| 摘要 |
The piezoelectric unit (4) is connected to the fluid pipe. A change in pressure changes the piezoelectric impedance from a high to a low value. A high voltage rail, connected through a light emitting diode (LED) to the piezoelectric unit, passes current and lights the diode. A self-test button (1) with internal spring (2) and actuator (3) simulates pressure to the piezoelectric unit. The self test unit is reset by a re-arming spring (5).
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