Dynamic weighing

This sample shows how the dynamic weighing process works with the Weighing PLC library.

Download: SampleDynamicWeighing (*.tnzip)

Description

The input signal, a noisy trapezoidal signal, is generated in the MAIN program using the method GenerateInputs() with a signal generator. The simulated signal is transferred to the function block FB_DynamicWeighing (fbDynamicWeighing), which forwards it internally to other function blocks. This includes filtering with the function block FB_WG_ComboFilter (fbComboFilter), scaling with the function block FB_WG_Scaling (fbScale) and evaluation with the function block FB_WG_Weighing (fbWeighing).

Program parameters

The table below shows a list of important parameters for configuring the function blocks used.

Variable	Description	Default value
fRawAmplitudeSignal	Amplitude of the trapezoidal signal	1000.0
fAbsoluteNoise	Absolute noise amount	200.0
fFrequency	Base frequency of the trapezoidal signal	1.0 Hz
bActivateSlope	A drifting test signal is activated/deactivated	FALSE
bAddWeight	Adds an offset value to the test signal once	FALSE
eAutoTareType	Selection for automatic taring	E_WG_AutoTareType.eContinously

The following global constants are defined.

Variable	Description	Default value
cOversamples	Number of oversamples of the input channel	10
cSamplingRate	Sample rate of the input channel in Hz	1000

Implementation:

First, the corresponding structures and function blocks are declared and initialized:

// Filter
    stParamsComboFilter : ST_WG_ComboFilter  := 
    (
        nOrder : =6,
        fCutoff : =10.0,
        fSamplingRate : =TO_LREAL(cSamplingRate),
        nSamplesToFilter : =200,
        bReset := FALSE
    );

    fbComboFilter := FB_WG_ComboFilter:=(stConfig := stParamsComboFilter);

// Scaling
    stParamsScale : ST_WG_Scaling : =
    (    
        fRawLow : =0.0,
        fReferenceLow : =0.0,
        fRawHigh : =1000.0,
        fReferenceHigh : =100.0
    );    
    
    fbScale : FB_WG_Scaling : =(stConfig : =stParamsScale, eTraceLevel : =TcEventSeverity.Info);


// Weighing
    stParamsWeighing : ST_WG_Weighing : = 
    (
        nWindowLength : =100,
        Validation:=(nValidationSamples : =100, fThresholdWeight : =20.0, fMaxStd : =5.0, fMaxWeightDeviation : =0.0),
        AutoTare : =(nValidationSamples : =100, fThresholdWeight : =10.0, fMaxStd:=1.0, fMaxWeightDeviation : =0.0)
    );

    fbWeighing : FB_WG_Weighing : =(stConfig : =stParamsWeighing);

In the implementation part, the function block instances are executed using the corresponding Call() methods.

// Execute weighing
IF NOT fbComboFilter.Call(ADR(aInput), SIZEOF(aInput), ADR(aOutFilter), SIZEOF(aOutFilter)) THEN
    SetError(fbComboFilter);
END_IF

IF NOT fbScale.Call(ADR(aOutFilter), SIZEOF(aOutFilter), ADR(aOutScaling), SIZEOF(aOutScaling)) THEN
    SetError(fbScale);
END_IF

IF NOT fbWeighing.Call(ADR(aOutScaling), SIZEOF(aOutScaling)) THEN
    SetError(fbWeighing);
END_IF

Automatic taring:

The instance fbScale can be automatically tared via the fbWeighing instance as follows:

// Execute AutoTare
IF NOT fbWeighing.AutoTare(fbScale, eAutoTareType)THEN
    SetError(fbWeighing);
END_IF

Depending on the eAutoTareType initialization value, there is the following case distinction:

E_WG_AutoTareType.eEnd (above): fbScale is tared with the value fAutoTareOffset if bNewAutoTareResult is equal to TRUE. E_WG_AutoTareType.eContinously (below): fbScale is tared with the value fAutoTareOffset if fAutoTareOffset is not equal to 0. After taring, a fbWeighing.Reset() is automatically executed each time.