Technical Field
[0001]
The present invention relates to a fluid analysis apparatus and a fluid analysis method adapted
to analyze the concentration of a component contained in exhaust gas discharged from, for example, an
5 internal combustion engine.
Background Art
[0002]
As apparatuses adapted to analyze the concentrations of hydrocarbon (HC) and nitrogen oxide
10 (NOx) contained in exhaust gas discharged from, for example, an internal combustion engine, there are
ones using a hydrogen flame ionization analysis method (FID) and a chemiluminescence analysis
method (CLD), respectively.
[0003]
When a required range for measuring the concentration of a measurement target component is
15 wide, such as in the case of FID or CLD, to deal with such a situation, the amplification factor of an
amplifier for amplifying an analog signal outputted from a detector is switched. For example, when
the concentration of a measurement target component is high, a small amplification factor is used,
whereas when the concentration is low, a large amplification factor is used. In addition, when
measuring a measurement target component of high concentration, the linearity between the analog
20 signal outputted from the detector and the concentration tends to be lost, and therefore it is necessary to
use a high order calibration curve coefficient.
[0004]
When measuring a measurement target component of high concentration, the above-described
measures may be taken; however, the following problems exist.
25 That is, a large amount of the measurement target component (molecules) flows into the
detector, and consequently, an introduction path to the detector may be contaminated to increase a
background level. Also, the amplifier is required to have multiple amplification factors, causing one of
adverse effects on miniaturization of a circuit board. Further, as the concentration of the measurement
target component increases, the linearity between the analog signal outputted from the detector and the
2
concentration is lost, and therefore it is necessary to ensure the linearity by employing a high order
calibration curve coefficient.
Citation List
5 Patent Literature
[0005]
Patent Literature 1: Japanese Unexamined Patent Publication JP-A 11-64339
Summary of Invention
10 Technical Problem
[0006]
Therefore, the present invention is made in order to solve the above-described problems, and a
main object thereof is to reduce the contamination level of an introduction path to a detector, miniaturize
a circuit board, and improve measurement accuracy by adjusting the number of molecules of a
15 measurement target component to flow into the detector.
Solution to Problem
[0007]
That is, a fluid analysis apparatus according to the present invention includes: a detector for
20 measuring concentration of a measurement target component contained in fluid; an introduction path
connected to the detector to introduce the fluid into the detector; and a flow rate switching mechanism
adapted to, depending on the concentration of the measurement target component, switch a flow rate of
the fluid to be introduced into the detector.
[0008]
25 The fluid analysis apparatus as described above can produce the following effects because
depending on the concentration of the measurement target component, it switches the flow rate of the
fluid to be introduced into the detector.
(1) By adjusting the flow rate so as to decrease the number of molecules of the measurement target
component contained in the fluid to flow into the detector, the contamination of the introduction path
3
caused by the measurement target component of high concentration can be prevented. By preventing
the contamination of the introduction path, an increase in background level can be suppressed.
(2) The number of molecules of the measurement target component to flow into the detector is adjusted,
and therefore a detection signal obtained by the detector can be kept within a predetermined range. In
5 doing so, the range of the amplification factor of an amplifier for amplifying the detection signal can be
narrowed (preferably, to one), and consequently, a circuit board can be miniaturized.
(3) Since the detection signal obtained by the detector can be kept within the predetermined range, the
concentration can be calculated in a range where linearity is ensured, and therefore the measurement can
be performed with high accuracy from a low concentration range to a high concentration range. In
10 addition, a concentration measurement range can also be expanded.
(4) Besides, the need for a switching circuit for switching the amplification factor can be eliminated, and
therefore the need to take account of noise caused by the switching circuit at the time of switching of the
amplification factor can be eliminated. Further, when the fluid analysis apparatus is applied to a
vehicle-mounted exhaust gas analysis apparatus, if there is the switching circuit, noise occurs in the
15 switching circuit due to vibration at the time of running; however, in the present invention, the switching
circuit is unnecessary, and therefore the need to take account of noise occurring in the switching circuit
due to vibration at the time of running can be eliminated.
