Query Historical Data with Read At Time

[alexschoeberl]

The OPC UA documentation for historical read of variables specifies different functionalities of the server, including "Read raw", "Read modified" and "Read at time". The "Read at time" option says: "This structure selects a set of raw or interpolated values from the history database by specifying a series of timestamps".

I did not find a method of the client class that implements this functionality. How can I read historical values at given timestamps or at a specified interval?

[alexschoeberl]

Any suggestions? Is this functionality simply not provided by the package?

[AndreasHeine]

params is:

opcua-asyncio/asyncua/ua/uaprotocol_auto.py

Line 7242 in 8fc26b8

class HistoryReadParameters:

which contains "HistoryReadDetails" which is https://reference.opcfoundation.org/v104/Core/docs/Part11/6.4.1

[alexschoeberl]

Thank you for the hint @AndreasHeine! I tried the following:

@dataclass(frozen=FROZEN)
class ReadAtTimeDetails(HistoryReadDetails):
    data_type = NodeId(ObjectIds.ReadAtTimeDetails)

    ReqTimes: List[UtcTime] = field(default_factory=list)
    UseSimpleBounds: Boolean = True

node = client.get_node("ns=2;...")
details = ReadAtTimeDetails()
details.ReqTimes = [datetime.utcnow() - timedelta(seconds=170), datetime.utcnow() - timedelta(seconds=130)]
details.UseSimpleBounds = True
history = []
continuation_point = None
while True:
    result = await node.history_read(details, continuation_point)
    result.StatusCode.check()
    continuation_point = result.ContinuationPoint
    history.extend(result.HistoryData.DataValues)  # type: ignore[attr-defined]
    # No more data available
    if continuation_point is None:
            break

However, I always get this error:
asyncua.ua.uaerrors._auto.BadNotImplemented: Requested operation is not implemented.(BadNotImplemented)

Am I missing something?

[AndreasHeine]

BadNotImplemented comes from Server...

does it work with UAExpert?

[schroeder-]

Most servers only support RawHistoryAccess. To do this you can copy the code of:

opcua-asyncio/asyncua/common/node.py

Line 652 in 8fc26b8

async def read_raw_history(

[alexschoeberl]

I see, so most likely the server does not allow it. I wanted to reduce the number of values I need to send in a request, only get one value every 30 seconds.
I don't think there is an option in UAExpert to test this.
Thank you anyway!