A Skywatcher HEQ5-Pro motorised mount and Starlight Express Superstar CCD guide camera with OpenCV image processing were tested in use as a solar tracker. The best performance in RA and declination respectively was 0.00 ± 6.15 arcseconds and −1.32 ± 6.62 arcseconds. This compares favourably with data captured on the standard BiSON mount in Carnarvon where the RA precision was measured to be 0.158 ± 8.434 arcseconds and declination −0.066 ± 3.823 arcseconds. The spectrometer was temporarily modified to accept a fibre-feed from the new mount. A low-frequency "footprint" was present in the data residuals that was not resolved, but otherwise results were as expected and comparable to the standard network performance. Two WiFi access points were installed, providing coverage over the whole tower

Hale, Steven J.

University of Birmingham Research Archive, E-papers Repository

BiSONBirminghamSolar-OscillationsNetworkTECHNICAL REPORT NO. 382Fibre-feed tests at Mount Wilson in 2016 SeptemberSteven J. HaleThe University of Birmingham, Edgbaston, Birmingham B15 2TT2016 December 24This technical report series is published by:SLHigh-Resolution Optical-Spectroscopy GroupSchool of Physics and AstronomyThe University of BirminghamEdgbaston, Birmingham B15 2TT, United KingdomTelephone: +44-121-414-4551Fibre-feed tests at Mount Wilson in2016 SeptemberSteven J. HaleThe University of Birmingham, Edgbaston, Birmingham B15 2TT2016 December 24AbstractA Skywatcher HEQ5-Pro motorised mount and Starlight Express Superstar CCD guidecamera with OpenCV image processing were tested in use as a solar tracker. The best per-formance in RA and declination respectively was 0.00± 6.15 arcseconds and−1.32± 6.62 arc-seconds. This compares favourably with data captured on the standard BiSON mount inCarnarvon where the RA precision was measured to be 0.158± 8.434 arcseconds and dec-lination −0.066± 3.823 arcseconds. The spectrometer was temporarily modified to accepta fibre-feed from the new mount. A low-frequency “footprint” was present in the dataresiduals that was not resolved, but otherwise results were as expected and comparableto the standard network performance. Two WiFi access points were installed, providingcoverage over the whole tower.1 IntroductionSteven Hale visited Mount Wilson from 2016 September 13 to October 4. The last visit toMount Wilson was in 2016 April to restart the systems for the summer, and to work on theguiding electronics and second-flat drive mechanism [1]. The purpose of this visit was to installand test a prototype optical-fibre based light collection system, and to temporarily modify theexisting spectrometer to accept a fibre input.It is not intended that this technical report provide significant detail on the hardware mod-ifications or the software controlling the new telescope mount — this will be published in alater report. While the changes are briefly summarised here, the intention is only to present theresults of the performance tests.2 Mount and Guide CameraAfter arriving on-site on September 13, the first four days of the visit were occupied entirely withinstallation of the new hardware. The mount is a Skywatcher HEQ5-Pro with a standard tripod.The fibre-collector and guider head attaches to the mount as a binocular arrangement. Bothuse 80mm focal length objective lenses to form an image of the Sun approximately 0.7mm in1(a) Skywatcher HEQ5-Pro mount. (b) Fibre-collector and CCD camera.