Read a value from an OPC UA server in C#

The code

// resolve the namespace index from its URI - never hardcode it
int nsIndex = session.NamespaceUris.GetIndex("http://opcfoundation.org/UA/MachineTool/");
Console.WriteLine($"MachineTool namespace index: {nsIndex}");

DataValue dv = session.ReadValue(new NodeId(2258));   // Server CurrentTime

Console.WriteLine($"value           : {dv.Value}");
Console.WriteLine($"status          : {dv.StatusCode}");
Console.WriteLine($"good?           : {StatusCode.IsGood(dv.StatusCode)}");
Console.WriteLine($"source timestamp: {dv.SourceTimestamp:O}");
Console.WriteLine($"server timestamp: {dv.ServerTimestamp:O}");

// batch reads: one round trip for many nodes
var toRead = new ReadValueIdCollection
{
    new ReadValueId { NodeId = new NodeId(2258), AttributeId = Attributes.Value },
    new ReadValueId { NodeId = new NodeId(2259), AttributeId = Attributes.Value },
};
session.Read(null, 0, TimestampsToReturn.Both, toRead, out var results, out _);
foreach (var r in results) Console.WriteLine($"  {r.Value} [{r.StatusCode}]");

What it prints

MachineTool namespace index: 4
value           : 08/09/2026 03:44:59
status          : Good
good?           : True
source timestamp: 2026-09-08T03:44:59.3210000Z
server timestamp: 2026-09-08T03:44:59.3210000Z
  08/09/2026 03:44:59 [Good]
  Running [Good]

Notes

• StatusCode.IsGood is the check to make. An Uncertain status still has a value attached, and averaging it silently corrupts a KPI.
• session.NamespaceUris.GetIndex(uri) is the habit that stops a client breaking after a PLC program download shifts the indexes.
• Batch with a ReadValueIdCollection. One request for two hundred nodes is dramatically cheaper, up to the server's operation limit.
• Attributes.Value is one of many. DataType, AccessLevel and EURange are all readable the same way, and you need them before writing or applying a percent deadband.

What breaks first

Last verified 7 September 2026 against OPC UA 1.05.07. OPC UA Connect is an educational resource and is not affiliated with the OPC Foundation.