Quality

Associated with: Most driver items

This status attribute indicates the ‘quality’ or reliability of an item’s data.

Possible Quality values vary, depending on the protocol, the type of item and its current State, but might include:

• Good—The quality of the data is good.
• High: Engineering Units Exceeded—Applies to analog points only. The point is overrange (the point’s value exceeds the specified upper limit).
• Low: Engineering Units Exceeded—Applies to analog points only. The point is underrange (the point’s value exceeds the specified lower limit).

  The point's full range of values is defined in the Alarm Limits section of the point's form. The labels used on point forms for the range fields vary between drivers. For example, Zero Scale to Full Scale or Underrange to Overrange.

  The Alarm Limits can appear as a grouping on the point form or as a separate tab, depending on the driver. For more information about a driver’s Alarm Limits, see the documentation for the relevant driver.

• Local Override—Applies to points only. A local Override is in force on the point. Points support overrides applied at the master station (ClearSCADA server); points on some drivers also support overrides applied at the point’s source (outstation).

  Use the point’s Override attribute and relevant Status attribute (such as Current Status) to ascertain more information about the override.

• Sub-Normal—The value is derived from more than one source, but data is not available from the required minimum number of sources. For example, if GPS data is normally retrieved from three satellites and one of those satellites is not reporting any data, the values reported to ClearSCADA might be assigned the Sub-Normal Quality flag.
• Last Usable Value—Applies to points on devices that rely on their own point values being updated by one or more external sources. This Quality value indicates that the point value should be deemed to be ‘stale’, in so far as the external source(s) have not updated the device’s value within the expected time period. Unlike the Last Known Value Quality, this Quality occurs when ClearSCADA is still able to communicate with the device.
• Last Known Value—The data is that for the last known value of the item. For instance, a point that has been re-activated after being disabled (see Enable Point) might indicate a Last Known Value Quality until ClearSCADA has retrieved its current value from the outstation or scanner. This Quality value might also indicate that ClearSCADA has detected a communications error, but the previous known data value is available.
• Waiting for Initial Data—ClearSCADA has not yet retrieved any data for the item. This Quality value can occur, for example, after a new point has been added to the database and placed In Service, and for which the driver has yet to retrieve any data.
• Uncertain—The quality of the item’s data is uncertain, as the last attempt to communicate with the device on which the item is located was unsuccessful.
• Sensor Not Accurate—The device with which the point is associated is reporting that its sensor (point) values are not accurate. If this Quality value is displayed, recalibrate the device.
• Out of Service—The item, or a device (such as an outstation) on which it is dependent, is not In Service. For more information, see Placing an Item In Service in the ClearSCADA Guide to Core Configuration.
• Sensor Failure—Applies to points on drivers that are able to report sensor or similar instrument failure to ClearSCADA. The sensor with which the point is associated has been reported as failed.
• Comm Failure—The device on which the item is located is not responding to requests from the server. ClearSCADA therefore deems communications with that device to have failed.
• Device Failure—ClearSCADA has detected that the item, or a device on which it is dependent, has failed.
• Configuration Error—An item that has invalid configuration has a Quality attribute of Configuration Error or Not Connected, depending on the specific configuration error(s). If the item has invalid configuration, display the item’s Form and correct the configuration as necessary (see Mandatory Configuration and Invalid Configuration Messages in the ClearSCADA Guide to Core Configuration).
• Not Connected—An item’s configuration is incomplete. The device with which it is associated (for instance, the server with which a scanner is associated) is yet to be specified.
• Bad—The quality of the data is deemed to be bad. No specific reason for this quality has been reported, or the reason reported by the device is not one of the standard OPC Quality flags. Other status attributes might clarify the reason for this quality.

Points have several ‘Quality’ attributes, including Current Quality and State Change Quality.

Channels on some advanced drivers have a Scan Quality attribute in addition to a Quality attribute (the latter indicating the quality of the channel itself, as opposed to the scanning undertaken on the channel).