| 摘要 |
<p>PURPOSE:To achieve a smaller size of the apparatus by detecting a change in mount of powder as caused by a piezo-electric element by variations in phase. CONSTITUTION:While a drive pulse is applied to a powder sensor element 7 from a sweep oscillation circuit 6, phases between a drive pulse signal and a terminal voltage of the powder sensor element 7 are compared with a phase comparing section 8a of a phase detection circuit 8 and a phase difference as results of the comparison is discriminated with a phase discriminating section 8b. Therefore, the phase difference thus detected is latched with a register as level '0', for example, when it is 80 deg. or 90 deg. or as level '1' when it is 0 deg. or 10 deg. based on a threshold of 45 deg. set beforehand. If so, a detection signal can be outputted as digital signal according to the presence of powder. In other words, a phase difference from the drive signal at a resonance point of a powder sensor element can be detected using the powder sensor element with two terminals thereby simplifying an electrode pattern of the sensor element.</p> |
