HP 8550 Service Manual - Page 200

Note Note Original-size sensors The original-size sensors (figure 91) are reflective and are mounted under the copyboard glass (callout 1) to identify the size of originals (callout 2) placed on the copyboard glass. When the copyboard glass cover (callout 3) is brought down to an angle of approximately 30°, a flag blocks photointerrupter PS102 (callout 4) and it turns on. For 15 seconds after PS 102 turns on, or until START is pressed, the output level of each sensor is read at intervals of approximately 0.1 seconds. If the level of the output remains the same during the period, the copy module assumes the presence of an original over the sensor, and identifies the size of the original as shown in tables 59 and 60. This way, the copy module can also identify the size of a black original. The level of the output of a sensor will not change under conditions a and b below; in the case of c, the copy module shows a screen on the control panel, in response to a press on COPY START, for selecting a cassette in the case of auto paper selection or for selecting an original size in the case of auto ratio selection. a A3-size black original b Book original (thickness prevents changes in the sensor level) c Copyboard cover open (PS 102 is off) In each case above, the copy module can incorrectly identify the size of the original. For automatic size-detection of ADF-fed originals, see "Detecting originals" on page 269. 24 23 30° 21 2 Figure 91. Sensor operation 198 Chapter 5 - Theory of operation EN