Manfred Weber
Metra Mess- und Frequenztechnik in Radebeul e.K.
PC Vibration Measurement System VibroMetra


The trigger control panel is available in all FFT modes except the automatic mode. Without trigger, the FFT is carried out continuously with the measured data from time domain. By using a trigger, the FFT only starts after defined conditions have been fulfilled. This way, the analysis can be carried out synchronized with rotation speed or shocks can be evaluated purposefully.
Use VM-SCOPE as trigger source if you also want to watch the respective time signal immediately.

Trigger on / off

1. Trigger on / off
Enables / disables the trigger function.

Trigger source

2. Trigger source
All channels of the instrument can be selected. If the signal in time domain exceeds the trigger level, the trigger is initiated.
All digital inputs of the USB devices with licenses for VM-FFT are available as trigger source. This way, several VM-FFT channels can be fed from the same digital input. It allows for instance triggering synchronized with rotation speed in several VM-FFTs. The trigger is initiated if the value switches from 0 to 1.

Trigger mode

3. Trigger mode
Trigger repeatedly
After a triggered FFT, the trigger is ready again. If the trigger condition is met again, a new FFT will be carried out.
Single shot
After having carried out a triggered FFT, VM-FFT stops.

Pretrigger and posttrigger

4. Pretrigger and posttrigger
The beginning of the time frame to be analyzed can be shifted with regard to the start of the trigger. A pretrigger of 0 means that the start of the trigger and the beginning of the time frame to be analyzed coincide. Accordingly, the beginning of the time frame is before the start of the tigger when entering a value >0.

Trigger level

5. Trigger level
When selecting an analog trigger source, the level of the measurand in time domain is displayed in a bar graph. The measurand is bandpass filtered with the frequency limits entered in the FFT settings and displayed as absolute peak value.
When selecting a digital trigger source, a colored field shows the current digital level.
  • white:
  • black:
level = 0
level = 1