[0009]
As a specific embodiment of the introduction path and the flow rate switching mechanism, it is
20 preferable that the introduction path includes a first introduction path and a second introduction path, and
the flow rate switching mechanism includes: a first flow rate regulating part provided in the first
introduction path to regulate the flow rate of the fluid to a first flow rate; a second flow rate regulating
part provided in the second introduction path to regulate the flow rate of the fluid to a second flow rate
that is a larger flow rate than the first flow rate; a flow path switching part that switches a flow path to be
25 connected to the detector between the first introduction path and the second introduction path; and a
switching control part that compares the concentration obtained by the detector with a predetermined
threshold value to control the flow path switching part.
Such a configuration makes it possible to switch between the first flow rate and the second
flow rate only by switching a flow path. In addition, by selecting the first flow rate when the
4
measurement target component is of high concentration, or by selecting the second flow rate when the
measurement target component is of low concentration, a change in the number of molecules of the
measurement target component to flow into the detector can be kept within as narrow a range as possible.
[0010]
5 In addition, as another flow rate switching mechanism, it is conceivable to provide, in the
introduction path, a device adapted to continuously switch a flow rate, such as a mass flow controller.
Such a configuration makes it possible to keep the change in the number of molecules of the
measurement target component to flow into the detector within a further narrower range as compared
with the above-described flow path switching case. Note that in terms of the control response speed of
10 a mass flow controller and the simplification of subsequent concentration conversion, the flow path
switching configuration as described above is preferable.
[0011]
In order to miniaturize the circuit board, it is preferable that the fluid analysis apparatus further
includes an amplifier that amplifies the detection signal obtained by the detector with a fixed constant
15 amplification factor.
[0012]
It is preferable that the fluid analysis apparatus further includes a calculation part that calculates
the concentration by on the basis of concentration conversion corresponding to the flow rate of the fluid,
calculating an output signal resulting from the amplification by the amplifier. Specifically, it is
20 conceivable that the calculation part has concentration conversion expressions respectively
corresponding to the flow rates of the fluid, selects a concentration conversion expression on the basis of
flow rate data obtained from the flow rate switching mechanism, and calculates the concentration of the
measurement target component using the selected concentration conversion expression.
[0013]
25 In order to reduce a noise component included in the output signal used for the concentration
calculation by the calculation part, it is conceivable to take a moving average of the output signal. Note
that at the first flow rate as a lower flow rate, a replacement time (signal rise time) is longer. As a result,
there occurs a problem that when taking the moving averages of the output signals at the first and second
flow rates using the same averaging time, a response time at the first flow rate becomes longer.
5
In order to preferably solve this problem to equalize both response times to each other, it is
conceivable to making a detection response on the second introduction path side slower than a detection
response on the first introduction path side. In particular, it is preferable that the calculation part makes
the averaging time for the output signal obtained at the first flow rate shorter than the averaging time for
5 the output signal obtained at the second flow rate.
[0014]
Also, a fluid analysis method according to the present invention is one using a fluid analysis
apparatus including a detector for detecting the concentration of a measurement target component
contained in fluid and an introduction path connected to the detector to introduce the fluid into the
10 detector, and depending on the concentration obtained by the detector, switches the flow rate of the fluid
to be introduced into the detector.
Advantageous Effects of Invention
[0015]
According to the present invention configured as described above, since the flow rate of the
15 fluid to be introduced into the detector is switched depending on the concentration obtained by the
detector, by adjusting the number of molecules of the measurement target component to flow into the
detector, it becomes possible to reduce the contamination level of the introduction path to the detector,
miniaturize the circuit board, and improve measurement accuracy.
