Quality control of diagnostic X-ray machines requires the monitoring of radiation parameters. The radiation quality is usually measured by photographic exposure using several filters. A similar approach is to measure the exposures with electrical devices, also using several filters. By comparing the output signals the effective kVp can be deduced. The authors' method is based on the exposure of several photovoltaic cells. One cell is exposed directly, while the others have different filters. The exposures were taken with a 12-pulse generator which had recently been calibrated for kVp and mA values. The output signal was a square pulse, with the duration of the exposure. Its height was equivalent to the kVp and mA. Photovoltaic cells and photodiodes are described by the manufacturers as detectors for visible light and infra-red. The authors' experiments have shown, however, that most of them are also sensitive in the X-ray region of the electromagnetic spectrum. Usually different photocells of a given type do not have the same characteristic in the whole X-ray useful spectrum, but selection of cells for close characteristics is possible.
