WTB: Sensors Unlimited Inc SU512 ingaas photodiode array - Page 1
Forum section: electronics / general

author: _Wim_
author_rank: Super Contributor
timestamp: May 02, 2020, 10:52:21 am
content: Hi,I recently bought a spectrometer on Ebay for spares or repair (a BW Tek BTC261E). I was hoping to fix this, or at least retrieve the sensor from it.Upon first inspection I could see the unit was already heavily worked on, not a good sign. Especially the TEC control circuit had many modifications/repairs, with flux residue all over the place. The soldering job was in many place not the best to say the least...Initially the spectrometer was not detected by USB, but I was able to fix that. Unfortunately then I discovered the sensor itself was damaged. The internal TEC is open circuit, and many pixels remain high independent of light input. This was probably the original issue, and the previous owner tried to modify the TEC control circuit hoping this would be the fix. Sensor sensitivity is also way down, maybe due to overheating (a non powered TEC is a good insulator).The sensor is a Sensors Unlimited Inc SU512LE (also sold under names UTC AEROSPACE SYSTEMS & Polytec). If any-one has one of these for sale (I know, a long shot), or knows a place to find an affordable one (nothing on Ebay, also not in the sold items), this would be much appreciated.Link to datasheet:http://www.sensorsinc.com/images/uploads/documents/1008620-1.pdf

author: ace1903
author_rank: Regular Contributor
timestamp: May 04, 2020, 11:04:55 am
content: Could you please provide us pictures of the internals of the spectrometer?Like teardown pictures, to get an idea about what kind of equipment it is.I have seen only spectrometers from the 1980ies with single wide spectra diode.Maybe to use some other electronics instead of the original one. Is it an option?TI has some interesting reference design with DLP mirror as optical grating.Maybe to take an idea from them for alternatives to that specific sensor.

author: _Wim_
author_rank: Super Contributor
timestamp: May 04, 2020, 08:36:02 pm
content: Hi, thanks for your reply. In this case the sensor is essential in creating the spectral pixels, and cannot be replaced with a single photo diode. Attached is a picture of the optical bench of the broken spectrometer, and the a picture of the used principle.I have seen the TI DLP sensor based system, and in theory, this could indeed be used to work with a single photodiode in my broken spectrometer, but this would be almost the same as building a spectrometer from scratch, as the splitted beam needs to be focussed in a specific way on the DMD chip for it to reflect each spectral pixel to the photo diode. Easier (but not easy) would be to add some mechanical movement on the current grating or mirror to allow a specific spectral pixel to reach the photo diode, but for the moment I am not going to do major mechanical changes, and will look a little longer for a replacement sensor.

author: mjs
author_rank: Regular Contributor
timestamp: June 03, 2020, 11:00:02 am
content: Now there's a camera with older SU256LX line sensor on eBay. The detector is 256 pixel instead of 512, but if it's a hobby project, you might place a low offer for that one. Manufacturers rarely change these, so it might be a drop-in with just less pixels or length.I've got a 256 pixel non-cooled spectrometer and without cooling InGaAs sucks big time compared to Si detectors.

author: _Wim_
author_rank: Super Contributor
timestamp: June 03, 2020, 07:50:41 pm
content: Quote from: mjs on June 03, 2020, 11:00:02 amThanks for the excellent tip, I have seen that one (it is from the same seller I bought the original spectrometer from, and he informed me before he put it online to ask if this would be an option)As the data is clocked out serially pixel by pixel using an analog video signal, I am afraid it will be not so easy to use a 256 pixel chip. These sort of camera's also exist in 512 pixel versions, so hopefully it is only a matter of being patient

author: _Wim_
author_rank: Super Contributor
timestamp: June 03, 2020, 08:47:11 pm
content: Quote from: _Wim_ on June 03, 2020, 07:50:41 pmIf somebody knows the password for the service menu in the BWSpec software, maybe there is an option to tell the spectrometer a 256 pixel chip is installed. This because the 512 pixel chip uses both video out 1 and video out 2 (odd and even pixels) and the 256 pixel chip not, I will otherwise end up with a spectrum with a each time a good pixel followed by a dead pixel.

