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

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Structural Temperature

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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

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Elevation Model Test

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Elevation Model Test

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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

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Azimuth Model Test

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Azimuth Model Test

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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

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The Details….

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Previous Focus Tracking Curves

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Previous Focus Tracking Curves

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Temperature Sensor Locations

TSR

TF1

TF4

TF5

TF3

TF2

TH2

TH3 TB2

TB1 TB3

TB5TB4

TE1

TE2

TA3

TA1

TA2

TA4

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Focus Model

• Gravity

• SR-Primary

• VFA-Primary

• HFA

• BUS

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Elevation Model

• Gravity

• BUS

• HFA

• VFA

• Alidade

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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