Examples - OPC XML-DA - Read a single value from the device

.NET

C#
VB.NET

// This example shows how to read a value of a single item from the device and display its value.
//
// 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.DataAccess;
using OpcLabs.EasyOpc.OperationModel;

namespace DocExamples.DataAccess.Xml
{
    partial class ReadItemValue
    {
        public static void DeviceSourceXml()
        {
            // Instantiate the client object.
            var client = new EasyDAClient();

            Console.WriteLine("Reading item value...");
            object value;
            try
            {
                // DADataSource enumeration:
                // Selects the data source for OPC reads (from device, from OPC cache, or dynamically determined).
                // The data source (memory, OPC cache or OPC device) selection is based on the desired value age and
                // current status of data received from the server.

                value = client.ReadItemValue("http://opcxml.demo-this.com/XmlDaSampleServer/Service.asmx", "Dynamic/Analog Types/Double", DADataSource.Device);
            }
            catch (OpcException opcException)
            {
                Console.WriteLine("*** Failure: {0}", opcException.GetBaseException().Message);
                return;
            }

            Console.WriteLine(value);
        }
    }
}

' This example shows how to read a value of a single item from the device and display its value.
'
' 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.DataAccess
Imports OpcLabs.EasyOpc.OperationModel

Namespace DataAccess.Xml
Partial Friend Class ReadItemValue
Public Shared Sub DeviceSourceXml()
' Instantiate the client object.
Dim client As New EasyDAClient()

Console.WriteLine("Reading item value...")
Dim value As Object
Try
' DADataSource enumeration:
' Selects the data source for OPC reads (from device, from OPC cache, or dynamically determined).
' The data source (memory, OPC cache or OPC device) selection is based on the desired value age and
' current status of data received from the server.

value = client.ReadItemValue("http://opcxml.demo-this.com/XmlDaSampleServer/Service.asmx", "Dynamic/Analog Types/Double", DADataSource.Device)
Catch opcException As OpcException
Console.WriteLine("*** Failure: {0}", opcException.GetBaseException().Message)
Exit Sub
End Try

Console.WriteLine(value)
End Sub
End Class
End Namespace

Python

Python (.NET)

# This example shows how to read a value of a single item from the device and display its value.
#
# 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 .NET namespaces.
from OpcLabs.EasyOpc import *
from OpcLabs.EasyOpc.DataAccess import *
from OpcLabs.EasyOpc.OperationModel import *

# Instantiate the client object.
client = EasyDAClient()

print('Reading item value...')
try:
    # DADataSource enumeration:
    # Selects the data source for OPC reads (from device, from OPC cache, or dynamically determined).
    # The data source (memory, OPC cache or OPC device) selection is based on the desired value age and
    # current status of data received from the server.

    value = IEasyDAClientExtension.ReadItemValue(client, 
                                                 ServerDescriptor('http://opcxml.demo-this.com/XmlDaSampleServer/Service.asmx'), 
                                                 DAItemDescriptor('Dynamic/Analog Types/Double'), 
                                                 DAReadParameters(DADataSource.Device))
except OpcException as opcException:
    print('*** Failure: ' + opcException.GetBaseException().Message, sep='')
    exit()

# Display results
print('value: ', value, sep='')

QuickOPC supports OPC XML-DA also on Linux and macOS.

Examples - Client OPC Data Access

Examples - OPC Data Access - Read a single value from the device

Concepts

Reading from OPC Classic Items

Reading just the value (OPC Classic)

Reading in OPC XML-DA