Spectroradiometer Photo Research PR-703A Teardown + Software Request - Page 1
Forum section: electronics / testgear

author: _Wim_
author_rank: Super Contributor
timestamp: November 05, 2023, 01:43:25 pm
content: Hi All,I bought a Photo Research Spot spectroradiometer on Ebay to play around with, and tough I would share some pictures. This meter is based on a 256 element diode array that is thermoelectrically cooled. It can measure from 380nm to 780nm, with an estimated resolution of 5nm (1.7nm per detector element) It is intended to be controlled by a matching ISA PC-card, which was luckily also included in the auction. Unfortunately, the matching software is missing (also contacted the supplier, but they do not have the software available any longer, only a more recent version of SpectraWin2, which does not work with this camera type).After the objective lens, a mirror is placed with a tiny hole (called a Pritchard mirror). Light that passes through this hole is analyzed, the rest of the light is bounced of a second mirror and sent to the viewing port. Between the viewing port and that second mirror a shutter is placed, which can be opened and closed electronically via the software.Also between the pritchard mirror and the grating a shutter wheel is installed. This allows to measure the dark current each cycle using the same sensitivity as for the light measurement. This ensures minimal drift of the sensor.Both motors have to control signals and a ground. By switching between the 2 control signals the motors advances 1 step (so open/closes the viewer shutter or switches between dark and light measurement). The control signals appear to be -12V.With the use of the ISA board I was able to reverse engineer the DSUB 37 connector. I was also able to measure a spectrum. The ISA pc-card only needs a 5V supply (approx. 3A), there is no need for -5V, 12V or -12V.The desiccant cell can be dissembled and its contents dried in an over. The cell is now again nicely blue in color, avoiding condensation on the thermoelectrically cooled sensor.With the original software it would allow to take the following measurements: spectroradiometry, photoometry, colorimetry, spectral transmittance and reflectance.If anyone would happen to have a copy of the original Spectraview software, or an older version of SpectraWin (V1?) they can share, this would be much appreciated.

author: _Wim_
author_rank: Super Contributor
timestamp: November 05, 2023, 01:45:24 pm
content: Some pictures

author: _Wim_
author_rank: Super Contributor
timestamp: November 05, 2023, 01:48:34 pm
content: Continued

author: _Wim_
author_rank: Super Contributor
timestamp: November 05, 2023, 01:50:16 pm
content: Continued...

author: _Wim_
author_rank: Super Contributor
timestamp: November 05, 2023, 01:51:15 pm
content: Continued...

author: _Wim_
author_rank: Super Contributor
timestamp: November 05, 2023, 01:52:57 pm
content: Continued...

author: _Wim_
author_rank: Super Contributor
timestamp: November 05, 2023, 01:54:58 pm
content: Continued...

author: _Wim_
author_rank: Super Contributor
timestamp: December 29, 2023, 03:41:34 pm
content: As the software is nowhere to be found, I finally found some time to roll my own.I first connected an ESP32 to the minimum required signals on the PCB (clock pulse generation for integration time setting, ADC bits, Start of spectrum pulse, ADC Valid pulse and the outputs to control the 2 shutters). This way I could re-use the ADC & Sample/Hold, the analog TEC temperature control and the hardware to control the shutters.The ESP32 reads the 12 data bits from the ADC, and generates the required clock and pulse signals. All other processing will done in C#. A first screenshot of the working application is attached. I can get a plot update approximately every 50ms. For faster integration times (fastest = 6.4ms) the PC cannot follow, but the ESP32 can successfully send the data out. Both dark and bright captures can be performed.At this stage certainly already usable and fun to play around with. Goal is also to integrate a webcam to show the view through the eyepiece. I am hoping to implement a chromaticity diagram in a later stage, but need some serious reading to understand how to implement this (have not yet found a C# library for this, only one in python (colour-science).

author: _Wim_
author_rank: Super Contributor
timestamp: January 03, 2024, 07:34:38 pm
content: Some more progress: I 3D printed a housing that fits the eye-piece and contains one of these camera modules from Ali-Express (fitted with a 3.6mm lens, also from Ali-express):"IMX179 8 Megapixel USB Camera Module 8MP HD Webcam,3264x2448 15fps,Fixed Focus,Static High-Speed Shooting,Plug And Play"This give a very nice image of the view through the viewfinder, and makes aligning the spectroradiometer in an optical test setup much easier. I have attached a view pictures while playing around with the spectrum of a small halogen bulb.

author: _Wim_
author_rank: Super Contributor
timestamp: January 03, 2024, 07:54:06 pm
content: I also verified the spectral response using a monochromator (type Bentham M300 bought of Ebay) and a halogen bulb at the input on the monochromator. When I wrote the software, calibration was done using only a couple of points near the edges of the visible spectrum, and just divided this by the number of pixels between the 2 measured wavelengths.Here I have stepped the monochromator in steps of 10nm, each time measuring the peak with the spectroradiometer (peak was measured by taking the -3db wavelengths at both sides of the peak and averaging them). With the 2 point calibration the error was already within +-1.5nm. Because it was possible to fit a curve to the observed error, I added this wavelength non linearity correction also to the software. The monochromator was checked and aligned in the past by me with all the spectral lines I can generate (neon, mercury, xenon and a deuterium bulb). I think it is fairly accurate (+-0.2nm), but no official calibration off course.Attached also the measured spectral response together with a zoomed view of the monochromator output port. It is nice to compare the color of the camera with the color in the spectrum chart.

author: _Wim_
author_rank: Super Contributor
timestamp: January 03, 2024, 08:09:23 pm
content: For those of you that also would like to know more about color science, this is in my opinion a fantastic video on the subject: