Examples - OPC Data Access - Read items from the device

.NET

C#
VB.NET

// This example shows how to read 4 items from the device, and display their values, timestamps and qualities.
//
// 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 System.Diagnostics;
using OpcLabs.EasyOpc.DataAccess;
using OpcLabs.EasyOpc.DataAccess.OperationModel;

namespace DocExamples.DataAccess._EasyDAClient
{
    partial class ReadMultipleItems
    {
        public static void DeviceSource()
        {
            // Instantiate the client object.
            var client = new EasyDAClient();

            // 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 will be based on the desired value age and
            // current status of data received from the server.

            DAVtqResult[] vtqResults = client.ReadMultipleItems(
                new []
                    {
                        new DAReadItemArguments("OPCLabs.KitServer.2", "Simulation.Random", DADataSource.Device),
                        new DAReadItemArguments("OPCLabs.KitServer.2", "Trends.Ramp (1 min)", DADataSource.Device),
                        new DAReadItemArguments("OPCLabs.KitServer.2", "Trends.Sine (1 min)", DADataSource.Device),
                        new DAReadItemArguments("OPCLabs.KitServer.2", "Simulation.Register_I4", DADataSource.Device)
                    });

            for (int i = 0; i < vtqResults.Length; i++)
            {
                Debug.Assert(vtqResults[i] != null);

                if (vtqResults[i].Succeeded)
                    Console.WriteLine("vtqResults[{0}].Vtq: {1}", i, vtqResults[i].Vtq);
                else
                    Console.WriteLine("vtqResults[{0}] *** Failure: {1}", i, vtqResults[i].ErrorMessageBrief);
            }
        }


        // Example output:
        //
        //vtqResults[0].Vtq: 0.00125125888851588 { System.Double} @2020-04-10T12:44:16.250; GoodNonspecific(192)
        //vtqResults[1].Vtq: 0.270812898874283 {System.Double} @2020-04-10T12:44:16.248; GoodNonspecific(192)
        //vtqResults[2].Vtq: 0.991434340167834 {System.Double} @2020-04-10T12:44:16.250; GoodNonspecific(192)
        //vtqResults[3].Vtq: 0 {System.Int32} @1601-01-01T00:00:00.000; GoodNonspecific(192)
    }
}

' This example shows how to read 4 items from the device, and display their values, timestamps and qualities.
'
' 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.DataAccess.OperationModel

Namespace DataAccess._EasyDAClient
    Partial Friend Class ReadMultipleItems
        Public Shared Sub DeviceSource()
            ' Instantiate the client object.
            Dim client = New EasyDAClient()

            ' 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 will be based on the desired value age and
            ' current status of data received from the server.

            Dim vtqResults() As DAVtqResult = client.ReadMultipleItems(New DAReadItemArguments() {
                New DAReadItemArguments("OPCLabs.KitServer.2", "Simulation.Random", DADataSource.Device),
                New DAReadItemArguments("OPCLabs.KitServer.2", "Trends.Ramp (1 min)", DADataSource.Device),
                New DAReadItemArguments("OPCLabs.KitServer.2", "Trends.Sine (1 min)", DADataSource.Device),
                New DAReadItemArguments("OPCLabs.KitServer.2", "Simulation.Register_I4", DADataSource.Device)
            })

            For i = 0 To vtqResults.Length - 1
                Debug.Assert(vtqResults(i) IsNot Nothing)

                If vtqResults(i).Succeeded Then
                    Console.WriteLine("vtqResults[{0}].Vtq: {1}", i, vtqResults(i).Vtq)
                Else
                    Console.WriteLine("vtqResults[{0}] *** Failure: {1}", i, vtqResults(i).ErrorMessageBrief)
                End If
            Next i
        End Sub

        ' Example output
        '
        'vtqResults[0].Vtq: 0.00125125888851588 { System.Double} @2020-04-10T12:44:16.250; GoodNonspecific(192)
        'vtqResults[1].Vtq: 0.270812898874283 {System.Double} @2020-04-10T12:44:16.248; GoodNonspecific(192)
        'vtqResults[2].Vtq: 0.991434340167834 {System.Double} @2020-04-10T12:44:16.250; GoodNonspecific(192)
        'vtqResults[3].Vtq: 0 {System.Int32} @1601-01-01T00:00:00.000; GoodNonspecific(192)
    End Class
End Namespace

COM

VBScript

Rem This example shows how to read 4 items from the device, and display their values, timestamps and qualities.
Rem
Rem Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .
Rem OPC client and subscriber examples in VBScript on GitHub: https://github.com/OPCLabs/Examples-QuickOPC-VBScript .
Rem Missing some example? Ask us for it on our Online Forums, https://www.opclabs.com/forum/index ! You do not have to own
Rem a commercial license in order to use Online Forums, and we reply to every post.

