Oce 3121 Technical & Service Manual page 230

The output level of each sensor is read for 15 seconds. Or, when the platen cov-
er is down, at intervals of 0.128 seconds until the copy button is pressed. If the
output level remains unchanged during the period, a document is presumed to
be present at the sensor position. The size of the document is identified as
shown in the tables.
For cases a & b: the output level will remain unchanged.
For case of c: A3 will be given priority. If no cassette contains A3 paper, the
cassette that is selected under standard mode will be selected.
a) A3 black document
b) Book document (the thickness of a book prevents any changes to the output
level from the sensor.)
c) The platen cover is not closed. (PS3 is OFF.)
In cases of a, b, or c, the size detection could be incorrect.
Note:
Document
PS3:ON
Document
detection 1
Detecting the Size of the Documents
The combination of the outputs from the sensors represents the presence or ab-
sence of a document. Using this information, the image processor PBA deter-
mines the size of the document.
Unchanged
I
Indicates that there has been no change in the sensor output. The presence of
a document is assumed. (The sensor output is checked every 128 ms).
Changed
I
Indicates that a change has occurred in the sensor output. The absence of a
document is assumed.
ed.1
Platen cover
ON OFF
30°
Platen
Document
detection 2
ON ON
No change in Change in
the level the level
04 Exposure 507