Timing Measurement

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Timing Measurement

Estimating frequency requires an accurate reference frequency as well as a model of the system under test. Desktop computer sound systems are ideal to make measurements, however the sampling clock is often not very precise. A sound system asked to sample at 44100 Hz, might sample at 44062.8 Hz. We have built a microphone system that provides a precise reference clock on the left-channel of a stereo microphone input, and the signal to be analyzed is placed on the right channel.

Using this system, extremely accurate frequency measurements can be made on any desktop computer.

Hardware

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GPS calibrated microphone system, connected to an ETA-2824-2 watch.

GPS calibrated microphone system.

Accuracy: 1 second every 100,000 years.

The system uses a Telit Jupiter IV GPS chipset to get GPS timing pulses. These are then fed into the left channel of the audio system to allow accurate timing of signals on the right channel.

Software

The software is written in python and works on Linux machines only at the moment.

Status: Basic time-graphing is done.

TODO: Lift angle setting. Amplitude measurement.

ETA 2824-2

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Timing of an ETA 2824-2 Movement

The image on the right shows the timing trace for an ETA 2824-2 movement on a Muhle Terranaut II at various orientations. The top part of the trace is the watch in the face-up orientation (and gaining 4.5 seconds per day). At the crown-up and crown-down positions, the watch was accurate to within 0.5 seconds per day.