CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. national stage application of the PCT International Application No. PCT/JP2019/010444 filed on Mar. 14, 2019, which claims the benefit of foreign priority of Japanese patent application No. 2018-067342 filed on Mar. 30, 2018, the contents all of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a gas safety device that measures a gas flow rate, blocks a gas flow path when an abnormal flow rate is measured, and secures safety in use of a gas.

BACKGROUND ART

Among gas meters that measure the amount of gas consumption, some gas meters having become widespread in recent years contain a gas safety device that ensures safety by determining that an abnormality has occurred to block a gas flow path when a high flow rate is measured or when the gas has been consumed for an unusually long period of time.

In addition, some gas safety devices have a function of notifying a center that a minor gas leakage has occurred when the gas flow rate remains constant over a certain period of time although the flow rate is very low.

For this type of gas safety device to measure a flow rate, either a diaphragm meter that measures a flow rate based on the volume that has passed through the meter within a predetermined time period or an ultrasonic meter that measures an instantaneous flow rate by activating an ultrasonic sensor at predetermined time intervals is used.

However, in cases where, for example, a gas cooling and heating apparatus of a gas heat pump (GHP) type is installed downstream of the ultrasonic meter that measures a gas flow at predetermined time intervals, the ultrasonic meter is problematic in that the flow rate measurement result varies with pulsation of a gas pressure generated after start of operation of the gas cooling and heating apparatus. Against this phenomenon, some conventional ultrasonic meters employ measures by which a continuous time period equal to an integer multiple of the pulsation frequency is used as a flow rate measuring time to reduce the influence of the pulsation. Furthermore, some gas safety devices prevent erroneous detection by stopping the function of detecting a gas leakage when a fluctuation in the flow rate is detected.

A conventional gas safety device is described below with reference toFIG. 7.

FIG. 7is a configuration diagram of a conventional gas safety device. The conventional gas safety device measures the flow rate of a gas flowing through flow path2with a pair of ultrasonic sensors1and ultrasonic sensor drive circuit3. Control circuit4integrates the amount of gas consumption using the flow rate measurement data piece measured in ultrasonic sensor drive circuit3. A general gas safety device usually has a function of displaying the integration result. Then, when control circuit4determines that the gas usage pattern is abnormal, control circuit4sends a shutoff instruction signal to shutoff valve drive circuit7to close shutoff valve8disposed across flow path2so that the gas is shut off. In addition, control circuit4includes leakage detector14that determines that a gas leakage has occurred when the flow rate measurement result continues to be a value other than 0 (L/h) for at least a predetermined time period. When it is determined that a leakage has occurred, leakage alarm13disposed in control circuit4indicates that a gas leakage has occurred. Furthermore, pulsation recognizer5is disposed in control circuit4in consideration of the pulsation that may occur depending on the gas installation conditions, and control circuit4has a function of preventing leakage alarm stopper12from erroneously alerting that a gas leakage has occurred when pulsation recognizer5recognizes the occurrence of pulsation (see, for example, PTL 1). Moreover, a gas safety device of this type reduces the influence of pulsation of a gas flow rate by setting flow rate measuring time Ta to a time period equal to an integer multiple of the period of pulsation of the gas flow rate as illustrated inFIG. 8(see, for example, PTL 2). Here, T in the figure represents a measurement interval at which flow rate measurement data piece is output from the ultrasonic sensor drive circuit.

CITATION LIST

Patent Literature

PTL 1: Unexamined Japanese Patent Publication No. 2001-241985PTL 2: Unexamined Japanese Patent Publication No. 2003-315132

SUMMARY OF THE INVENTION

However, for ultrasonic meters disposed on a conventional gas safety device, specifications about a flow rate measuring time are defined on the assumptions that fluctuations in flow rate due to pulsation in a forward direction and a reverse direction are symmetrical and that the frequency of the pulsation is a predetermined value. As a result, conventional gas safety devices remain problematic in that a flow rate measurement result may unexpectedly greatly vary depending on the structure of the flow rate measuring unit or environmental change in the market, and that the leakage detecting function of detecting a gas leakage may often fail to work properly.

The present invention provides a gas safety device that normally fulfils the function of detecting a leakage even when a considerable influence of pulsation of a gas flow rate is exerted.

A gas safety device of the present invention includes: a flow path through which a gas flows; an ultrasonic sensor for measuring a flow rate of the gas flowing through the flow path; a flow rate calculator that calculates a flow rate measurement data piece from a measurement value of the flow rate measured by the ultrasonic sensor; and a leakage detector that detects a minor leakage of the gas. In addition, the gas safety device of the present invention includes: a pulsation recognizer that recognizes that pulsation is occurring in the gas flow rate when a fluctuation in the flow rate measuring data piece calculated by the flow rate calculator is greater than or equal to a predetermined value; and a pulsating flow rate corrector that corrects, when the pulsation recognizer determines that the pulsation is occurring in the gas flow rate, the flow rate measurement data piece by a predetermined value.

Furthermore, in the gas safety device of the present invention, when the pulsation recognizer determines that the pulsation is occurring, the leakage detector determines whether a leakage is present using the flow rate measurement data piece corrected by the pulsating flow rate corrector. With this configuration, it is made possible to reliably determine whether a leakage is detected even when a greater influence of pulsation of a gas flow rate is exerted due to difference in structure or installation conditions of the meter.

The gas safety device of the present invention eliminates the need for symmetrical shapes of buffers and a flow rate measuring unit that have been conventionally needed, the buffers being disposed at an inlet and an outlet of the measuring unit. Therefore, the gas safety device of the present invention can have a more flexible meter configuration, which not only reduces the cost of the gas safety device but also achieves more reliable leakage detection, thereby improving the safety of the gas usage environment.

