Test equipment for measuring flashlights - Page 1
Forum section: electronics / testgear

author: thburns
author_rank: Contributor
timestamp: August 13, 2015, 03:38:28 pm
content: Hi everyone, first time poster here! I came here by recommendation of several people to ask questions about scientific test equipment, and it looks like I'm in the right place!I'm a budding flashlight enthusiast and I've become more and more interested in the physics and electrical engineering aspects of my lights now to the point that I'd like to get something a little better than my cheap equipment that I started out with, partly so that I don't need to do runtime measurements of my lights by locking myself in a closet for an hour and spying on the light meter every few minutes while simultaneously pointing my cheap infrared thermometer at the head of the lightI've also decided that I'd like to get an oscilloscope and a better DMM to measure the current draw of my lights and other things like the frequency for the strobe/beacon modes, and learn some electrical engineering in the process.So far I've gotten my list of equipment down to these choices, and I would love to get your feedback!Light metersEither theExtech SDL400or theGeneral Tools DLM112SD. Both of these light meters have a thermometer, and one of my questions here is if the built-in thermometer that comes with these is as good (or as good for my needs) as one that I'd get on a dedicated data logging thermometer. The thermometer would be used during flashlight runtime tests with a surface temperature probe attached to the head of the light, to analyze things like the automatic thermal stepdown that some flashlights have. Right now I'm leaning towards the General Tools instrument, because I can get it with a NIST calibration for pretty much the same amount as the Extech meter without a NIST certificate.OscilloscopeThis is an area where all I know is that I want one of these, but I have no idea what I need because I am an absolute beginner when it comes to electrical engineering. As I said above, I want to measure things like the strobe frequency of my lights, determine whether they're current controlled or use PWM, and learn more about the electrical side of things in general. The only thing I do know right now is that I'm leaning towards a PC oscilloscope for the convenience that would provide (I want to be able to easily create GIFs/screenshots of the waveforms for things like flashlight review posts). I read a very long review of thePico 2205Alast night, and while I didn't understand 90% of what it was talking about, my takeaway was that it seems like a very good oscilloscope for the price and my hobbyist use cases. I've also been told that the Rigol DS1054Z is a good one to get, but $400 is a bit above what's in my budget (< $300).DMMRight now I just have a cheap Etekcity DMM, and I'd like to make the jump to something better, but not over $250 if possible. I always here Fluke, Fluke, Fluke when it comes to these, and I'm sure one of their more inexpensive models like the 115 or 117 would be good for my needs, but I don't know which one or necessarily what questions to ask myself to make that determination. I will also be using my DMM pretty much exclusively at my workbench, so if anyone has a suggestion for a benchtop DMM that might work well for me in my price range, I'd love to hear what it is and the reason why. I've also seen now that I might be able to get a used Fluke 87V for under $200. One thing I realized recently is that I actually need a DMM that can measureuA, for the purpose of measuring parasitic battery drain from standby modes on my lights.Thank you ahead of time for your feedback, I'm really looking forward to hearing it!

author: georges80
author_rank: Frequent Contributor
timestamp: August 13, 2015, 04:22:06 pm
content: To 'properly' measure the light 'output' of a light source you need an integrating sphere and a spectrometer. Do some searching for those terms on the web to learn what they are and why they are needed, especially for LEDs. A run of the mill light meter will only give you very rough comparative values for your tests that are similar to standing outside and saying that the sky is very blue versus hazy...If you go visit candlepower forums which is more specific to lighting than electronics (this forum) you can search there as well for all things lighting. Though the past 5+ years it has become quite a boring site that focuses on the lastest chinese light and very few people are left that make custom lights/drivers etc.If you want to measure current and characterise it you'll need more than a DMM. Many LED drivers will use a variety of PWM techniques and they have time variant current draws that require faster sampling than what a DMM can measure, unless you're just after some average.So, first step is to define exactly what you are trying to measure and for what reason, i.e. hobby interest or ?? That will narrow your instrument search to something in $1k range versus in the $5k - $10k+ range.cheers,george.

author: thburns
author_rank: Contributor
timestamp: August 13, 2015, 04:33:30 pm
content: Quote from: georges80 on August 13, 2015, 04:22:06 pmThanks for your reply, George! I actually should've stated in my original post that I'm a frequent lurker of CPF, and that I actually don't want the level of measurement at the moment that an integrating sphere would provide. I realize that it's difficult without a properly calibrated IS to get things like absolute lumen measurements versus just relative output over time. I'm more interested in using a light meter with a data logging and thermometer capability to measure output relative to 100% and temperature over time for the purpose of measuring runtime, and particular measuring relative output level changes that happen during either timed or thermal-based stepdown on turbo modes, since these are values that manufacturers seem to specify vaguely or not at all.Essentially, reviews like the ones by selfbuilt over on CPF are what got me interested in taking more detailed measurements of my lights. I'd like to start writing reviews of flashlights myself as well, and I feel like some of these measurements, especially the presence or not of PWM, parasitic drain on standby, and the current draw are valuable things to know. The other reason I have is that flashlights have turned into a broader interest in electrical engineering for me, and I feel they're also a good subject to begin learning more in that regard. I'm definitely not looking to spend more than $1000 on all this equipment combined between the DMM, light meter, and oscilloscope, but hopefully that's a good enough budget to really get me started!

