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GBT PTCS In Progress Review – December 3-4, Structural Temperature 19 locations, 0.2C interchangeable accuracy, 0.01C resolution, 1Hz, range –35 to 40C. (actual accuracy is ~0.1C, temp control of conversion elex) Design documentation: –PTCS Wiki (AntennaInstrumentation) –PTCS Project Note PTCS/PN12 Accuracy tested in lab: –Solar/convective loading –Selected unit-to-unit accuracy, repeatability –Electronics temperature range RFI mitigated, ESD protected Two thermistor failures, forensics with YSI Integrated into M&C First cut pointing, focus predictive algorithms tested
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December 3-4, Green BankGBT PTCS In Progress Review
Thermal Focus and Pointing CorrectionsK. Constantikes
2GBT PTCS In Progress Review – December 3-4, 2003
Status
• New thermal model, new gravity model parameters– Uses 19 structural temperature sensors– Linear thermal, tradional gravity– Focus peformance ~< 3 mm (excludes midday) during ~30 mm
thermal focus shift– Elevation performance ~<3” 1 , <1”/hour (excludes midday) during
~ 30” thermal pointing shift– Azimuth performance ~<3” 1 , <1”/hour (excludes midday)– Unanticipated dominance of horizontal feed arm influence
• PTCS/PN/25 “Thermally-Neutral Traditional Pointing Models and Thermal Corrections to Pointing and Focus”
• Test of real-time focus corrections (Balser and Prestage,11/20/03)
3GBT PTCS In Progress Review – December 3-4, 2003
Structural Temperature
• 19 locations, 0.2C interchangeable accuracy, 0.01C resolution, 1Hz, range –35 to 40C. (actual accuracy is ~0.1C, temp control of conversion elex)
• Design documentation:– PTCS Wiki (AntennaInstrumentation) – PTCS Project Note PTCS/PN12
• Accuracy tested in lab:– Solar/convective loading– Selected unit-to-unit accuracy, repeatability– Electronics temperature range
• RFI mitigated, ESD protected• Two thermistor failures, forensics with YSI• Integrated into M&C • First cut pointing, focus predictive algorithms tested
4GBT PTCS In Progress Review – December 3-4, 2003
Structural Temperature
5GBT PTCS In Progress Review – December 3-4, 2003
Structural Temperature
6GBT PTCS In Progress Review – December 3-4, 2003
Algorithms
• Use existing GBT gravity pointing and focus models• Structure is linear: Thermal effects superpose• Temperature effect on focus, pointing assumed linear
in temperatures• No dependence on air or bulk temps, just differences• Simultaneously estimate gravity and temperature
model coefs• Estimate coefs using 9/11, 10/2, 11/10 data• Test models using 9/5, 11/20 data
7GBT PTCS In Progress Review – December 3-4, 2003
Focus Model
Term Coefficient Min-Max Significance Parameter
M1 1.086 13.1 14.3 SR-PriM2 -0.697 6.2 -4.3 VFA-PriM3 3.981 15.6 62.0 HFAM4 -7.326 0.9 -6.8 BUS V1M5 -0.688 12.1 -8.3 BUS V2M6 -2.576 12.1 -31.2 BUS FM7 -180.630 0.0 0.0 Offset
M8 66.189 .7 43.1 sin term
M9 196.949 0.6 110.8 cos term
8GBT PTCS In Progress Review – December 3-4, 2003
Focus Model Estimation
9GBT PTCS In Progress Review – December 3-4, 2003
Focus Model Tests
• Wind < 2.5 m/s• 15° < elevation < 85° • 9/5 is NCP • 11/20 is all-sky• Excludes 1000-1800• Graphs show thermal
contributions only
10GBT PTCS In Progress Review – December 3-4, 2003
Focus Model Tests
11GBT PTCS In Progress Review – December 3-4, 2003
Elevation Model
Term Coefficient Min-Max Significance Parameter
M1 -4.6455 1.2 -5.3 BUSM2 1.7830 15.6 -27.8 HFAM3 4.4488 5.9 26.4 VFAM4 -8.4477 1.6 -14.0 AlidadeM5 62.2218 0.0 +0.000 -IE,d(0,0)M6 -55.8624 0.7 -62.792 HZCZ,b(0,1)M7 -22.8268 0.9 -38.216 HZSZ,d(0,1)M8 2.4960 2.0 +2.169 -AW,c(1,0)M9 -1.3360 2.0 -1.750 AN,d(1,0)
12GBT PTCS In Progress Review – December 3-4, 2003
Elevation Model Estimation
= 3.6
13GBT PTCS In Progress Review – December 3-4, 2003
Elevation Model Test
14GBT PTCS In Progress Review – December 3-4, 2003
Elevation Model Test
15GBT PTCS In Progress Review – December 3-4, 2003
Azimuth Model
Term Coefficient Min-Max Significance ParameterM1 5.5862 4.0 22.4 Alidade M2 -8.0331 2.7 21.3 HFAM3 -1.6289 2.4 3.8 BUSM4 1.3683 2.0 2.8 VFAM5 3.4124 0.0 0.0 CA, d(0,0)M6 1.3223 0.7 1.0 NPAE, b(0,1)M7 3.5152 0.9 3.0 IA, d(0,1)M8 -2.4960 1.9 4.8 AW, b(1,1)M9 -1.3360 1.8 2.5 AN, a(1,1)
16GBT PTCS In Progress Review – December 3-4, 2003
Azimuth Model Estimation
= 3.9
17GBT PTCS In Progress Review – December 3-4, 2003
Azimuth Model Test
18GBT PTCS In Progress Review – December 3-4, 2003
Azimuth Model Test
19GBT PTCS In Progress Review – December 3-4, 2003
Why does it work?
• Didn’t for 140’ (von Hoerner), why should GBT?– Thermal diffusivity?– Time constants?– Characteristic length of perturbations?– Surface area of structural supports?– Better temperature measurement technology !– Better homology?
pck
20GBT PTCS In Progress Review – December 3-4, 2003
Conclusions
• Focus and elevation greatly improved with thermally-neutral traditional model and temperature corrections
• Azimuth performance improvement marginal (but it’s already pretty good)
• Use of thermal imaging to improve locations• Add sensors to HFA, BUS• Work on graceful degradations• Production implementation• Further tests for confidence• Thermal stability model
21GBT PTCS In Progress Review – December 3-4, 2003
The Details….
22GBT PTCS In Progress Review – December 3-4, 2003
Previous Focus Tracking Curves
23GBT PTCS In Progress Review – December 3-4, 2003
Previous Focus Tracking Curves
24GBT PTCS In Progress Review – December 3-4, 2003
Temperature Sensor Locations
TSR
TF1
TF4
TF5
TF3
TF2
TH2
TH3 TB2
TB1 TB3
TB5TB4
TE1
TE2
TA3
TA1
TA2
TA4
25GBT PTCS In Progress Review – December 3-4, 2003
Focus Model
• Gravity
• SR-Primary
• VFA-Primary
• HFA
• BUS
26GBT PTCS In Progress Review – December 3-4, 2003
Elevation Model
• Gravity
• BUS
• HFA
• VFA
• Alidade
27GBT PTCS In Progress Review – December 3-4, 2003
Azimuth Model
• Gravity
• Alidade
• HFA
• BUS
• VFA
28GBT PTCS In Progress Review – December 3-4, 2003
Optimization
• Focus optimization using pseudo-inverse for LSE solution
• Coupled Az and El gravity models (AN, AW constraint)– Gradient descent
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