when the DS2072 is Chan 1 AC coupled and Trigger Setting is set to DC coupled
ACTs the Same as Chan 1 AC coupled and Trigger Setting is set to AC coupled
So why not show the orange line!!
Because it is not the same.....
If trigger mode is in DC, there is a relation with the showed grid on the display ( not the displayed signal )so the DSO can display a orange line.
If trigger on DC and is on 1 volt, there is a relation with 1 volt on the screen.
But in AC mode there is NO relation the the value next to the displayed grid
and the DSO does not now where to display the line, so it does not.
In AC trigger mode 1 volt can be anywhere on the screen.
Does this go back to old Scope devices,
because I would think this DS2000 can determine the trigger value that is used to set the position on the display ,
thus show the trigger level line
Below are 4 displays , (note trigger level in low left corner)
1. Input DC coupled with trigger DC coupled
2. Input DC coupled with trigger AC coupled (no trigger line)
3. Input AC coupled with trigger DC coupled
4. Input AC coupled with trigger AC coupled (no trigger line)
What is the Difference between 3 & 4?
Just my small preference
The difference is about 100 mV
In picture 3 trigger level is DC+AC, in picture 4 trigger level is AC
if the DC component is 0 or very small, then DC+AC=AC, thats why there is little difference.
More theory:
In DC trigger mode the trigger is fixed, even with no input, the level is fixed and kown.
In AC trigger mode the trigger is dynamic, trigger level is depeding of average AC signal, so not fixed
and its position is not kown.
If in AC trigger mode you change the shape of the waveform, the trigger point will shift, how do you want
this in an orange line on the screen, it will be not steady.
In AC trigger mode the average value of the AC voltage is the 0, this is the reference for the trigger, from there it calculating
the offset. Not from a fixed point.