Filter data by a tag value and write data to a database only when the value will change. Tutorial.

Problem scenario

I have this item: Kemro.opc.4.IF1.1.92.Mars1.SVs.system.sv_ShotCounter[14]="1562" in OPC Data Logger. I want to take data and write it to MySQL, only when this counter changes.

Requirements:

• Advanced OPC Data Logger Enterprise or a trial version.
• Script Execute plugin.

It is assumed that:

1. You've created a configuration (using the "Green Plus" button in the main window and added an OPC group in the OPC logger and can receive any data from a selected OPC server.

2. You've configured a data export to MySQL.

Solution:

1. Enable highlighted options in the OPC group settings.

Fig.1. OPC group settings

2. Download and install the "Script Execute" plugin.

3. Enable it (fig. 2).

Fig.2. Script Execute plugin

4. Select the plugin in the list and click the "Setup" button below.

5. In the script editor window select "PascalScript" from the "Script type" list

6. Copy and paste the following code. Modify it if necessary. The row sName1:string = 'Kemro.opc.4.IF1.1.92.Mars1.SVs.system.sv_ShotCounter'; contains the name of the controlled OPC tag.

7. Click the "Check" button and verify that the script was compiled successfully.

8. Click the "OK" button and save all changes.

The PascalScript code

var v1,v2:double;
    sName1:string = 'Kemro.opc.4.IF1.1.92.Mars1.SVs.system.sv_ShotCounter';
    sName2:string = 'LAST_VALUE';
begin
 // checks that a variable is stored before
 if IsVariableStored(sName2) then
   // retrieves a stored variable
   v1 := PopVariable(sName2)
 else
   // otherwise initialize our value
   v1 := 0;

 // checks a variable in a data packet
 if IsVariableDefined(sName1) then
  begin
    v2 := GetVariable(sName1);
    // stores a value between script executions
    PushVariable(sName2, v2);

    // the script will discard data packets by the following condition
    if v1 = v2 then
     DiscardDataPacket();
  end
 else
  // discard data also when the counter didn't read yet
  DiscardDataPacket();

end.