Witschi Electronic Ltd Analyzer Q1 Page 29
A deviation due to the aging of the quartz and to the temperature is added to the initial deviation.
For quartz watches of medium quality, one should therefore expect a rate deviation between
-0.1 s/d and +0.3 s/d.
The manufacturer data are binding as regards the maximal acceptable deviations.
16.5 Motor Pulse Analysis
16.5.1 Drive Level
Two kinds of motor pulses are used in analogue quartz watches.
a) A fixed pulse, during which the battery voltage is applied to the motor coil for the entire
duration of the pulse.
b) A chopping pulse, which switches the voltage of the motor coil on and off with a fixed
frequency (mostly 1 kHz) during the pulse duration.
The energy sent to the coil with chopping pulses can be varied by changing the ratio between switch-
on and switch-off duration (chopping level). The energy, and hence the consumption, can thus be
matched to the characteristics of the module.
The
Graph of the motor pulse
function displays the shape of the current pulse as an oscillogram.
16.5.2 Watches with Adaptive Motor Pulses (Asservissement)
A watch with adaptive motor pulses determines itself the minimal pulse energy necessary for its
reliable operation. The chopping level and sometimes also the pulse duration can be adapted in
several steps to the power requirements of the watch.
Such watches include an additional circuit that determines if the motor has performed a step. If the
step hasn’t been performed, a second motor pulse with the highest power level is sent (fixed pulse).
During operation, the power level is regularly lowered to the next lower level (e.g. every 4 minutes)
until the watch misses a step. The power level is raised again when a missing step is detected.
One sees that the chopping level, and therefore also the consumption, vary according to the power
requirements of the watch. The consumption increases in the case of shocks, of change of date, of
sinking battery voltage, but also of mechanical faults.
The Analyzer Q1 allows for the first time to test the chopping level, hence the power level, of closed
watches.
Take into account the fact that it needs several minutes to the power level to return to the initial level
after a perturbation (e.g. shock, voltage variation).
16.5.3 Interpretation of the Oscillograms
Please note: In the case of chopping pulses, the current behaviour is determined by the current
spikes of the individual chopping pulses.
- If the watch functions correctly, the current rises continuously at the start of the pulse, reaches a
maximum, then decreases, to increase again at the end of the pulse.
- If the watch is mechanically blocked, the current increases continuously to reach a maximal
value, where it remains until the pulse is over. If the watch is blocked, there is often a strong
asymmetry between positive and negative pulses, since every second pulse has the wrong
polarity.
- A strong asymmetry between positive and negative pulses of a functioning watch points to a
problem with the step motor.
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