If you don't have one already I would suggest just getting a good multimeter. Unless you plan to design your own circuitry there isn't much that you can't do with a meter vs a scope. I have been using scopes since the early '60s and can only think of a few times I fired one up trying to diagnose a problem with the layout or engine. Sorting a faulty Cab1 comes to mind. My $.02

Pete

You really will not find it useful in your layout.  A scope provides a picture of a signal, and used by engineers and technicians for troubleshooting waveforms of errant operation.  It really of very little value for a layout which is just AC or DC power on the rails. Unless you are an engineer and want to analyze the data packets (if this is possible) on the DCS rails, you are wasting money and investing in the proverbial "doorstop".  A (maybe poor) analogy is buying an expensive multipurpose workshop power tool that used once twice and never again.

Best bet is investing in a good portable handheld digital meter capable of measureing AC and DC voltage and can measure low (less than 1 ohm) resistance, and measure low AC and DC amperages (less than 20 amps).  Fluke, Meterman, and HP, are good brands albeit expensive.  Check at Harbor Freight or ebay and google for the device specifications.

Let us know what you find and gurus here can advise yeah or nay.

Phil,

Norton is right but Scopes are very cool.  You can find them at thrift shops for next to nothing.  They are fun to mess with.  Just my opinion.

Search youtube for oscilloscope tutorial and you will find more than you ever wanted to know.  Oscilloscopes let you see the electrons, Robert Moog let you hear them.

One such vid

1. No.  If this guy is your friend, he'll let you borrow his IF you ever need it!

2. Yes.  As a tool it provides unmatched insight.  Like an MRI in medicine, it is the gold standard for viewing exactly what's going on with electrical signals.

3. If you're an electronics novice, don't bother.  As others say, if you need to make measurements, a basic digital meter will be more bang for the buck.

You can waste a lot of time with a scope if you don't know what you're doing.  I have run into countless cases of degree'd engineers making faulty scope measurements on train circuits because they aren't familiar with the way our O-gauge AC train circuits operate (isolated rails, phased transformers, etc).  Of course you can also make mistakes using digital meters with some of the curiosities of O-gauge circuits (chopped sinewave controllers, pulsed motor drives, etc.).

We used to give prospective technicians a 'scope test.  We'd screw up a scope settings as much as we could, then maybe unplug it for good measure.  Bring him in and ask him to measure a simple waveform out of a signal generator.  You'd be surprised how many had no idea how to proceed.

While you can waste a lot of time with a 'scope, you can also see things you'd never see any other way.  Obviously, it helps to actually know what you're looking at.  Having used everything from simple analog 'scopes to some really expensive digital logic analyzers, I'd say this.  For the hobbyist the most useful model would probably be a dual-trace digital storage 'scope.  Analog models just don't allow you to see many of the things that you're trying to analyze.  With the price of digital 'scopes really plummeting, that's what I'd be looking at if you want the capability.

Thx, folks, for the varied & useful replies!  But, now I'll admit that my 1st post was a bit of a 'white lie', in order to obtain 1st reactions....Truth be told, I have already bought one!       Tektronix 1062 [60MHz BW, 2-channel, up to 1 GS/sec sample rate].

   Now I will move to 'phase 2' of my [nefarious?] plan: Let's please focus on my 3rd Q:

          What should i measure? [HOW, will hopefully be learned in due course.]

I'd like to be able to examine smoke units, radio boards, current & voltage spikes, and just maybe, some other PC boards.....BIG challenge!

            Any further tips/advice would be very-much appreciated!

BTW, I have several multi-meters, which I have used profitably....for resistors, voltages, and currents.

P.S. At this point in time while riding up the 'learning curve', I would probably fail the 'scope test mentioned above....

Phil,

As to what you can measure, that really depends on what you're trying to accomplish.  A 'scope is a tool, just like a hammer.  If I'm trying to drive a nail, I use a hammer.  If I'm trying to analyze what's happening in a circuit, I may well break out the 'scope.

Just curious, what did you pay for that unit?  It's certainly a quality unit, and will probably serve you well for most anything you might want to see around model trains.

GRJ:  For openers, I'd like to learn, for a given smoke unit:  What's its supply voltage?  AC or DC?  What's the heater's resistance?  Its current?  Its power? [Yes, I know the formulas.]  Is there a voltage regulator?  How do I find out, and measure its performance?  [660$ @ Amazon]

Good price on the 'scope.

Many of those things you don't really need a 'scope for.

Resistance, current, and power are some good examples.  Rarely is a 'scope more useful than a meter for those tasks.

One thing you can do if you're experiencing issues with a VR is to check the ripple on the output side.

As far as what supplies the smoke unit, that would depend on the specific type and brand.  MTH PS/1 usually is supplied directly from AC track power.  MTH PS/2 receives a chopped DC signal from the FET on the PS/2 board, it's modulated to control smoke intensity.  That might be interesting to look at.

Lionel smoke units come in various types, depending on the specific type and vintage of the locomotive.  The fan driven models have come in many forms with different drive voltages and currents.

I get more use out of my 'scope designing digital circuits.  There you have stuff that you really have trouble measuring any other way.  Also remember the recent thread on TMCC/Legacy base output signals?  The 'scope was useful there in measuring the amplitude and frequency of the signals.

Phil,

Word of STRONG caution.  Be very careful where you put the probe especially on the boards.  One slip of the probe tip between say power or ground  and a signal input/output and you may wonder why lights don't work, sound dead or worst everything is dead .  Ask me how I learned this from 40+ years of engineering and benchwork (but at least I could replace the fried part of my design  where***$ DC$$$/TMCC, not so much.)

