PURPOSE: To detect the clogging of a pressure introduction pipe by an apparatus easy to maintain and improve the pressure-measuring reliability, by detecting a clogging state of one or both of the pressure introduction pipes from the correlation of oscillations of a differential signal and a static pressure signal.
CONSTITUTION: A differential pressure value of an object 11 to be measured which is transmitted by pressure introduction pipes 14a, 14b and a static pressure value (pressure PH at the high pressure side) are detected by a differential pressure detector 15, and a pressure value PL at the low pressure side is calculated from the detected pressure value by a differential circuit 16. The differential pressure value, static pressure value and pressure value PL are stored in 17. At the same time, the oscillation degree of each pressure is calculated at 18. Thereafter, the correlation of oscillation degrees of the pressures is calculated in a prescribed method at a correlation-calculating circuit 19 and output to a clog-diagnosing circuit 22. The circuit 22 compares values of the correlation in each mode of the pressure introduction pipes 14a, 14b held in a correlation- recording circuit 21 beforehand and the correlation output from the circuit 19, thereby to calculate how the pressure introduction pipes 14a, 14b clog and output a clog diagnosis result signal 23.
KUWAYAMA HIDEKI
TOYODA SHOJIRO
SUZUKI ATSUKO
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