20 Brief Description of Drawings
[0016]
FIG. 1 is a schematic diagram illustrating the configuration of a fluid analysis apparatus
according to the present embodiment;
FIG. 2 is a diagram illustrating a flowchart of the operation of the fluid analysis in the same
25 embodiment;
FIG. 3 is a schematic diagram illustrating the configuration of a fluid analysis apparatus
according to a variation;
FIG. 4 is a graph illustrating a variation of signal processing by the calculation part;
FIG. 5 is a schematic diagram when the fluid analysis apparatus of the present invention is
6
used as a vehicle-mounted type; and
FIG. 6 is a schematic diagram illustrating the configuration of the vehicle-mounted fluid
analysis apparatus.
5 Description of Embodiments
[0017]
In the following, one embodiment of a fluid analysis apparatus according to the present
invention will be described with reference to the drawings.
[0018]
10
A fluid analysis apparatus 100 of the present embodiment is an exhaust gas analysis apparatus
adapted to measure the concentration of a component contained in exhaust gas discharged from, for
example, an internal combustion engine E. Note that the fluid analysis apparatus 100 of the present
embodiment is of a direct sampling type that without diluting sampled exhaust gas, directly measures the
15 concentrations.
[0019]
Specifically, as illustrated in FIG. 1, the fluid analysis apparatus 100 includes: a detector 2 for
measuring the concentration of a measurement target component contained in the exhaust gas; an
introduction path 3 connected to the detector 2 to introduce the exhaust gas into the detector 2; and a
20 flow rate switching mechanism 4 adapted to, depending on the concentration of the measurement target
component, switch the flow rate of the exhaust gas to be introduced into the detector 2.
[0020]
As the detector 2, when the measurement target component contained in the exhaust gas is
hydrocarbon (HC), an FID detector adapted to measure the concentration of total hydrocarbons (THC)
25 using a hydrogen flame ionization analysis method (FID) can be used, and when the measurement target
component is nitrogen oxide (NOx (= NO + NO2)), a CLD detector adapted to measure the
concentration of nitrogen compounds using a chemiluminescence analysis method (CLD) can be used.
In addition, as the detector 2, detectors using various analysis methods respectively suitable for
measurement target components can be used, such as a Fourier transform infrared spectrometer (FTIR)
7
and a non-dispersive infrared analyzer (NDIR). Also, as a light source for FTIR or NDIR, a quantum
cascade laser (QCL) can be used.
[0021]
A detection signal (current or voltage signal (analog signal)) obtained by the detector 2 is
5 outputted to an amplifier 5. The amplifier 5 is one that is configured using an operational amplifier and
amplifies the detection signal with a fixed constant amplification factor.
[0022]
Then, an output signal (analog signal) resulting from the amplification by the amplifier 5 is
outputted to an A/D converter 6, and converted to a digital signal by the A/D converter 6. The digital
10 signal is outputted to a calculation part 7 and converted into concentration by the calculation part 7.
[0023]
An introduction path 3 is one of which one end is provided in an exhaust pipe (tail pipe) E1
through which the exhaust gas flows and the other end is connected to the detector 2. Note that “one
end of the introduction path 3 is provided in the exhaust pipe E1” means that the one end of the
15 introduction path 3 is provided at a position where the exhaust gas can be sampled, e.g., provided near or
inside a discharge port of the exhaust pipe E1.
[0024]
Specifically, the introduction path 3 includes: a sampling port 31 provided at the one end to
sample the exhaust gas; and a suction pump 32 provided downstream of the sampling port 31. In
20 addition, the introduction path 3 is provided with dust filters 33 and 34, a pressure regulation valve 35,
and the like. Note that FIG. 1 illustrates the case where the sampling port 31 is provided with the dust
filter 33, but not limited to the case.
[0025]
Also, the introduction path 3 includes a first introduction path 3a and second introduction path
25 3b that branch on the downstream side of the dust filter 34. The first introduction path 3a and the
second introduction path 3b merge on the downstream side, and are connected to the detector 2
downstream of the merging point therebetween.
[0026]
A flow rate switching mechanism 4 is one adapted to switch the flow rate of the exhaust gas to
8
be introduced into the detector 2 stepwise (in the present embodiment, in two steps).
