Test and Measurement (T&M) Equipment You’ll Need for a Home Laboratory
For some of us, at-home work may be an extended reality beyond 2020. You’ll need the proper tools to accomplish your goals.
One of the realities of 2021 is that many engineers are still stuck at home with all the cool gadgets and gizmos collecting dust at work. How will you remain productive in the new world we live in? How much work can you do at home? That’ll depend on your projects. You’ll need the proper tools to accomplish your goals.
The Logistics of Bringing Test and Measurement Equipment Home
Many kindergarten teachers who have led their class to create macaroni sculptures will tell you, “There is only so much crap you can make with crap.” That’s also true of tools and test equipment. If you cannot go to work, either you or your employer will have to open up your pocketbooks to bring the work home to you.
If your employer provides a stipend for the equipment, you should be able to keep it and depreciate it on your taxes. But however the equipment enters your home, you might investigate insurance options; homeowners' insurance might not be keen on replacing a $50,000 oscilloscope that you brought home from work.
For electrical engineering test equipment, I recommend the “Buy once, cry once” philosophy. Pay for quality tools that will last a decade or more. Alternatively, if your company has a less strenuous development cycle, take advantage of one of the many test equipment rental companies out there to rent the equipment you need for only the time you need it.
I work at Advanced Assembly, and my boss and I each have a Tektronix MDO3104 in our home workshops. These multifunction devices function as an oscilloscope, spectrum analyzer, function generator, multimeter, and a few other things I haven’t figured out yet. Until recently, this device was worth substantially more than my car. And that’s only because I bought a new car.
Consequently, I’m a bit more conservative with it than I probably should be, and since there is a new child in the home, it spends most of its life locked in a fire-proof safe where it does me little to no good.
What Bandwidth Do You Need?
Your scope and probe might not have adequate bandwidth to measure every signal that’s out there. For example, even a 1 GS/s oscilloscope like the MDO3104 can’t really capture a 40 ps rise time coming out of a GaN switching element.
This capture of a GaN switch has a stated rise-time of 40 ps, but the scope says it’s closer to 280 ps. But is it? Let’s turn the bandwidth down and see what the signal looks like. At 250 MHz bandwidth, it looks like a completely different signal, and the scope has a rise-time of 750 ps.
So what am I really measuring here? The only thing I know with some modicum of certainty is that this is a fast signal. It’s beyond the scope and probes' capabilities, and my boss needs to buy me a new toy.
As a very, very general rule of thumb, divide your fastest component rise time into 0.6 to determine your needed bandwidth (I skipped steps about discussion harmonics and just included a tiny safety margin).
I have no idea why I have adopted this device as my sacred cow. It can’t even keep up with my fastest pulses, and tools are meant to be used. But I do use it when careful measurement, protocol analysis, or spectrum analysis are required and it serves its purpose well.
A year ago, it was mounted above my workbench on an articulating VESA mount. And it will return there again when there is no longer the worry of a child tugging on a test lead that’s fallen over the edge of the desk.
MDO3104 oscilloscope. Image used courtesy of Tektronix
Simple, Low-Cost Oscilloscopes Can Do the Job
Fortunately, most of the board design mistakes or soldering mistakes I make are stupid ones—a solder bridge during hand-assembly, or perhaps I have the wrong footprint for an IC. I haven’t yet miscalculated the capacitance of an I2C line, and there’s no chance, ever, that I’ve attached a UART Tx driver to a UART Tx driver on another IC, and anybody who says I did and ruined the board is a damn liar!
So 60% of my debugging needs can be met by the simplest of oscilloscopes. For board bring-up, I just need to know if there is logic low or logic high, an approximate voltage, or if a data line actually has data on it. For those purposes, the cheapest of oscilloscopes can usually do. When troubleshooting escalates to “let’s decode some packets,” the big-boy tools come out.
I’ve come to appreciate the small size and usefulness of the pocket oscilloscopes. 2-channel versions run around $100 and 4-channel versions around $200.