author: mjs
author_rank: Regular Contributor
timestamp: June 10, 2020, 05:26:05 am
content: This kind of items may pop up on eBay under strange names if the seller is getting rid of some lab or inside instruments. I've bought a few *very* expensive CCD/InGaAs cameras and sensors on the cheap this way over the years. So patience may pay off.Life sciences instruments for pharma and DNA sequencing stuff seem to have no BOM cost constraints due to budgets and new methods popping up all the time. Just check out the full genome DNA sequencing cost and equipment used 2000-2020 - on that field Moores law would be considered full stop!I did not check the sensor geometry (i.e. is 256px shorter). You can also probably tie the single output to both inputs of the electronics board to get same value on two consecutive pixels (don't remember for CDS is done on these, though, so check that timing) or just accept that every second pixel is zero.

author: _Wim_
author_rank: Super Contributor
timestamp: June 10, 2020, 06:02:52 pm
content: Quote from: mjs on June 10, 2020, 05:26:05 amYes, it is indeed a challenge. Or the seller puts it under a strange name for an affordable price, or the seller knows what it is which make the price typically too high.Quote from: mjs on June 10, 2020, 05:26:05 amThat is my main source of optical components and lasers...Quote from: mjs on June 10, 2020, 05:26:05 amI do not think so. The 256 arrays have 20µm pixels, and the 512 10µm pixels. The thickness of the complete array is however thinner due to the absence of the cooler. This could be fixed with some standoffs. The units with a multistage cooler are thicker than mine and would not fit.Quote from: mjs on June 10, 2020, 05:26:05 amEvery second pixel zero would not be very differenent from the the current state I am afraid. I think I have currently approx 75 dead pixels and no cooling. I can zero the dead pixels by taking a dark reference, but this is not at all perfect. It also makes making automated measurements like FWHM difficult. Due to the lack of cooling noise is also quite high. Initially I thought this was caused by sensor sensitivity being low, but I am not sure of that any more after some more testing.Connecting left and right pixel together might indeed be an option.But first I will keep on looking on Ebay for a 512 cooled replacement. As you said, patience may pay off.Also still hoping to find the service password for the software. This maybe allows to disable the dead pixels and/or change the installed sensor config.

author: _Wim_
author_rank: Super Contributor
timestamp: August 29, 2020, 06:59:40 am
content: Just a quick update. I bought this sensor on Ebay:https://www.benl.ebay.be/itm/USED-Raman-1064nm-TECooled-InGaAs-SingleLine-Detector-and-Socket-PCB-Rescued/254673590606?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649I was listed as probably a Hamamatsu device, but it was off course clearly a Sensors Unlimited Inc device. Off course the seller had no idea of the number of pixels, but as the price was ok, I took the gamble.Sensor has in the meanwhile arrived, and it is a 256 pixel sensor. Luckily it is indeed possible to tie left and right pixels together, to simulate the 512 pixels. So this works again ok.Cooling and temperature read-out are still broken, probably due to the failed "repair" attempts of the previous owner. I verified the cooling and temperature read-out of the sensor itself, that works ok. So if I cannot fix the current control board, it should be fairly straightforward to build a separate board handling the temperature control separately.

author: ace1903
author_rank: Regular Contributor
timestamp: September 01, 2020, 01:59:01 pm
content: Nice to hear that you found replacement sensor.Think you will guess my next questionCan we get pictures of control circuit for peltier cooling?And unit electronic parts?

author: _Wim_
author_rank: Super Contributor
timestamp: September 01, 2020, 06:24:59 pm
content: This is a picture of the relevant part of the circuit. I am still trying to reverse engineer the circuit in detail, but due to many unpopulated parts and configuration options, progress is slow. The output FET (ndp6060l) is connected to U370 via R634A16. The FET is a logic level FET that switches towards GND and connected to the negative terminal of the peltier. The positive terminal of the peltier is connected to 5V.The analog devices part (marked with 6A) is a 3V voltage reference (out on pin 6), but not completely sure which part it is. The thermistor of the sensor is connected to the negative terminal of opamp 1 of the OP295.Current status: FET is not switching but remains in its transition region, heating it up to approx. 110°C. Both opamps are working ok, and also the voltage reference.

author: _Wim_
author_rank: Super Contributor
timestamp: September 01, 2020, 06:44:41 pm
content: Success!I removed the resistor that was clearly not original on the OP295, and now current is nicely switching between 0 and 2.3A at a rate of approximately 0.25 Hz