Obtaining Information (OPC UA Alarms & Conditions)

For obtaining information related to Alarms & Conditions (such as the state of conditions), OPC UA does not introduce any new mechanism over what we have already described for OPC Data (in OPC UA). Please refer to the “Obtaining Information” under “Imperative Programming Model for OPC Data (Class and UA)” for all necessary information.

Methods (and extension methods) such as EasyUAClient.Read, ReadMultiple, ReadValue, ReadMultipleValues can be used.

// This example shows how to read a Low state of a limit alarm. Note that you should not normally read a state of an alarm
// from inside its event notification, because the state might have already changed. Instead, include the information you
// need in the Select clauses when subscribing for the event.
//
// Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .
// OPC client and subscriber examples in C# on GitHub: https://github.com/OPCLabs/Examples-QuickOPC-CSharp .
// Missing some example? Ask us for it on our Online Forums, https://www.opclabs.com/forum/index ! You do not have to own
// a commercial license in order to use Online Forums, and we reply to every post.

using System;
using OpcLabs.EasyOpc.UA;
using OpcLabs.EasyOpc.UA.AddressSpace;
using OpcLabs.EasyOpc.UA.Navigation;

namespace UADocExamples.AlarmsAndConditions
{
    class ReadAlarmState
    {
        public static void Main1()
        {
            UAEndpointDescriptor endpointDescriptor =
                "opc.tcp://opcua.demo-this.com:62544/Quickstarts/AlarmConditionServer";

            UANodeDescriptor alarmNodeDescriptor = new UANodeId(
                namespaceUriString:"http://opcfoundation.org/Quickstarts/AlarmCondition", 
                identifier:"1:Colours/EastTank?Yellow");

            // Knowing the alarm node, and the fact that is an instance of NonExclusiveLevelAlarmType (or its subtype),
            // determine what is its LowState/Id node.
            UANodeDescriptor lowStateIdNodeDescriptor = new UABrowsePath(alarmNodeDescriptor,
                new []
                {
                    UABrowsePathElement.CreateSimple("ns=0;s=LowState"),
                    UABrowsePathElement.CreateSimple("ns=0;s=Id")
                });

            // Instantiate the client object.
            var client = new EasyUAClient();

            Console.WriteLine("Reading alarm state...");
            var lowStateId = (bool)client.ReadValue(endpointDescriptor, lowStateIdNodeDescriptor);

            Console.WriteLine($"Id of LowState: {lowStateId}");
        }
    }
}

' This example shows how to read a Low state of a limit alarm. Note that you should not normally read a state of an alarm
' from inside its event notification, because the state might have already changed. Instead, include the information you
' need in the Select clauses when subscribing for the event.
'
' Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .
' OPC client and subscriber examples in VB.NET on GitHub: https://github.com/OPCLabs/Examples-QuickOPC-VBNET .
' Missing some example? Ask us for it on our Online Forums, https://www.opclabs.com/forum/index ! You do not have to own
' a commercial license in order to use Online Forums, and we reply to every post.

Imports OpcLabs.EasyOpc.UA
Imports OpcLabs.EasyOpc.UA.AddressSpace
Imports OpcLabs.EasyOpc.UA.Navigation

Namespace AlarmsAndConditions
    Friend Class ReadAlarmState
        Public Shared Sub Main1()
            Dim endpointDescriptor As UAEndpointDescriptor =
                "opc.tcp://opcua.demo-this.com:62544/Quickstarts/AlarmConditionServer"

            Dim alarmNodeDescriptor As UANodeDescriptor = New UANodeId(
                namespaceUriString:="http://opcfoundation.org/Quickstarts/AlarmCondition",
                identifier:="1:Colours/EastTank?Yellow")

            ' Knowing the alarm node, and the fact that is an instance of NonExclusiveLevelAlarmType (or its subtype),
            ' determine what is its LowState/Id node.
            Dim lowStateIdNodeDescriptor As UANodeDescriptor = New UABrowsePath(alarmNodeDescriptor,
                New UABrowsePathElement() {
                    UABrowsePathElement.CreateSimple("ns=0;s=LowState"),
                    UABrowsePathElement.CreateSimple("ns=0;s=Id")
                })

            ' Instantiate the client object.
            Dim client = New EasyUAClient()

            Console.WriteLine("Reading alarm state...")
            Dim lowStateId = CBool(client.ReadValue(endpointDescriptor, lowStateIdNodeDescriptor))

            Console.WriteLine($"Id of LowState: {lowStateId}")
        End Sub
    End Class
End Namespace

Python

Python (.NET)

# This example shows how to read a Low state of a limit alarm. Note that you should not normally read a state of an alarm
# from inside its event notification, because the state might have already changed. Instead, include the information you
# need in the Select clauses when subscribing for the event.
#
# Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .
# OPC client and subscriber examples in Python on GitHub: https://github.com/OPCLabs/Examples-QuickOPC-Python .
# Missing some example? Ask us for it on our Online Forums, https://www.opclabs.com/forum/index ! You do not have to own
# a commercial license in order to use Online Forums, and we reply to every post.
# The QuickOPC package is needed. Install it using "pip install opclabs_quickopc".
import opclabs_quickopc
import time

# Import .NET namespaces.
from OpcLabs.EasyOpc.UA import *
from OpcLabs.EasyOpc.UA.AddressSpace.Standard import *
from OpcLabs.EasyOpc.UA.AlarmsAndConditions import *
from OpcLabs.EasyOpc.UA.OperationModel import *


def eventNotification(sender, eventArgs):
    print()
    # Display the event.
    if eventArgs.EventData is None:
        print(eventArgs)
        return
    baseEventObject = eventArgs.EventData.BaseEvent
    print('Source name: ', baseEventObject.SourceName, sep='')
    print('Message: ', baseEventObject.Message, sep='')
    print('Severity: ', baseEventObject.Severity, sep='')


# Define which server we will work with.
endpointDescriptor = UAEndpointDescriptor('opc.tcp://opcua.demo-this.com:62544/Quickstarts/AlarmConditionServer')

# Instantiate the client object and hook events.
client = EasyUAClient()
client.EventNotification += eventNotification

print('Subscribing...')
IEasyUAClientExtension.SubscribeEvent(
    client,
    endpointDescriptor,
    UANodeDescriptor(UAObjectIds.Server),
    1000)

print('Processing event notifications for 30 seconds...')
time.sleep(30)

print('Unsubscribing...')
client.UnsubscribeAllMonitoredItems()

print('Waiting for 5 seconds...')
time.sleep(5)

print('Finished.')