Ultrasonic apparatus and method for measuring the concentration of gas
In an ultrasonic apparatus for measuring the concentration of gas provided with two ultrasonic oscillators for transmitting/receiving an ultrasonic wave, arranged opposite to each other in piping through which a sample gas flows, a temperature sensor, and a pressure sensor, an ultrasonic method and apparatus that can accurately measure gas concentration regardless of pressure of the sample gas are provided as an ultrasonic apparatus for measuring the concentration of gas comprising concentration calculating means for calculating sample gas concentration based on a propagation speed correction coefficient by pressure.
1. An ultrasonic method for measuring the concentration of a specific component gas in a sample gas based on a propagation time till an ultrasonic wave transmitted from two ultrasonic transducers transmitting/receiving the ultrasonic wave, arranged opposite to each other in piping through which the sample gas flows, is received by the ultrasonic transducer arranged on the opposite side, the method comprising steps of:
measuring a propagation time till the ultrasonic wave transmitted from each of the two ultrasonic transducers is received by the other ultrasonic transducer;
measuring a sample gas temperature
measuring a sample gas pressure; and
correcting the propagation time till the ultrasonic transducer receives the ultrasonic wave based on a propagation speed correction coefficient according to the temperature and pressure of the sample gas, wherein
the step for correcting the propagation time till the ultrasonic transducer receives the ultrasonic wave is a step for correcting a propagation speed (C) of the ultrasonic wave by the following expression:
C
=
k
RT
M
(
1
+
P
RT
B
(
T
)
)
where k: ratio between constant-volume molar specific heat and constant-pressure molar specific heat, R: gas constant, T: measured temperature of sample gas, M: average molecular weight of sample gas, P: measured pressure of sample gas, B(T): propagation speed correction coefficients, and
the propagation speed correction coefficient B(T) is acquired as an approximate function of the measured temperature T calculated from an ultrasonic propagation speed C at a given temperature T under different pressure conditions, measured from an ultrasonic propagation time till the ultrasonic wave transmitted from the two ultrasonic transducers transmitting/receiving the ultrasonic wave and
wherein B(T)=αT 2 +βT+γ where α, β and γ are constants.
2. An ultrasonic apparatus for measuring a concentration of gas comprising piping extending along an axis and through which a target gas to be measured flows, a first ultrasonic transducer arranged inside the piping for transmitting/receiving an ultrasonic wave, a second ultrasonic transducer arranged inside the piping and opposed to the first ultrasonic transducer for transmitting/receiving the ultrasonic wave, a transmission/receiving switch for switching control an ultrasonic transmission mode in which the ultrasonic wave is transmitted from the ultrasonic transducer and an ultrasonic receiving mode in which the transmitted ultrasonic wave is received between the first and second ultrasonic transducers, a temperature sensor arranged at the piping for measuring a temperature of the target gas, and a pressure sensor arranged at the piping for measuring a pressure of the target gas,
wherein concentration calculating means for calculating the concentration of the target gas is provided based on a propagation speed correction coefficient by a propagation time till the ultrasonic wave transmitted from each of the two ultrasonic transducers is received by the other ultrasonic transducer, an output value of the temperature sensor, and a pressure value of the pressure sensor;
wherein the concentration calculating means is provided with means for correcting a propagation speed (C) of the ultrasonic wave by the following expression:
C
=
k
RT
M
(
1
+
P
RT
B
(
T
)
)
where k: ratio between constant-volume molar specific heat and constant-pressure molar specific heat, R: gas constant, T: measured temperature of sample gas, M: average molecular weight of sample gas, P: measured pressure of sample gas, B(T): propagation speed correction coefficient, and
means for correcting a propagation speed based on a function of a temperature T of the propagation speed correction coefficient by acquiring a propagation speed correction coefficient wherein the propagation speed correction coefficient B(T) is acquired as an approximate function of the measured temperature T calculated from an ultrasonic propagation speed C at a given temperature T under different pressure conditions, measured from an ultrasonic propagation time till the ultrasonic wave transmitted from the two ultrasonic transducers transmitting/receiving the ultrasonic wave; and
wherein B(T)=αT 2 +βT+γ where α, β and γ are constants.