author: georges80
author_rank: Frequent Contributor
timestamp: August 13, 2015, 04:47:27 pm
content: Well, other than the lightmeter, the rest is typical equipment for anyone starting in electronics that has a small initial budget for equipment.One of the cheap/low end Rigol scopes to get a reasonable starting digital scope. Or ebay for a better brand but used with whatever risk that involves.Something to measure adapt the scope for measuring current. The uCurrent unit that Dave sells wouldn't be a bad choice and puts some $ back into Dave's pocket to fund this site and feed his kidLot's of DMMs to choose from and of course ebay again as an option.The lightmeter will be a rough measuring device since it will have a response to match the human eye versus something that can discriminate between the various wavelength peaks of different colour temp white LEDs, but you probably know that already. So, it can only be used for rough comparative measurements.Anyhow, good luck with your venture into electronics, it will be a lot more interesting and rewarding than just playing with various torches/flashlightscheers,george.

author: thburns
author_rank: Contributor
timestamp: August 13, 2015, 05:06:30 pm
content: Quote from: georges80 on August 13, 2015, 04:47:27 pmThanks again for your feedback, and thanks for the suggestion of the uCurrent! That looks like it'll be useful for some of the measurements I want to take. And yeah, I don't plan on doing the kind of light measurements that I'd need a spectrometer for any time soonI'm a little skittish about buying used on Ebay, but I might give it a shot just so I can possibly get some better equipment to start out with.Really excited to see what this world of electronics has to offer once I get beyond just using it to mess with my lights! I could see it leading me quickly towards building my own custom lights or who knows.

author: Smith
author_rank: Frequent Contributor
timestamp: August 13, 2015, 05:37:47 pm
content: You might want to check the spectral response of both meters. Specially some white leds have quite a wide band of emitted light. This can really mess up your measurement. The DLM112SD can use a AC adapter, could come in handy.As a DMM, you cant go wrong with a (used) Fluke. Remember, they are quite expensive, but they can last for multiple decades (if you treat them decent). Often they run longer on batteries (specially the 87V), and they tend to keep within spec for 10/20/30+ years.As a scope, probably any decent storage scope (20MHz and up) will do. Two channels should suffice, but more could come in handy. I REALLY like a scope with an LCD, it works much easier than a USB scope.

author: AG6QR
author_rank: Frequent Contributor
timestamp: August 13, 2015, 06:05:35 pm
content: Quote from: thburns on August 13, 2015, 03:38:28 pmEven the cheapest semi-modern standalone digital oscilloscope can very easily take screen shots. They can normally do so either by tethering the scope to a computer via USB, or by plugging a USB thumb drive directly into the scope and saving the screen shot to the thumb drive. In addition to doing screen shots, they can save the raw waveform data to a thumb drive, for analysis in a spreadsheet or other program.Here's an example of some waveforms I captured from my Rigol DS1052E:http://ag6qr.net/Radio/HR50Clicks/I captured those using a thumb drive plugged in to the scope.Even though I own the 1052E, I would recommend the Rigol 1054Z that gets recommended so often around here. I bought my oscilloscope before the 1054Z was available. But that web page linked above could have significantly benefitted from the four channels, gradient shaded display, and higher resolution screen of the 1054Z. If I were buying today, it would be a 1054Z.Generally, a standalone scope with real knobs is a lot easier and more convenient to operate than a PC-based one.

author: thburns
author_rank: Contributor
timestamp: August 13, 2015, 07:44:07 pm
content: Quote from: Smith on August 13, 2015, 05:37:47 pmI think I'm definitely going to try to find a used 87V. If I buy one used though, would it be advisable for me to send it off for a calibration immediately?

author: thburns
author_rank: Contributor
timestamp: August 13, 2015, 07:48:15 pm
content: Quote from: AG6QR on August 13, 2015, 06:05:35 pmI've seen the 1054Z recommended a lot here now and other places as well. I suppose if I invest a little bit more upfront, something like that is really going to last me a long time! If the 1054Z is truly the thing that's recommended as the best entry level scope, I'm sure I'll be fun adjusting my cost expectations a little bit.

author: retiredcaps
author_rank: Super Contributor
timestamp: August 13, 2015, 08:08:52 pm
content: Quote from: thburns on August 13, 2015, 07:44:07 pmYou can easily get an used Fluke 87V for under $200 USD on ebay, craigslist, pawn shop, etc.I buy used/abused meters and unless there is a problem with the input protection (usually due to an oops moment from previous owner), the calibration is likely to be within specifications. Checking the calibration will likely cost you between $60 and $100 USD.By the way, you may want to see if the multimeter burden voltage will affect your desired standby/parasitic readings?http://www.eevblog.com/projects/ucurrent/PS. eevblog member, excavatoree, wrote a nice Fluke multimeter buying guide athttp://www.ebay.com/gds/Fluke-Meters-Main-Read-First-/10000000007231862/g.html

author: retiredcaps
author_rank: Super Contributor
timestamp: August 13, 2015, 08:11:04 pm
content: Martin does a great video explaining burden voltage (with the 87V as a bonus) ...

author: thburns
author_rank: Contributor
timestamp: August 13, 2015, 08:11:51 pm
content: Quote from: retiredcaps on August 13, 2015, 08:11:04 pmThanks, I was just hunting around for something to explain that after reading your previous reply!

author: retiredcaps
author_rank: Super Contributor
timestamp: August 13, 2015, 08:19:13 pm
content: Quote from: Smith on August 13, 2015, 05:37:47 pm400 hours for a Fluke 87V using a 9V battery. The Fluke 28 II is rated at 800 hours using 3 AA cells.The Fluke 28 II would be a good alternative, but finding under $200 USD will require patience on ebay.

author: AG6QR
author_rank: Frequent Contributor
timestamp: August 13, 2015, 08:21:08 pm
content: Quote from: thburns on August 13, 2015, 07:44:07 pmProbably not needed, though it depends on how important it is that you be able to prove your meter is correct. If you have some sort of contractual arrangement or other explicit need for a calibrated, traceable measurement standard, then sure, send it off. Otherwise, there are a few other less expensive strategies people often use. If you have two or more meters, you can check them against each other, and if they agree to within their published accuracy specs, they're probably OK. If you prefer, you can get a precision voltage reference to check your meter against, such as the DMMCheck and similar items fromhttp://www.voltagestandard.com.A true certified calibration lab will check all the meter's ranges, not just spot check one or two voltage values, so there can be some value to doing that. If everything is within spec, as it most likely will be, they probably won't adjust anything.It's extremely rare to hear of a Fluke 87V giving readings that are outside of its published specs, though.

author: thburns
author_rank: Contributor
timestamp: August 13, 2015, 08:39:26 pm
content: Quote from: retiredcaps on August 13, 2015, 08:08:52 pmSo I just finished watching that video explaining burden voltage, and while I didn't understand all of it (I'm really that much of a newbie to the EE world), my takeaway was that since I'm looking to measure currents on the order of 10s of uA, sounds like I do need something like the uCurrent along with my DMM in order to accurately measure standby drain.

author: thburns
author_rank: Contributor
timestamp: August 13, 2015, 08:39:55 pm
content: Quote from: AG6QR on August 13, 2015, 08:21:08 pmThat's good to know, guess I can save that money for the uCurrent then instead!

author: retiredcaps
author_rank: Super Contributor
timestamp: August 13, 2015, 10:14:47 pm
content: Some more info for you.HKJ is a member here.https://www.eevblog.com/forum/profile/?u=24271and also at candlepowerforum.HKJ's website has a ton of information flashlights, batteries, multimeters to measure current, parasitic drain, etc.http://www.lygte-info.dk/http://www.lygte-info.dk/info/standbyCurrent%20UK.htmlhttp://www.lygte-info.dk/info/Measurement%20UK.htmlYou may want to get HKJ to take a look at your thread and ask for input?

author: thburns
author_rank: Contributor
timestamp: August 13, 2015, 10:16:52 pm
content: Quote from: retiredcaps on August 13, 2015, 10:14:47 pmThanks, that's great to know! HKJ's reviews and articles have been inspirational in me wanting to learn more about the EE side of things.

author: retiredcaps
author_rank: Super Contributor
timestamp: August 13, 2015, 10:33:05 pm
content: Quote from: thburns on August 13, 2015, 03:38:28 pmI haven't spent too much time researching the bench market, but you can find new bench meters for under $200 USD. In the used market, you can get good deals on used Fluke and Keithley in the $50 USD range or less.If I were to buy a new bench meter, I would give serious consideration to the new color big LCD displays. However, I can't find a new one listed in the $200 USD range.This recent thread here discusses some of the options in the $200 range.https://www.eevblog.com/forum/testgear/best-low-cost-(lt$200)-bench-multimeter/

author: thburns
author_rank: Contributor
timestamp: August 13, 2015, 10:37:10 pm
content: Quote from: retiredcaps on August 13, 2015, 10:33:05 pmI was actually wondering about bench multimeters, considering I'm never going to be taking my multimeter with me anywhere and I'm sure that factors into the cost a bit. Really my whole initial setup is going to be very static except for the light meter, which I can't just leave hanging on the wall in the bathroomHeading over to that thread now to check it out!