TRND – Real-time trend recording

Block SymbolLicensing group: STANDARD

Function Description
The TRND block is designed for storing of up to 4 input signals (u1 to u4) in cyclic buffers in the memory of the target device. The main advantage of the TRND block is the synchronization with the real-time executive, which allows trending of even very fast signals (i.e. with very high sampling frequency). In contrary to asynchronous data storing in the higher level operator machine (host), there are no lost or multiply stored samples. For better clarity, the individual trends can be assigned names by the Title parameter and the individual signals by the SigNames parameter.

The actual number of stored signals is determined by the parameter n. In case the trend buffers of length l samples get full, the oldest samples are overwritten. Data can be stored once in pfac executions of the block (decimation), i.e. with the period $pfac\cdot T_s$, where $T_s$ is the period of the block execution [s]. The stored data can be further processed according to the values of the parameters ptype1 to ptype4. The other decimation factor afac can be used for storing data in archives. The period of storing is then given by $afac\cdot pfac\cdot T_s$. Each value is stored with a time stamp. The source of the time stamp can be set by the timesrc parameter (see the TS block for more information).

The list of archives for storing is specified by the arc parameter, e.g. 1,3..5,8. The event will be stored in all specified archives. Each archiving block must have a unique event identification code in the archive given by the id parameter. For more information about these parameters see the introduction of Chapter 10.

The type of trend buffers can be specified in order to conserve memory of the target device. The memory requirements of the trend buffers are defined by the formula $s\cdot \mathtt{\text{n}}\cdot \mathtt{\text{l}}$, where $s$ is the size of the corresponding variable in bytes. The default type Double consumes 8 bytes per sample, thus for storing $\mathtt{\text{n}}=4$ trends of this type and length $\mathtt{\text{l}}=1000$, $8\cdot 4\cdot 1000=32000$ bytes are required. In case the input signals come from 16-bit A/D converter the Word type can be used and memory requirements drop to one quarter. Memory requirements and allowed ranges of individual types are summarized in table 1.1 in this reference guide.

It can happen that the processed input value exceeds the representable limits when using different type of buffer than Double. In such a case the highest (lowest) representable number of the corresponding type is stored in the buffer and an error is binary encoded to the iE output according to the following table (the unused bits are omitted):

In case of simultaneous errors the resulting error code is given by the sum of the weights of individual errors. Note that underflow and overflow cannot happen simultaneously on a single input.

It is possible to read, display and export the stored data by the REXYGEN Studio in the Watch mode. After double-clicking on the corresponding TRND block, a new card with the prefix Trend will open.

WARNING: set any of the parameters arc, afac, id to 0/empty disable writing data into archive. The data are available in diagnostic tools only in this case.

This block does not propagate the signal quality. More information can be found in the 1.4 section.

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