No.34 Trigger level and Hysteresis
The trigger function is used to set the timing of capturing the impact test data or the signal from the external device. One of trigger function settings is hysteresis. There are cases when the hysteresis value is set higher than the trigger level, the data may not be captured, or when the signal may be too small to trigger repeatedly, the expected signal may not be captured. We’ll explain about hysteresis this time
Trigger level： Specifies the voltage level at which the trigger is activated.
Hysteresis： Unless the band range set by hysteresis exceeds. the next trigger wait state will not occur.
Trigger position：Specifies the number of points before or after the trigger point, at which sampling start.
If 0, it is the beginning of the frame.
If -0340, it is 340 points of the one frame.
If +100, it is 100 points after the trigger point
Hysteresis and Pre-trigger1. There is no problem even if hysteresis is 0%.
If the signal is lower than the trigger level within one frame, the trigger position should be at the beginning of one frame since the impact waveform and response waveform must be captured within one frame.
Once the trigger is activated, the signal of one frame is captured and analyzed. After capturing one frame, the trigger is wait mode, thus the trigger will not be activated again within the one frame.
2. There is a problem if the hysteresis is not set correctly.
For example, if you analyze the signal that occurs before the trigger signal.
Correct setting； In the figure below, the hysteresis range is wider than the range of the waveform fluctuation, thus it responds only to the beginning of the first signal and the signal you want to analyze can be maintained.
As the hysteresis range is narrow, trigger is applied each waveform fluctuation. The waveform you want to analyze will be missed.
In the figure below, the hysteresis is narrow, thus the trigger is activated due to the fluctuation of the following signals, and the data acquisition is delayed. (orange framed)
By widening the hysteresis, it enables to detect the first rising waveform to be triggered and capture vibration waveform before the rising to perform averaging process. (red framed)
Before the measurement, check the time waveform on the screen and adjust the trigger level and hysteresis.