Panasonic FP-D250 User Manual page 49

5) Toner Density Control (TDC) sensor
• The TDC sensor, which is installed under the developer transport screw, is an
inductance type sensor used to detect the ratio of toner to carrier in the developer
unit. The sensor measures changes of magnetic flux density, and monitors
the toner density in this way.
• The developer is a mixture of carrier which is a magnetic substance and toner
which is not a magnetic substance. When the amount of toner is over the
standard, the magnetic flux density reduces. The TDC sensor output drops
below the standard voltage as a result. When the amount of toner is less than
the standard, the carrier percentage is high raising the magnetic flux density,
resulting in a lower TDC sensor output voltage than the standard.
• The lower density of toner causes the increase of TDC sensor output. Being
over the standard, the toner hopper motor drives and toner is supplied to the
developer mixing unit to keep the toner density consistent.
<Change of toner density and change of TDC sensor output voltage>
Amount of carrier passing TDC sensor
Less
More
<Control>
The following controls are necessary for normal control of toner density
(1) Automatic adjustment of TDC sensor gain (during execution of F8-09)
(to attain the standard reference level).
(2) Maintain the standard level by control of toner density during use.
<Explanation of the control system>
(1) Automatic adjustment of TDC sensor gain
Automatically adjusts the reference of the TDC sensor by executing service
mode F8-09.
The operation flow is as shown below.
2-12
Toner density condition Sensor output voltage
High Lower than normal
Low Higher than normal