(c) Guider image processing with OpenCV.Figure 1: Fibre-feed mount and telescope. The guider image has been inverted for printing.diameter, with one focussing onto a 1.0mm diameter optical-fibre and the other onto a StarlightExpress Superstar CCD camera. The mount and telescope system are shown in Figure 1.During the installation of the long optical-fibre down the entire length of the tower, there wasconcern that the fibre would not be able to support 60 feet of its own weight without breaking.To avoid this problem, the cable was unrolled into the shaft with both ends held at the top,meaning that at most 30 feet of cable was ever unsupported. This allowed the fibre to be cable-tied and supported at two points within the shaft, before one end of the cable was lowered allthe way to the bottom using a length of string. The cable was installed successfully with nodamage.The mount was guided throughout the day by capturing images from the CCD camera andprocessing the position of the Sun using the OpenCV (Open-source Computer-Vision) library.An example of the image captured by the camera is shown in Figure 1c. Images were read fromthe camera as fast as possible — approximately once per second. The image exposure timeis 79ms. The image cadence limit is due to the CCD read-out time and USB transfer rate.The centroid position of the solar disc was found using OpenCV by applying a black and whitethreshold, finding the contours in the image, and subsequently reading out the contour centroidposition. A measure of guiding error was determined by comparing the current solar position2with the pixel values found when the solar image was observed to be directly on the centre ofthe fibre. The position error for each axis was then passed through a PID controller in order todetermine the correct mount drive rate, and the mount updated with the new rate. The opticswhen mounted are short enough to allow the mount to move from the east horizon to the westhorizon without requiring a meridian-flip at solar-noon, and so this greatly simplifies the mountcontrol algorithm.Currently the mount does not have any absolute position sensors installed and so it wasrequired to manually point the system each morning. First light was achieved on September 17.3 Modifications to Klaus for Fibre-FeedFigure 2: Fibre-feed modification to Klaus.All the BiSON spectrometers are designed to point directly at the Sun. This is done byeither swinging the spectrometer on an equatorial mount, or via mirrors using a coelostat.The conversion required to change “Klaus” from the standard direct-feed system to a fibre-feedsystem is quite simple. The front lens tube holds the pre-filters and two lenses in a telescopearrangement. The objective lens (L1) forms an image of the Sun, and a second lens (L2) re-collimates the light ready to be processed by subsequent optics. The entire front lens tube wasremoved and a new lens installed in the L2 position to collimate the output from a fibre, ratherthan collimate the image formed by an objective lens, after which the spectrometer operatesas normal. An iris aperture was also installed to allow the beam intensity to be controlledand prevent the detectors from saturating. The optical modification as installed in “Klaus” areshown in Figure 2.When installing the fibre and collimating lens, the focus of the system was checked usinga 770 nm fibre-coupled LED as a light source. This was done by adjusting the position of the3fibre relative to the focal point of the collimating lens and observing the beam size at L4, thelens immediately before the entrance to the first magnet and oven. The second magnet andoven has been removed from the chassis, and so it was also possible to check the beam focus atthe position of the second vapour cell. It is very important to optimise the beam focus sincethis minimises the beam diameter, and so minimises the non-resonantly scattered light from thevapour cell. If the beam is too large, then it has the effect of lighting up the entrance throughthe magnet and significantly increasing the cold-counts, reducing the instrument sensitivity.The intensity of the LED was controlled to ensure the scattering-detectors were just belowsaturation with the vapour-cell hot, and then the hot-to-cold ratio was measured. The starboarddetector measured 57.7k counts cold, and 450.9k counts hot, a ratio of 7.8. The port detectormeasured 62.0k counts cold, and 491.2k counts hot, a ratio of 