Oscilloscope: How to use Z-Axis input?

[Cifrocco]

I just purchased a new 20-MHz analog oscilloscope (GW Instek GOS-622G). Information on using a scope is difficult to find on the 'net, and the book I bought, by Stan Prentiss, "The Complete Guide to Oscilloscopes" is the most awful technical book ever written.

Anyways, I thought I'd throw some questions out to you folks on this forum to see if I could get some insight. One question I have at the moment is regarding the Z-Axis input found on the back of my scope. It is a female BNC connector. What uses does this input have? How does it appear on my scope? If anyone can give some application examples, I'd be grateful. Thanks.

 

[Nigel Goodwin]

One of my scopes is a GW GOS-522 20MHz scope, I bought it second hand, I've found it quite a decent little scope!.

Anyway, Z input - this is simply a brightness modulation input, so X is left to right, Y is up and down, Z is 'backwards and forwards'. Generally you need a high signal level to modulate it (spec on mine says 3V p-p, 50V max), but personally I've never had occasion to use it either at home, or at work.

One nice feature on mine (I don't know if your's has it?) is an output on the back from CH1, this allows you to connect a frequency counter after the preamp in the scope.

 

[mechie]

Z axis modulation

Cifrocco
"Z-mod" is not used for very much; I guess that's why it is demoted to a back-panel connection and with a fixed sensitivity :!:

The one application I can think of where it is used is in rotating machinery vibration diagnostics (still reading? good - stay with me on this...)
Imagine an engine (a car engine will do ). The crankshaft is rotating at some speed - say 3000 rpm (50 cycles per second, 20ms per cycle).
I want to measure the vibration of the crankshaft so I have installed two probes at right-angles to each other (see drawing), both watching the shaft move, one in the 'X' axis and one in the 'Y' axis.
If I connect these to the 'scope's two channels and switch the timebase to 'CH2' or however your 'scope displays Lissajous figures the 'scope display will start to scribble a rough cicle in the middle of the screen, the shape and size of this circle is proportional to the movement of the crankshaft (see attached drawing).
This is great if you just wan t to see how well the engine is balanced or how much play there is in the bearing but you can estimate the amount of unbalance in the crankshaft and where to fit a balancing weight if you can relate this display to shaft rotational position.
By adding a third probe (crank angle sensor?) to look for a single tooth on the shaft you can see a breif pulse as this tooth passes the probe. Use this to drive the Z-Axis and your lissajous display suddeny has a 'bright-up' on it showing exactly how the shaft moves and allowing its angle to be seen.

Well you did ask :!:

 

[Sebi]

When You use a wobbulator, maybe need this input for "intensity markers".
Anyway a friend of mine - in the very old time - made a TV receiver for scope. (when the chief appear, just switch the scope to analyzer...)

 

[Cifrocco]

Thank you, people, for your very informative responses, especially mechie, that was very interesting, thanks for taking the time. Nigel, you also answered another question I was intending to ask, regarding the Channel 1 output in the rear, which my scope possesses, too. I'll have to get a male-male BNC patch cable to connect a frequency counter to that output, as soon as I buy one (I'm looking at the GFC-8270 from GW Instek).