Opcclient
Contents |
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. It is necessary 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. The names of any items to be accessed on the server must be known. 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
Some simplifications have been made to the full OPC DA communication. Opcclient makes the following simplifications to user access:
1. Uses a default group only. The user cannot specify groups.
2. Items read from the OPC server into Matlab are of type double, rather than mapped to specific types for int8, int32, float32, double.
3. Opcclient has only been tested communicating with an OPC server located on the local computer which is protected by firewall. Security issues arise if the OPC server is on a remote computer because of sending user login and password info to the OPC server computer.
4. A more complete package supporting OPC communications is available from the Mathworks in their OPC Toolbox ([3]).
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 structure with fields: value, quality, timestamp and errorcode.
% If the call fails, the quality will be set to a value other than 192 (Good).
itemname = 'Bucket Brigade.Int4'; % This server item tag, is read/write
iteminfo = client.read(itemname);
value = iteminfo.itemvalue;
timestamp = iteminfo.itemtimestamp;
quality = iteminfo.itemquality;
errorcode = iteminfo.itemerrorcode;
% Writing a single item
newvalue = 23;
res = client.write(itemname, newvalue);
% And read its value back
iteminfo = client.read(itemname);
value = iteminfo.itemvalue;
timestamp = iteminfo.itemtimestamp;
quality = iteminfo.itemquality;
errorcode = iteminfo.itemerrorcode;
% Writing an array item
itemname = 'Bucket Brigade.ArrayOfReal8';
newvalue = rand(6,1)*10;
res = client.write(itemname, newvalue);
% And read its value back
iteminfo = client.read(itemname);
value = iteminfo.itemvalue;
timestamp = iteminfo.itemtimestamp;
quality = iteminfo.itemquality;
errorcode = iteminfo.itemerrorcode;
% Close connection
client.disconnect;