Option Explicit

' 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 will be based on the desired value age and current status of 
' data received from the server.
Const DADataSource_ByValueAge = 0
' OPC reads will be fulfilled from the cache in the OPC server.
Const DADataSource_Cache = 1
' OPC reads will be fulfilled from the device by the OPC server.
Const DADataSource_Device = 2

Dim ReadItemArguments1: Set ReadItemArguments1 = CreateObject("OpcLabs.EasyOpc.DataAccess.OperationModel.DAReadItemArguments")
ReadItemArguments1.ServerDescriptor.ServerClass = "OPCLabs.KitServer.2"
ReadItemArguments1.ItemDescriptor.ItemID = "Simulation.Random"
ReadItemArguments1.ReadParameters.DataSource = DADataSource_Device  ' read will be from device

Dim ReadItemArguments2: Set ReadItemArguments2 = CreateObject("OpcLabs.EasyOpc.DataAccess.OperationModel.DAReadItemArguments")
ReadItemArguments2.ServerDescriptor.ServerClass = "OPCLabs.KitServer.2"
ReadItemArguments2.ItemDescriptor.ItemID = "Trends.Ramp (1 min)"
ReadItemArguments2.ReadParameters.DataSource = DADataSource_Device  ' read will be from device

Dim ReadItemArguments3: Set ReadItemArguments3 = CreateObject("OpcLabs.EasyOpc.DataAccess.OperationModel.DAReadItemArguments")
ReadItemArguments3.ServerDescriptor.ServerClass = "OPCLabs.KitServer.2"
ReadItemArguments3.ItemDescriptor.ItemID = "Trends.Sine (1 min)"
ReadItemArguments3.ReadParameters.DataSource = DADataSource_Device  ' read will be from device

Dim ReadItemArguments4: Set ReadItemArguments4 = CreateObject("OpcLabs.EasyOpc.DataAccess.OperationModel.DAReadItemArguments")
ReadItemArguments4.ServerDescriptor.ServerClass = "OPCLabs.KitServer.2"
ReadItemArguments4.ItemDescriptor.ItemID = "Simulation.Register_I4"
ReadItemArguments4.ReadParameters.DataSource = DADataSource_Device  ' read will be from device

Dim arguments(3)
Set arguments(0) = ReadItemArguments1
Set arguments(1) = ReadItemArguments2
Set arguments(2) = ReadItemArguments3
Set arguments(3) = ReadItemArguments4

Dim Client: Set Client = CreateObject("OpcLabs.EasyOpc.DataAccess.EasyDAClient")

Dim results: results = Client.ReadMultipleItems(arguments)

Dim i: For i = LBound(results) To UBound(results)
    Dim VtqResult: Set VtqResult = results(i)
    If VtqResult.Succeeded Then
        WScript.Echo "results(" & i & ").Vtq.ToString(): " & VtqResult.Vtq.ToString()
    Else
        WScript.Echo "results(" & i & ") *** Failure: " & VtqResult.ErrorMessageBrief
    End If
Next

Python

Python (.NET)

# This example shows how to read 4 items from the device, and display their values, timestamps and qualities.
#
# 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.DataAccess.OperationModel import *
from OpcLabs.EasyOpc.OperationModel import *


# Instantiate the client object.
client = EasyDAClient()

# 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.

#
vtqResultArray = client.ReadMultipleItems([
    DAReadItemArguments(ServerDescriptor('OPCLabs.KitServer.2'), DAItemDescriptor('Simulation.Random'), DAReadParameters(DADataSource.Device)),
    DAReadItemArguments(ServerDescriptor('OPCLabs.KitServer.2'), DAItemDescriptor('Trends.Ramp (1 min)'), DAReadParameters(DADataSource.Device)),
    DAReadItemArguments(ServerDescriptor('OPCLabs.KitServer.2'), DAItemDescriptor('Trends.Sine (1 min)'), DAReadParameters(DADataSource.Device)),
    DAReadItemArguments(ServerDescriptor('OPCLabs.KitServer.2'), DAItemDescriptor('Simulation.Register_I4'), DAReadParameters(DADataSource.Device)),
    ])

for i, vtqResult in enumerate(vtqResultArray):
    assert vtqResult is not None
    if vtqResult.Succeeded:
        print('vtqResultArray[', i, '].Vtq: ', vtqResult.Vtq, sep='')
    else:
        print('vtqResultArray[', i, '] *** Failure: ', vtqResult.ErrorMessageBrief, sep='')

.NET

COM

Python

Concepts

Reference

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