Mass flow meter with self-diagnostic function and mass flow controller using the same
In a mass flow meter comprising two flow sensor units with identical specifications, flow rate deviations between these two flow sensor units are initially measured at various mass flow rates under a circumstance having the same fluctuating factors as those when a mass flow is actually measured. Subsequently, based on these flow rate deviations, a correction value for matching the values of the mass flow rates measured by these two flow sensor units is calculated and stored in a data storage device. Thereafter, when measuring a mass flow rate, a flow rate deviation, from which the influence by the individual difference in the response to a fluctuating factor between these two flow sensor units has been removed, is calculated by correcting a measured value based on the correction value. The existence or non-existence of an occurrence of a malfunction is judged based on whether the flow rate deviation exceeds a predetermined threshold value t or not.
1. A mass flow meter, comprising:
a flow passage through which a fluid flows,
a first flow sensor unit which outputs a first signal that is an output signal corresponding to a mass flow rate of said fluid which flows through said flow passage,
a second flow sensor unit which outputs a second signal that is an output signal corresponding to a mass flow rate of said fluid which flows through said flow passage, and
a first control unit which determines whether there is a malfunction in said first flow sensor unit or said second flow sensor unit based on the extent of a deviation between the intensity of said first signal and the intensity of said second signal, and
said first flow sensor unit and said second flow sensor unit have an identical specifications; wherein
said first control unit is configured so as to:
flow said fluid through said flow passage at a plurality of different mass flow rates in a predetermined range and at a predetermined temperature and pressure,
execute a learning function for each of said plurality of different mass flow rates, in which:
said first control unit measures the intensity of said first signal and the intensity of said second signal,
said first control unit calculates a flow rate deviation, which is a deviation between the intensity of said first signal and the intensity of said second signal, and a correction value for correcting the intensity of a signal S, which is one of said first signal and said second signal, to make the absolute value of said flow rate deviation less than a predetermined threshold value d, and
said first control unit stores said flow rate deviation and said correction value in a data storage device in relation to a mass flow rate at the time of measuring the intensity of said first signal and the intensity of said second signal, and
execute a self-diagnostics function when measuring a mass flow rate of said fluid in said predetermined temperature and pressure after the execution of said learning function, in which:
said first control unit measures the intensity of said first signal and the intensity of said second signal,
said first control unit corrects the intensity of said signal S based on said correction value stored in said data storage device,
said first control unit calculates a corrected flow rate deviation which is a deviation between the intensity of said corrected signal S and the intensity of a signal M which is one of said first signal and said second signal and a signal other than said signal S, and
said first control unit judges that there is a malfunction in either one of said first flow sensor unit and said second flow sensor unit when said corrected flow rate deviation is larger than a predetermined threshold value t.
2. The mass flow meter of claim 1 , wherein:
in the execution of said self-diagnostics function,
said first control unit determines a value of a correction value corresponding to a mass flow rate of said fluid obtained from said signal M, based on a relation between said mass flow rates and said correction values stored in said data storage device, and
said first control unit corrects the intensity of said signal S, based on the value of said determined correction value.
3. The mass flow meter of claim 1 , wherein:
in the execution of said self-diagnostics function,
said first control unit corrects the intensity of said signal S, based on a representative value of all said correction values stored in said data storage device.
4. The mass flow meter of claim 1 , wherein:
said first control unit calculates as said correction value a value obtained by subtracting the intensity of said signal S from the intensity of said signal M, in the execution of said learning function, and
said first control unit corrects the intensity of said signal S by adding said correction value to the intensity of said signal S, in the execution of said self-diagnostics function.
5. The mass flow meter of claim 1 , wherein:
said first control unit calculates as said correction value a value obtained by dividing the intensity of said signal M by the intensity of said signal S, in the execution of said learning function, and
said first control unit corrects the intensity of said signal S by multiplying the intensity of said signal S by said correction value, in the execution of said self-diagnostics function.
