Polling Driver Tag Type Properties: I/O Tab (VTScada)
The I/O tab for the polling driver tag consists of properties used to identify the communication driver tag to be associated with this polling driver, and to establish the poll group, the I/O device's sequence in the poll, and the interval at which the equipment associated with the communication driver tag should be polled for data.
(Click title to expand text)
The I/O Device field enables you to specify the communication driver tag for which this polling driver will set the scan rate.
The I/O Device field can be used to associate this tag with
a new or existing communication driver tag using the tag browser button. The
button opens the Tag
Browser, which displays only the existing communication driver tags for your
application, and enables you to create a new communication driver tag using its
New button.
The Poll Group Name field enables you to enter a name by which this poll group will be known (or the name of the existing poll group to which this polling driver should belong) .
Note: Multiple polling drivers can associate multiple communication drivers with a single poll group.
For example, you can create 5 polling drivers, each of which is associated with a different communication driver, and enter the same polling group name for each of the polling drivers (e.g. "Poll Group 1", or "East Side Stations Poll Group"). The result is that the 5 communication drivers associated with the 5 polling drivers will be polled as a single group. Instructions on configuring a poll group can be found in Setting Up a Poll Group (VTScada).
The Poll Sequence Number field enables you to specify a number that identifies this polling driver's place in the polling sequence for the identified poll group.
For example, if you have created 5 polling drivers, each of which is associated with a different communication driver (e.g. Modbus1, Modbus2, etc.), and all 5 polling drivers have the same poll group identified (in their Poll Group Name property), you must enter a number from 1 to 5 for each of the polling drivers to determine the order in which the 5 communication drivers belonging to the poll group will be polled.
The Scan Interval field enables you to enter a number representing the amount of time (in seconds or in fractions of a second) between requests for data from this polling driver tag to the I/O device with which it is associated. The Delay After Scan Interval (Seconds) property enables you to specify the amount of time that the polling driver should wait before polling the I/O device (see below).
If Scan Interval is set to 0, the I/O device is scanned for data as fast as is possible.
Note: All data that is set to the same Scan Interval is read in the same poll of the I/O device. For this reason, it is recommended that you limit the number of different scan intervals for a single I/O device to optimize the reading to a minimal number of blocks, and improve overall system update performance. For example, if you have 12 analog inputs connected to one I/O device, it is recommended that the scan intervals for these tags be set to the same value (e.g. 1 (second)).
Delay After Scan Interval (Seconds)
The Delay After Scan Interval (Seconds) property indicates the amount of time that this polling driver should wait before polling the communication driver identified in the I/O Device field.
The system works on a 12-hour clock, starting at midnight. The value entered in the Delay After Scan Interval field therefore indicates the amount of time after 12:00 am before the system begins to scan according to the time schedule identified for the Scan Interval property.
For example, if you wish the system to begin polling at 1:00 am, and continue to poll every 2 hours (i.e. 1:00 am, 3:00 am, 5:00 am, 7:00 am, etc.), you should set the Delay After Scan Interval property to 3600 seconds (1 hour), and then set the Scan Interval to 7200 seconds (2 hours).
The section that follows provides polling driver configuration examples (see Polling Driver Scan Interval and Delay After Scan Interval Examples (VTScada)).
Note: The Delay After Scan Interval must always be less than the Scan Interval value.
Allows you to disable and enable polling for this poll driver.
The following section provides examples of polling driver configurations.