FFT+ for AVEVA PI Vision

PI Vision FFT chart to find oscillations in PI data

See which cycles hide in a PI tag. FFT+ turns the values of a time range into a frequency spectrum in your PI Vision display, so a loop that cycles every minute or a disturbance that returns every hour shows up as a clear peak.

Request a trial Explore Vision Library+

Read the FFT+ documentation →

FFT+ in PI Vision showing the frequency spectrum of a one-second demo tag on a logarithmic period axis from 2 seconds to 1 hour, with its three strongest peaks labelled at about 20 seconds, 30 seconds and 1 minute, next to the Spectrum settings with spectrum type Peak, averaging None, peak markers on, top peaks 3, linear detrend, remove mean and the Hann window
FFT+ v2.0 in PI Vision: one hour of a one-second tag as a spectrum of periods, with the top three peaks labelled. Demo data. Select the image to enlarge.

PI Vision FFT chart from interpolated PI data

FFT+ samples each PI tag at an even interval over the time range and turns it into a spectrum, with the signal processing options an engineer expects.

Even sampling from the PI archive

The spectrum is only as good as its samples, so FFT+ picks an even interval that fits the time range and shows you the interval it applied.

  • Automatic interval from the time range and Max samples, or a fixed interval of one second or longer, rounded up to a preset step.
  • From 256 to 4,096 samples per trace; more samples give a finer frequency resolution.
  • The target or requested interval and the applied interval shown in the settings.
  • Display time range, a custom range, or a duration and offset, with Sync Time.
FFT+ Sampling settings with Interval Mode Auto, an auto target and applied interval of 1 second, the note that the auto interval is based on the selected duration and Max samples, Max samples 4096, Sync Time and the display time range
Sampling settings with the target and the applied interval. Select the image to enlarge.

Spectrum type, averaging and windows

Choose how amplitude is expressed and how the signal is prepared, so the real cycles stand out from the noise.

  • Peak, RMS, Peak-to-Peak or power spectral density (PSD).
  • Welch averaging with an automatic or manual segment length and 0, 25, 50 or 75 % overlap.
  • Remove mean and linear detrend, so offsets and slow drift do not swamp the spectrum.
  • Hann, Hamming, Flat Top or Blackman-Harris window, or none.
FFT+ spectrum of the same demo tag with Welch averaging, smoother and with broader peaks labelled at about 20 seconds, 30 seconds and 57 seconds, next to the Spectrum settings with averaging Welch, segment length Auto, overlap 50 %, peak markers, top peaks 3, linear detrend, remove mean and the Hann window
Welch averaging smooths the spectrum at the cost of broader peaks. Demo data. Select the image to enlarge.

Find the dominant frequencies and match known ones

Let the chart label the strongest peaks, and mark the frequencies you already know, so you can tell at a glance which cycle is which.

Top peaks labelled on the spectrum

Switch on peak markers and FFT+ finds the strongest peaks of every trace and labels them with their frequency or period.

  • One to 100 top peaks per trace.
  • Each peak marked with a dot, a label and a dashed guide line.
  • Labels in Hz, or as the length of one cycle when the axis shows Duration.
  • Top peaks switched on or off from Quick Settings on the chart.
FFT+ spectrum on a logarithmic period axis with the three strongest peaks labelled 00:00:19.98, 00:00:29.898 and 00:01:00.235, each with a dot and a dashed guide line, and the Quick Settings gear on the chart
The three strongest peaks labelled as periods: about 20 s, 30 s and 1 min. Demo data. Select the image to enlarge.

Overlays at known frequencies

Add the frequencies you expect, such as a pump’s stroke rate, an agitator speed or a known control cycle, and see whether a peak lines up with them.

  • Overlays added one by one, each with a label, a frequency in Hz and a colour.
  • Drawn as labelled dashed lines across the spectrum.
  • Converted to the period automatically when the axis shows Duration.
FFT+ spectrum with two labelled dashed overlay lines, Agitator at 0.04 Hz (25 seconds) and Pump stroke at 0.0167 Hz (about 1 minute), the second lining up with the strongest peak, next to the Fault Overlays settings with the hint that frequencies are entered in Hz and converted for the Duration axis, Add Overlay, and the label, frequency and colour of each overlay
Two known cycles as overlays; the pump stroke lines up with the strongest peak. Demo data. Select the image to enlarge.

Frequency spectrum scales, traces and quick settings

Read the spectrum the way your process works, compare several tags, and change the view right on the chart.

Frequency or period, linear or logarithmic

Process cycles are often easier to read as a period, other signals as a frequency, and small peaks next to a large one need a different scale.

