Transient photoconductivity techniques for an electrophotographic photorecetor are described with some related problems.

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The new measuring method of toner charge of magnetic brush developer is developed. The principle of the new method is almost same as that of usual Blow-off method. The distinctive feature of this method is in making use of a magnet as a sample holder instead of a screen mesh that is used in the usual method. With the usual Blow-off method, a triboelectricity between developers and the mesh influences on the measured value. So, the measured value greatly depends on the blow off conditions. On the contrary, the measured value of the new method slightly depends on the blow off conditions.
In the measurement, the developer for test is placed on the magnet sample holder and is blowed by dry compressed gas. Since the electrostatic force between toners and carriers is far weeker than the magnetic force between magnet and carriers, only toners are driven from the carriers. The toner charge is determined by measuring the potential of the known capacitor which is connected to the magnetic sample holder.
As a result, the absolute values of toner charge is obtained with accuracy better than ±4%. Moreover the measuring instruments are very simple and easy to operate. This method should be vely useful for studying developer and development.

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