On accurate tools and calibration

first_img Leave a Reply Cancel reply You must Register or Login to post a comment. This site uses Akismet to reduce spam. Learn how your comment data is processed. Share this:TwitterFacebookLinkedInMoreRedditTumblrPinterestWhatsAppSkypePocketTelegram Tags: Design Methods Continue Reading Previous Mark your calendar for the Programmable Logic Meet-up at ESC Minneapolis 2016Next Book Review: The Innovators by Walter Isaacsoncenter_img I’m a sucker for tools that measure things, especially when they offer a great deal of precision. Or, better, accuracy, for accuracy is how closely a measurement conforms to reality, and precision is a measure of repeatability. Most of us, myself included, in casual conversation carelessly conflate these terms.Perhaps one of the more incredible measuring tools we all carry around is a smart phone GPS. In 1991 a friend and I sailed to England with an early Magellan unit. Big, costly and clunky it burned through AAs at an amazing rate so had to be left off except when we needed a position. The slow MCUs of the day required 20 minutes to obtain and reduce a position; I used to race it with the sextant. Today it’s amazing that a tiny bit of electronics can suck data from the spacecraft 20,000 km above the earth and almost instantly compute a position accurate to a few meters. What Captain Cook would have given for such technology! (I bet he would have liked decent charts even better.)One of my favorite measuring tools in the woodworking shop is this 6” scale:6” scale and calipers. Photo by author. These were available at Home Depot for $2 each. I bought two and now wish I had purchased more, for Home Depot, in the inevitable cheapening of things, replaced these with Chinese crap.One side is divided into 32nds, the other into 64ths. The calipers confirm as much accuracy as I can discern with aging eyes. But are the calipers accurate? According to a precision calibration block they’re within about 2 thousandths of an inch at the one inch setting. That’s more than good enough for my woodworking.But how accurate is the cal block? It was sold as being good to one ten-thousandth but that was years ago. And what about its tempco? Presumably at room temperatures the variation is low, but who knows? We all rely on some sort of faith as guiding our philosophical underpinnings; mine is in that cal block but it could be that it isn’t the One True Religion after all.One neat little item is this $30 Wixey tilt-box which measures angles.Wixey tilt box. Photo by author. MEMS accelerometers are so cheap today that a lot of these sorts of devices are available. A rare-earth magnet in the bottom of the unit sticks it to something to be measured; in this photo it’s measuring the angle of a table-saw blade. At $30 it has a claimed accuracy of +/- 0.2 degrees. I’ve checked it against my best square which is supposed to be within 0.0001” over 6”. But is the square really that good?I have to rely on faith. But these accuracies are good enough for woodworking.The tilt-box can’t measure absolute angles; they are all referenced to a value when one presses the “zero” button. So I put it on the saw’s table, zero it, and then mount it on the blade.The darn thing eats coin cells. After six months the CR2032 is dead, though I probably use it a total of ten minutes in that time. This puzzle got me interested in embedded systems that have to work for a long time from a battery which resulted in this study. The unit pulls 10 uA when “off” – the MCU is probably in some inefficient sleep mode. Interestingly, those $4 digital thermometers that live for years in a medicine cabinet yet spring to life when needed draw about a single nA when off. “Off” means different things to different engineers.How about tape measures? Here’s two:Two tape measures. Photo by author. One is a ¾” Dewalt, the other a ½” Stanley. At 7 feet they disagree by 1/16”. Which one is correct? An old saw states that a man with one clock knows what time it is; one with two has no idea, which seems to be the matter with these two tapes. We’re building a 30’ long barn so I imagine that the total difference over that run is a quarter inch. Horrors! But the truth is I screwed it up and there’s over an inch of skew in the building. Entirely my fault, though it would be nice to blame the tools.In the electronics lab we all have a plethora of equipment for measuring things. My work is mostly experimentation and really doesn’t need much in the way of high accuracy (or precision). Obviously, others will have different requirements. It is nice to know that the gear isn’t lying too much, but for me it makes no economic sense to send the stuff out to a cal lab every year.Take, for instance, a DMM. This HP 3468A is old but, with the exception of a display that’s a little hard to read, is quite a nice unit. Does “old” mean “out of calibration”?DMM being tested by the DMMCheck. Photo by author. The little board in front of the meter is a DMMCheck from VoltageStandard. For about $50 this thing provides a 5.000 volt output reference, accurate to 0.01% +/- 500 µV, a 1.000 mA reference, accurate to 0.1% +/- 1 µA, and three 0.1% resistors. Recalibration of the unit is free for the first two years and $10 after that. It’s really not important that my meter is super-accurate… but it sure feels good to know that it’s pretty darn close. (I know that a measurement at just one voltage doesn’t mean the meter is accurate at any voltage; the DMMCheck is just a reassuring sanity check.)Other gear is harder to evaluate. I check various instruments against each other from time to time. For instance, the HP 8640B signal generator’s indicated frequency is always within 1 KHz of what the Advantest R3132 spectrum analyzer reports – not bad at the signal generator’s max 500 MHz. My scopes are all digital and, connected to that signal generator, display the correct frequency to within the relatively low (few digits) resolution that most scopes provide as part of their automatic measurements.Voltage measurements are much more distressing since scopes generally are rated at -3 dB for frequencies at their max bandwidth. Even if in-calibration it bugs me to see the amplitude drop off as one cranks up the sig gen’s frequency. If you don’t know how a piece of test equipment is spec’d you may be deceived by what is displayed.My Agilent MSO-X 3054A scope does have an internal calibration feature, but I can’t find any information about how accurate this is. The manual does say that for NIST traceability one must follow a normal (and carefully-outlined) procedure using traceable test equipment.A recent EDN article discusses the merits of having an in-house calibration capability. For me, it doesn’t make much sense but for others the trade-offs are different.What are your favorite precision tools and instruments, and do you routinely calibrate them? Jack G. Ganssle is a lecturer and consultant on embedded development issues. He conducts seminars on embedded systems and helps companies with their embedded challenges, and works as an expert witness on embedded issues. Contact him at . His website is . last_img read more