  • Hz, or Duration to show the length of one cycle, such as 00:01:00 for one cycle a minute.
  • Linear or logarithmic frequency axis, so short and long cycles fit on one chart.
  • Linear or logarithmic amplitude axis, to bring small peaks into view.
  • Automatic or custom scale range, axis position, title and ticks.
FFT+ spectrum of the same demo tag in Hz on a logarithmic axis from 0.0005 to 0.5 Hz, with the strongest peak near 0.0167 Hz, further peaks near 0.033 and 0.05 Hz and their harmonics
The same spectrum in Hz on a log axis: the one-minute cycle at about 0.0167 Hz and its harmonics. Demo data. Select the image to enlarge.

Several tags on one spectrum

Compare the spectra of related tags, such as a controller’s process value and output, to see whether they share the same cycle.

  • One shared amplitude scale, one scale per trace, or named custom scales.
  • Label, colour, curve and markers per trace.
  • Legend with size and colour options.
  • Grid lines, bands and border.
FFT+ comparing the spectra of four demo sinusoid tags in different colours with a legend, the two one-second tags overlapping, next to the Trace Options with the trace list and the label, colour, curve and markers of the selected trace
Four tags on one spectrum, with the Trace Options of one trace. Demo data. Select the image to enlarge.

Quick Settings, zoom and download

Change the view without opening the configuration pane, zoom into a band, or take the spectrum with you.

  • Quick Settings on the chart: Hz or duration, linear or log axes, layout, spectrum type, window and top peaks.
  • Pan, box zoom, zoom in, zoom out and reset on the toolbar.
  • Full screen view of the spectrum.
  • Download as PNG, SVG or PDF, or the spectrum as CSV, JSON or XLSX with one row per frequency.
FFT+ with the Quick Settings menu open over the chart, with X axis format Hz or Duration and spacing Linear or Log, Y axis values Linear or Log and layout Single, spectrum type Peak, window Hann and Show Top Peaks
The Quick Settings menu, opened from the gear on the chart. Demo data. Select the image to enlarge.

PI Vision FFT chart examples

Four common ways teams use FFT+ on their displays.

Oscillating control loop

Data
Process value and controller output of one loop, recorded every second
Settings
Fixed 1-second interval, Duration format, top three peaks
Shows
The period at which the loop cycles, and whether value and output share it

Repeating process disturbance

Data
A flow, pressure or temperature over several hours
Settings
Automatic interval, Welch averaging, log period axis
Shows
Cycles that return every few minutes or hours, for example from a switching compressor or a batch step

Known equipment cycles

Data
A process tag and the known cycle of a pump, agitator or timer
Settings
Fault overlays at the known frequencies, peak markers on
Shows
Whether a peak in the data lines up with a known cycle

Before and after a tuning change

Data
The same tag in two FFT+ symbols with custom time ranges
Settings
Same interval, samples and window in both
Shows
Whether the dominant peak disappeared after the change

Related symbols: Combo Chart+ for the signal itself as a trend with limits and statistics, Period Comparison Chart+ to compare the same period across days or weeks, Histogram+ for the distribution of a value, and Box Plot+ for quartiles and outliers.

FFT+ FAQ

Questions we are asked most often. Read the FFT+ documentation or ask a technical question.

When should I use an FFT chart in PI Vision?

Use FFT+ when a signal repeats and you want to know how often: a control loop that cycles, a disturbance that comes back every few minutes, or a pattern that repeats every shift. Each repeating component appears as a peak at its frequency or period. To see the signal itself over time, use a trend.

Which frequencies can FFT+ show?

FFT+ samples interpolated values from the PI archive at an even interval of one second or longer. The highest frequency it can show is half the sample rate: 0.5 Hz, or a period of two seconds, at a one-second interval. The longest cycle is limited by the time range. The tag should be recorded at least as often as the interval, because interpolating between sparse archive values adds no information. Machine vibration at running speed or bearing frequencies needs high-rate data from a dedicated vibration monitoring system.

Should the axis show Hz or the period?

For process data the Duration format is usually easier to read: a peak at 00:01:00 is a cycle that repeats once a minute. Hz suits signals you already think of in frequencies. Fault overlays are always entered in Hz and are converted when the axis shows durations.

How do I get a cleaner spectrum?

Switch on Welch averaging to smooth random noise, at the cost of broader peaks. Keep Remove mean and Linear detrend on so offsets and slow drift do not hide the peaks, and choose a window: Hann for general use, Flat Top for accurate peak heights, and Blackman-Harris for a small peak next to a large one. More samples give sharper peaks.

What do we need to run it?

PI Vision 2021 or later with PI Web API, and PI AF Server 2018 SP2 or later. FFT+ runs in PI Vision and uses each user’s existing PI permissions.

How do we get FFT+?

FFT+ is part of Vision Library+, together with the other Vision Library+ symbols. Request a trial to test it in your own PI Vision environment.

Try FFT+ in your PI Vision

FFT+ is included in Vision Library+, the PI Vision custom symbol library from Software Athlete. Test it on your own displays and data.

Request a trialBook a live demo

Browse all Vision Library+ symbols · FFT+ documentation