A measurement device for measuring a response to actuation of an electro-mechanical transducer in a print head assembly for an inkjet printing system includes a sensing circuit and a measurement circuit. Pressure in the third space is lower than that in the second space. The power cleaning head comprises two or more regions, wherein at least one of the regions is configured to move and wherein at least one of the regions comprises a squeegee element. The amount of delay is adjusted responsive to a change in the DC input to effectively maintain a constant switching frequency of the inverter. The organic image sensor further comprises a first protective structure covering a top surface and a sidewall of the organic photoelectrical conversion structure. Reducing the number of accesses to the system memory increases processing speed, and reduces the load of a main processor, when image data is to be encoded or decoded.