The DSO213 4-channel handheld mini digital oscilloscope. Image used courtesy of SainSmart
These devices are small, portable, and very limited in what they can do. They supplement a fully-featured oscilloscope—they do not replace it. These are not logic analyzers, and they have no protocol analysis capabilities.
But the nice thing is that due to the price, I have no qualms about leaving this around my desktop or taking it out to the garage to troubleshoot my CNC machines. Its latest job in life was determining whether the output on the BNC port of a security camera was digital or analog. That gave me the idea it might be 3G-SDI.
A Word of Caution on Pocket T&M Equipment
After you fall in love with the pocket oscilloscopes, it’s likely tempting to find all the pocket-sized test equipment on the internet and add it to your shopping cart. But I encourage you not to go too hog wild.
These devices are more difficult to use and are counterfeited off-shore en mass. They also have a clunky user interface that takes some getting used to and have a limited operating frequency range. And I can’t imagine that they are calibrated all that carefully either.
Vector Network Analyzer
There are pocket-sized vector network analyzers available. That means they are able to capture the amplitude and the phase of a signal. The frequency range usually starts at 10 kHz and peaks around 1–1.5 GHz.
I have one for amateur radio antenna projects but do not use it regularly for work-related tasks. I don’t know how effective or accurate they are at capturing s-parameters, but I’m sure that the answer is disappointing. If you have experience with them in a production environment, please leave a comment below.
The SeeSii vector network analyzer (10 kHz–1.5 GHz). Image used courtesy of SeeSii and Amazon
You might instead consider the DG8SAQ VNWA 3SE fully-automatic, 2-port vector network analyzer. This device plugs straight into your computer and can be used for time-domain analysis, cable fault detection, and network matching. It also has high stability and high dynamic range. The operating frequency is from 1 kHz to 1.3 GHz, which covers several ISM bands.
SDR Kits' DG8SAQ VNWA 3, a low-cost 1.3 GHz VNA. Image used courtesy of SDR Kits
This is an S11 plot of standing wave ratio (red), dB of loss (blue), and impedance (green). The plots indicate that this particular antenna is tuned for 453 MHz, but should perform adequately across the range of 445–455 MHz.
Sadly, moving up to 3 GHz maximum frequency requires a serious piece of kit and will require that you sell your car to afford it. To move up to 53 GHz requires that you sell a kidney or your first-born child. Personally, I recommend the child since you can’t make another kidney.
The multimeter you choose depends greatly on the type of work that you do. The level of precision, the number of functions, and data logging, among many other features are all options available to you. But you should also know that the multimeter no longer means simply resistance/capacitance/voltage.
Multimeters exist with infrared cameras built right in! FLIR and Fluke both have models available to choose from.
FLIR's industrial imaging multimeter, the DM285. Image used courtesy of FLIR
The resolution of the IR camera might not be as good as a standalone IR camera, and the multimeter might have specifications that don’t lend it directly to microelectronics work. But if you work with line-voltage level devices, a compelling argument can be made to add this to your toolkit.
If you intend to use the IR camera for inspecting electronics circuits, you should choose a different model with higher resolution. A good rule of thumb is that the minimum width of the component you wish to inspect should be 3 pixels wide.
Alternatively, you might go with a benchtop multimeter that is capable of greater precision.
The SDM3045X 4 1/2 digits dual-display digital multimeter. Image used courtesy of Siglent Technologies
Something to keep in mind is that these devices, used carefully, last a very long time. I still have the same portable and benchtop multimeters that I purchased from RadioShack over two decades ago, and they still work as well today as they did when they were new—which is to say I can check battery voltages and perform other basic troubleshooting.
Consider investing in something that you plan to keep for a very long time.
Invest in Long-Lasting T&M Equipment
If you have to troubleshoot or bring up new designs, you need test equipment. It’s not cheap and someone has to pay for it. So your new job is to convince your boss that you need all of these tools to do your job. That can be difficult, but I have a simple solution: just let your boss know that I said it was okay.