What is the difference between edge and level triggering in an oscilloscope?

What's the exact difference between edge and level triggering in an oscilloscope? I have searched the Tectronix book but I couldn't find level triggering at all. I am quite confused. Could you help me?


Thanks a lot...

When I turn the knob on my Tektronix scope to 'Auto' (full left)...

Then it will begin a trace when the incoming signal crosses zero going upward.

What if the incoming signal isn't going anywhere? Then traces go across the screen anyway although with a miniscule pause between each one.

This mode is convenient as an all-purpose mode. It's less trouble to see where the beam is at all times.

When I turn the knob to 'Level'...

Then I can select an arbitrary volt level. The incoming signal must cross it in order for a trace to begin.

It allows me to examine all parts of a waveform at a greater magnification. I turn the knob and I can simply dial the entire waveform so it moves from left to right or right to left.

For a complicated waveform, I can set the knob near the peak of the waveform and see a stable image. Otherwise it would trigger at different points on the waveform, and give me jittery images.

What if the incoming signal isn't going anywhere? Then the screen stays dark. If I were uninitiated, I might think something was wrong with the beam.

So this mode is sort of an advanced mode.

AS the "edge " trigger relies on a fast transition to trigger the time base if you looked at a slow (20 HZ sinewave) wave form the Dv/Dt might not be high enough to trigger so you use the "level" setting.
Frank

BradtheRad said:

When I turn the knob on my Tektronix scope to 'Auto' (full left)...

Then it will begin a trace when the incoming signal crosses zero going upward.

What if the incoming signal isn't going anywhere? Then traces go across the screen anyway although with a miniscule pause between each one.

This mode is convenient as an all-purpose mode. It's less trouble to see where the beam is at all times.

When I turn the knob to 'Level'...

Then I can select an arbitrary volt level. The incoming signal must cross it in order for a trace to begin.

It allows me to examine all parts of a waveform at a greater magnification. I turn the knob and I can simply dial the entire waveform so it moves from left to right or right to left.

For a complicated waveform, I can set the knob near the peak of the waveform and see a stable image. Otherwise it would trigger at different points on the waveform, and give me jittery images.

What if the incoming signal isn't going anywhere? Then the screen stays dark. If I were uninitiated, I might think something was wrong with the beam.

So this mode is sort of an advanced mode.

Click to expand...

I know about level triggering (that we change the voltage level) but what really happens in "edge" triggering?

Thanks a lot...

Differentiator, it looks for a high rate of change, like a digital state transition on a data line.

Dear Sherlock,
Tektronics have long been for >50yrs masters of the trigger design. They use a wide variety of input signal conditioning for HPF, LPF and once used a PLL for retriggerable stable windowed time base control. They also have video trigger so the negative sync pulses are not used but rather the flat level after sync pulse which is defined as the black level for clamping to gnd and triggering off the trailing edge of sync tip, even if the video has a larger swing in same direction and is AC coupled.

Consider using the View trigger source signal and view the threshold cursor to see where you are. If you are unable to gain sync. you may need a clock recover cct or use the transmit source for trigger if there is excessive noise. If the noise is spurious a band shaping filter may need to be designed to tune in the spurious signal and reject the unwanted signal using a simple external cct. If you are doing receiver eye pattern tests for example a PLL clock recovery a stable trigger is critical. Sometimes a delayed holdoff to provide sub-harmonic re-triggering. e.g. edge/4 rate or edge / 16 rate or frame rate is needed. But the jitter in your measurement is also controlled by the jitter of your trigger source, so a stable reference is critical. One method is a synthesizer with low phase noise to arm the scope and then next edge to trigger it at the slicer level of the trigger.

I have been a Test Engineer & designer since 1975 and presently use 150MHz Tek DSO but have used all the great CRT SS and tube design scopes made by HP and Tek. Another approach is simply a Logic Analyzer with Analog input and sufficient memory to record a large interval.


all triggering is done by direction of edge and threshold of trigger, but many parameters can modify the source signal as stated above such as delayed trigger, input filters and delayed sweep from frame-rate or fundamental base-rate trigger or PLL or BPF clock recovery to reduce jitter of trigger.

I once used 60Hz to measure doppler and diurnal shift of VLF 15KHz, since our grid power is synch'd to better than 1e-12 frequency source for grid sharing AC. until I designed a PLL clock trigger.

Can you expand on your signal properties? f, level, SNR, interference qualities. desired outcome?

SherlockBenedict said:

I know about level triggering (that we change the voltage level) but what really happens in "edge" triggering?

Thanks a lot...

Click to expand...

if you recall that 'trigerring' in oscilloscope refers to ' when to start the timebase".
in level triggering, you set the level and timebase will start everytime only when the set level is reached in input.

in edge triggering , you specify the edges(rising or falling).
so that when the specified edge is seen , time base starts.
edge triggering is useful mostly in digital circuits. you trigger on reqd edge of say , "'clock' pulse +ve edge" and see stable waveforms on the channels.