7.9.When tested with real sunlight both scattering-detectors saturated very quickly. This is dueto the fibre-collector using a slightly larger objective aperture than the original Klaus telescopesystem, and also the new coarse red-filter having better transmission at 770 nm. A 30mmcardboard aperture matching the original diameter was fabricated and installed on the fibre-collector, and the internal iris-aperture also reduced to bring the intensity within the dynamicrange of the detectors. The hot-to-cold ratio was measured again and with real sunlight thishad reduced to 3.6 for starboard and 3.9 for port. It is expected that this could be significantlyimproved by reducing the detector gains and removing the apertures, similar to the tests usingthe fibre-coupled LED.Klaus was returned to the standard mirror-fed configuration on September 30. The hot-to-cold ratio remained at 3.7 for starboard and 4.0 for port, similar to that achieved with the fibreon September 18.4 Performance Tests(a) Radio antenna (b) Guider shadowFigure 3: Radio antenna shadowing.The first test of the new system was on September 17. Most of the day was taken finalisingthe PID guiding functions, and so only three hours of data were collected in the afternoon. Thedata, shown in Figure 4, suffer a oscillation at 8.165mHz but otherwise look very good. Shortlybefore sunset, the Sun passed behind one of the radio towers to the west of the observatory,shown in Figure 3, causing a temporary issue with guiding.4Mount Wilson/Klaus - 2016 September 17-30-25-20-15-10-50510150200,000400,000600,000800,0001e+0612 14 16 18 20 22 24 2605001,0001,5002,0002,5003,0000 2 4 6 8 10FOM high: 17.1, FOM low: 12.5InvSens: 4672 m/s  Oﬀset: 604 m/s-4-3-2-10123418 19 20 21 22 23 24 25 26Figure 4: 2016 September 17Weather was poor over the next few days, with only two hours of data collected on bothSeptember 18 and September 21, shown in Figures 5 and 6 respectively. A full day of data wasacquired on September 23, show in Figure 7, although some high level haze resulted in poorquality.A further four days of data were acquired before it was time to restore Klaus to the originalmirror-fed configuration. Additional guider telemetry logging was also added in order to assessthe guider performance and stability. Results from September 24 are shown in Figures 11. Thecause of the low-frequency drifts in the residuals is not clear. It is possibly a footprint-likeproblem which has been previously solved by tilting the front coarse red filter, and so the causeis most likely back-reflections somewhere in the system. The RA proportional gain was reducedwhich eliminated the 8.165mHz guider oscillation. The jumps in RA position error shortly aftersunrise and shortly before sunset, shown in Figure 8, are due to backlash in the RA drive-trainas the telescope weight shifts on the axis. Both axes have a minimum drive rate of 6 microsteps-per-second, and this is visible in the declination drive rate, Figure 9, where the PID controlbecomes essentially an on/off switch at minimum-rate around zero-error. The distribution ofposition-error for both axes, calibrated in arcseconds, is shown in Figure 10.Several different guider PID coefficients were tested over the next few days. Results fromSeptember 25 are shown in Figure 15, 12, 13, and 14.Results from September 26 are shown in Figure 19, 16, 17, and 18. At the end of the daythe movement of the declination axis was found to be very notchy. The movement cleared asthe axis was manually exercised several times through the full range of motion. The is possiblythe cause of the slightly asymmetric error distributions on the declination axis.Results from September 29 are shown in Figure 23, 20, 21, and 22. The morning was clear,but became cloudy in the afternoon.5Mount Wilson/Klaus - 2016 September 18-30-20-10010200200,000400,000600,000800,0001e+0612 14 16 18 20 22 24 2605001,0001,5002,0002,5000 2 4 6 8 10FOM high: 11.5, FOM