FFT_SPECTRUM
Dominant-frequency and amplitude estimator by hysteretic zero-crossing timing — an honest scan-based estimator, NOT a Fourier transform.
When to use it
Use FFT_SPECTRUM when the repetition rate of a periodic signal is wanted from inside the PLC scan — a shaft or fan turning, a compressor surging, a control loop hunting, a level oscillating in a tank — and a single dominant frequency is the answer, not a spectrum.
Interface
The published port signature. This is the whole of what the block exposes to your program — the implementation body is not shown here and ships with the download.
Inputs
| Port | Type | Unit |
|---|---|---|
| IN | REAL | EU |
| IN_OK | BOOL | — |
| FS | REAL | Hz |
| MIN_HZ | REAL | Hz |
| HYST | REAL | EU |
| DC_TAU | TIME | — |
| MIN_CYCLES | UINT | — |
| RESET | BOOL | — |
| ACK | BOOL | — |
Outputs
| Port | Type | Unit |
|---|---|---|
| PEAK_HZ | REAL | Hz |
| PEAK_AMP | REAL | EU |
| VALID | BOOL | — |
| CYCLES | UINT | — |
| SETTLING | BOOL | — |
| FS_USED | REAL | Hz |
| ALM_NO_SIGNAL | BOOL | — |
| ALM_UNRESOLVED | BOOL | — |
| ALM_SIG_FAULT | BOOL | — |
| ALM_CFG_ERR | BOOL | — |
IEC 61499 event interface
EI INIT, REQ·EO INITO, CNF
Validation evidence
- Tests
- 11
- Simulated scans
- 4521
- Simulator
- v0.1.0
Complete IEC 61131-3 implementation with a published test suite that runs on the vplant simulator. The counts above are that suite, executed on this build.
- Conforms to IEC 61131-3
- Conforms to IEC 61499
Download FFT_SPECTRUM — free
Create a free Ri Tech account to download the block. You get the Structured Text body, the Rockwell Add-On Instruction (.L5X), the Schneider Control Expert DFB (.XDB), PLCopen XML, the IEC 61499 function block type (.fbt) and the datasheet.
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Source is never published on this page. The implementation is released to a signed-in Ri Tech account — free of charge, but never anonymously.