PURPOSE: To detect the clogging of a capillary at a sensor part by comparing the signal set by an electric signal setting means with the drive signal applied to a control valve of a comparison control means and displaying the result of this comparison.
CONSTITUTION: In a normal operation state, the control valve drive signal transmitted from a comparison control circuit 7 is kept at a constant level lower than the Vref signal. Thus a comparison means 9 is turned on and an operation lamp is also turned on. When a capillary 31 has the clogging at a sensor part 3, the mass flow rate is reduced for the gas flowing through the capillary 31 and the output of the bridge circuit constructing the part 3 is reduced. Thus the circuit 7 increases the level of the control valve drive signal and also increases the opening amount of a control valve 5. At the same time, the level of the control valve drive signal supplied to the means 9 is also increased and then exceeds the hysteresis of the means 9. Thus the means 9 is turned off and also the operation lamp is turned off. Meanwhile an alarm lamp is turned on.
NEMOTO HIDEYUKI
ITO YUTAKA
HITACHI LTD
| JPS61107407A | 1986-05-26 |