low: 14.8InvSens: 5050 m/s  Oﬀset: 608 m/s-4-3-2-10123418 19 20 21 22 23 24Figure 5: 2016 September 18Mount Wilson/Klaus - 2016 September 21-30-20-10010200100,000200,000300,000400,000500,000600,00012 14 16 18 20 22 24 2601,0002,0003,0004,0000 2 4 6 8 10FOM high: 21.0, FOM low: 5.6InvSens: 4876 m/s  Oﬀset: 610 m/s-4-3-2-10123414.2 14.4 14.6 14.8 15 15.2 15.4 15.6 15.8 16Figure 6: 2016 September 216Mount Wilson/Klaus - 2016 September 23-30-20-1001020300100,000200,000300,000400,000500,000600,00012 14 16 18 20 22 24 2601,0002,0003,0004,0005,0000 2 4 6 8 10FOM high: 9.8, FOM low: 8.1InvSens: 5084 m/s  Oﬀset: 600 m/s-8-6-4-2024616 18 20 22 24 26Figure 7: 2016 September 23−4−2024Error(pixels)−4−2024Guidercoefficients(microstepss−1)14 15 16 17 18 19 20 21 22 23 00 01Time (UTC)9698100102104106108110DriveRate(microstepss−1)Error Proportional Integral Drive RateFigure 8: Guider RA performance on 2016 September 24. Each dot represents the median of50 points, and the banding represents ±1 sigma on each median value.7−4−2024Error(pixels)14 15 16 17 18 19 20 21 22 23 00 01Time (UTC)−15−10−5051015DriveRate(microstepss−1)Error Drive RateFigure 9: Guider declination performance on 2016 September 24. Each dot represents themedian of 50 points, and the banding represents ±1 sigma on each median value.−40 −30 −20 −10 0 10 20 30 40RA guider error (arcseconds)0.000.010.020.030.040.050.060.070.08Probabilitydensityµ = −0.04x˜ = 0.00σ = 6.94−40 −30 −20 −10 0 10 20 30 40Dec guider error (arcseconds)µ = −2.58x˜ = −1.56σ = 8.04Figure 10: Guider performance histogram on 2016 September 24. The dashed red line indicatesthe equivalent Gaussian for the measured median and standard deviation.8Mount Wilson/Klaus - 2016 September 24-10-5051015200100,000200,000300,000400,000500,000600,00012 14 16 18 20 22 24 2601,0002,0003,0004,0005,0000 2 4 6 8 10FOM high: 14.2, FOM low: 16.0InvSens: 4944 m/s  Oﬀset: 636 m/s-8-6-4-20246814 16 18 20 22 24 26Figure 11: 2016 September 24−4−2024Error(pixels)−4−2024Guidercoefficients(microstepss−1)14 15 16 17 18 19 20 21 22 23 00 01Time (UTC)9698100102104106108110DriveRate(microstepss−1)Error Proportional Integral Drive RateFigure 12: Guider RA performance on 2016 September 25. Each dot represents the median of50 points, and the banding represents ±1 sigma on each median value.9−4−2024Error(pixels)14 15 16 17 18 19 20 21 22 23 00 01Time (UTC)−15−10−5051015DriveRate(microstepss−1)Error Drive RateFigure 13: Guider declination performance on 2016 September 25. Each dot represents themedian of 50 points, and the banding represents ±1 sigma on each median value.−40 −30 −20 −10 0 10 20 30 40RA guider error (arcseconds)0.000.010.020.030.040.050.060.070.08Probabilitydensityµ = 0.03x˜ = 0.00σ = 6.15−40 −30 −20 −10 0 10 20 30 40Dec guider error (arcseconds)µ = −2.48x˜ = −1.56σ = 7.18Figure 14: Guider performance histogram on 2016 September 25. The dashed red line indicatesthe equivalent Gaussian for the measured median and standard deviation.10Mount Wilson/Klaus - 2016 September 25-10-5051015200100,000200,000300,000400,000500,000600,00012 14 16 18 20 22 24 2601,0002,0003,0004,0000 2 4 6 8 10FOM high: 14.0, FOM low: 19.4InvSens: 4958 m/s  Oﬀset: 640 m/s-8-6-4-2024614 16 18 20 22 24 26Figure 15: 2016 September 25−4−2024Error(pixels)−4−2024Guidercoefficients(microstepss−1)14 15 16 17 18 19 20 21 22 23 00Time (UTC)9698100102104106108110DriveRate(microstepss−1)Error Proportional Integral Drive RateFigure 16: Guider RA performance on 2016 September 26. Each dot represents the median of50 points, and the banding represents ±1 sigma on each median value.11−4−2024Error(pixels)14 15 16 17 18 19 20 21 22 23 00Time (UTC)−15−10−5051015DriveRate(microstepss−1)Error Drive RateFigure 17: Guider declination performance on 2016 September 26. Each dot represents themedian of 50 points, and the banding represents ±1 sigma on each median value.