OPC DA driver

Connecting to classic OPC (Data Access 2.05a) servers via COM / DCOM and reading and writing tags by item ID; settings for ProgID, local / remote server, DCOM identity and update rate.

When to use it

OPC DA is the classic, Windows-specific OPC interface (COM / DCOM). The driver connects as a client to an OPC DA 2.05a server; the server can be on this computer or on another computer on the network. Use this driver if a device is accessible only through an OPC DA server; if the server also supports OPC UA, prefer the OPC UA driver.

This driver is new and has no connection in the demo project. At the time this manual was written, it had not been tried in the field with a real commercial OPC server, nor with remote DCOM using a user name / password.

Prerequisites

• The OPC Core Components (OPC Foundation) must be installed on the Live computer. If they are not installed, the error IOPCServer interface is not available is returned when connecting to the server.
• The OPC server must be installed and running. Find out its ProgID (e.g. Matrikon.OPC.Simulation.1, Kepware.KEPServerEX.V6) from the server's documentation or from an OPC client tool.
• If the server is 64-bit, it must also be accessible with a 32-bit client: Live runs as 32-bit (x86).
• If the server is on another computer, DCOM on that computer must grant launch and access permission to the user who runs Live (or to the user entered in the connection); the firewall must allow DCOM / RPC traffic (Connection security).

Setting up a connection

1. Add a connection

   In the Connections section: Add, driver OPC DA. This driver has no port; the cell is locked.

2. Specify the location of the server

   Leave the IP address / computer name cell empty: the server is on this computer. If the server is on another computer, enter its name or IP address (DCOM).

3. Enter the parameters

   

   OPC server (ProgID)

   Required. If empty, Check project reports an error and Live cannot connect.

   Update rate (ms)

   10 – 60000, default 250. This is the interval at which the server refreshes its values; it should not be greater than the read cycle of the tags.

   Read source

   Server cache (fast) (default) or Device (goes to the device on every read; slow).

   DCOM identity

   The Windows user running Live (default) or User name and password. Required only for a server on another computer.

   User name

   It can also be written in the form ALAN\kullanıcı. The password is not written to the project file; it is entered in Live.

4. Add a tag

   Enter the full name of the item on the server (ItemID) as the address.

Address and operating principles

• The syntax of the item ID is determined by the server (Random.Int4, Kanal1.Cihaz1.Tag1). Studio only checks that it is not empty, contains no control characters and does not exceed 1024 characters; the actual validation is done by the server. A wrong ID appears in Live as a tag error.
• The driver opens a single active OPC group and adds one item per tag (at most 250 items per request); reading is done in bulk (at most 500 items per request). A write is made as a single value, converted to the data type of the item on the server.
• Quality: if the server reports the quality as good or uncertain, the value is used; if it is bad, the tag gets an error (the message gives the reason: configuration error, not connected to the device, device / sensor fault, communication error …); while the server is waiting for the first data, the tag stays in the waiting state instead of an error state.
• WString is not supported; use String (OPC DA strings are already Unicode).
• The connection address and port rule is relaxed for OPC DA: several OPC DA connections can be defined to the same computer (each with a different ProgID).

Driver reference

OPC DA

Classic OPC (Data Access 2.05a, COM / DCOM). If the OPC server is on this computer, leave the IP address empty; if it is on another computer, enter its name or IP address (DCOM). OPC Core Components (OPC Foundation) must be installed. For servers that support OPC UA, prefer the OPC UA driver.

Driver ID

opcda (name in the project file)

Connection

There is no port; the address is optional (empty = this computer)

Data types

Bool Byte SInt Int UInt DInt UDInt Real LReal String DateTime

Same address

Multiple connections can be defined to the same address.

Connection parameters

Appears in the Inspector window when a connection is selected.

Address formats

Sample addresses

Common errors

The marker at the start of each line tells where the message will appear in Live: [connection] in the Connections section of the system menu; [write] in the notification window of the operator who performed the write; [Studio] in the address cell in Studio. [tag] is a tag error during reading: the tag is left with bad quality, the text of the message is not shown in Live in this version (Tag errors); read the text to understand the cause.

Limits