metrology

20 Articles

The HP3458A: King Of Multimeters For Three Decades

October 18, 2021 by 16 Comments

[Marco] looks at a lot of meters. However, he considers the HP3458A the best even though they were introduced more than 30 years earlier in 1989. Someone donated one to [Marco] but it presented some error messages on startup and exhibited erratic behavior, so he had some repairs to do.

The error codes hinted there were issues with the multislope analog to digital converter and that’s what sets the meter apart, according to [Marco]. The meter has 8.5 digits, so a normal conversion stage won’t cut it.

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Sub-mm Mechanical 3D Scanner With Encoders And String

July 1, 2021 by 29 Comments

[Scott Rumschlag] wanted a way to precisely map interior spaces for remodeling projects, but did not want to deal with the massive datasets created by optical 3D scanning, and found the precision of the cost-effective optical tools lacking. Instead, he built a 3D cable measuring device that can be used to map by using a manual probe attached to a cable.

The cable is wound on a retractable spool, and passes over a pulley and through a carbon fiber tube mounted on a two-axis gimbal. There are a few commercial machines that use this mechanical approach, but [Scott] decided to build one himself after seeing the prices. The angle of rotation of each axis of the gimbal and the length of extended cable is measured with encoders, and in theory the relative coordinates of the probe can be calculated with simple geometry. However, for the level of precision [Scott] wanted, the devil is in the details. To determine the position of a point within 0.5 mm at a distance of 3 m, an angular resolution of less than 0.001° is required on the encoders. Mechanical encoders could add unnecessary drag, and magnetic encoders are not perfectly linear, so optical encoders were used. Many other factors can also introduce errors, like stretch and droop in the cable, stickiness of the bearings, perpendicularity of the gimbals axis and even the spring force created by the encoder wires. Each of these errors had to accounted for in the calculations. At first, [Scott] was using an Arduino Mega for the geometry calculations, but moved it to his laptop after he discovered the floating point precision of the Mega was not good.

[Scott] spend around 500 hours building and tuning the device, but the end result is really impressive. There are surprisingly few optical machines that can achieve this level of precision and accuracy, and they can be affected by factors like the reflectivity of an object.

If you do want to get into real 3D scanning, definitely take the time to read [Donal Papp]’s excellent guide to the practical aspects of the various technologies. Most of us already have a 3D scanner in our pocket in the form of a smartphone, which can be used for photogrammetry.

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3D-Printed Laser Scanning Confocal Microscope Measures Microns

April 26, 2021 by 15 Comments

When one thinks about microscopy, it seems to be mostly qualitative. Looking at a slide teeming with bacteria or protozoans is less about making measurements and more about recognizing features and describing their appearance. Not all microscopes are created equal, though, with some being far more optimized for making fine measurements of the microscopic realm.

This 3D-printed confocal laser scanning microscope is a good example of an instrument for measuring really small stuff. As [Zachary Tong] points out, confocal scanning microscopy uses a clever optical setup to collect light from a single, well-defined point within a sample; rather than getting an image of all the points within a two-dimensional focal plane, the scanning function moves the focal point around through the sample in three dimensions, capturing spatial data to go along with the optical information.

The stage of [Zach]’s microscope is based on OpenFlexure’s Delta Stage, an open-source, 3D-printed delta-bot motion control platform that’s capable of positioning samples with sub-micron precision. Above the stage are the deceptively simple optics, with a laser diode light source, an objective lens, and a photodiode detector behind a pinhole. The detector feeds a homebrew trans-impedance amplifier that captures data at millions of points as the sample is moved through a small three-dimensional space. All that data gets crunched to find the Z-axis position corresponding to the maximum intensity at each point.

It takes a while to gather all this data — up to several days for even a small sample — but it works pretty well. [Zach] already has some ideas for reducing noise and speeding up the scan time; perhaps a stage based on DVD parts like this one would be faster than the delta stage. We look forward to seeing his improvements.

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Homebrew Metrology The CERN Way

February 26, 2021 by 18 Comments

We won’t pretend to fully grok everything going on with this open-source 8.5-digit voltmeter that [Marco Reps] built. After all, the design came from the wizards at CERN, the European Organization for Nuclear Research, home to the Large Hadron Collider and other implements of Big Science. But we will admit to finding the level of this build quality absolutely gobsmacking, and totally worth watching the video for.

As [Marco] relates, an upcoming experiment at CERN will demand a large number of precision voltmeters, the expense of which led to a homebrew design that was released on the Open Hardware Repository. “Homebrew” perhaps undersells the build a bit, though. The design calls for a consistent thermal environment for the ADC, so there’s a mezzanine level on the board with an intricately designed Peltier thermal control system, including a custom-machined heat spreader blocker. There’s also a fascinatingly complex PCB dedicated solely to provide a solid ground between the analog input connector — itself a work of electromechanical art — and the chassis ground.

