In most cases, it is about the measurement of periodic signals; a good example would be our alternating current. The so-called “trigger” helps us to create a static image.
Over time, many different triggers have been developed. A simple variant is based only on exceeding or falling below a predetermined voltage level. In this way, the individual signal periods can always be superimposed exactly with the result that this results in a sort of static picture. Modern oscilloscopes offer the option of feeding and using external trigger signals if required. For the less professional user, oscilloscopes (today) are equipped with an automatic trigger mode. In this case, the (intelligent) device recognizes recurring signal states and accordingly controls the beam run itself.
A trigger synchronizes the horizontal deflection at a fixed point on the signal. The benefit for you is evident with a trigger you can:
- stabilize repetitive signals (appear static)
- you can accurately capture single-shot signals
Which triggering methods are there?
Recognize specific extreme characteristics of impulses take a closer look at these features. For example, edge triggering is one of the simple trigger methods. Of course, depending on the oscilloscope, there are various other triggering methods. These automatically start at individual states of the signal and make the evaluation easier for you. With trigger methods can be, for example:
- isolate certain events
- Determine impulses that have an absolute amplitude (e.,g. runt pulses)
- Determine pulses determined by time factors (pulse width, glitch, slew rate, setup-and-hold, and timeout)
- Identify impulses that stand out due to a logical pattern (logic trigger)
Specifically, there are the following extended trigger methods:
- Pattern lock-triggering
- Marking and search triggering
- trigger correction
- Serial bit pattern triggering
- A and B triggering
- Bit pattern triggering on standard signals (I2C, CAN, LIN)
The trigger mode setting determines whether your device is signaling based on a signal condition. Here one differentiates generally under the car and the normal mode.
- Auto Mode: In this mode, the oscilloscope always shows a signal. Even if no trigger is applied – then the next period of the sawtooth voltage is generated. This will also show the display if no trigger has been triggered.
- Normal mode: In this mode, the screen will be blank until the signal reaches the trigger point and thus really triggers the trigger.
You can also force the trigger on different sources. The following settings are available for most oscilloscopes:
- CH: any input channel (CH)
- EXT: external source
- INT: a signal generated internally by the oscilloscope
- LINE: a power signal
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.
Your digital oscilloscope is continuously recording and storing the message. In this memory (defined by the memory depth), you can always recall the last N samples of the signal. However, only with triggered triggering, these signals are shown. This data storage in the memory you can also signal components before the trigger point display (pre-triggering, English pre-triggering).
By default, the trigger point is always in the middle. However, you can move it with the horizontal positioning to the left or right to make comprehensive analyzes around it.
What else you should know about triggers
Modern digital oscilloscopes also allow trigger options on defined waveforms, which could, for. B. be a slope or the pulse width. For serial data transmission measurements, the following triggers play an essential role:
- The start/stop condition on the I2C buses
- For CAN signals, the “Start of Frame.”
- TV signals
In many applications, the sensitivity of the trigger must be switched off for specified minimum periods. This is achieved by the vital holdoff (hold-off) function.