Is an oscilloscope necessary?

[Richards]

For decades, I've been asked what testing equipment I use to reliably design and build a DIY controller. My answer has always been, "It depends".

If I need to measure voltage, I need a volt meter.

If I need to measure current, I need a current meter.

A multimeter does both. Home Depot has adequate multimeters for $50. Fluke has excellent multimeters starting at about $100. To me, a multimeter is essential.

If I need to see waveforms, I need an oscilloscope.

That's the simple answer. If I need to see something, I need the proper instrument to see it.

Teknic provides its MSP software to setup and tune ClearPath motors. One of the great features of that software is its built-in oscilloscope. Every time I change a parameter, I can see what that change accomplished by watching the waveforms on the built-in oscilloscope. By using that MSP software, I realized that Teknic's base model ClearPath servo is much more capable than I ever imagined. By doing something as simple as extending the acceleration ramp, that little servo can move incredible loads.

If after thinking up an excuse to buy an oscilloscope, you decide to buy one, you might ask which one should I buy? My old oscilloscope is a basic two-channel scope. It is not a storage 'scope. It is not a high speed 'scope. It works perfectly for typical trouble-shooting. If I didn't already own it, I wouldn't buy it. It costs too much while offering too little. Instead of paying $2,000 for that 'scope, I would buy something from Amazon for less than $100. The inexpensive 'scope would have storage, so I could recall a missed signal. It would have more channels, so I could watch a ClearPath, a VFD, and noise on the power supply at the same time.

Do I use a 'scope everyday, or in other words, at what point do I take the oscilloscope off the shelf and use it in a project? If I'm building an open-loop stepper system, I rarely use a 'scope. My ears can hear missed steps. I don't need a 'scope for that. However, I used a 'scope as soon as I wired up a ClearPath servo on the test bench. The ClearPath servo has much higher performance. It can run circles around an open-loop stepper. To use to the fullest, I needed to watch it in motion with an instrument that could show how it was performing.

The test bench is not the same environment as an electronics cabinet. Signals often do the unexpected inside a closed metal container. I used a 'scope extensively when I built the Taig's controller, even though that controller uses open-loop stepper motors. By watching waveforms, I rerouted a few wires. That controller works great. It doesn't take a lot to run a Taig, but it's nice knowing that its controller is providing clean signals.

I think that few of us would try to build a controller without a multimeter. I think that if we visited a "design shop" where controllers are designed and built, we would expect to see oscilloscopes being used on every bench. In some ways, deciding which equipment is essential reveals a lot about us. I get frustrated easily. If I know that a circuit is supposed to do something and it doesn't do it, I get frustrated. You would probably hear me muttering something about the idiots who sell parts that are out of spec. Too often, I'm that idiot. Too often I missed an essential stop when designing a circuit. Too often, the blame is mine. Proper equipment, properly used, can quickly show where the fault lies and what the problem is. After knowing the problem, it's usually a simple process to fix it.

[Black Forest]

Mike do you know of any videos that show how to use a "scope" specifically in troubleshooting a control for a CNC machine? One aimed at inexperienced builders? If not then I nominate you to make one!!!! All those in favor say AYE.

[DrLocke]

I bought a SIGLENT 2 channel 200 MHz scope on Amazon to use in trouble shooting step/direction problem. Cost $400-$500. Worked fine after a little time to figure out controls.

[cncsnw]

Here are some interesting shots. I was working yesterday on a router table with an Oak controller and DMM DYN4 drives (not my choice of drive).

240V power comes in through the main breaker; then goes through a line reactor (LR-2015 from A-D); then to circuit breakers for each drive. Logic power for each drive comes directly off the circuit breaker. Motor line power for each drive goes through an emergency stop contactor (one per drive), then on to the drives. Therefore, when Emergency Stop is pressed, power through the line reactor goes only to the logic circuits of all five drives. When Emergency Stop is released, then power through the line reactor also goes to the power sections of all five drives.

The character of the AC wave upstream vs. downstream of the line reactor is remarkable.

The yellow trace is L1 upstream of the line reactor (to its A1 terminal).
The blue trace is L1 downstream of the line reactor (from its A2 terminal).

