TrackBar

TrackBar (Adjustment Bar)

The TrackBar is a control object that allows the operator to select a value within a predefined Minimum and Maximum range by dragging a slider (thumb) along a “tick” mark system.

Although functionally similar to the HScrollBar, the TrackBar is generally preferred for more user-friendly “adjustment” or “precision” controls (e.g., Volume, Speed settings). It can be configured as either Horizontal or Vertical using a single object.

For standard Properties, Advanced, and Events Panel settings not covered here, please refer to the Common Object Features page.

Basic Configuration and Operation

1. Defining Range and Orientation (Advanced Panel) The object’s operational logic is defined in the Advanced panel.

  • Determines whether the object is horizontal or vertical.
  • Sets the lowest and highest values the slider can reach.
  • Determines the frequency of “ticks” (marks) displayed on the bar.

2. Binding the Value (Properties Panel)

  • The value selected by the operator is linked to a SCADA tag via the Value property in the Properties panel.

Properties Panel – Key Properties

Value

  • Tag:
    • Function: This is a two-way link connecting the slider’s current position (within the Minimum and Maximum range) to a tag.
    • Read: If the linked tag (e.g., Motor_Speed) is set to 50 by a script or the PLC, the TrackBar slider automatically moves to the middle position (assuming Min=0 and Max=100).
    • Write: If the operator drags the slider to the 75% position (assuming Min=0 and Max=100), the value 75 is written to the Motor_Speed tag.

Advanced Panel – Key Properties

  • Orientation
    • The Most Important Feature. Determines whether the object is Horizontal or Vertical.
  • TickFrequency
    • Determines how often ticks are drawn on the bar.
    • Example: If Min=0, Max=100, and TickFrequency=20, ticks will appear at points 0, 20, 40, 60, 80, and 100.
  • TickStyle
    • Determines where the ticks appear relative to the bar (BottomRight, TopLeft, Both, None).
  • SmallChange
    • The amount the value changes when the operator presses the arrow keys on the keyboard (Usually 1).
  • LargeChange
    • The amount the value changes when the operator clicks on the empty track area instead of dragging the slider (Usually 5 or 10).

Note: Minimum and Maximum Value Precedence

The TrackBar object allows for defining minimum and maximum limits in two different ways:

  1. Fixed Values (Advanced Panel):
    • The Minimum and Maximum fields in the Advanced tab set a static operating range for the control.
    • These are used when a fixed range is required (e.g., 0–100).
    • These values do not change during runtime.
  2. Values Defined via Tag (Properties Panel):
    • The Minimum and Maximum fields in the Properties -> Value tab allow the control to retrieve its range dynamically from a tag.
    • This ensures the slider automatically updates based on the current value range of the connected variable.

Priority Rule: If both static (Advanced) and Tag-based (Properties) minimum/maximum values are defined, the values coming from the tag take precedence. This ensures the control behaves according to real-time system data.

Common Usage Example

Example: Fan Speed Adjustment (Horizontal, 0-100)

  1. Add a TrackBar and a Label to the screen.
  2. Go to the Advanced panel of the TrackBar object:
    • Orientation: Horizontal
    • Minimum: 0
    • Maximum: 100
    • TickFrequency: 10 (Show a tick every 10 units)
    • TickStyle: BottomRight
  3. Go to the Properties panel of the TrackBar object:
    • Bind Value -> Tag to the Fan_Speed_Setpoint tag.
  4. Go to the Properties panel of the Label object:
    • Bind Value -> Tag to the same Fan_Speed_Setpoint tag (to visualize the exact value).

Result:

  • As the operator moves the slider, the Fan_Speed_Setpoint tag takes a value between 0 and 100, and the Label displays this value instantly.
  • Conversely, if the PLC writes “25” to this tag, the slider automatically moves to the quarter position.

Leave a Reply