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ILRS Home  Engineering Technology Timing Devices TOF Devices TOF Error Sources
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| Error Sources |
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TOF Device Error Sources
Below are the error equations for a general TOF timing device (i.e. a time interval unit or an event timer):
To get the best performance from TOF devices it is ALWAYS
a good idea/necessary to supply the device with the best high-quality,
noise-free external frequency signal that you can (see "Oscillators"
for more information about suitable frequency sources). This is because
the internal crystal oscillators in timing devices generally have poor
long term frequency stability - and any frequency error shows up as
a range-dependent error in the range measurement (see
table below and chart).
For the best laser ranging accuracy you need the best frequency stability,
and any steps taken to monitor and improve frequency stability will
pay handsome dividends.
Other errors can be handled in other ways:
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>SYSTEMATIC errors can be greatly reduced or eliminated
through special calibration tests and procedures;
- >RANDOM errors can be reduced by averaging the results from more than one timer, by increasing the number of measurements by, say, increasing the laser repetition rate, and by minimizing the noise on the input signal.
For 1mm LEO, LAGEOS, High, Lunar, and Mars ranging you need a clock accuracy in one part in 1010, 1010, 1011, 1012, and 1015, respectively.
Responsible Government Official: Carey Noll
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