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Update Rate for OPC Group

DIAdem 2012 Help

Edition Date: June 2012

Part Number: 370858K-01

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The update rate specifies the rate at which the OPC server updates its data. Many OPC servers use an internal data cache and use the update rate to update the values in the cache. If you select asynchronous communication in the block, the uprate is also the rate at which the OPC server informs DIAdem about data changes. The update rate should correspond to the clock rate of the DIAdem clock system. A yellow clock cable connects the clock system and the acquisition block. The two values, expressed as time, should be approximately the same.

The update rate setting affects the performance of the entire system. The OPC update rate and the clock rate of the DIAdem clock system affect each other in the following ways:

  • If the OPC update rate is substantially lower than the DIAdem sampling rate, the OPC server must supply its data faster than DIAdem can process the data. In this case, the communication system uses more computer power than necessary for the solution of the task. The moment when the input signal is measured is not earlier than the previous impulse in the DIAdem clock system.

  • If the OPC update rate is substantially higher than the DIAdem sampling rate, the OPC server supplies its data much less frequently than DIAdem requests the data. DIAdem always displays the date that the OPC server determined at the last update. The moment when the input signal is measured might be earlier than the previous impulse in the DIAdem clock system. The data must not be older than the OPC update rate.

When DIAdem validates signals, DIAdem also requests the OPC server whether the server supports the value entered in the Update rate box. If not, the OPC server suggests a new value. DIAdem automatically includes this new value in the dialog box.


 

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