A couple 'scope questions

Been wondering these for quite a while but I never get around to asking:
1. On my scope I have a button for slope on/off. What does that do?
2. Why are there different coupling options? I have:
AC
HF TV-H
DC/LF TV-V
LINE
Which one should I use for what? I've always just used AC.
3. How do I use the external trig?

Thanks :lol:

1) it's not on/off, it's up/down. Selects whether the scope triggers on the rising or falling slope of the waveform.
2) AC triggering simply means that the dc component of the signal is removed. There should also be a DC position on the switch. These will be used with the level control to determine precisely where on the waveform the scope is triggered.
The tv-line position filters the trigger signal such that the trigger is more sensitive to high frequencies, the scope will be more likely to trigger on a fast change than a slow one. The tv-frame is the opposite of this, the scope is more likely to trigger on a gradual slope than a fast change. Use the tv-line if you are more interested in a sharp spike in a waveform, or the tv-frame if you are interested in low frequencies, say 200Hz or lower.
Line causes the scope to be triggered from the power line. Use this if you are interested in a signal derived from the power line. Looking for hum in an audio amplifier is a good example. The hum component will stay still on the screen while everything else moves.
External trig, you simply select ext and connect another probe to the ext trig socket. If you connect this to your signal source, you will get a trace locked to the signal, and you can look for that signal in a load of noise much more easily.
Play with the scope and try these things. You can't break it by twiddling knobs.

zachtheterrible said:

Been wondering these for quite a while but I never get around to asking:
1. On my scope I have a button for slope on/off. What does that do?
2. Why are there different coupling options? I have:
AC
HF TV-H
DC/LF TV-V
LINE
Which one should I use for what? I've always just used AC.
3. How do I use the external trig?

Thanks :lol:

Click to expand...

Zach, lets say you want to look at noise that is on a power supply rail. Maybe your 12V supply has 1mV of noise imposed on it. Well, normally you would hook the scope up with DC coupling and try and see the 1mV. The 1mV is very small compared to the 12V so it will be very tough to discern. The AC input coupling will block your 12V and only let the AC component pass so you can set the scope on say the 10mV range and look at the noise just fine. That's one example on when/how to use AC coupling.

Optikon said:

Zach, lets say you want to look at noise that is on a power supply rail. Maybe your 12V supply has 1mV of noise imposed on it. Well, normally you would hook the scope up with DC coupling and try and see the 1mV. The 1mV is very small compared to the 12V so it will be very tough to discern. The AC input coupling will block your 12V and only let the AC component pass so you can set the scope on say the 10mV range and look at the noise just fine. That's one example on when/how to use AC coupling.

Click to expand...

I think you've misunderstood? (or I have :lol: ), he's asking about triggering options, NOT input options.

Yeah, I already know about using AC to block the DC component of the signal. Nigel was right, I'm interested in the triggering part of it. I'm not interested in anything to do w/ the level controls, I already fully undertand those.

Spuffock, the AC that I'm talking about is not the one that is with the level controls. It is one of the four options under COUPLING. In other words, there are two AC settings. One with the level controls, and other w/ HF, LF, LINE. You explained everything beautifuly for me accept for the AC option under the COUPLING.

And as for slope, how do I know when to have it up or down?

I hope you understand, its sort of hard to explain :lol:

zachtheterrible said:

Yeah, I already know about using AC to block the DC component of the signal. Nigel was right, I'm interested in the triggering part of it. I'm not interested in anything to do w/ the level controls, I already fully undertand those.

Spuffock, the AC that I'm talking about is not the one that is with the level controls. It is one of the four options under COUPLING. In other words, there are two AC settings. One with the level controls, and other w/ HF, LF, LINE. You explained everything beautifuly for me accept for the AC option under the COUPLING.

Click to expand...

His explanation was still really correct, it's done for the same purpose, to allow triggering from a small AC signal sat on a large DC offset. It's always worth trying selecting either AC or DC and see if one is better than the other.

And as for slope, how do I know when to have it up or down?

I hope you understand, its sort of hard to explain :lol:

Click to expand...

Basically it determines where the trace starts, if you input a squarewave it means you can start the trace on either the LOW cycle or the HIGH cycle, switching the slope switch toggles betweent he two.

And again, you may sometimes find it's easier to lock if you selct the opposite slope setting, again simply try them both.

For an example:

Setting the head switching point in an old VCR, you trigger the scope externally from the head switching signal. The input of the scope is connected to the video output of the VCR.

With the VCR playing an alignment tape (or at least a known good recording) you expand the trace until you can see eight or nine lines across the screen (picture lines that is).

You then adjust one of the head switching point presets (essentially timing on a monostable) to match the required specification - something like 4.5 lines after frame sync.

To adjust the other one you don't need to move any probes, just flick the slope switch, and adjust the second switching point with it's corresponding preset.

Thanks Nigel, I fully understand my scope now :lol:

zachtheterrible said:

2. Why are there different coupling options? I have:

Click to expand...

Oh, I thought he was asking about coupling as a seperate #2 question.. which is assumed to be input coupling.. whoops! Sorry!