Trigger system and controls
The trigger makes repetitive signals appear static on the oscilloscope display by repeating the same part of the input signal. The display on the screen would be completely confusing if any distraction would begin at a different location on the signal (Figure 2).The trigger function of an oscilloscope synchronizes the horizontal deflection at a fixed point of the signal. This is essential for accurate signal reconstruction. Trigger controls can be used to stabilize repetitive signals and record single-shot signals.
The simplest and most common trigger mode is edge triggering. Also, many digital oscilloscopes offer a variety of special trigger settings. These triggers respond to certain states of the input signal. This makes it easy to detect, for example, an impermissibly narrow pulse. It would be impossible to detect this condition with just a flank trigger (voltage threshold).
Advanced trigger features include:
- Pattern lock-triggering
- Serial bit pattern triggering
- A and B triggering
- Search and mark triggering
- trigger correction
- Bit pattern triggering on certain standard signals (I2C, CAN, LIN)
The pre-trigger display
By changing the horizontal trigger position, you can gain insights into the signal behavior before a trigger event. This is called pre-triggering. The detected signal is divided into parts before and after a trigger point.
The pre-trigger display is a valuable tool for troubleshooting. If a problem occurs intermittently, you can trigger on the problem and record the events that led to the problem, thereby identifying the cause.
Various trigger sources
The oscilloscope does not necessarily have to be triggered by the displayed signal. Several sources can trigger the distraction:
- An arbitrary input channel
- Another external source except for the signal of the input channel
- The power supply signal
- An internally generated by the oscilloscope signal from one or more input channels defined
In most cases, you can leave the oscilloscope set to trigger on the channel shown. Some oscilloscopes have a trigger output that can transmit the trigger signal to another device.
The two trigger modes
The trigger mode determines whether the oscilloscope displays a signal based on a signal condition or not. Common trigger modes are:
- Normal mode: The oscilloscope only produces a representation of the signal when the input signal reaches the trigger point. Otherwise, the screen is blank or frozen on the last detected signal.
- Auto Mode: In auto mode, the oscilloscope will signal even if there is no trigger. If no signal is present, a timer in the oscilloscope triggers the distraction. This ensures that the display does not disappear when the signal does not trigger.