[0027]
Specifically, the flow rate switching mechanism 4 includes: a first flow rate regulating part 41
that is provided in the first introduction path 3a to regulate the flow rate of the exhaust gas to a first flow
5 rate Q1; a second flow rate regulating part 42 that is provided in the second introduction path 3b to
regulate the flow rate of the exhaust gas to a second flow rate Q2 (> Q1) that is a higher flow rate than the
first flow rate Q1; a flow path switching part 43 that switches a flow path to be connected to the detector
2 between the first introduction path 3a and the second introduction path 3b; and a switching control part
44 that compares the concentration of the measurement target component contained in the exhaust gas
10 with a predetermined threshold value to control the flow rate switching part 43. Note that as the
concentration of the measurement target component to be compared with the predetermined threshold
value by the switching control part 44, not only a concentration value but a concentration-related value is
also possible, such as the detection signal (current or voltage signal (analog signal)) from the detector 2,
the signal resulting from the amplification by the amplification part 5, or the digital signal from the A/D
15 converter 6.
[0028]
The first flow rate regulating part 41 and the second flow rate regulating part 42 are configured
respectively using constant flow rate devices such as capillary tubes or orifices. In the present
embodiment, for example, the first flow rate regulating part 41 is one adapted to regulate the flow rate to
20 a constant flow rate of 10 cc/min, and the second flow rate regulating part 42 is one adapted to regulate
the flow rate to a constant flow rate of 100 cc/min.
[0029]
The flow path switching part 43 includes: a first on-off valve 431 provided downstream of the
first flow rate regulating part 41 in the first introduction path 3a; and a second on-off valve 432 provided
25 downstream of the second flow rate regulating part 42 in the second introduction part 3b. The first and
second on-off valves 431 and 432 are solenoid valves, and respectively on/off controlled by control
signals from the switching control part 44. Note that the flow path switching part 43 may be one
adapted to merge the first introduction path 3a and the second introduction path 3b via a three-way
solenoid valve, and control the three-way solenoid valve to switch between the flow paths.
9
[0030]
The switching control part 44 compares the concentration of the measurement target
component obtained by the calculation part 7 and the predetermined threshold value (e.g., 1000 ppm)
with each other, and when the concentration is equal to or more than threshold value, opens the first on-
5 off valve 431 and closes the second on-off valve 432 to introduce the exhaust gas into the detector 2
through the first introduction path 3a. On the other hand, when the concentration is less than the
threshold value, the switching control part 44 closes the first on-off valve 431 and opens the second onoff
valve 432 to introduce the exhaust gas into the detector 2 through the second introduction path 3b.
Note that the predetermined threshold value can be arbitrarily determined on the basis of the relationship
10 between the concentration of the measurement target component and the flow rate of the exhaust gas to
be introduced into the detector 2 (i.e., the amount of molecules of the measurement target component).
For example, by changing the predetermined threshold value to a lower concentration side, resolution on
the lower concentration side can be increased to perform the measurement with accuracy. Note that the
switching control part 44 may compare the voltage or current signal outputted from the detector 2 or the
15 output signal outputted from the amplifier part 5 with a corresponding threshold value, and on-off
control the first and second on-off valves 431 and 432 to switch between the first introduction path 3a
and the second introduction path 3b.
[0031]
Also, in the present embodiment, the voltage signal outputted when the amplification part 5
20 amplifies the detection signal obtained from the detector 2 when the exhaust gas is introduced into the
detector 2 through the first introduction path 3a or the detection signal obtained from the detector 2 when
the exhaust gas is introduced into the detector 2 through the second introduction path 3a is set to have 0
to 1 V. That is, the analog signal (the output signal from the amplification part 5) to be inputted to the
A/D conversion part 6 is set to have 0 to 1 V.
25 [0032]
Further, in the present embodiment, the calculation part 7 calculates the concentration by
calculating the digital signal from the A/D conversion part 6 on the basis of concentration conversion
corresponding to the flow rate of the exhaust gas. Specifically, the calculation part 7 includes a first
concentration conversion expression corresponding to the first flow rate and a second concentration
10
conversion expression corresponding to the second flow rate, and selects a concentration conversion
expression on the basis of flow rate data obtained from the switching control part 44 or the like to
calculate the concentration of the measurement target component using the selected concentration
conversion expression.
