Optoelectronics group meeting, 27 Jan 2006

1. Optoelectronics group meeting, 27 Jan 2006 A software solution for the 12-fibers ribbon cable test Daniel Ricci Web page: http://indico.cern.ch/categoryDisplay.py?categId=482 Optoelectronics group – CERN, Jan 2005

2. What do we need? • A first-level system to test a 12-fibers ribbon cable. • For the moment we don’t care: • which kind of cable (single-ribbon or multi-ribbon); • when the test should be done (cable arrival or during installation). • We started to use the cable prototypes with MPO connectors on both ends. Test system should be: efficient, automatic, cheap, easy-to-use... Optoelectronics group – CERN, Jan 2005

3. What is the idea? • The aim is to verify the cables integrity (in some way...) being sure that: • fibers are not broken; • fibers are not over-bended; • connectors are ok. • This can be done, in a first approach, by inserting light into the fibers and looking at the end if: • we are able to see 12 lighted spots; • the light level, for each spot, is above a minimum value that we can consider acceptable. A system LED-based, capable to insert light into a MPO-connector, has been recently developed by R.Grabit, C. Sigaud and J. Troska. Optoelectronics group – CERN, Jan 2005

4. What is the method? How to recognize the spots? The idea is to acquire a digital image of the 12 spots and analyze it, using a software instrument, to understand the cable status. • Shopping list: • light emitter; • camera (Nikon Coolpix 995 with serial cable); • camera objective–MPO adapter; • software. Optoelectronics group – CERN, Jan 2005

5. Full resolution with digital zoom Width 1536 pixels Length 2048 pixels The software concept 1 Let’s imagine to have (in some way to be defined later) an image to analyze. With LabVIEW it is possible to convert an image in a map of pixels. The image depth in full resolution is 24 bit. The 24 bits are grouped by 8 according to the RGB color representation. Of such image is so possible to give a tri-dimensional view: Optoelectronics group – CERN, Jan 2005

6. The software concept 2 • The image needs to be cleaned  three types of cuts: • length (10%) and width (15%) cuts: without effects on the area of interest; • depth cut (variable): to eliminate the spots halo, preparing the image to the peaks recognition. depth cut: 85% • It is now possible to define a spots recognition subroutine which should: • recognize if the spots are 12 (in case not, identify which is missing); • “decide” if the spots have enough intensity. Optoelectronics group – CERN, Jan 2005

7. The software concept 3 Integration process Width (Y) integration: 12 peaks can be recognized by using a specific function in LabVIEW (we need to define an “expected” peaks width). Lenght (X) integration: observe that peaks apparently higher don’t correspond to highest intensities. Now we need to define a threshold (absolute? and? relative?). Optoelectronics group – CERN, Jan 2005

8. The software concept 4 • Two examples of problems encountered: • - peaks phantasm (solved) • - how to find the missing fiber number (limit) Due to the depth cut effects, we could not be able to identify the right number of peaks another peaks check was introduced during the second step of integration by defining a different algorithm  double check delete small (< 5%) peaks and gives useful feedback on image resolution. A grid on the expected peaks positions has been defined  we need a starting point  we cannot identify the number of fibers if missing one on the edges. Optoelectronics group – CERN, Jan 2005

9. How to acquire a good image? • Remarks: • Resolution and zoom: we want to avoid any possible digital treatment during the image acquisition  no digzoom and no compressed resolutions; • Focus: cannot be automatic (sensor is outside the objective)  must be set at 0.24m (tube length); • Shutter speed: le light intensity is not compatible with the automatic mode  to avoid over-exposure a proper value must be set; • Aperture: cannot be automatic  dark background force to find the right value;  due to shutter/aperture constraints, the camera must work in full manual mode; • Metering: exposure based on a small area of the picture with dark background -> method suggested: “spot”. • Over this settings, we can also play with the software cut. Optoelectronics group – CERN, Jan 2005

10. Camera software 1 A good compromise is: Can we set these parameters through the serial cable? We would like to be able to communicate with the camera using a LabVIEW code... • Nikon has its own serial protocol not published  impossible to use directly the hexadecimal commands  we need to adapt something existing. • Four free software are available online but only one can be used for our purposes: • PHOTOPC (http://www.math.ualberta.ca/imaging/ ) • it is a remote control driver for Nikon Coolpix cameras; • it allows to use command line for serial communication (can be integrated in LabVIEW); • doesn’t use the original protocol: some commands may generate an error; • not all commands are available (ex.: shutter and aperture). Optoelectronics group – CERN, Jan 2005

11. Camera software 2 • A LabVIEW code was written in order to automate the camera settings. • The software can: • set the resolution, optical zoom, metering; • take a picture (saved on camera flash memory) and transfer it to the HD. The software cannot set a manual focus, shutter and aperture. • Time required to set the camera: 30s (but this has to be done only one time). • Time to take a picture and download it: 20s. • This delay is due to various factors: • camera is using a serial port (no USB control is available for this model); • camera always save the pictures on the flash card; • camera needs few seconds after a command is sent to close the protocol transactions. Both programs (picture analysis and camera controller) were integrated in a unique one. Optoelectronics group – CERN, Jan 2005

12. Testing The aim is to test the software capability to: 1) recognize peaks  no problems found until now if the tube position is horizontal; 2) decide if a fiber has enough light  discussion is opened to decide about threshold. Some online examples About point (2), 10 photos has been taken consecutively without touching the hardware. Results show that light variation is considerable (AC?, T effects?) Remarks: - light intensity for fiber #0 is systematically lower than the others; - software cut affects the integrated light! Optoelectronics group – CERN, Jan 2005

13. Some results Optoelectronics group – CERN, Jan 2005

14. Summary • A software instrument for 12 ribbon cable test was developed. • camera parameters were defined: some can be automatically set, for others a manual operation is required; • the software works well on spots recognition (if picture is horizontal); Limits: - picture must be horizontal; - missing border fibers makes impossible to properly identify the fiber(s) number...but it is able to point out this! • the double peaks check is able to point out problems in the image resolution; • spots intensity measurement is possible but evaluation method needs to be understood. Optoelectronics group – CERN, Jan 2005

15. Future developments • The cable test will be done under our supervision we don’t need an instrument for monkeys we can tolerate to set manually the camera, we can avoid to spend time for vertical image recognition, etc... • We need: • to test the setup on different cables for a better debugging; • to clarify the light variations behaviour to see if we can achieve a more stable condition; • define the thresholds; • some “maquillage” actions on the code (put a control to verify if barcode is correct, possibility to scan a barcode with a scanner, etc...); • to define which kind of cable we want to test. Optoelectronics group – CERN, Jan 2005