Applies To:
  • CitectSCADA 1.00 1.01 1.10 1.11 1.20 2.00 2.01 3.00
Summary:
Question: All our symbols are drawn depending on some variables, but always one of these variables is the variable of quality. We have developed our own driver using the driver tool kit and the drivers sets these variable to "1" when the RTU or PLC is offline. The problem is that the symbols remain in the state previous to the break of communication. Why don't the symbols display correctly? 

Solution:
When Citect sees that the RTU or PLC is offline or any other error, Citect will ignore the data being returned from the driver. When an error is returned from a read, Citect assumes that the read data is bad and so will not save it. Because of this Citect will retain the last valid data that was returned from the PLC. The only way to get an error message back to Citect and to allow Citect to still save the data is to make the error message a warning only. When Citect sees a warning error from a response it will assume that the data is valid and save it. However you should not use a warning error to indicate that the PLC is offline as Citect treats warnings at a lower level and warning will not cause a redundancy swapover. You maybe able to solve this problem by making the driver first return warning errors so that the initial data is saved with the variable of quality as failed then make the driver return offline errors.

The communication break feature in version 3.0 will process the variable quality automatically whenever an error is returned from the driver.

 
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