4.2.Configuring Bridges

It is easy to configure the OPC DataHub to bridge existing points—just point and click. If necessary, you can quickly configure linear transformations and specify the direction of data flow of the bridge. And should you want to create a new point for a bridge, it's just few more clicks of the mouse. All configuration and any changes are done on the fly, taking effect as soon as you click the Apply button.

4.2.1.Point-to-point configuration

  1. With the DataHub running, right click on the OPC DataHub system-tray icon and choose Properties.
  2. In the Properties window, select Bridging .
  3. Click the Configure Bridges button. The Bridging Configuration window will open.
    The three top panes in this window correspond to the three basic steps in making the configuration: specify a source, a destination, and any desired transformations. The horizontal pane across the bottom shows the bridges that exist on the system.
  4. From the tree diagram in the Source panel, select a source point that you want to bridge.
    For example, if you have the DataSim program running, you can select the point Sine in the DataSim data domain. The name of the point gets automatically entered in the field at the top of the panel. Alternatively, you can type the name of the point in the entry field.
  5. In the tree diagram in the Destination panel, select a destination point.
    When you select a destination point, its name gets automatically entered in the field at the top of the panel. Or you can type the name of a point in the entry field.
  6. Specify direct copy or transformation.
    To make a direct copy, just leave the default Direct copy selected. To make a linear transformation, select Linear Transformation or Linear Range Mapping and enter the appropriate data, as explained in Section4.2.2, “Making transformations” below.
  7. Determine which direction you want the bridge to apply.
    Select Forward to change the destination point when the source point changes, but not change the source when the destination changes. Select Inverse to change the source point if the destination point changes, but not vice-versa. Select both boxes for a bidirectional bridge, where either point changes whenever the other point changes.

    Selecting the inverse direction will apply the inverse of the transformation, as explained below.

  8. Click the Apply button to create and activate the bridge. The DataHub will create the bridge and update the bridged points immediately.
  9. In the bottom panel you can see all the bridges that exist in the system, and the significant information about them.
    If you click on a transformation, the source point, destination point, and transform information get displayed in their respective panels. Use the check box at the front of each bridge to activate or deactivate it.

4.2.2.Making transformations

  1. Specify the type of transformation by clicking one of the three radio buttons:

      Direct copy makes no transformations. It just copies the point.

      Linear Transformation lets you multiply by one value and add another value, such as in the equation y = mx + b where the destination point is y, the source point is x, the multiply by value is m, and the then add value is b. For example to transform a Celsius source point to a Fahrenheit destination point, you would multiply by 1.8 and add 32, or

      Fahrenheit = (1.8 X Celsius) + 32

      If you have selected the Inverse direction for a transformation, you will get the inverse of the transformation. In this example, you would get a conversion from Fahrenheit to Celsius, or the results of this equation:

      Celsius = (Fahrenheit - 32) / 1.8

      As an alternative to entering transformation values, the DataHub also offers Linear Range Mapping.

      Linear Range Mapping lets you enter a range for the source and destination, and the DataHub automatically calculates the corresponding linear transformation. For example, to create the same Fahrenheit to Celsius transformation, you could use the defaults of 0 and 100 for the Min and Max of the source point. Then you would enter 32 and 212 for the Min and Max of the destination point. As soon as you make these entries, the correct values get entered automatically in the Linear Transformation.

      When you use linear range mapping, you can limit the transformed value to the maximum and minimum by checking the Clamp boxes. The clamps get applied to the point being changed, ie. to the destination point for forward direction, to the source point for inverse direction, and to both points for bidirectional bridges.

  2. If you want to save this transformation for future use, click the Store... button at the top of the Transformation panel, and enter a name in the box that pops up.
    Once stored, the transformation will become available by name in the drop-down list.
  3. To load a transformation, simply select its name from the drop-down list.