The real gem of this whole build, though, is the vapor-phase reflow soldering technique [Marco] used. Rather than a more-typical infrared process, vapor-phase reflow uses a perfluropolyether (PFPE) solution with a well-defined boiling point. PCBs suspended above a bath of heated PFPE get bathed in inert vapors at a specific temperature. [Marco]’s somewhat janky setup worked almost perfectly — just a few tombstones and bridges to fix. It’s a great technique to keep in mind for that special build.

The last [Marco Reps] video we featured was a teardown of a powerful fiber laser. It’s good to see a metrology build like this one, though, and we have a feeling we’ll be going over the details for a long time.

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Digital Caliper Talks For Accessibility, With This App

August 2, 2020 by 37 Comments

A good instrument stays with its owner for a lifetime, becoming part of their essential trusted toolkit to be consulted as a matter of habit. If you use a caliper to measure dimensions  you’ll know this, and a quick glance at its scale or digital display will be second nature. But if you aren’t fortunate enough to have the eyesight to see the caliper, then it’s off-limits, and that’s something [Naomi Wu] has addressed with her open-source accessible speaking caliper app. It’s an Android app that connects to digital calipers that contain Bluetooth connectivity, and as well as speaking aloud the caliper reading it also displays it in very large text on the device screen. As well as the source link from which you can build the app, it’s available for installation directly from the Google Play Store.

If you’re used to [Naomi] from her video tours of the electronics businesses in her native Shenzhen, her eye-catching wearable projects, or her exploits with an industrial CNC machine in her living room, you might be interested to know that aside from this app she’s been a long-time proponent of open-source in China. She was responsible among other projects for the Sino:bit educational computer board, which holds the distinction for her of having secured the first ever Chinese OSHWA certification.

You can see the caliper app in action below the break.

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No Assembly Required For This Compliant Mechanism Dial Indicator

July 15, 2020 by 10 Comments

If you’ve ever had the good fortune — or, after a shop mishap, the misfortune — to see the insides of a dial indicator, you’ll know the workings of these shop essentials resemble nothing so much as those of a fine Swiss watch. The pinions, gears, and springs within transmit the slightest movement of the instrument’s plunger to a series of dials, making even the tiniest of differences easy to spot.

Not every useful dial indicator needs to have those mechanical guts, nor even a dial for that matter. This compliant mechanism 3D-printed dial-free indicator is perfect for a lot of simple tasks, including the bed leveling chores that [SunShine] designed it for. Rather than print a bunch of gears and assemble them, [SunShine] chose to print the plunger, a fine set of flexible linkage arms, and a long lever arm to act as a needle. The needle is attached to a flexible fulcrum, which is part of the barrel that houses the plunger. Slight movements of the plunger within the barrel push or pull on the needle, amplifying them into an easily read deflection. When attached to the head of a 3D-printer and scanned over the bed, it’s easy to see even the slightest variation in height and make the corresponding adjustments. Check it out in the video below.

We’re big fans of compliant mechanisms, seeing them in everything from robot arms and legs to thrust vectoring for an RC plane. This might look like something from a cereal box, and it certainly doesn’t have the lasting power of a Starrett or Mitutoyo, but then again it costs essentially nothing, and we like that too.

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Vernier Calipers And Micrometer Screw Gauges, Measuring Without Compromise

June 8, 2020 by 62 Comments

I needed a temperature controller module recently, so off I went to Banggood to order one. As one does I found myself browsing, one thing led to another, and I bought a micrometer screw gauge. While micrometers are pretty expensive devices, reflecting their high precision engineering and construction, this micrometer cost me only about £8, or just under $10, definitely in the spirit of our long-running series of reviewing very cheap tools in search of a diamond in the rough. But perhaps more importantly, this is also the cue for an examination of high precision dimensional measurement. So I’ve assembled a collection of micrometers and vernier calipers of varying quality, and it’s time to dive in and measure some very small things.

Some of you will be metrology enthusiasts with an array of the finest devices available, but I am guessing that many of you will not. The ubiquitous precision measurement device in our community appears to be the digital caliper, a sliding clamp with an LCD display, an instrument that can be had in its most basic form for a very small outlay indeed. For the purposes of this piece though we’re not looking at digital devices but their analogue precursors. If you want a feel for metrology and you’d like some of those heritage tools that parents pass onto their kids then it’s time to learn something about the vernier caliper and the micrometer. Continue reading “Vernier Calipers And Micrometer Screw Gauges, Measuring Without Compromise” →