Check and measurement gear (T&M) you want for a house laboratory

One of the realities of 2021 is that a lot of engineers are still stuck at home with all those cool gadgets and things that collect dust at work. How do you stay productive in the new world we live in? How Much Work Can You Do at Home? That depends on your projects. You need the right tools to achieve your goals.

The logistics for bringing test and measurement equipment home

Many kindergarten teachers who got their class to create macaroni sculptures will tell you, “There’s only so much crap you can do with crap.” This also applies to tools and testing equipment. If you can’t go to work, either you or your employer will have to open your paperbacks to bring work to your home.

If your employer provides a grant for the equipment, you should be able to keep it and write it off on your taxes. Regardless of how the equipment gets into your home, you can look for insurance options. Homeowner Insurance may not be interested in replacing a $ 50,000 oscilloscope that you brought home from work.

For electrical testing devices, I recommend the “buy once, cry once” philosophy. Pay for quality tools that will last a decade or more. Alternatively, if your business has a less strenuous development cycle, you can use one of the many test equipment rental companies to rent the equipment you need only for the time you need it.

Oscilloscopes

I work at Advanced Assembly and my boss and I each have a Tektronix MDO3104 in our home workshops. These multifunction devices act as an oscilloscope, spectrum analyzer, function generator, multimeter, and some other things that I haven’t figured out yet. Until recently, this device was worth a lot more than my car. And that’s only because I bought a new car.

As a result, I’m a little more conservative about it than I probably should be, and with a new kid in the house, they’ll spend most of their lives in a fireproof safe of little to no use to me.

What bandwidth do you need?

Your oscilloscope and probe may not have enough bandwidth to measure every signal that is out there. For example, even a 1 GS / s oscilloscope such as the MDO3104 cannot really capture a rise time of 40 ps that comes from a GaN switching element.

This detection of a GaN switch has a reported rise time of 40 ps, ​​but the oscilloscope says it is closer to 280 ps. But is it? Let’s decrease the bandwidth and see what the signal looks like. At 250 MHz bandwidth it looks like a completely different signal and the oscilloscope has a rise time of 750 ps.

What am I really measuring here? The only thing I know for certain is that this is a fast signal. It’s beyond the scope and capabilities of the probes and my boss has to buy me a new toy.

As a very, very general rule of thumb, divide your fastest component rise time in 0.6 to determine your needed bandwidth (I skipped steps on discussion harmonics and added just a tiny margin of safety).

For example:

$$ text {Scope ; BW} frac {0.6} {40 ; text {ps}} = 15 ; text {GHz} $$

I have no idea why I adopted this device as my sacred cow. It can’t even keep up with my fastest impulses, and tools are meant to be used. But I use it when careful measurements, protocol analysis, or spectrum analysis are required and it does its job well.

A year ago, it was mounted on an articulating VESA mount above my workbench. And it will go back there again when no more children tug at a test lead that has fallen over the edge of the table.

MDO3104 oscilloscope. Image courtesy of Tektronix

Simple, inexpensive oscilloscopes can get the job done

Fortunately, most of the design flaws or soldering mistakes I make are stupid – a solder bridge during hand assembly, or maybe I have the wrong footprint for an IC. I haven’t miscalculated the capacitance of an I2C line yet, and there’s no chance I’ve connected a UART Tx driver to a UART Tx driver on another IC, and anyone who says I did the board and ruined is a fucking liar!

So 60% of my debugging needs can be met with the simplest oscilloscope. All I need to do to get the card is know if it is logic low or logic high, an approximate voltage, or whether a data line actually contains data. The cheapest oscilloscope can usually be used for these purposes. When the fix escalates to Let’s Decode Some Packets, the Big Boy Tools come out.

I have come to appreciate the small size and usefulness of pocket oscilloscopes. 2-channel versions are around $ 100 and 4-channel versions are around $ 200.

The 4-channel handheld mini digital oscilloscope DSO213. Image courtesy of SainSmart

These devices are small, portable and very limited in their capabilities. They complement a full-featured oscilloscope – they don’t replace it. These are not logic analyzers and they do not have any protocol analysis capabilities.

But the nice thing is that because of the price, I have no qualms about leaving this on my desktop or taking it to the garage to fix my CNC machines. The last task in life was to determine if the output on the BNC connector of a surveillance camera was digital or analog. That gave me the idea that it could be 3G-SDI.

A word of caution with Pocket T&M devices

After falling in love with the pocket oscilloscopes, it is probably tempting to find all the pocket-sized test equipment on the internet and add them to your shopping cart. But I encourage you not to get too wild.

These devices are more difficult to use and are counterfeited en masse offshore. They also have a clunky user interface that takes some getting used to and has a limited operating frequency range. Nor can I imagine they are calibrated so carefully.

Vector network analyzer

Pocket-sized vector network analyzers are available. That is, they can capture the amplitude and phase of a signal. The frequency range usually starts at 10 kHz and peaks from 1 to 1.5 GHz.

I have one for amateur radio antenna projects, but don’t regularly use it for work-related tasks. I don’t know how effective or accurate they are at capturing S-parameters, but I’m sure the answer will be 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 courtesy of SeeSii and Amazon

Instead, you can consider the fully automatic 2-port vector network analyzer DG8SAQ VNWA 3SE. This device connects directly to your computer and can be used for time domain analysis, cable fault detection and network adjustment. It also has high stability and high dynamic range. The operating frequency is between 1 kHz and 1.3 GHz, which covers several ISM bands.

DG8SAQ VNWA 3 from SDR Kits, a low cost 1.3 GHz VNA. Image courtesy of SDR Kits

This is an S11 graph of the standing wave ratio (red), dB loss (blue), and impedance (green). The diagrams show that this particular antenna is tuned to 453 MHz but should perform adequately over the range of 445 to 455 MHz.

Unfortunately, reaching a maximum frequency of up to 3 GHz requires a serious part of the kit and requires that you sell your car in order to afford it. To get to 53 GHz, you have to sell a kidney or your firstborn child. Personally, I recommend the child as you cannot do another kidney.

Multimeter

The multimeter you choose depends a lot on the nature of your job. The accuracy, number of functions, and data logging are available to you, among many other functions. But you should also know that the multimeter is no longer just about resistance / capacitance / voltage.

Multimeters exist with built-in infrared cameras! FLIR and Fluke have both models to choose from.

FLIR’s industrial imaging multimeter, the DM285. Image courtesy of FLIR

The resolution of the IR camera may not be as good as a stand-alone IR camera, and the multimeter may have specifications that do not directly lend it to work with microelectronics. However, if you are working with line voltage level equipment, a compelling case can be made for adding this to your toolkit.

If you plan to use the IR camera to inspect electronic circuits, you should choose another model with a higher resolution. As a rule of thumb, the minimum width of the component to be examined should be 3 pixels wide.

Alternatively, you can use a benchtop multimeter, which offers greater precision.

The SD 1 / 23045X 4 1/2 digit digital multimeter with two displays. Image courtesy of Siglent Technologies

Note that these devices will last a very long time if used carefully. I still have the same portable and benchtop multimeters I bought from RadioShack over two decades ago, and they work just as well today as they did when new – that is, I can check battery voltages and do other basic troubleshooting.

Consider investing in something that you will want to keep for a very long time.

Invest in durable T&M equipment

If you need to fix bugs or get 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 get your job done. This can be difficult, but I have a simple solution: just let your boss know I said it was okay.

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