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A system for sensing imaging media along a transport path. System includes a light source positioned proximate to a selected location along transport path. A transducer in optical alignment with light source so as to receive light from light source after light crosses transport path provides an out

A system for sensing imaging media along a transport path. System includes a light source positioned proximate to a selected location along transport path. A transducer in optical alignment with light source so as to receive light from light source after light crosses transport path provides an output signal having a frequency representative of the presence of imaging media at the selected location.

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What is claimed is: 1. A detector for monitoring movement of imaging media along a transport path, the detector comprising: a light source positioned to transmit light across the transport path at a selected location; a sensor positioned to receive light from the light source after the light crosse

What is claimed is: 1. A detector for monitoring movement of imaging media along a transport path, the detector comprising: a light source positioned to transmit light across the transport path at a selected location; a sensor positioned to receive light from the light source after the light crosses the transport path and configured to provide an output signal having a frequency based on an irradiance of the received light, wherein imaging media positioned at the at least one location affects the irradiance of the received light based on an optical density of the imaging media; and a controller configured to measure the frequency of the output signal, to compare the measured frequency to a threshold frequency, and to provide a control signal indicative of the presence of imaging media at the selected location based on the comparison; wherein the controller determines the threshold frequency based on a no-media frequency, wherein the no media frequency comprises a measured frequency of the output signal when imaging media is known not to be present at the selected location along the transport path; and wherein the controller periodically adjusts the threshold frequency by periodically measuring the no-media frequency and determining an adjusted threshold frequency based on the measured no-media frequency. 2. The detector of claim 1, wherein the controller determines the threshold frequency by reducing the no-media frequency by a safety margin. 3. The detector of claim 2, wherein the safety margin is as low as ten percent of the no-media frequency. 4. The detector of claim 2, wherein the safety margin comprises a value that enables the detector to sense imaging media having optical densities as low as 0.03 density units. 5. The detector of claim 2, wherein the safety margin is substantially equal to twenty percent of the no-media frequency. 6. The detector of claim 1, wherein the controller adjusts the threshold frequency at a regular interval. 7. The detector of claim 1, wherein the controller adjusts the threshold frequency after each time imaging media passes the selected location along the transport path. 8. The detector of claim 1, wherein the controller measures the frequency of the output signal every two milliseconds. 9. The detector of claim 1, wherein the frequency of the output signal is proportional to the irradiance of the received light. 10. A system for monitoring imaging media along a transport path, the system comprising: a plurality of detectors positioned along the transport path, wherein the plurality of detectors are spaced at intervals to form a linear array across a width of the transport path, each detector located at a different position in the linear array, each detector comprising: a light source transmitting light across the transport path at a selected location; a transducer receiving at least a portion of the light after the light crosses the transport path and providing an output signal having a frequency based on an intensity of the received light; and a controller configured to compare the frequency of the output signal to a threshold frequency and to provide a detector signal indicative of the presence of imaging media at the selected location based on the comparison; and a monitor configured to provide a control signal related to a characteristic of the imaging media based on the detector signal from each detector. 11. The system of claim 10, wherein the monitor is configured to provide a control signal indicative of a width of the imaging media by counting a number of detectors of the linear array having a detector signal indicating that imaging media is present at the selected location. 12. The system of claim 10, wherein the monitor is configured to provide a control signal indicative of whether the imaging media is skewed relative to the transport path by comparing the positions of detectors in the linear array having detector signals indicating that imaging media is present at a first time to the positions of detectors in the linear array having detector signals indicating that imaging media is present at a second time. 13. The system of claim 10, wherein the monitor provides a control signal indicating that the imaging media is skewed relative to the transport path when the positions of detectors in the linear array having detector signals indicating that imaging media is present at the first time do not match the positions of detectors in the linear array having signals indicating that imaging media is present at the second time. 14. The system of claim 10, wherein the monitor provides a control signal indicating that imaging media is present at the selected location when any one of the detectors of the linear array has a detector signal indicating that imaging media is present at the selected location. 15. The system of claim 10, wherein the plurality of detectors are spaced to form a matrix, the matrix comprising at least a first and a second column of detectors positioned respectively at first and second selected locations along the transport path, each column comprising a plurality of detectors with each detector located at a different row position across a width of the transport path. 16. The system of claim 15, wherein the monitor is configured to provide a control signal indicative of whether the imaging media is skewed relative to the transport path by comparing the row positions of detectors of the first column to row positions of detectors of the second column having detector signals indicating that imaging media is present. 17. The system of claim 15, wherein the monitor is configured to provide a control signal indicating that imaging media is respectively present at the first and second selected positions when any one of the detectors of the first and second columns has a detector signal indicating that imaging media is present. 18. The system of claim 15, wherein the monitor is configured to provide a control signal indicative of the width of the imaging media by counting a number of detectors in any one of the columns of the matrix having a detector signal indicating that imaging media is present. 19. The system of claim 10, wherein the system includes a laser imager. 20. The system of claim 10, wherein the system includes a thermal processor. 21. A method of monitoring the position of imaging media along a transport path, the method comprising: transmitting light across a selected location along the transport path; receiving at least a portion of the light after the light crosses the transport path; converting the received light to an output signal having a frequency indicative of the presence of imaging media at the selected location; measuring the frequency of the output signal; comparing the measured frequency to a threshold frequency; and providing a control signal indicative of whether imaging media is present at the selected location based on the comparison; and periodically updating the threshold frequency. 22. The method of claim 21, wherein converting the received light includes converting the received light to an output signal having a frequency based on an intensity of the received light. 23. The method of claim 21, further comprising: determining the threshold frequency based on a no-media frequency, wherein the no-media frequency comprises a measured frequency of the output signal when imaging media is known not to be present at the selected location. 24. The method of claim 21, further comprising: updating the threshold frequency each time imaging media passes the selected location along the transport path. 25. A system for sensing imaging media along a transport path, the system comprising: means for transmitting light across a selected location along the transport path; means for receiving at least a portion of the light after the light crosses the transport path; means for converting the received light to an output signal having a frequency based on an intensity of the received light and indicative of the presence of imaging media at the selected location; means for measuring the frequency of the output signal; means for comparing the measured frequency to threshold frequency; and means for providing a control signal indicative of whether imaging media is present at the selected location based on the comparison; and means for periodically updating the threshold frequency. 26. The system of claim 25, further comprising: means for determining the threshold frequency based on a no-media frequency, wherein the no-media frequency comprises a measured frequency of the output signal when imaging media is not present at the selected location. 27. The system of claim 25, wherein said means for updating updates the threshold frequency each time imaging media passes the selected location along the transport path.