FB_PMA_Frequency_Period_1Ph
The function block FB_PMA_Frequency_Period_1Ph calculates the base frequency of the given input signal. To do this, the signal is first filtered with a Butterworth low-pass filter. The zero crossings of the input signal are then determined from the filtered values, and the frequency is calculated from their difference. The results refer to one or more periods, depending on the configuration. The statistical results refer to the entire runtime or the time at which the statistical results were last reset.
The input buffer is provided via the function block FB_PMA_Source_1Ph. This can include one or more signal periods or individual fragments of oversampling arrays.
Syntax
Definition:
FUNCTION BLOCK FB_PMA_Frequency_Period_1Ph
VAR_INPUT
nOwnID : UDINT;
tTransferTimeout : LTIME := LTIME#500US;
stInitPars : ST_PMA_Frequency_Period_InitPars;
END_VAR
VAR_OUTPUT
bError : BOOL;
ipResultMessage : I_TcMessage;
bNewResult : BOOL;
nCntResults : ULINT;
fFreq : LREAL;
fFreq_Min : LREAL;
fFreq_Max : LREAL;
fRocof : LREAL;
bValidStatistics : BOOL;
bOutOfRange : BOOL;
END_VAR
Inputs
The input parameters of this function block represent initialization parameters and have to be assigned during the declaration of the function block instance (alternatively: 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 correlate to the above 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. |
fFreq | LREAL | Frequency determined by two or more zero crossings. |
fFreq_Min | LREAL | Smallest value of fFreq that has occurred. Can be reset via bResetStatistics of the Call method. |
fFreq_Max | LREAL | Largest value of fFreq that has occurred. Can be reset via bResetStatistics of the Call method. |
fRocof | LREAL | Rate of change of frequency (ROCOF). |
bValidStatistics | BOOL | TRUE if the Min and Max value calculation has been performed. These values are valid. |
bOutOfRange | BOOL | TRUE as soon as the input value or the frequency is not within the configured limits. |
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. | |
The method is called in order to reconfigure the function block during the runtime. | |
The current calculations are reset with the method. |
Sample
VAR CONSTANT
cOversamples : UDINT := 10;
cSourceInitPars: ST_PMA_Source_InitPars := (
nBufferLength := cOversamples);
cFrequencyInitPars : ST_PMA_Frequency_Period_InitPars := (
nBufferLength := cOversamples,
fSampleRate := cOversamples * 1000,
fMinFreq := 45.0,
fMaxFreq := 55.0,
nPeriods := 1,
nFilterOrder := 2,
fCutOff := 70.0,
eInputSelect := E_PMA_InputSelect.Voltage,
fMinInput := 200.0);
END_VAR
VAR
aVoltage AT%I* : ARRAY[1..cOversamples] OF LREAL;
aCurrent AT%I* : ARRAY[1..cOversamples] OF LREAL;
fbSource : FB_PMA_Source_1Ph := (nOwnID := 1, aDestIDs := [2], stInitPars := cSourceInitPars);
fbFrequency : FB_PMA_Frequency_Period_1Ph := (nOwnID := 2, stInitPars := cFrequencyInitPars);
END_VAR
// Call source
fbSource.Call(ADR(aVoltage), ADR(aCurrent), SIZEOF(aVoltage), 0);
// Call algorithm
fbFrequency.Call(FALSE);
Requirements
Development environment | Target platform | PLC libraries to include |
|---|---|---|
TwinCAT v3.1.4024.0 | PC or CX (x86, x64) | Tc3_PowerMonitoring |