Love the word nanny **** out the "where a $ $" !!

Come on Rich we are all grownups here and believe me my 6 year old heard worst in Kindergarten.

One tip on your 'scope, now that DCS (Protosound 2/3) was mentioned.  You MUST isolate the scope if the ground is tied to the 3rd prong on the plug.  There is chassis common with DCS, so your 'scope ground should float if you're looking at anything there.

GRJ: On March 7, you mentioned, "TMCC/Legacy base output signals".  I did a search on this & failed.  Can you provide a pointer, please?

Measuring the TMCC/Legacy track signal strength

New TMCC/Legacy Track Signal measurement device

GRJ:  Thank you....and, WOW; this is 'heavy' stuff.  More to follow via email.

I have always been confused on when to worry about the scope ground, so when using a PC scope I have run on battery power.

With a plain transformer-powered layout, would I be correct that the secondary of the layout transformer provides the necessary isolation, and that a grounded scope is ok?

If so, where does the isolation break down?  The connection in a TMCC or Legacy base?

The reason you can't use the common ground around a lot of train electronics is that the "common ground" isn't really earth ground.  TMCC frame ground (wheels) is the TMCC signal, and it is not earth ground.  PS2/3 circuit has no common to frame ground (wheels), and connecting pretty much anything in a PS/2 locomotive to frame ground will kill something in the PS/2 electronics.

Since my 'scope has no battery provision, I just float the 'scope from earth ground and use it that way, no issues. 

GRJ: My understanding is that 'one-half' of the TMCC signal, the part that's radiated from the house wires in the room to the engine's antenna, IS connected to earth ground, thru that 'special' TMCC wall wort...if that's relevant to the discussion.   ???

I encourage you guys to read this application note from Tektronix (an oscilloscope manufacturer) that discusses floating scope measurements. Quoting verbatim:

A common, but risky, practice is to disconnect the scope's AC mains power cord ground and attach the probe ground lead to one of the test points. Tektronix strongly recommends against this unsafe measurement practice. Unfortunately, this puts the instrument chassis ­ which is no longer grounded to earth ­ at the same voltage as the test point. The user touching the instrument becomes the shortest path to earth ground. Figure 2 illustrates this dangerous situation.

I personally NEVER break the ground-wire connection on a scope's power cord.  Instead, I use other techniques as discussed in the above note such as differential probes - albeit expensive alternatives for the average hobbyist.  As train electronics goes more and more "digital" with higher frequencies, I also wonder if measurement integrity comes into play more so than in years past.

Few scopes today offer a differential pre amp but most all have at least two channels and you use a probe in each channel and set your input to A minus B and get a similar effect. Not super accurate but at least you won't be connecting your source to ground.

Pete

Stan, notes like that are the source of my confusion. i understand the issue when the unit under test is line powered; then the scope and use become a potential path for current back to earth ground.

But in our layouts, equipment is powered off the secondary of our transformers.   Doesn't  this provide isolation?  I don't see the path for current to return from the layout to earth ground through the user in the simple case.

While I understand Stan's point, all the stuff I'm working on is already isolated through a transformer from the power line.  Since my common for the TMCC stuff is the chassis (wheels), I seriously doubt I'm at any risk.

I don't have differential probes in my budget, so I'll continue to do it my way.

I agree the note can be confusing to the casual reader.  What I like is how they used the 3 inter-connected legs-of-a-stool model.  As Norton points out, you used to be able to find differential pre-amps built right into higher priced scopes so that each channel could connect to random grounded or ungrounded circuit points.  That is, in an ideal world all measurements are floating differential measurements.  The single-ended measurements with common returns on multiple scope channels is a compromise that works in the vast majority of cases. 

It would have been nice if they included real-life examples where measurements are compromised.  They do mention capacitance which is the issue.  So when you say the scope is isolated and you don't see a return path, that's at DC.  There is an AC return path due to the "massive" capacitance-to-ground of the probe return cables and the metal chassis/box of the scope itself.  This will corrupt the displayed signal particularly in high frequency "digital" circuits or lower speed circuits where the voltage swing is large.  In either case, these are so-called high dv/dt or high slew-rate measurements where the commonly used spec is CMRR or common-mode-rejection-ratio.  All differential measurement techniques whether they be differential pre-amps, differential probes, or even the "A minus B" method have a CMRR associated with it.  When/how to know if your specific measurement will be compromised to the point of making a false conclusion about a signal is complicated.  To GRJ's point, if you're happy with what you have, then it's not for me to say otherwise!

The probes are not differential. You use two separate probles in two separate channels and measure the difference. Digital scopes have their place but I will never be without a good analog one.

Pete

For most of the measurements I'm doing on either TMCC or DCS locomotives, I'm already at a "ground" reference for the probe common, either the DC ground for DCS, or the frame ground for TMCC.  I have not had any significant issues operating this way with my digital scope. I don't see the excess stray capacitance to ground as any issue in this mode of operation.  I'm measuring single-ended, which has known limitations, but it works just fine.  I'm just making the 'scope "ground" the wheels of the locomotive working on TMCC, and the DC ground working on DCS.

If I were connecting the 'scope common in the middle of some circuit, I'd be more concerned about the excess capacitance.

If I'm working on something that actually has an earth ground common reference, I leave the scope ground to the power in place.