SPINNING TOP

Typical Number in Hospital: 1

Cost Bands: 1

References: 7

This is a very simple device for checking the exposure timer on a diagnostic X-ray set. It consists of a round lead disc, 10 cm or so in diameter with holes (e.g. seven of 3 mm diameter) drilled at various distances from the centre. The disc has a knob at the centre with which it can be set spinning by hand upon its solid base.

The output from an X-ray set is pulsating at the mains supply frequency (50 or 60 Hz), or at twice or six times this frequency depending on the rectification method employed in the set. The spinning top is placed over an X-ray film cassette and an exposure made while the disc is rotating, thus imprinting a series of dots on the film showing the number of pulses delivered during the exposure. For instance, for half wave rectification at 50 Hz, ten dots would indicate an exposure time of 0.2 second.

Only one hole is uncovered at a time (the others being plugged) so that a number of time checks can be conducted using the same film.