scope.getAmplitudes()
scope.getAmplitudes(freqs, [binWidth], [aggregation]) → objectExtracts amplitudes at named fault frequencies or frequency bands from the most recent FFT.
Reads amplitudes out of the most recent capture's spectrum and returns an
object with the same keys as the input, ready to assign to an io group for
datalogging.
Each entry in freqs maps a label to either:
- a single frequency in Hz — read using the default
binWidthandaggregation; or - an array
[fMin, fMax, aggregation]— a band, e.g.[3500, 12000, "RMS"]or[3500, 24000, "AVG"].
Each label also automatically creates a marker on the FFT amplitude chart for the associated capture.
Bearing fault frequencies. Fault frequencies are usually derived from the measured RPM using the bearing's geometry coefficients, e.g. for a Link-Belt F-B22463H:
function getFaultFrequencies(rpm){
return {
"Fundamental": rpm/60,
"Fundamental Train": 0.0071*rpm,
"Inner Ring Defect": 0.1717*rpm,
"Outer Ring Defect": 0.1283*rpm,
"Roller Defect": 0.0548*rpm,
"Pelton Cup": rpm/60*16,
"Generator Pole": rpm/60*10,
};
}
Arguments
| Name | Type | Required | Default | Description |
|---|---|---|---|---|
| freqs | object | yes | — | Map of "label": frequencyHz or "label": [fMin, fMax, aggregation] entries. |
| binWidth | number | optional | 3 | Width in FFT bins used for entries given as a single precise frequency. |
| aggregation | string | optional | "MAX" | Default aggregation for single-frequency entries: "MAX", "AVG" or "SUM" (bands may also use "RMS"). |
Returns
object
Same keys as freqs, with the measured amplitude for each.
Example
let amplitudes = scope.getAmplitudes(getFaultFrequencies(rpm),
2, // bins wide per precise frequency
"MAX"); // aggregation: "MAX","AVG","SUM"
// band amplitudes for lubrication film health
let hf = scope.getAmplitudes({ lubricationFilm: [3500, 24000, "AVG"] });
amplitudes.speed = rpm; // datalog the speed too
for(let i in hf){ amplitudes[i] = hf[i]; } // merge the hf measurements
io["Front Bearing"] = amplitudes; // everything in io is logged