FB_PMA_Spectrum_3Ph
The function block FB_PMA_Spectrum_3Ph calculates the magnitude spectra of the current and voltage values. These are suitable for analyzing the input signals in the frequency range.
The input buffer is provided via the function block FB_PMA_Source_3Ph. The size of the input buffer is half the window length.
By way of example, possible FFT and window lengths are shown in the following table:
FFT length | Window length | Buffer length | |
|---|---|---|---|
512 | 29 | 400 | 200 |
1024 | 210 | 800 | 400 |
2048 | 211 | 1600 | 800 |
4096 | 212 | 3200 | 1600 |
8192 | 213 | 6400 | 3200 |
16384 | 214 | 12800 | 6400 |
Memory properties
Since the Welch method is used, in each case the current input buffer together with the last transferred buffer is used for the calculation.
The frequency analysis takes step changes in the time series into account. In order to achieve a correct result, the last two input buffers should therefore be consecutive without step changes.
Syntax
Definition:
FUNCTION BLOCK FB_PMA_Spectrum_3Ph
VAR_INPUT
nOwnID : UDINT;
tTransferTimeout : LTIME := LTIME#500US;
stInitPars : ST_PMA_Spectrum_InitPars;
VAR_OUTPUT
bError : BOOL;
ipResultMessage : I_TcMessage;
bNewResult : BOOL;
nCntResults : ULINT;
END_VAR
Inputs
The input parameters of this function block represent initialization parameters and must be assigned when declaring the function block instance (alternative: Init method). They may only be assigned once. A change at runtime is not possible.
Name | Type | Description |
|---|---|---|
nOwnID | UDINT | Identifies the function block instance with a unique ID. This must always be greater than zero. A proven approach is to define an enumeration for this purpose. |
tTransferTimeout | LTIME | Setting of the synchronous timeout for internal multi-array forwardings. See Parallel Processing in Transfer Tray. |
stInitPars | Function-block-specific structure with initialization parameters. The parameters must match the definition of the input and output buffers. |
Outputs
Name | Type | Description |
|---|---|---|
bError | BOOL | TRUE if an error occurs. |
ipResultMessage | I_TcMessage | The interface offers detailed information about the return value. |
bNewResult | BOOL | TRUE once new results have been calculated. |
nCntResults | ULINT | Count value is incremented with new output data. |
Methods
Name | Description |
|---|---|
The method is called in each cycle to execute the calculations from the input buffer when new data is present. | |
Alternative to the function block initialization | |
As an alternative to the Call method, the method can be called in each cycle if no calculation is to take place. The incoming input buffer is then forwarded accordingly. | |
This method deletes all the data sets already added. |
Sample
VAR CONSTANT
cOversamples : UDINT := 10;
cFFT_Length : UDINT := 4096;
cWindowLength : UDINT := 3200;
cSourceInitPars: ST_PMA_Source_InitPars := (
nBufferLength := cWindowLength/2);
cSpectrumInitPars : ST_PMA_Spectrum_InitPars := (
nFFT_Length := cFFT_Length,
nWindowLength := cWindowLength,
fSampleRate := cOversamples * 1000,
eScalingType := E_PMA_ScalingType.PeakAmplitude,
eWindowType := E_PMA_WindowType.HannWindow,
bTransformToDecibel := FALSE,
fDecibelThreshold := GVL_PMA.cMinArgLog10);
END_VAR
VAR
aVoltage AT%I* : ARRAY[0..2] OF ARRAY [1..cOversamples] OF LREAL;
aCurrent AT%I* : ARRAY[0..2] OF ARRAY [1..cOversamples] OF LREAL;
fbSource : FB_PMA_Source_3Ph := (nOwnID := 1, aDestIDs := [2], stInitPars := cSourceInitPars);
fbSpectrum : FB_PMA_Spectrum_3Ph := (nOwnID := 2, stInitPars := cSpectrumInitPars);
aSpectrumVoltage : ARRAY[0..2] OF ARRAY[1..cFFT_Length/2 + 1] OF LREAL;
aSpectrumCurrent : ARRAY[0..2] OF ARRAY[1..cFFT_Length/2 + 1] OF LREAL;
END_VAR
// Call source
fbSource.Call(
ADR(aVoltage[0]),
ADR(aVoltage[1]),
ADR(aVoltage[2]),
ADR(aCurrent[0]),
ADR(aCurrent[1]),
ADR(aCurrent[2]),
SIZEOF(aVoltage[0]),
0);
// Call algorithm
fbSpectrum.Call(
ADR(aSpectrumVoltage[0]),
ADR(aSpectrumVoltage[1]),
ADR(aSpectrumVoltage[2]),
ADR(aSpectrumCurrent[0]),
ADR(aSpectrumCurrent[1]),
ADR(aSpectrumCurrent[2]),
SIZEOF(aSpectrumVoltage[0]));
Requirements
Development environment | Target platform | PLC libraries to include |
|---|---|---|
TwinCAT v3.1.4024.0 | PC or CX (x86, x64) | Tc3_PowerMonitoring |