Opcclient

Purpose

Creates an opcclient object which allows access to OPC servers.

Synopsis

client = opcclient(1);  % create OPC client, with client id=1.

Description

The opcclient object allows the Matlab user to connect to an OPC DA server and read item values from or write item values to the server. Opcclient is available in PLS_Toolbox Version 7.3 and later and provides access to OPC servers supporting OPC Data Access standard v2.05a.

The code example below shows how to interact with an OPC server running on the local computer. There are some prerequisite steps to take before running the example code: System Set-up 1. Start an OPC server on the local computer. Free demo OPC servers are available from Matrikon or Graybox, and others..

2. Ensure computer is configured for DCOM communication. See, for example, [1], or [2].

3. Create a user with admin privileges, for example, "testuser", with example password "test", or use any user with admin privileges and with an account password. It may be necessary to cycle the Windows firewall off and back on after performing steps 2 and 3.

4. Find the computer's IP address. This can be obtained from the "IPv4 address" entry in the results from the "ipconfig" command.

Notes

1. You need to know the Program ID of the OPC server you want to connect with. The Program ID is a human readable form of the server's COM unique identification, its Globally Unique Identifier (GUID). Graybox's progID is 'Graybox.Simulator'.

2. You will need to know the names of any items you want to access on the server. Item names (or tags) are usually in a hierarchical namespace specific to a server. Matrikon example: Bucket Brigade.ArrayOfReal8, Graybox example: numeric.saw.float.

3. Opcclient is implemented using the Java-based openscada.org Utgard package. OPC DA communication is based on the Windows COM protocol.

Simplifications

1. Uses default group only.

2. Item types on Matlab side are simply doubles, rather than mapping to int8, int32, float32, double

3. Only tested on local computer which is protected by firewall. Security issues would exist if the OPC server is on a remote computer because of sending user login and password info to the OPC server computer

Inputs

• id = Integer ID for this client.

Outputs

• client = opcclient object.

Example

% Create client instance
client = opcclient(1);

% Connect to OPC Server
% client.connect(IPaddress, domain, username, password, OPC_server_progID);
client.connect('10.0.2.15', 'localhost', 'testuser', 'test', 'Matrikon.OPC.Simulation');

% Reading a single item
%Read the specified OPC item. The function returns a (value, quality, timestamp) tuple. If the call fails, the quality will be set to 'Error'.
itemname   = 'Bucket Brigade.Int4';         % This server item tag, is read/write
[value timestamp quality] = client.read(itemname);

% Writing a single item
newvalue = 23;
res = client.write(itemname, newvalue);

% And read its value back
[value timestamp quality] = client.read(itemname);

% Writing an array item
itemname = 'Random.ArrayOfReal8';
newvalue = rand(6,1)*10;
res = client.write(itemname, newvalue);

% And read its value back
[value timestamp quality] = client.read(itemname);

% Close connection
client.disconnect;