PURPOSE: To compensate zero drift due to wear so as to maintain characteristics by detecting degree of opening of a control valve, confirming actual zero or 100% position condition of the valve, and compensating zero point of output of detection means based on the signal.
CONSTITUTION: As for an air-to-open control valve 4, degree of opening of the valve becomes 0% when input pressure is Po, 100% when it is P100, and constant when it is above P100, respectively. Zero 100% position confirmation means 11 detects operating input pressure of the control valve 4, 0% position and 100% position of degree of valve opening. When 0% position of degree of valve opening is changed due to wear of plug or sheet and input pressure is reduced below Po- which is lower than Po, it detects this. Output of a valve opening detection means 5 at this time is specified as Do, and zero resetting is done by a compensation operational means 12 so that Do becomes a new zero point of a control operational means 2. Consequently, it is possible to compensate zero drift due to wear and obtain electropneumatic positioner which has good characteristics.
KIMURA ATSUSHI
YAMAGUCHI MASAAKI
NISHIJIMA TSUYOSHI
MIDORIKAWA MINORU
KASAHARA YASUO
SUGAWARA FUJIKAZU
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