OPC UA: Read#

The OPC UA: Read Node allows you to read multiple node values from your OPC UA Server and connected programmable logic controller (PLC). This node is only available in edge workflows.

OPC UA Read Node

Node Properties#

There are four main parts of the properties for this node ...

Connection Configuration#

OPC UA Read Node Configuration

Connection Configuration contains:

  • OPC UA URI: (Required) A string template for the OPC UA server URI.
  • Username: (Optional) A string template for login username.
  • Password: (Optional) A string template for login password.

Security Settings#

You can optionally select a SSL/TLS Security Policy for the connection to the OPC UA server through the dropdown selector. Example: Basic-128 RSA-15

OPC UA Read Node SSL/TLS Security

If a Security Policy is selected, you will have the option to select between Sign or Sign and Encrypt security modes. You'll then be required to provide a valid SSL/TLS client certificate and private key.

Read Instructions#

OPC UA Read Node Read Instructions

You may define multiple read instructions for the OPC UA: Read Node, and you must define at least one. Each instruction has the following fields:

  • Namespace Index (ns): (Required) A string template or positive integer.
  • Identifier: (Required) A string template or string for the node identifier. The identifier string should begin with one of the following types:
    • i=: for unsigned integer (UINT).
    • s=: for string.
    • g=: for global unique identifier (GUID).
    • b=: for byte string.
  • Result Key: (Required) The key at which to store the result of this read operation. This key will exist on the Destination Path defined below the instructions. This can resolve to any string except errors, since that key is reserved for any errors that occur during reads.

Destination Path#

OPC UA Read Node Result

The results of each read instruction will be placed in an object at the Destination Path (a payload path) at each instruction's Result Key. It is important that each key is named uniquely so the node does not overwrite another read result.

If the key is not present in the Destination Path of the payload, it means the read failed, and there will be a list of errors at the Destination Path under the key errors. For this reason, this node restricts Result Keys to not resolve to the path errors. Because the tags are read as a group one failed read for a tag may cause the other keys in the group to not appear.

Result#

The following is an example of a successful read, where an instruction's Result Key is Power, and the Destination Path is OPCUA_PLC:

{
  "OPCUA_PLC": {
    "Power": 10.01
  }
}

Node Errors#

The following is an example of a failure to read, and the destination path is OPCUA_PLC:

{
  "OPCUA_PLC": {
    "errors": [ { "type": "OPC-UA_READ_ERROR", "message": "Something useful to help you fix the issue." } ]
  }
}