Use the fields within the Value section of the OPC tab to specify the type of source value that is used to derive the value of the point in the ClearSCADA database. ClearSCADA processes the point data differently, according to the type of source value that it represents.
- Value Source—Use this combo box to specify the type of source value from which ClearSCADA is to read or write data. Choose from:
- Single Value—The source value is a single data value.
For Digital points, specify this option if the lowest bit to which ClearSCADA is to read or write is the first or only bit within an individual value. (If the lowest bit to which ClearSCADA is to read or write is a bit other than bit zero, specify the Bit Offset within Single Value option.)
- Array Element—The source value is an element within a data array. Use the Array Element field (below) to specify the actual element from which ClearSCADA is to read or write data.
For Digital points, specify this option if the lowest bit to which ClearSCADA is to read or write is the first bit of an element within the array. (If the lowest bit to which ClearSCADA is to read or write is another bit within an element, specify the Bit Offset within Single Value option.)
- Bit Offset within Single Value—Applies to Digital points only. Specify this option when the lowest bit to which ClearSCADA is to read or write is not the first bit in the source value. Use the Bit Offset field (below) to specify the actual bit from which ClearSCADA is to read or write data.
- Bit Offset within Array Element—Applies to Digital points only. Specify this option when the lowest bit to which ClearSCADA is to read or write is not the first bit in an array element. Use the Array Element field (below) to specify the actual element, and the Bit Offset field to specify the actual bit within that element.
- Array Element—Applies if the Value Source is set to Array Element. Specify the actual element within the data array, which is used to derive the value for the point.
- Bit Offset—Displayed on the OPC tab of Digital points only. Use this field to denote the offset into the source value that is to be retrieved for the database point (the lowest bit being bit zero).
You only need to specify a Bit Offset when the Value Source is Bit Offset within Single Value or Bit Offset within Array Element.
Example:
The Source of a 3-bit OPC Digital point is a 16-bit Value, of which the Digital Point comprises bits 3 to 5. In order for ClearSCADA to retrieve the point’s value from the correct location in the point source, the Digital point is given this configuration:
Value Source:Bit offset within single value
Bit Offset:3 (as 3 is the lowest, or starting bit, of the point value that comprises
bits 3, 4, and 5)