6. The mass flow meter of claim 1 , wherein:
said first flow sensor unit and said second flow sensor unit are thermal type flow sensor units, comprising:
a bypass disposed in the middle of said flow passage,
a sensor tube which branches from said flow passage at the upstream side of said bypass and joins said flow passage at the downstream side of said bypass,
a pair of sensor wires disposed so as to be able to conduct heat to a fluid flowing through said sensor tube,
a power supply for supplying an input signal for making said sensor wires generate heat, and
a sensor circuit which comprises a bridge circuit containing said sensor wires.
7. The mass flow meter of claim 6 , wherein:
said first flow sensor unit and said second flow sensor unit comprise an individual bypass, respectively.
8. The mass flow meter of claim 6 , wherein:
said first flow sensor unit and said second flow sensor unit comprise a common bypass.
9. The mass flow meter of claim 1 , comprising:
a flow regulation unit which controls the flow rate of a fluid flowing through said flow passage, and
a second control unit which controls said flow regulation unit, wherein:
said second control unit controls said flow regulation unit based on the intensity of signal C which is one of said first signal and said second signal to bring the flow rate of said fluid close to a target value.
10. The mass flow meter of claim 9 , wherein:
in the execution of said learning function, said first control unit stores a control input when said flow regulation unit is controlled based on the intensity of said signal C, in addition to said flow rate deviation and said correction value, in a data storage device, in relation to the mass flow rate at the time of measuring the intensity of said first signal and the intensity of said second signal, and
in the execution of said self-diagnostics function,
said first control unit determines the value of the control input of said flow regulation unit corresponding to the mass flow rate of said fluid obtained from said signal M, based on a relation between said mass flow rates and said control inputs stored in said data storage device,
said first control unit calculates a control input deviation, which is a deviation between said determined value of said control input and the value of a control input when said flow regulation unit is controlled based on the intensity of said signal C in the execution of said self-diagnostics function, and
said first control unit judges that there is a malfunction in either one of said first flow sensor unit, said second flow sensor unit, said flow regulation unit and said second control unit, when said control input deviation is larger than a predetermined threshold value c.
11. A mass flow meter, comprising:
a flow passage through which a fluid flows,
a first flow sensor unit which outputs a first flow sensor signal corresponding to a mass flow rate of the fluid through the flow passage,
a second flow sensor unit which outputs a second flow sensor signal corresponding to a mass flow rate of the fluid through the flow passage, and
a first control unit which determines whether there is a malfunction in the first flow sensor unit or the second flow sensor unit based on the extent of a deviation between the first sensor signal and the second flow sensor signal, and
the first control unit includes a processor and non-transitory processor executable instructions, the non-transitory processor executable instructions, when executed by the processor, effectuate:
flow of the fluid through the flow passage at a plurality of different mass flow rates in a predetermined range and at a predetermined temperature and pressure,
execution of a learning function for each of the plurality of different mass flow rates, wherein execution of the learning function includes:
calculating a flow rate deviation based upon a deviation between the first flow sensor signal and the second flow sensor signal, and calculating a correction value for correcting the intensity of a signal S, which is one of the first flow rate signal and the second flow rate signal, to make an absolute value of the flow rate deviation less than a predetermined threshold value d, and
the first control unit stores the flow rate deviation and the correction value in a data storage device in relation to a mass flow rate at the time of measuring the first flow rate signal and the second flow rate signal, and
execution of a self-diagnostics function when measuring a mass flow rate of the fluid in the predetermined temperature and pressure after the execution of the learning function, wherein execution of the self-diagnostics function includes:
measuring the first flow rate signal and the second flow rate signal,
correcting one of the first flow sensor signal and the second flow sensor signal based on the correction value stored in the data storage device;
calculating a corrected flow rate deviation between the corrected signal S and a signal M which is one of the first flow rate signal and the second flow rate signal and a signal other than the signal S, and
determining that there is a malfunction in either one of the first flow sensor unit and the second flow sensor unit when the corrected flow rate deviation is larger than a predetermined threshold value t.