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2019-11-18

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Chief David Nisleit on New Years Eve safety in San Diego

first_img KUSI Newsroom December 31, 2018 Posted: December 31, 2018 SAN DIEGO (KUSI) – If you’re celebrating New Year’s Eve in San Diego, you can be assured the San Diego Police will be working hard to keep everybody safe.But of course, it’s up to each of us to make the right choices to ensure our safety too. San Diego Police Chief David Nisleit joined us on Good Morning San Diego to explain what they have been doing to prepare for the celebratory night. KUSI Newsroom, center_img Updated: 12:13 PM Chief David Nisleit on New Year’s Eve safety in San Diego Categories: Good Morning San Diego, Local San Diego News FacebookTwitterlast_img read more

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2019-09-17

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School Committee Accepts 100K Grant Donation To Strengthen STEM Extracurricular Programs Create

first_imgWILMINGTON, MA — At a specially scheduled meeting, the Wilmington School Committee recently accepted a donation of $100,000 in the form of a grant from the Cummings Foundation.Wilmington High School AP Chemistry Teacher Julie Kim successfully applied for the grant through the Cummings Foundation’s annual “$100K For 100” charitable giving initiative.  Wilmington Public Schools will be the recipient of $33,333.33 per year over the next three years.The purpose of the grant is to provide “financial support to strengthen and build STEM extracurricular programs like the Engineering Career Club, the Science Club, and the Robotics Club at the High School and Middle School levels.”The Engineering Career Club is run under the guidance of WHS math teacher Ms. Steph Murray, a former engineer. The club, which has approximately 20 regular members, meets twice a month for two hours after school. Club members have previously designed, built and launched catapults. They’re currently learning about solar energy and other renewal resources, while designing and building tree-like structures to harness solar energy.The Science Club is run under the guidance of WHS science teacher Mrs. Michelle Hooper. The club meets once  a month on Fridays to run experiments and investigate science phenomenon. The Club has considered joining the North Shore Science League.The Robotics Club is attempting to start up under the guidance of WHS AP Physics Teacher Marlene King and WHS AP Chemistry Teacher Julie Kim.  The idea for the club came out of a discussion that took place in Kim’s AP Chemistry class.“Students and teachers are trying to figure out how to fundraiser for the very expensive robotics supplies and for new computers to write the codes and design the robots,” Kim wrote in her application, where she also noted that most of her AP Chemistry students are female, as are most of the science and math teachers at Wilmington High School and Middle School.“The teachers have a passion for sharing our loves of math and science with the students of our schools, but we’d especially love to encourage more female students to pursue these fields,” added Kim.Because of the grant Kim secured, a robotics club will, indeed, launch at Wilmington High School, and necessary supplies for the other two science clubs will be purchased.  Previously, the clubs’ resources were severely limited and based solely on the amount of money fundraised or contributed by students and teachers.“This grant is very exciting and great news for the Wilmington Public Schools,” announced Interim Superintendent Paul Ruggiero, after reading Kim’s grant application.Kim, unfortunately, could not attend the School Committee Meeting at which she was being recognized as she was stuck in traffic returning from the 8th Grade Science Field Trip to Fenway Park.  Kim will, however, be present at a reception held by the Cummings Foundation on Thursday, June 7 where she will be honored.Wilmington School Committee Chair Julie Broussard with WHS Chemistry Teacher & Grant Recipient Julie Kim after a recent meeting.(Photo courtesy of School Committee member Jennifer Bryson.)Like Wilmington Apple on Facebook. Follow Wilmington Apple on Twitter. Follow Wilmington Apple on Instagram. Subscribe to Wilmington Apple’s daily email newsletter HERE. Got a comment, question, photo, press release, or news tip?Share this:TwitterFacebookLike this:Like Loading… RelatedWilmington High School Receives $100,000 Grant From Cummings FoundationIn “Community”Wilmington’s CLASS Inc. Receives $200,000 Grant From Cummings FoundationIn “Community”SCHOOL COMMITTEE NEWS: Homework, Bullying, Vaping, Grants, Gymnastics & More To Be Discussed At June 12 MeetingIn “Education”last_img read more

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2019-09-11

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Scientists suggest staring down seagulls to protect your snacks

first_img 20 Photos Tags Share your voice This seagull tried to snatch my shrimp in Illinois. Amanda Kooser/CNET A pleasant meal beside a scenic body of water can quickly turn into an Alfred Hitchcock movie if you’re not careful. Seagulls are notorious for strolling right up to people and stealing their lunches. But the good news is you might be able to battle this avian crime wave with a simple tool: your eyes.Researchers at the University of Exeter in the UK wanted to know if staring at seagulls might dissuade them from abducting your dinner, so they headed to coastal towns in Cornwall.The team put a bag of chips (that’s fries for us US folks) on the ground and monitored how long it took the gulls to approach the food. “On average, gulls took 21 seconds longer to approach the food with a human staring at them,” the university said in a release on Tuesday.The researchers initially tried to test 74 herring gulls, but most of them weren’t interested in sticking around or stealing food, so only 19 gulls were usable for the study. 1 Comment Watch a leviathan of a shark nibble on a sub’s speargun Oh snap! Weird ocean worms make a racket when they rumble Cool critters “Gulls are often seen as aggressive and willing to take food from humans, so it was interesting to find that most wouldn’t even come near during our tests,” said Madeleine Goumas, lead author of the study Herring gulls respond to human gaze direction, published in the journal Biology Letters.The researchers found that individual gulls behaved very differently from each other. Goumas suggested “a couple of very bold gulls might ruin the reputation of the rest.”The study had a small sample size, so your gull-staring mileage may vary. It’s worth a shot, though. If you want to protect your food and still enjoy your time at the seaside, then it may just be a matter of playing stare down with the local birds. A spider’s erection, and other cool things trapped in amber Sci-Techlast_img read more

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2019-09-10

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