Trigger

A trigger decides when recording starts and when it stops. With no trigger set, recording starts when you press Record and ends when you press Stop — that is the default. With a trigger set, pressing Record arms the recorder instead: the software watches the channel you nominated and only writes to disk once the condition is met.

The Trigger tab is where you set this up (Start page → Acquisition → Trigger Setup; it is also created alongside Channel Setup and Online Monitor when you pick a frontend). The page itself is a live scope; the parameters sit in the properties panel on the right, in three groups: Start Trigger, Stop Trigger and After Stop.

Triggers apply to recording only. Preview is for looking at the signal and tuning the threshold; it is not gated by the trigger conditions and writes nothing to disk.

Start trigger

Type	Meaning
Manual	Recording starts when you press Record (default).
Level	Starts when the source channel crosses a threshold. The threshold is in the source channel's physical unit (Pa, m/s², N, V…) — not volts, unless that channel is itself a voltage channel.
RPM	Starts when the speed crosses a threshold. The source is a pulse / speed channel and the threshold is in rpm.

Slope

Up triggers on a crossing from below; Down on a crossing from above. Use Up for a run-up, Down for a coast-down.

Hysteresis

Hysteresis is an arming band, not a debounce time. With slope Up the signal must first fall below Level − Hysteresis before another crossing counts as a new trigger; with slope Down it must first rise above Level + Hysteresis.

Set it above the noise floor and a signal that sits near the threshold stops re-triggering — the usual cause of "it recorded fifteen takes for no reason" in multi-take runs.

Pre-trigger

Also keep this much data from before the trigger instant. Essential for impact / SRS work: by the time the level is crossed the rise is already over, so without a pre-trigger you cut off the part that matters. 0 means none.

The pre-trigger buffer starts filling when recording is armed (when you press Record). If the trigger fires before the buffer is full, whatever has been collected is kept — the take is not discarded. So if you need the full pre-trigger length, arm the recorder a moment before the event.

Stop trigger

Type	Meaning
Manual	Recording stops when you press Stop (default).
Level	Stops on a threshold crossing. Parameters mirror the start side (source, level, hysteresis, slope).
RPM	Stops when the speed crosses a threshold.
Duration	Stops after the number of seconds set in Duration. The simplest option: every take has exactly the same length.

Post-stop

Keep recording for a while after the stop condition is met — used to capture the tail of an event: decay, settling, the residual vibration after the machine has stopped.

Minimum record time

A hold-off for the stop condition: it is not evaluated at all until this much has been recorded.

When start and stop use the same channel and threshold, a single crossing can satisfy both and produce a zero-length take. The minimum record time is what prevents that. Set it whenever you record multiple takes.

After stop

Option	Meaning
Stop session	Write the take, return to idle, done (default).
Re-arm for next take	Write the take as its own file → clear the buffers and reset the detectors → wait for the next start condition. This is how you record many takes in a row.

Max takes limits how many are recorded automatically; 0 means unlimited.

Re-arm has a dead time: events occurring while a take is being written and the buffers are reset are NOT captured. The dead time of every take is written to the acquisition log — when events come close together, check the log before concluding "the test produced N events".

When Re-arm + unlimited takes + no minimum record time + no hysteresis are combined, the software refuses to start: that combination produces empty takes indefinitely. Set a minimum record time, a maximum number of takes, or a hysteresis.

Tuning: where to put the threshold

That is what the live scope on the Trigger page is for. With Preview running you see the waveform, the threshold line and the hysteresis band together, and you drag the line to where you want it — grabbing it works from about 9 pixels away, you do not have to hit the line exactly. The readouts at the bottom give the current peak and RMS, which is what you normally size a threshold against.

The Y range is fixed by default. It is fitted once to the first signal and the trigger lines, then held. A range that keeps rescaling changes the height of the threshold line relative to the waveform on every frame, which makes "where does this threshold sit in the signal" unreadable. Press Fit to refit; tick Y auto if you do want continuous rescaling.
The plot is drawn even with no data stream: the curve is empty (no fake zero line is drawn) but the threshold line and hysteresis band are still there — you can set thresholds before the hardware is connected.
If a threshold is typed outside the current range, the range expands so the line stays on screen.

"Source channel … is not present in the live stream" means that channel is not enabled in Channel Setup. Trigger detection reads the live stream, and a disabled channel is not in it.

How accurate is an RPM trigger?

Speed is evaluated once per data block, so the trigger instant is accurate to about one block — not to the sample, as a level trigger is. The first speed reading also needs two rising pulse edges, so there is no speed reading for the first moment after a start from standstill.

When the trigger instant has to be precise, use a level trigger (you can put one on the tacho pulse channel itself) rather than an RPM trigger.

Common setups

A fixed-length steady-state take: start = Manual or Level, stop = Duration. Equal-length takes make later batch comparison much easier.
A run-up: start = RPM, slope Up, at the starting speed; stop = RPM, slope Up, at the final speed. Put the hysteresis above the speed ripple.
Impacts: start = Level, slope Up, threshold above the noise floor; a pre-trigger is mandatory (tens to hundreds of ms); stop = Duration; for a series of hits use Re-arm with a minimum record time.
Unattended waiting for an event: start = Level; stop = Duration, or Level with a post-stop time; Re-arm with a maximum number of takes so the disk cannot fill up.

Checking what you actually configured

The summary line at the top of the properties panel condenses the whole setup into one sentence, e.g.

Start: Sound ↑ 1.5 Pa (hyst 0.3), pre 200 ms | Stop: after 30 s · Re-arm ×5

Reading that line before you arm is quicker than checking each field, and it is where a wrong source channel or a threshold that is off by a decade shows up first.