Qt Quick Water Pump▲

Qt Quick Water Pump example shows how to use Qt OPC UA QML API to interact with an OPC UA server to build a QML based HMI for a simple machine.

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Building the Server▲

Before you can use the Water Pump examples, you need to build the simulation server. The simulation server project resides next to the Water Pump examples. You can open and build it in QtCreator or from the terminal as usual.

The Simulation▲

The OPC UA server included in this example runs a simulation of a machine containing two tanks, a water pump and a valve. Water can be pumped from the first tank into the second tank and then be flushed from the second tank by opening the valve. Both operations have a user-configurable setpoint which controls how much water is pumped to or flushed from the second tank.

The following nodes exist on the server:

NodeId

Function

ns=2;s=Machine

The folder containing the method and variable nodes for the machine

ns=2;s=Machine.State

The state of the machine

ns=2;s=Machine.Tank1.PercentFilled

The current fill status of the first tank

ns=2;s=Machine.Tank2.PercentFilled

The current fill status of the second tank

ns=2;s=Machine.Tank2.TargetPercent

The setpoint for pumping and flushing

ns=2;s=Machine.Tank2.ValveState

The state of the valve of the second tank

ns=2;s=Machine.Designation

A human readable designation of the machine for display purposes

ns=2;s=Machine.Start

Call this method to start the pump

ns=2;s=Machine.Stop

Call this method to stop the pump

ns=2;s=Machine.FlushTank2

Call this method to flush tank 2

ns=2;s=Machine.Reset

Call this method to reset the simulation

Implementation▲

This example uses QML items to read and write values as well as method calls. All operations are asynchronous and handled by QML in the background.

A QML item represents the machine and its components. This item does not have any graphical interface and only provides access to the properties of the machine. It has two tanks which are instances of a separate Tank component.

Properties▲

The machine item exposes all properties and subitems as properties.

 
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    ...
    readonly property alias tank1: tank1
    readonly property alias tank2: tank2
    readonly property alias state: machineState.value
    readonly property alias tank2PercentFilled: tank2.percentFilled
    readonly property alias tank2valveState: tank2.valveState
    readonly property alias designation: designation.value
    property alias resetMethod: resetMethod
    property alias startMethod: startMethod
    property alias stopMethod: stopMethod
    property alias flushMethod: flushMethod
    ...

Asynchronous Handlers▲

The asynchronous parts of the API are handled by QML automatically because signals are emitted for every property change by default.

For example, the button to flush the second tank is enabled only if the backend is connected to the server, the machine is idle, and the tank level is above the setpoint. On click, the flushTank2() method is called on the server.

 
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    Tank2Unit {
        flushButtonEnabled: connection.connected && machine.state === Machine.MachineState.Idle
                            && machine.tank2.percentFilled > machine.t