National Conference of Astronomers of Serbia, Belgrade, 10-12 October 2011

1. AMBIENT TEMPERATURE CHANGES
AND THE IMPACT TO
TIME MEASUREMENT ERROR
Vukan Ogrizović, Jelena Gučević, Siniša Delčev
University of Belgrade
Faculty of Civil Engineering
Department of Geodesy and Geoinformatics

2. Vertical deflections
Natural coordinates (Φ,Λ) Elipsoidal coordinates (φ,λ)
- astronomical - - geodetic -
Φ 5 = const. φ5 = const.
Φ 4 = const. φ4 = const.
Φ 3 = const. φ3 = const.
Φ s = const. φs = const.
ξ = Φ − φ = const.
φ
Φ1 = const. 1
η = ( Λ − λ ) cos φ
A − α = ( Λ − λ ) sin φ

3. Measuring systems for
(Φ,Λ) determination
TZK2 - D DIADEM
(Institut für Erdmessung, (Eidgenössishe Technische
Hannover) Hochschule, Zürich)

4. Time-keeping in field
• 1PPS from GPS to DB9 via RS232
• GPST to quartz oscillator ticks
• RTOS

5. Frequency vs temperature plots
• Variations in temperature -> major influence on the
crystal frequency
• Changing the curvature of a crystal cut can make the
slope less steep

6. Experiment set-up
• Time reference: Trimble NetRS w Zephyr Geodetic
• UTC source: 1PPS output (BNC type) wired to DB9
• SI second acquisition: Interrupt handler under RTOS
• Resolution:
133 MHz ≈ 7 ⋅10 −9 s

7. Set-up #1
- Testing performed outdoors
- Ambient temperature: ~17°C
- Measuring session: ~2 h
Raw data
After removing the blunders

8. Set-up #2
- Testing at different environmental conditions
- Ambient temperature increased from 0°C to 21°C
- Measuring session: ~5 h
Raw data
After removing the blunders
Set-up 2a Set-up 2c Set-up 2b

9. Calculation of the clock model
• Four tests, each cca 2 h long:
– #1: T = 17°C
– #2a: T = 0°C
– #2b: T = 21°C
– #2c: 0°C < T < 21°C
• Clock drift & bias according to the linear
model:
UTCi = T0 + (1 + h )Ti

10. Calculated biases (tab'd)
Set-up # T [ °C] h [s/h] sh [s/h]
1 16 0,003 0,001
2a 0 -0,033 0,002
2b 20 0,006 0,002
2c 0-21 -0,026 0,003

11. Calculated biases (graph)

12. Conclusion and remarks
• Clock bias strogly dependent on temperature
• Need for stable environmental conditions
• Shorter session -> linear clock model

13. Thank you for your attention!
University of Belgrade
Faculty of Civil Engineering
Department of Geodesy and Geoinformatics
Vukan Ogrizović, vukan@grf.bg.ac.rs
Jelena Gučević, jgucevic@grf.bg.ac.rs
Siniša Delčev, delcev@grf.bg.ac.rs