OPC DA Driver

dc3-driver-opc-da connects OPC DA servers to IoT DC3 — it targets an OPC DA server and periodically reads real-time tag (item) values over DCOM.

OPC DA (OPC Data Access) is the classic industrial data-access specification on the Windows platform. SCADA systems, HMI/configuration software, and PLC gateways mostly ship with an OPC DA Server that exposes field points as "items". This driver acts as an OPC DA client, using DCOM/J-Interop to connect to one or more OPC DA Servers and read real-time values according to the group name (group) and tag name (tag) configured on each Point.

Use case: an OPC DA Server (OPC DA 2.0 / 3.0) already exists on site, and its tags need to be brought into DC3 for unified collection and storage.

• Driver name / code: OPC DA Driver / OpcDaDriver
• Type: DRIVER_CLIENT (actively connects to the OPC DA Server)

DCOM is a prerequisite

OPC DA is built on Windows COM/DCOM. The Server must run on a Windows host reachable over DCOM, with DCOM permissions configured to allow remote access from the driver host. This is done at the OS level and is not part of the driver configuration.

Driver configuration (device-level driver-attribute)

When onboarding an OPC DA device, fill in these attributes on the Device:

Attribute	code	Type	Default	Description
Host	host	STRING	localhost	OPC DA host
CLSID	clsId	STRING	F8582CF2-88FB-11D0-B850-00C0F0104305	OPC DA server CLSID
Username	username	STRING	dc3	OPC DA username
Password	password	STRING	dc3dc3	OPC DA password

CLSID is the OPC DA Server's COM identifier

OPC DA locates a Server through a COM class identifier (CLSID), not a TCP port. The CLSID is determined by the vendor of the target OPC DA Server and can be found in the registry on the server host or via an OPC server browsing tool. The default value is only a placeholder — always replace it with the real Server's CLSID when onboarding.

Point configuration (point-attribute)

Fill in these on each collected Point:

Attribute	code	Type	Default	Description
Group	group	STRING	GROUP	OPC DA item group name
Tag	tag	STRING	TAG	OPC DA item tag name

OPC DA organizes tags under groups. The driver finds (or creates) the group by the Point's group, then locates the tag within that group by tag and reads its value; the COM variant type returned by the tag (such as VT_I4, VT_R8, VT_BOOL, VT_BSTR, etc.) is converted by the driver into the point value.

Collection and health

• Collection cycle: default cron 0/30 * * * * ? (one read round every 30 seconds).
• Health/online: device health check defaults to cron 0/15 * * * * ?, with a lease timeout of 45 seconds — see Device for the online-status mechanism.

Minimal onboarding example

Onboard one tag from an OPC DA Server running at 192.168.1.10:

1. Create a Device using OPC DA Driver, and set the driver attributes host=192.168.1.10, clsId= (the real Server's CLSID), and username/password (a Windows account allowed to access the Server remotely).
2. Add a Point to the Profile bound to the device, and set the point attributes group=Group1 and tag=Channel1.Device1.Tag1 (per the target Server's actual naming).
3. Start the driver, and within 30 seconds you will see the collected value in PointValue.

Common pitfalls

The Server runs on Windows, and DCOM must allow access

The most common reason for a failed connection is not the driver but DCOM: the firewall is not opened, the remote account is not authorized, or the Server host has not enabled remote activation permissions. First verify with an OPC client tool on the driver host that you can connect to that CLSID, then onboard into DC3.

group/tag must match the Server's naming

group is the OPC DA group name, and tag is the tag's full item name (naming styles differ by vendor, commonly something like Channel1.Device1.TagA). With a wrong name, the driver cannot find the tag under that group and the read fails — these names must come from browsing the target Server, not from guesswork.

Further reading

• Driver — the general driver model and registration mechanism
• Attribute and Config — the three-layer origin of attributes like host / group
• Device onboarding — a complete onboarding walkthrough
• Modbus TCP Driver — another industrial field-protocol driver