With emergency stop pressed: logic power only

With emergency stop released, feeding drives' power sections

Detail of emergency-stop-released case

What does this illustrate? Admittedly, I am not entirely sure. I used the scope because I wanted to know why my volt meter showed a steady 241VAC line-to-line upstream of the line reactor, but a very erratic ca. 226VAC downstream. It turns out that there is a lot of high-frequency noise on the drives side of the line reactor. Mostly what the scope shows, is that the line reactor is doing its job, preventing that high-frequency noise from getting back up the power lines to where it could affect other devices.

[RogDC]

Has anyone had experience with one of the PC USB oscilloscopes? Would a 20MHz 2 channel be adequate for troubleshooting the acorn/drive circuits?

[Richards]

Thanks for posting your experiences with 'scopes and the screen shots. I just checked YouTube to see what has been posted about oscilloscope basics. There's a lot there. The first video I looked at had 101 in the label. It covered basic usage using clear and understandable language. ( You definitely wouldn't want me to make a video. Some of my best friends are Greek. They taught me how to spend hours philosophizing. I'm afraid any video that I made would have more philosophizing than content.)

I haven't used a USB 'scope, but I there are lots of Videos showing what they do.

[slodat]

When I was chasing down issues with DYN4 drives on my CNC router an oscilloscope was the only way to finally get down to what my problem was.

[carboncymbal]

Here are some interesting shots. I was working yesterday on a router table with an Oak controller and DMM DYN4 drives (not my choice of drive).

240V power comes in through the main breaker; then goes through a line reactor (LR-2015 from A-D); then to circuit breakers for each drive. Logic power for each drive comes directly off the circuit breaker. Motor line power for each drive goes through an emergency stop contactor (one per drive), then on to the drives. Therefore, when Emergency Stop is pressed, power through the line reactor goes only to the logic circuits of all five drives. When Emergency Stop is released, then power through the line reactor also goes to the power sections of all five drives.

The character of the AC wave upstream vs. downstream of the line reactor is remarkable.

The yellow trace is L1 upstream of the line reactor (to its A1 terminal).
The blue trace is L1 downstream of the line reactor (from its A2 terminal).
ACDistort0.png
ACDistort1.png
ACDistort2.png

What does this illustrate? Admittedly, I am not entirely sure. I used the scope because I wanted to know why my volt meter showed a steady 241VAC line-to-line upstream of the line reactor, but a very erratic ca. 226VAC downstream. It turns out that there is a lot of high-frequency noise on the drives side of the line reactor. Mostly what the scope shows, is that the line reactor is doing its job, preventing that high-frequency noise from getting back up the power lines to where it could affect other devices.

Interesting to see the scope outputs. Can I ask why model of oscilloscope you are using? Is that a PC interface?

[cncsnw]

Mine is a Tektronix MDO3014. It is probably beyond what most hobbyists can justify. Probably beyond what I can justify too, but I have a fondness for Tektronix, and I like the "digital phosphor" feature.
https://www.newark.com/tektronix/mdo301 ... dp/29X1615

Just about any scope at all is better than none. Something that will show you at least two channels, with even 20MHz resolution, at levels up to 30V, will cover 90% of the troubleshooting you would need to do on an Acorn installation. The ability to look at line-level power, or multi-MHz signals, or four things at once, are bonuses that you will only need on rare occasions.

[carboncymbal]

Mine is a Tektronix MDO3014. It is probably beyond what most hobbyists can justify. Probably beyond what I can justify too, but I have a fondness for Tektronix, and I like the "digital phosphor" feature.
https://www.newark.com/tektronix/mdo301 ... dp/29X1615

Just about any scope at all is better than none. Something that will show you at least two channels, with even 20MHz resolution, at levels up to 30V, will cover 90% of the troubleshooting you would need to do on an Acorn installation. The ability to look at line-level power, or multi-MHz signals, or four things at once, are bonuses that you will only need on rare occasions.

Thanks for the suggestion on the scope. I owned a cheap ($400) scope for years but hadn't touched in a while. Ha, I donated it to a local makerspace 2 weeks before I started having issues with my control panel. Looks like I'm in the market again!

-Clay