Common-mode termination within communication systems. The at least one tube has a plurality of conductors in electrical communication with the control box. A damper chamber 12 for releasing pressure change inside the liquid reservoir is formed at a part of the head case or seal plate 5 corresponding to the liquid reservoir 9. To implement the adjustments, a compensation factor is calculated based on a difference between the basal scanning rate of the device and the measured actual scanning rate. This method suppresses generation of internal DC voltage and thus prevents impurity ions from deteriorating the quality of displayed pictures.