How to: DoNothing

The manual demonstrates how to filter out part of values using an expression. Before starting, create a data source – a tag named Sine, which will generate a source signal, e.g. a sinusoid.

Open Monokot Server Administrator and double-click Scripts on the Server Explorer pane. Click New Expression and set the name HalfSine for the expression that appears. Insert the following code into the expression code editor:

var state = context.data['trig_sine'].state;

if (state.value < 0)
    return MosUtils.doNothing;

return state;

Press Ctrl + Enter to apply the change in the code editor.

Go to the Triggers tab and click Add Data.... Select the tag Sine as the data source for the trigger. Enter the name (key) trig_sine for the trigger.

In order for the changes to take effect on the server, click the Sync button. Thus, the expression will filter out all negative values received from the tag. You can read more about the ValueState object here.

If you set up saving tag values and expressions as time series, you will see the following picture: