DIY UV power meter for photo exposure film? - Page 1
Forum section: electronics / projects

author: coppercone2
author_rank: Super Contributor
timestamp: December 14, 2023, 02:33:38 am
content: I want to measure my UV exposure source to better handle solder resistor and etching film.Data sheets for the films want Joules/second.How do you do this? I was hoping for something cheap as hell. I don't like working with the films but I wanna give it a chance but I defiantly do not want to buy a assembled UV light measurement unit. This rabbit hole is almost defunded.I am working with LED that is like 385 nm,I was hoping some kind of op amp photo diode circuit or whatever

author: Someone
author_rank: Super Contributor
timestamp: December 14, 2023, 03:02:10 am
content: Without a filter, photodiodes have a broadband response. Fancy meters will be calibrated against a reference matching the source spectrum.If you just want guidance then any cheap photodiode based meter will do. Calibrate the figure/time against your setup manually.

author: coppercone2
author_rank: Super Contributor
timestamp: December 14, 2023, 05:27:22 am
content: well I know what it is, and work in darkness with itthose meters seem to be built for dealing with false positives from room lights ?

author: Terry Bites
author_rank: Super Contributor
timestamp: December 17, 2023, 01:25:46 pm
content: How about just old school, the exposure test strip way?I think that's Joule seconds not Joules per second.You'd need a UV bandpass filter, a sensor and possibly some way of calibrating the thing.A 390nm UV LED can be used as a cheap 385nm photodiode in Photoconductive Mode. Loads of PD amplifier design stuff on the interweb.That gives you a nice log response. You could just stick the amplifier output into a meter and use it as a relative guide. ie What works Vs Volts at your working temeprature.You can even go super cheap and just use a resistor for PV mode (shabby)www.build-electronic-circuits.com/photodiode/

author: LaserSteve
author_rank: Super Contributor
timestamp: December 17, 2023, 02:08:37 pm
content: Go to Thorlabs.comOrder a FDS100 Si Photodiode for 16.95$The web site data sheet curve should have a response curve in Amps per Watt of incident light.Don't worry about the fact that the window is Borosilicate glass. At your longer wavelength you won't notice the slight adsorptive and fluorescence loss.FDS100 are consistent and well characterized.The part is used in many instrument designs.You then have a choice of:1. No filter.. [Good Enough] May need a glass or plastic diffuser.2. Glass doped with ions to be opaque to vis and pass UV, typically made by Hoya. 3. Dichroic Filter, optical version of a multi-resonator microwave wave guide bandpass. [As good as it gets] Order one about 40-60 nm wide centered on 365 nm. [common part]Your looking for a short pass or band pass filter.These come from Thorlabs, Edmund Optics, Newport, IGS glass, etc.Don't worry about temperature compensating the FDS100.You may need a diffuser made of frosted glass, or a pinhole or iris to attenuate and integrate. That's the fun part.Calibration... Who cares. Solar flux chart will probably get you to +/- 10 on a sunny day if you have a good transmission plot on your filter and like math. Otherwise find the owner of a decent thermal laser power meter.Testing... is it linear? Inverse square law and a single UV led.Resistive load is good enough. Forrest Mims has a UA or Lm 741 photometer schematic out there,Search for open source materials from UDT Inc on photodiodes, and open source documents by Phil or Phillip Hobbs.Avoid anything polycarbonate in your optical path.International Light Technologies, ILT, Radiometer on Ebay, 1500$ handheld instrument that is common and sells for a pittance used.Most of them have a coated solar cell, A thin plastic or glass integrator cover, and an ICL7107 chip driving an LCD. Ones calibrated for 365 nm or 405 nm will be good enough for a hobbyist, even if 20 years out of calibration.I had an ILT at work.Accurate calibration at optical wavelengths requires a known standard and a large collection of very expensive gear. I keep multi-line ion lasers around the shop for this, have a substantial collection of laser power meters, and I'm doing good to hit +/- 3% of full scale with used gear. Don't calibrate, for once just insinuate or assume, and you'll be fine.Accurate, tracable, light flux measurement is bought, not made.Run a test strip..Steve

author: jpanhalt
author_rank: Super Contributor
timestamp: December 17, 2023, 02:15:18 pm
content: According to this, UV LED's have a relatively narrow emission spectrum plus some visible:https://phoseon.com/in-the-news/understanding-ultraviolet-led-wavelength/There are "short pass" filters (https://www.asahi-spectra.com/opticalfilters/uv_shortpass_filters.asp) that will attenuate the visible, but that is probably unnecessary. As for measuring the intensity, there are calibrated detectors and one can always turn to actinometric methods (e.g., a photochemical reaction with well characterized quantum efficiency). For example:https://onlinelibrary.wiley.com/doi/full/10.1111/php.13429#:~:text=Actinometers%20are%20physical%20or%20chemical,fluxes%20for%20specific%20photochemical%20reactions.However, none of that is needed for photoresist. Just pick an appropriate LED, and as already said, do an exposure strip test.

author: coppercone2
author_rank: Super Contributor
timestamp: December 17, 2023, 02:24:37 pm
content: for some reason dealing with PCB related issues makes me super crazy and the long solution proposed with the thorlabs diode seems appealing because there seems like there is less to go wrongbecause I have 3 types of films, of various age, and numerous PCB. If I knew the strength I can get an idea if the damn age and type is problems. and idk if i can even trust my source

author: LaserSteve
author_rank: Super Contributor
timestamp: December 17, 2023, 02:53:26 pm
content: Reread my post. I'm done editing. Exposure meter circuits using pure analog for home processing of bw/color film used to be common. Others even control the shutter on the enlarger. Some integrate and time. Some just count. But if you dig into the archives, you will find something in some old magazine to make you happy. At least your not doing Grey Scale and thus would have to worry about Gamma.Properly driven , properly heat sinked leds do not drift much. They age very slowly when underdriven. Monitor the led current.Steve

author: LaserSteve
author_rank: Super Contributor
timestamp: December 17, 2023, 03:15:31 pm
content: Old school 4 watt germicidal lamp tubes don't drift much. Good for several thousand hours of "relative standard" once thermally stable after about 10 minutes of warmup.However they and leds both certainly come with both short and long term corneal exposure problems, UV exposure can result in very painful, very nerve wracking trips to the ER to beg for a local anesthetic.Conjunctivitis aka corneal keratitis is something you will only do once... No matter what source. Two to three days of your eyes swollen shut is a great teacher. Make sure shielding is in place with all UV sources.Be careful, it is easy to do. Back in college I had 400 Eproms to erase. The leakage was considerable. At least Hg based sources came with a sickening blue-green warning glow.Never, Never, again.Thank Jpanhalt for a great post.Steve

author: coppercone2
author_rank: Super Contributor
timestamp: December 17, 2023, 04:31:05 pm
content: well another good reason for a meter is to check your own exposure!but I think those EEPROM erasers are worse no? that is like 200's. This is 385I have one. I turned it on once. I agree its creepy as fuck.but uh... compare to plasma cutter and weldin machines, it maybe not so bad? i would not panic too much because there are TONS of half ass welders that get a nuclear dose in comparison to your chip eraser. Like basically the entire third world. Also how many percent of day laborers outdoors actually put on sunscreen? WIth how 'macho' it is you probobly get made fun of for wearing lotion in the majority of these 'outfits'.And I am not entirely sure, but since I fixed the TIG welder, having compared welding O/A to TIG, I kinda maybe feel that despite the reduced UV emissions, fire (O/A) is not that good for you either. Idk if its trading immediate stress for down the road stress but if you spend a while on a flame torch its not that pleasant a feeling after IMO. Like heat stress. The gases can be taken care of, but there is like heavy radiant heat. Can't be that good for you either. probobly can't get away from being exposed to something bad regardless of the process you choose

author: shapirus
author_rank: Super Contributor
timestamp: December 17, 2023, 04:38:27 pm
content: Quote from: Terry Bites on December 17, 2023, 01:25:46 pmThat wouldn't make sense. It's got to be either Joules/(seconds*m^2), aka Watts/m^2, i.e., power per unit of area, or Joules/m^2, i.e., total energy received per unit of area during exposure.

author: LaserSteve
author_rank: Super Contributor
timestamp: December 17, 2023, 06:19:30 pm
content: 365 and 380 nm light are very close together. Biologically there are differences about every 20-30 nm. I wouldn't count on those differences to protect me with concentrated sources like leds.I know many glassblowers with frosted corneas from radiated heat and UV emission.Welders have Goggles.The Argon plasma in the plasma cutter emits more in the near infrared, but it's UV lines are in the 170 nm region, gets adsorptive effects from air.Steve

author: jonpaul
author_rank: Super Contributor
timestamp: December 17, 2023, 07:30:32 pm
content: Hi the measurement of UV energy/spectra is not trivial.Many poor design/fab/QC photo diodes and LEDs for UV.The old Spectroline UV were merchury types and in all bands.No need for measuremens as the lamp watts ><energy UVA/UVC were predictable.See Spectroline website, look for EPROM erager lampsJ

author: tooki
author_rank: Super Contributor
timestamp: December 17, 2023, 07:31:30 pm
content: Quote from: shapirus on December 17, 2023, 04:38:27 pmYep. All the datasheets I found give it in mJ/cm2(some also additionally give mW/cm2recommendations for optimal performance):Photoresist:https://www.dupont.com/content/dam/dupont/amer/us/en/ei-transformation/public/documents/en/DEC-Riston-LDI300-DataSheet.pdfhttps://www.ccieurolam.com/en/products/dry-films/Solder mask:http://www.cipeldistribution.com/uploads/default/Dynamask-5000-161130.pdfhttps://taiyo-america.com/docs/files/5314/0779/7735/TDS_PSR-4000_CC01SE_August_2014.pdfhttps://safe-pcb.com/SAFE_PCB_WEB/Aide_Document/PDF/PDF_PDF_KSM-6188.pdfhttps://floridacirtech.com/wp-content/uploads/2018/04/LPI-950-C-8GD_TDS.pdf

author: TimFox
author_rank: Super Contributor
timestamp: December 17, 2023, 08:59:42 pm
content: When photographic emulsions are exposed for longer than, say, 1 second to obtain the required exposure, "reciprocity failure" can rear its ugly head.Hence, rating sensitivity in J/m2deposited energy at a specific value of W/m2incident power.https://shootitwithfilm.com/understanding-reciprocity-failure/

author: the Chris
author_rank: Regular Contributor
timestamp: December 17, 2023, 09:45:12 pm
content: Quote from: LaserSteve on December 17, 2023, 02:08:37 pm@coppercone2: IMHO, LaserSteve's advice is a very good solution. The FDS100's sensivity is considerably lower in UV than in IR, but for light intensities usually to be expected in exposure applications, the signal should be measurable sufficiently easy. I used a commercial TIA to do so, but a high-Z DMM over a low ohmic shunt might work as well, I guess.If your exposure unit offers even illumination and you can measure inside near the film level, you might be able to do without the integrator and use the specified ~0.5A/W@385nm in combination with its active area of 13mm² to get a rough estimate of the total power level. I could look up the exact sensitivity of the calibrated sample i worked with at 385nm to narrow down your ballpark, if you like. Better than estimating ghe curve in the datasheet, I suppose.

author: LaserSteve
author_rank: Super Contributor
timestamp: December 17, 2023, 09:53:22 pm
content: https://www.ebay.com/sch/i.html?_from=R40&_trksid=p4432023.m570.l1313&_nkw=UV+radiometer+&_sacat=0You've got options...Steve

author: Terry Bites
author_rank: Super Contributor
timestamp: December 18, 2023, 02:40:51 pm
content: OK, yes, its has to be an energy per unit area (or emulsion volume). A joule per second is power so are they relating that to the optical output of the illuminator?Eg 100W for 10s per sqm

author: shapirus
author_rank: Super Contributor
timestamp: December 18, 2023, 03:03:59 pm
content: Quote from: Terry Bites on December 18, 2023, 02:40:51 pmNah. The requirements are spec'ed at thereceivingside, i.e., the photosensitive material, because you can't specify what the illuminator's output has to be without knowing all its parameters and the distance from it to the material being illuminated.So it has to be measured at the illuminated surface. Well you could calculate it knowing the output power of the illuminator, too, but that involves knowing the values of a lot of variables and how to use them.

author: Someone
author_rank: Super Contributor
timestamp: December 18, 2023, 10:26:20 pm
content: Quote from: shapirus on December 18, 2023, 03:03:59 pmThere is a method to practically eliminate spatial distribution of lamps:https://en.wikipedia.org/wiki/Integrating_sphereBut thats not the question of this thread. Just measuring intensity at the film plane.