PURPOSE: To make the provision of a pressure detecting device unnecessary in a valve positioner for an adjusting valve or the like by providing a solenoid valve to open/close an air feed route to an operation portion, conducting the closing of the solenoid valve for a fixed time by means of a diagnosis start signal, and at the time of closing, outputting an abnormality signal by means of the valve opening signal of the adjusting valve when a valve opening valve has lowered to less than a prearranged set value.
CONSTITUTION: At the time of the diagnosis of an operation portion 4, a start signal is inputted into a control operator 61 from a start signal generator 38. By means of this start signal, the control operator 61 outputs a pulse signal to a solenoid valve 35 and closes the solenoid valve 35 for a fixed time. At this closing time, a valve lift detector 34 detects the valve opening of a detection adjusting valve 6, and a valve opening signal is outputted to the control operator 61. This valve opening signal drives an alarm 37 when a valve opening value is less than a previously set value, and alarming is carried out. Accordingly, a micro leak at the seal portion of the operation portion 4 can be detected by means of a valve lift detection valve opening signal, and also a whole circuit is driven by means of a small power input signal transmitted through two transmission lines, and the saving of power and the mounting of multi- functions can be realized.
INOUE AKIRA
HAYASHI HIROSHI
NISHIJIMA TSUYOSHI
