FB_CMA_MeanStressCorrection
Calculates mean stress-free reversal points from classified reversal points.
The function block FB_CMA_MeanStressCorrection implements the mean stress corrections according to Goodman and Gerber for the conversion of range-mean counts into mean value-free range-mean counts. The counts are processed in the form of multidimensional multi-arrays.
The fatigue damage of a component can be calculated with the function block FB_CMA_MinersRuleon the basis of the half loops counted by the function block FB_CMA_RainflowCounting. In the case of damage monitoring, a mean stress correction of the counting result can be carried out with the help of the function block FB_CMA_MeanStressCorrection.
Behavior when processing multi-channel input data
When processing several channels (nChannels > 1), there is a possibility of each channel having different return values. In this case, return values can be queried separately on the function block. If the results from one or more channels are impermissible, but not all channels, the value on the function block corresponds to eCM_InfRTime_AmbiguousChannelResults. If the results of all channels are impermissible, then the value on the function block corresponds to eCM_ErrRTime_ErrornousChannelResults.
A list of return values of all channels can be queried using the method GetChannelErrors().
Sample implementation
A sample implementation is available under the following link: Fatigue Analysis
Inputs and outputs
The input and output buffers correspond to one of the following definitions (input / output shape). The variable parameters are part of the function block input stInitPars.
Versions | Input buffer (MultiArray input stream) | Output buffer (MultiArray output stream) |
|---|---|---|
Standard variant |
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Multichannel variant |
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*: The length of this dimension can be selected as desired and can thus adapt itself to the application or to the output buffer of the preceding algorithm.
VAR_INPUT
stInitPars : ST_CM_MeanStressCorrection_InitPars; // init parameter
nOwnID : UDINT; // ID for this FB instance
aDestIDs : ARRAY[1..cCMA_MaxDest] OF UDINT; // IDs of destinations for output
nResultBuffers : UDINT := 4; // number of MultiArrays which should be initialized for results (0 for no initialization)
tTransferTimeout : LTIME := LTIME#500US; // timeout checking off during access to inter-task FIFOs
END_VARInput parameters
The input parameters of this function block represent initialization parameters and must already be assigned in the declaration of the FB instance! (Alternatively: Init() method). They may only be assigned once. A change at runtime is not possible.
stInitPars: Function block-specific structure with initialization parameters of the type ST_CM_MeanStressCorrection_InitPars. The parameters must correlate to the above definition of the input and output buffers.nOwnID: 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.aDestIDs: Defines the destinations to which the results are to be forwarded by specifying the IDs of the destinations. The definition of the output buffer (as described above) must correlate to the definition of the input buffer of each selected destination.nResultBuffers: The function block initializes a Transfer Tray Stream with the specified number of MultiArray buffers. The default value is four.tTransferTimeout: Setting of the synchronous timeout for internal MultiArray forwardings. See section Parallel processing.
Output parameters
VAR_OUTPUT
bError : BOOL; // TRUE if an error occurs. Reset by next method call.
hrErrorCode : HRESULT; // '< 0' = error; '> 0' = info; '0' = no error/info
ipErrorMessage : I_TcMessage := fbErrorMessage; // Shows detailed information about occurred errors, warnings and more.
nCntResults : ULINT; // Counts outgoing results (MultiArrays were calculated and sent to transfer tray).
END_VAR-
bError: The output isTRUEif an error occurs. -
hrErrorCode: If an error occurs, a corresponding error code of the typeHRESULTis output. Possible values are described in the List of error codes. -
ipErrorMessage: Contains more detailed information on the current return value. Refer here to the section Error description and information. This special interface pointer is internally secured so that it is always valid/assigned.
Methods
Call():
The method is called each cycle in order to apply the algorithm to the current input data. The function block waits for input data if the method indicates neither new results nor an error. This is a regular behavior in the process of the analysis chain.
- Return value: If an error occurs, a corresponding error code of the type
HRESULTis output. Possible values are described in the List of error codes.
