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Setting the Database Read Rate (DSC Module)

Use the Historical VIs to obtain or read historical information about shared variables and to manage Citadel databases. All VIs that read information from the Shared Variable Engine can return information immediately or wait for the database to update with new information before returning information. The timeout input controls this behavior. This timeout value tells the VI how long to wait, in seconds, for the shared variable information to update in the Shared Variable Engine. The following table describes the behavior for each timeout value.

VI Timeout Input Behavior
0 VI immediately reads the database and returns the current shared variable information.
Less than 0 VI continues to wait until the shared variable updates.
Greater than 0 VI waits until the shared variable updates in the database or the time between updates exceeds the timeout period, whichever occurs first, then reads the database and returns the current shared variable information.

If you leave the timeout input unwired, the default value is 0. How you use the timeout input depends on whether you want to implement event-driven or polled programming techniques in the HMI.


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