Get RevisedSamplingRate from server

[DasCapschen]

Hello,

I currently have the problem that some data from the OPC UA server I'm subscribed to does not arrive in my application, but my customer does receive the data.
It's a machine error code node that quickly changes its value, let me give an example:

1. node value = 0 -> machine running
2. node value = 5 -> real stop error of the machine
3. node value = 7 -> non-helpful follow-up error

In my application, I only see node values 0 and 7, but 5 never arrives.
The problem is, my customer, who is using a sampling rate of no faster than 100ms, does receive the value.

I'm using client.create_subscription() with period = 0 for the publish interval, which means as fast as the server can handle, and I already saw that I can check the RevisedPublishRate in the returned subscription.
This doesn't help me, because the Publish and Sampling interval are completely independent.

I'm then using subscription.subscribe_data_change() with sampling_interval = 0, which should be the fastest sampling interval the server supports.
Unfortunately, I was unable to find out how I can check the RevisedSamplingInterval of this data change subscription.
Could you let me know if it is possible to find out which sampling rate the server actually uses?

Thank you.

[AndreasHeine]

even with period ("PublishingInterval") 1s you would recv the change as long the queue is not full!
the period in create subscripion just tells you how often the queued changes will be transported...

https://github.com/AndreasHeine/opcua-tutorial/blob/main/client/subscribe.py#L43-L60

edit:

the revised params will be available in the subscription-class-instance itself:

opcua-asyncio/asyncua/client/client.py

Line 746 in bec2907

results = await subscription.update(new_params)

[DasCapschen]

My Problem is not with the PublishInterval (period), but with the sampling rate.
I suspect the SamplingRate used is larger than the time interval between changes.

example:

v=0  v=0      v=5    v=7
|    |        |      |
t=0  t=5      t=7    t=10
     |               |
    sampling        sampling

In this case I would never receive value = 5, because it changed faster than the OPCUA Server samples data changes.
So I'm not looking for the revised publish interval (i already found that), but the revised sampling interval (from subscription.subscribe_data_change())

[AndreasHeine]

hey, did you use the UaClient or the Client Class?

[AndreasHeine]

With the UaClient calls its like following

For the subscription:

opcua-asyncio/asyncua/client/ua_client.py

Line 500 in b9e2af4

async def create_subscription( # type: ignore[override]

returns:

opcua-asyncio/asyncua/ua/uaprotocol_auto.py

Line 8646 in b9e2af4

class CreateSubscriptionResponse:

contains:

opcua-asyncio/asyncua/ua/uaprotocol_auto.py

Line 8627 in b9e2af4

class CreateSubscriptionResult:

For the MonitoredItem:

opcua-asyncio/asyncua/client/ua_client.py

Line 643 in b9e2af4

async def create_monitored_items(self, params):

returns:

opcua-asyncio/asyncua/ua/uaprotocol_auto.py

Line 8153 in b9e2af4

class CreateMonitoredItemsResponse:

contains:

opcua-asyncio/asyncua/ua/uaprotocol_auto.py

Line 8067 in b9e2af4

class MonitoredItemCreateResult:

With the Client calls its like following

For the subscription:

opcua-asyncio/asyncua/client/client.py

Line 721 in b9e2af4

async def create_subscription(

returns:

opcua-asyncio/asyncua/common/subscription.py

Line 134 in b9e2af4

self.parameters: ua.CreateSubscriptionParameters = params # move to data class

For the MonitoredItem:

opcua-asyncio/asyncua/common/subscription.py

Line 259 in b9e2af4

async def subscribe_data_change(

returns the info

[DasCapschen]

I'm using the Client class. subscribe_data_change only returns ints as handles to the monitored items, not actually the revised parameters returned from the server, or do I misunderstand that?

But I could try to use self.uaclient of the Client class to create the monitored items myself and then check the result.

[AndreasHeine]

my fault your right...

so you need to rewrite the subscrition.subscribe_data_change part to client.uaclient.create_monitored_items()

opcua-asyncio/asyncua/client/ua_client.py

Line 643 in b9e2af4

async def create_monitored_items(self, params):

similar to:

opcua-asyncio/asyncua/common/subscription.py

Line 450 in b9e2af4

async def create_monitored_items(self, monitored_items: Iterable[ua.MonitoredItemCreateRequest]) -> List[Union[int, ua.StatusCode]]:

[AndreasHeine]

the thing is the Client-Class was ment to be highlevel for ease of use but it lacks some details which in most situations aren't important...

[DasCapschen]

Thanks! I will give that a try :)