Conversion
The OPC server offers the feature to online convert process data.
The OPC-Server takes care of online-conversion in both communication directions : :
- Processvalue --> Communication to OPC-Server --> convertion within OPC-Server --> Communication to OPC-Client --> OPC-Client
- OPC-Client --> Communication to OPC-Server --> convertion within OPC-Server --> Communication to process --> Processvalue
Sample :
- KL3202 offers process value of temperatures in unit 1/10 Grad Celsius, e.g. 200.
- The opc-server is configured with a conversion "Factor 10" which is linked to this plc-variable.
- The opc-client gets the process value 20 Grad.
- If opc-client writes a new value 25 Grad celsius to OPC-server, the server will convert this to 250 and writes this value to the PLC.
Sample
The complete sample contains a PLC project and an OPC conversion definition.
 | OPC-Server presents a converted variable as Datatyp "VT_R8 / Double" to OPC-client - independend of numerical datatyp in the PLC. |
1. Step: Configuration of conversion for TwinCAT OPC Server
Start TwinCAT-OPC-Configurator "Start - All Programs - TwinCAT System - TwinCAT OPC - TwinCAT OPC Configurator"
Navigate to "Conversions", right click and select menue "New".
For "Name" please enter a name for this alarm definition.
This name has to be OPC conform, no special characters allowed.
With "OK" you see the dialog to configure in detail your new "Conversion".
Following settings can be done:
Type | Req./Opt. | Description |
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Conversion ID | Required |
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Type | Required |
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Claming |
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High EU | Req |
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Low EU | Optional |
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High IR | Optional |
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Low IR | Optional |
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H Clamping |
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L Clamping |
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Disable | Optional | Disables this conversion. OPC-Server will ignore this conversion. |
Step: Check and save configuration
Save new configuration by selecting menue "File - Save As...".
After successfully creating and saving of new OPC-configurationfile the next dialog offers to activate this new configuration.
Select "OK" to activate the configuration. With next startup the OPC-Server will work with new settings.
| In case of opc server offers old previous configuration to opc-clients but a new configuration was activated this means, that OPC-server was not restarted to load fresh configuration. |
3. Step: Link of PLC-Variable with Conversion-template
With previous steps we defined a "conversion-Template" with detailed information about conversion handling.
Now we define, which PLC variable should be handled with conversion.
This link is configured in PLC-Control as and additional information for IEC1131-variable declaration.
Take care on following settings :
Add a comment behind PLC-variable declaration. This comment will be interpreted by the opc-server and links this plc-variable to a previous defined conversion-template.
The conversion-template with the unique conversion-ID was configured in step 1.
| Today just global PLC-variables can be linked to conversion-templates. Elements of structures or arrays can not be configured as an OPC-conversion. Future versions of OPC-Server will not have this limitation. |
Sample :
- PLC-Variable of Typ INT intMemCounterConversion is an OPC-DA variable which is converted by the opc-server as defined in conversion template 102.
The syntax is important :
intMemCounterConversion : INT; (* ~
(OPC : 1 : available for
OPC-clients)
(OPC_PROP[6010] : 1 :
OPC_PROP_CONV_ENABLE)
(OPC_PROP[6011] : 102 :
OPC_PROP_CONV_ID)
*)
Each time compiling the PLC-project the PLC-Control will create the file <PLC-projectname>.tpy. This XML based file contains information about PLC-variables and their link to the OPC-server.
The OPC server will analyze this information of the TPY file., so configure the OPC-Server to know the file <PLC-projectname>.tpy Details