METHOD Call : HRESULT
VAR_OUTPUT
bNewResult : BOOL; // TRUE every time when outgoing MultiArray was calculated and sent to transfer tray.
bError : BOOL; // TRUE if an error occurs.
hrErrorCode : HRESULT; // '< 0' = error; '> 0' = info; '0' = no error/info
END_VARbError: The output isTRUEif an error occurs.hrErrorCode: If an error occurs, a corresponding error code of the typeHRESULTis output. Possible values are described in the List of error codes. This output is identical to the return value of the method.
 | If a timeout occurs or no MultiArray buffer is available for the result, then neither the input data nor the result data are lost. They are forwarded on the next call. |
Configure():
The method for mean stress correction can be configured by calling this method. The selection is made via values of the type E_CM_MeanStressCorrection. Further information can be found in the section Fatigue life analysis and damage calculation.
- Return value: If an error occurs, a corresponding error code of the type
HRESULTis output. Possible values are described in the List of error codes.
METHOD Configure : HRESULT
VAR_INPUT
pArg : POINTER TO UDINT; // pointer to 1-dimensional array (UDINT) of arguments
nArgSize : UDINT; // size of arguments buffer in bytes
END_VARThe input buffers correspond to one of the following definitions (input shape). The variable parameters are part of the function block input stInitPars.
Versions | Input buffer (MultiArray input stream) |
|---|---|
Identical configuration of all channels and subchannels |
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Channel-specific configuration |
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METHOD Init : HRESULT
VAR_INPUT
stInitPars : ST_CM_MeanStressCorrection_InitPars; // init parameter
nOwnID : UDINT; // ID for this FB instance
aDestIDs : ARRAY[1..cCMA_MaxDest] OF UDINT; // IDs of destinations for output
nResultBuffers : UDINT := 4; // number of MultiArrays which should be initialized for results (0 for no initialization)
END_VARInit():
This method is not usually necessary in a Condition Monitoring application. It offers an alternative to the function block initialization. The Init() method may only be called during the initialization phase of the PLC. It cannot be used at runtime. You are referred to the use of an FB_init method or the attribute 'call_after_init' (see TwinCAT PLC reference). In addition, this facilitates the function block encapsulation.
The input parameters of the function block instance may not be assigned in the declaration if the initialization is to take place using the Init() method.
- Return value: If an error occurs, a corresponding error code of the type
HRESULTis output. Possible values are described in the List of error codes.
stInitPars: Function block-specific structure with initialization parameters of the type ST_CM_MeanStressCorrection_InitPars. The parameters must correlate to the above definition of the input and output buffers.nOwnID: 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.aDestIDs: Defines the destinations to which the results are to be forwarded by specifying the IDs of the destinations. The definition of the output buffer (as described above) must correlate to the definition of the input buffer of each selected destination.nResultBuffers: The function block initializes a Transfer Tray Stream with the specified number of MultiArray buffers. The default value is four.
PassInputs():
As long as an FB_CMA_Source instance is called and signal data are thus transferred to a target block, all further function blocks of the analysis chain have to be called cyclically as explained in the API PLC Reference.
Sometimes it is useful not to execute an algorithm for a certain time. For example, some algorithms should be executed only after prior training or configuration. The function block must be called cyclically, but it is sufficient for the data arriving at the function block to be forwarded in the communication ring. This is done using the PassInputs() method in place of the Call() method. The algorithm itself is not called here, and accordingly no result is calculated and no output buffer generated.
- Return value: If an error occurs, a corresponding error code of the type
HRESULTis output. Possible values are described in the List of error codes.
METHOD PassInputs : HRESULT
VAR_INPUT
END_VARGetChannelErrors():
The method enables the querying of a list of the channel-specific return values when processing several channels (nChannels > 1). A call is useful in the case that the return value of the function block corresponds to one of the values eCM_InfRTime_AmbiguousChannelResults or eCM_ErrRTime_ErrornousChannelResults.
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Return value: Information on the reading process of the list of error codes. The value is set to
TRUEif the query was successful, otherwise toFALSE.
METHOD GetChannelErrors : BOOL
VAR_IN_OUT
aChannelErrors : ARRAY[*] OF HRESULT;
END_VAR
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aChannelErrors: Error list of the typeHRESULTof the lengthnChannels.
Similar function blocks
The function block FB_CMA_RainflowCounting uses a counting matrix of load and mean values calculated on the basis of the three-point rule.
The algorithm of the function block FB_CMA_MinersRule can be used to calculate the fatigue damage of components based on the counted half-cycles.
Requirements
Development environment | Target platform | PLC libraries to include |
|---|---|---|
TwinCAT v3.1.4022.25 | PC or CX (x86, x64) | Tc3_CM, Tc3_CM_Base |