WITHDRAWAL OF RAILWAY RAILWAY TRAINING REQUIREMENTS

摘要

A number of randomly distributed pixels in a solid state X-ray imager are designated reference pixels. The distribution of reference pixels may be either totally random or in a limited number of rows or columns. The reference pixels may include predetermined pixels or pixel like elements located in rows or columns distributed in at least two different locations on the sensor. The reference pixels are well distributed to avoid missed exposures due to shading of the reference pixels by dense objects. To determine commencement of exposure the reference pixels are continuously monitored for signal. If the signal level in a predetermined minimum number of pixels exceeds the predetermined threshold, an image capture sequence starts. Otherwise, the entire image sensor is cleared and the signal monitoring continues. The threshold level is set to prevent accidental triggering by dark current at all operating temperatures of interest. Image readout is either initiated after waiting a fixed amount of time or by monitoring the change in the accumulated signal at the reference pixels. If the signal no longer changes then it is determined that the X-ray pulse has terminated and readout can be initiated.