A display panel is designed such that a pixel including sub-pixels indicative of red, green, blue and at least one other color includes two sub-pixels at least in a longitudinal scanning direction and a color filter is provided for each of the sub-pixels. The bypass capacitance accommodates changes in the output voltage of the inverter to suppress the feedback effect from the output side to the input side of the inverter. This sensor design enables the sensor to be rotate after installation to obtain a desired coverage patterns. In another embodiment, the well is optimized by measuring the production of the well in one cycle of operation. A horizontal shield and a vertical shield are disposed in the housing and shield the contacts from one another. The substrate includes main channels electrically connected to the probes; and at least one spare channel for replacing the main channels when at least one of the main channels is damaged.