-
Type: READ
Mfg: Allen-Bradley
PlcType:
Desc: A DDE/OPC Client has passed an invalid server handle while attempting an Async IO Read call. Handle value is 0x79ac130.
Number of occurrences: 814
Last Error occurred: 11/29/13 - 07:59:02
-none- : -none- : 11/29/13 - 08:07:00 : 00h
Items: -none-
Type: READ
Mfg: Allen-Bradley
PlcType:
Desc: A DDE/OPC Client has passed an invalid server handle while attempting a Remove Item call. Handle value is 0x79ac130.
Number of occurrences: 1
Last Error occurred: 11/29/13 - 08:07:00
----------------------------------------------------------------------------------------------------------------
Any help would be brilliant.
Thanks.
