Spinner (ca. 1950s) |
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The
quality of radiograph (x-ray picture) depends on several parameters:
the high voltage, the tube current, the exposure time, the film,
etc. Unfortunately, the mechanical timer used by the early x-ray units
were particularly unreliable. These
x-ray units used a transformer to obtain the high voltage required by
x-ray tubes. Since the input current was 110 volts AC, the x-ray beam
would consist of 60 pulses per second if half-wave rectification was
employed and 120 pulses if full-wave rectification was used. This provided
a convenient method for calibrating the x-ray unit’s timer. The
spinner, with a single hole (ca. 1 mm diameter) at its edge, was placed on
a piece of x-ray film and spun gently. The x-ray unit was then operated
with the timer set for a particular exposure. If the timer was set for one
second, 60-120 spots should appear on the processed film depending on the
rectification (in reality, one second is a bit long because you would want
to avoid a complete rotation of the top). If a different number of spots
appeared, the timer was faulty. |
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