−40 −30 −20 −10 0 10 20 30 40RA guider error (arcseconds)0.000.020.040.060.080.100.12Probabilitydensityµ = −0.37x˜ = −0.24σ = 6.51−40 −30 −20 −10 0 10 20 30 40Dec guider error (arcseconds)µ = −2.19x˜ = −1.32σ = 6.62Figure 18: Guider performance histogram on 2016 September 26. The dashed red line indicatesthe equivalent Gaussian for the measured median and standard deviation.12Mount Wilson/Klaus - 2016 September 26-30-20-10010200200,000400,000600,000800,0001e+0612 14 16 18 20 22 24 2605001,0001,5002,0002,5003,0000 2 4 6 8 10FOM high: 24.3, FOM low: 32.5InvSens: 4791 m/s  Oﬀset: 609 m/s-4-3-2-10123414 15 16 17 18 19 20 21 22 23Figure 19: 2016 September 26−4−2024Error(pixels)−4−2024Guidercoefficients(microstepss−1)15 16 17 18 19 20 21 22 23 00Time (UTC)9698100102104106108110DriveRate(microstepss−1)Error Proportional Integral Drive RateFigure 20: Guider RA performance on 2016 September 29. Each dot represents the median of50 points, and the banding represents ±1 sigma on each median value.13−4−2024Error(pixels)15 16 17 18 19 20 21 22 23 00Time (UTC)−15−10−5051015DriveRate(microstepss−1)Error Drive RateFigure 21: Guider declination performance on 2016 September 29. Each dot represents themedian of 50 points, and the banding represents ±1 sigma on each median value.−40 −30 −20 −10 0 10 20 30 40RA guider error (arcseconds)0.000.020.040.060.080.10Probabilitydensityµ = −0.08x˜ = 0.00σ = 7.02−40 −30 −20 −10 0 10 20 30 40Dec guider error (arcseconds)µ = −2.37x˜ = −1.32σ = 7.21Figure 22: Guider performance histogram on 2016 September 29. The dashed red line indicatesthe equivalent Gaussian for the measured median and standard deviation.14Mount Wilson/Klaus - 2016 September 29-30-20-1001020300200,000400,000600,000800,0001e+0612 14 16 18 20 22 24 2605001,0001,5002,0002,5003,0000 2 4 6 8 10FOM high: 28.9, FOM low: 17.6InvSens: 4792 m/s  Oﬀset: 613 m/s-3-2-10123414 15 16 17 18 19 20Figure 23: 2016 September 29The guider performance statistics are summarised in Table 1 and 2. The best performance inRA was achieved on September 25 with a precision of 0.00± 6.15 arcseconds. The best perfor-mance in declination was achieved on September 26 with a precision of −1.32± 6.62 arcseconds.This compares favourably with data captured on the standard BiSON mount in Carnarvon on2016 August 16 [2], where the RA precision was measured to be 0.158± 8.434 arcseconds anddeclination −0.066± 3.823 arcseconds.Table 1: RA guider parameters and performance results.Date kp ki Mean Median SigmaarcsecondsSeptember 17 -1.9 -0.007September 18 -1.9 -0.007September 21 -1.9 -0.007September 23 -1.9 -0.007September 24 -1.5 -0.02 -0.04 0.00 6.94September 25 -1.7 -0.01 -0.03 0.00 6.15September 26 -1.5 -0.007 -0.37 -0.24 6.51September 29 -1.5 -0.005 -0.08 0.00 7.0215Table 2: Declination guider parameters and performance results.Date kp ki Mean Median SigmaarcsecondsSeptember 17 1.9 0.0September 18 1.9 0.0September 21 1.9 0.0September 23 1.9 0.0September 24 5.0 0.0 -2.58 -1.56 8.04September 25 5.0 0.0 -2.48 -1.56 7.18September 26 5.0 0.0 -2.19 -1.32 6.62September 29 5.0 0.0 -2.37 -1.32 7.215 WiFi Access PointsTwo wireless access points were installed in the tower. There is one in the control room pluggedinto a ethernet switch. The second is at the top of the tower acting as a repeater for the first.The whole tower now has good WiFi coverage.References[1] Hale, S. J. Autoguider repairs at Mount Wilson in 2016 April. BiSON Technical Report Se-ries, Number 380, High-Resolution Optical-Spectroscopy Group, University of Birmingham,UK, 2016. URL http://epapers.bham.ac.uk/3132/. [page 1][2] Hale, S. J. Repairs to Jabba at Carnarvon in 2016 August. BiSON Technical Report Series,Number 381, High-Resolution Optical-Spectroscopy Group, University of Birmingham, UK,2016. URL http://epapers.bham.ac.uk/3133/. [page 15]16

Fibre-feed tests at Mount Wilson in 2016 September

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Fibre-feed tests at Mount Wilson in 2016 September

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