Node	Purpose
`tier0-opcda-server`	Stores the OPC DA server connection settings
`tier0-opcda-read`	Reads configured OPC item values
`tier0-opcda-write`	Writes one or more OPC item values

Before you begin

The Node-RED host or container can reach the OPC DA server.
Remote DCOM access is enabled on the OPC DA server.
TCP port 135 and the dynamic RPC ports used by the server are reachable.
The Windows account has DCOM Launch, Activation, and Access permissions, as well as access to the OPC server.
You know the CLSID of the target OPC DA server.

Installation

Online installation

Run the following command from the Node-RED user directory:

npm install @tier0/node-red-contrib-opcda-client

The Node-RED user directory is usually /data in Docker:

docker exec -it <node-red-container> sh
cd /data
npm install @tier0/node-red-contrib-opcda-client
exit
docker restart <node-red-container>

Offline Docker installation

The client .tgz contains all required runtime dependencies. Only this one file needs to be copied to an offline customer server.

docker cp tier0-node-red-contrib-opcda-client-1.0.34.tgz <node-red-container>:/data/
docker exec -it <node-red-container> sh
cd /data
npm install --offline --no-audit --no-fund ./tier0-node-red-contrib-opcda-client-1.0.34.tgz
exit
docker restart <node-red-container>

If online installation reports getaddrinfo EAI_AGAIN registry.npmjs.org, the container cannot reach the npm registry. Use the offline installation procedure instead.

Quick start

Add a tier0-opcda-read node to the flow.
Create a new tier0-opcda-server configuration.
Save and deploy the flow.
Open the server configuration and click Browse.
Click Export to download the item list.
Open the Read node and click Import to import the list.
Connect inject -> tier0-opcda-read -> debug.
Deploy again and wait for the Read node to show Ready.
Click Inject and inspect the result in the Debug sidebar.

[inject] -> [tier0-opcda-read] -> [debug / function / mqtt]

Server configuration

Field	Description
Name	Server name shown in Node-RED
Address	OPC DA server IP address or hostname, for example `192.168.31.31`
Domain	Windows/NTLM domain required by the server account
User Name	Account with DCOM and OPC server access
Password	Password for the account
ClsId	Class ID of the OPC DA server
Timeout	Timeout for each connection/initialization stage and read/write operation, in milliseconds
Reconnect cooldown	Retry cooldown in minutes after the server reports resource exhaustion; default: 5 minutes

For a slow server or a large item list, start with a Timeout of 15000 or 20000 ms.

Browsing items

Open the tier0-opcda-server configuration:

Click Browse.
Wait for the number of discovered items to appear.
Click Export to download export.json.
Open the Read node and click Import to load the file.

Notes:

Save and deploy the server configuration before the first Browse.
Node-RED does not display a saved password again in the editor. This is expected.
The same server configuration cannot run multiple Browse operations at the same time.
When Node-RED permission control is enabled, the user needs the node-opc-da.list permission.

Read node

Settings

Field	Description
Server	OPC DA Server configuration to use
Name	Node name
Cache Read	Read from the OPC server cache when selected; otherwise read from Device
Data Change	Only send output when at least one value has changed
Items	OPC item IDs to read

Cache Read

Enabled: reads the current OPC server cache. This is usually faster and creates less load on field devices.
Disabled: requests a Device read. Actual freshness depends on the OPC server and device communication state.

Triggering a read

Each input message triggers one read. The input payload is not used as a read parameter.

If the node is already Reading, another input message will not start a concurrent read.

Output

After a successful read, msg.payload is an array:

[
  {
    "itemID": "Channel1.Device1.Tag1",
    "errorCode": 0,
    "quality": "GOOD",
    "timestamp": "2026-08-05T08:00:00.000Z",
    "value": 123.45
  }
]

Property	Description
`itemID`	OPC item ID
`errorCode`	OPC DA result code; normally `0` on success
`quality`	`GOOD`, `UNCERTAIN`, `BAD`, or `UNKNOWN`
`timestamp`	Timestamp returned by the OPC server
`value`	Current value

The current version only sends an output message when all returned values have GOOD quality. If the node shows Bad Quality, inspect the corresponding items in the OPC server.

Write node

Set msg.payload to a non-empty array of values to write:

[
  {
    "itemID": "Channel1.Device1.Setpoint",
    "type": "float",
    "value": 42.5
  },
  {
    "itemID": "Channel1.Device1.Enabled",
    "type": "boolean",
    "value": true
  }
]

Supported type values:

double, short, integer, float, byte, long, boolean,
uuid, string, char, date, currency, array

Output:

Success: msg.payload is true.
Failure: msg.payload is false.
Input validation and server rejection errors may also include msg.error and msg.details.

Node status

Status	Recommended action
Ready	The node can read or write
Reading / Writing	Wait for the current operation to finish
Good Quality	The most recent read completed normally
Bad Quality	Check item communication and quality in the OPC server
Mismatch Data	Check whether every configured item is valid and was added successfully
Reconnecting	Wait for automatic reconnection
Resource cooldown	Wait for the configured cooldown and inspect OPC server client/resource usage
Reconnect stopped	Correct the account, permissions, or CLSID, then deploy again
Disconnected / Error	Check the Node-RED log; the node will normally attempt to reconnect

Troubleshooting

The node shows Ready, but Inject produces no output

Confirm that the Read node contains at least one item.
Check whether the node changes to Bad Quality.
Confirm that the previous read is not stuck in Reading.
Connect a Debug node after the Read node.
Add Catch and Status nodes to the flow.
Inspect the Node-RED container log, not only the editor sidebar.

Browse reports an account, permission, or password error

Save and deploy the Server configuration before browsing.
Re-enter the username and password, then deploy again.
Verify DCOM and OPC server permissions.
Verify that the CLSID belongs to the target OPC DA server.
Grant node-opc-da.list when Node-RED permission control is enabled.

`HRESULT 0x1c00001b (469762075)` or `0x800700A4`

Check whether the OPC server has reached its client, Session, Group, COM object, memory, or handle limits. Also check whether other collectors are connected to the same server. Three consecutive resource errors enter Resource cooldown; the node automatically makes one new connection attempt after the configured interval.