Test Equipment: Oscillocopes

[picowatt]

Brian,

I thought I would add this regarding the trigger holdoff.

As in my previous post, when the trace reaches the far right side it returns to the left side very quickly and sits off screen waiting for the next trigger pulse.  Once the trace gets back over to the left side, the trace has to rearm itself to prepare for the next trigger pulse.  The trace normally rearms itself very quickly so it responds almost immediately to the first incoming trigger pulse that arrives after the trace returns to the left.

Adding trigger holdoff using the trigger holdoff control causes the trace to just sit there on the left side off screen ignoring any incoming trigger pulses for the amount of time the holdoff control is set for.  Once the holdoff time expires, the trace again rearms and begins scanning to the right on the first trigger pulse received after the holdoff period.

This can be useful when looking at a series of brief pulses separated by a fair amount of time (such as data bursts).

For now, set the holdoff to normal and leave it there until you become more familiar with your scope.  You will not be needing to use any trigger holdoff for a while.

PW   

[Brian516]

Good stuff guys, it's all comin together nicely now. I'm finally starting to understand this nifty tool.

I noticed that the 'Scope' Visualization in VLC media player is pretty accurate. I'm able to get the settings right on the Tek to pretty much match the traces that it shows.
Too bad it doesn't have XY mode, though. Is there something that I am missing where I'm able to get a more focused X-Y trace? I notice that it's a little bit better when I unplug my headphones, so maybe it's just the quality of sound from the PC output?

It's not the quality of the music files... I downloaded the .flac files. Turned off all enhancements everywhere.

Seems I figured it out... X1 probe, Max volume from the PC, 50 or 100mv/div, high intensity, unplug headphones (   )   I'm sure there's a way to add a little power into the signal to compensate for the HP loss, but that's for some time later on. Unless it's uber easy..

Brian

[TinselKoala]

I'd still like to see what the X-Y trace looks like. With no inputs (both channel input coupling switches to Ground) the X-Y display should give a single non-moving dot, that you can position to exact center screen with the vert and horz position controls and focus to a tiny dot. Don't leave it there too long or too bright, it will burn the phosphor. Then if you give both channels the same input from the calibrator you should see a diagonal line. (Both channel V/div at same settings)

[Brian516]

TK -

Here's a video of me going through the X-Y display test that you suggested.  I am able to get the centered dot with the inputs at Ground, but I do not get the single diagonal that it sounds like I should be getting. Let me know if you need any more info than what I gave about my settings.  Hopefully it's just a human error issue, or at most a calibration issue.

In the video I had the probes on X1.  I tried it before the vid with X10 and the only difference it made was where I had to have my V/div set, and gave the exact same traces.

https://www.youtube.com/watch?v=jnsx32d2krY

[TinselKoala]

Hmm. That looks "almost" normal, but there should be only a single diagonal line between the endpoint dots. Let's make sure you have the scope set properly.

The Time/Div switches should be locked together and on X-Y mode, the "Var" knob in the cal detent. Horizontal Display in "A" . For looking at the calibrator signal, the V/div controls should both be set to the same value and the "var" knob in its cal detent. No Bandwidth Limit. Yes, the Vert Mode should be in CH2 for the x-y display. CH2 "invert" out, not inverted. AC-coupled inputs should help center the X-Y display, that at least looks like it is working right. The x-y display is not triggered so the trigger controls shouldn't make any difference. Be careful about the Intensity control. If the display is working correctly you should be able to get decent brightness of the diagonal line without blasting out the endpoint dots.

Don't connect your probe Grounds to the Calibrator output! This short-circuits the Calibrator! The probe grounds are already connected to the Chassis ground internally by the BNC connectors and you should not have to connect them to anything when using the Calibrator... especially not the Calibrator output!
Please use 10x probe attenuation whenever possible, and set the V/div knobs appropriately!

The display "should" be a single diagonal line between the two endpoints. The scaling and angle of the line depends on the V/div settings of the channels. If both V/div knobs are set the same the line should be 45 degrees, sloping up from left to right, and the length scaled by the V/div settings.

If the display is different from that, like with the two lines, and the scope is set properly, there may be an issue with calibration, or the probes themselves even. Please repeat the test with the probes set to 10x and let's see if you can get a nice single diagonal line, bearing in mind what I said above. You may want to check and adjust the probe compensation adjustments again, using 10x attenuation, the normal time-domain display and the nice square wave from the calibrator according to the instructions for doing that.

(When the x-y display deviates from the single diagonal line this normally means that the two signals are out-of-phase. With both V/div knobs set the same, a perfect circle means 90 degrees out-of-phase and a diagonal line sloping _down_ from L to R indicates 180 degrees out-of-phase. See the image attached below. Since both signals are coming from the same Calibrator source they should be perfectly in phase. So there is some issue here, again presuming that the controls and probes are set properly.)

I noticed that it looks like both V/div readout lights are on in the upper V/div switch. This is a fault. When there is no probe with a readout pin connected, only the "1x" light should be on, and you need to remember to read the knob scale at the unlit 10x position when you are using 10x attenuation on your probe.
OH>>> never mind, I took another look and it seems that that is just a glare from the room light reflecting on the switch. Never mind....