5 [0033]
Next, the operation of the fluid analysis apparatus 100 of the present embodiment from the
start of the measurement will be described with reference to FIG. 2.
[0034]
At the start of the exhaust gas analysis, the switching control part 44 opens the first on-off
10 valve 431 and closes the second on-off valve 432 to introduce the exhaust gas (the first flow rate Q1) into
the detector 2 through the first introduction path 3a (Step S1). In this state, it is determined whether or
not the concentration obtained by the calculation part 7 is less than the predetermined threshold value
(Step S2). Then, when the concentration is less than the threshold value, the first on-off valve 431 is
closed and the second on-off valve is opened to switch to the second introduction path 3b (the second
15 flow rate Q2) (Step S3). On the other hand, when the concentration is equal to or more than the
threshold value, the first on-off valve 431 remains opened and the second on-off valve 432 remains
closed to keep the introduction through the first introduction path 3a (Step S4). Note that it may be
configured to introduce the exhaust gas into the detector 2 through the second introduction path 3b first,
and then switch the flow path in a similar manner to the above.
20 [0035]
Subsequently, in either case, the detection signal obtained by the detector 2 is amplified with
the constant amplification factor by the amplification part 5 (Step S5), and then the amplified signal is
digital converted by the A/D conversion part 6 (Step S6). After that, the calculation part 7 calculates
the concentration from the digital signal using a concentration conversion expression corresponding to
25 the flow rate of the exhaust gas flowing into the detector 2 (Step S7).
[0036]
Note that when, after the start of the analysis, the concentration of the measurement target
component varies and thereby a magnitude relationship with the threshold value is changed, the first and
second on-off valves 431 and 432 are on-off controlled depending on the magnitude relationship with
11
the threshold value to switch the flow rate of the exhaust gas to flow into the detector 2, and also using a
concentration conversion expression corresponding to the resulting flow rate, the concentration is
calculated.
[0037]
5
The fluid analysis apparatus 100 according to the present embodiment configured as described
above can produce the following effects because depending on the concentration obtained by the
detector 2 or a concentration-related value related to the concentration, the flow rate of the exhaust gas to
be introduced into the detector 2 is switched.
10 (1) By regulating the flow rate so as to decrease the number of molecules of the measurement target
component contained in the exhaust gas to flow into the detector 2, the contamination of the introduction
path 3 caused by the measurement target component of high concentration can be prevented. That is,
on the higher concentration side, the flow rate of the exhaust gas to flow into the detector 2 is low, and
therefore the amount of molecules of the measurement target component can be kept low to thereby
15 prevent the contamination. On the lower concentration side, the flow rate of the exhaust gas to flow
into the detector 2 increases; however, the gas of high concentration does not flow, and therefore the
amount of molecules of the measurement target component can be kept low to thereby prevent the
contamination of the flow path. This also makes it possible to suppress an increase in background level.
(2) Since the number of molecules of the measurement target component to flow into the detector 2 is
20 adjusted, the detection signal obtained by the detector 2 can be kept within a predetermined range.
Therefore the number of amplification factors of the amplifier 5 for amplifying the detection signal can
be limited to one, and consequently, a circuit board can be miniaturized.
(3) Since the detection signal obtained by the detector 2 can be kept within the predetermined range, the
concentration can be calculated in a range where linearity is ensured, and therefore the measurement can
25 be performed with high accuracy from a low concentration range to a high concentration range.

WE CLAIM:
1. A fluid analysis apparatus comprising:
a detector for measuring concentration of a measurement target component contained in fluid;
5 an introduction path connected to the detector to introduce the fluid into the detector; and
a flow rate switching mechanism adapted to, depending on the concentration of the
measurement target component, switch a flow rate of the fluid to be introduced into the detector.
2. The fluid analysis apparatus as claimed in claim 1, wherein
10 the introduction path includes a first introduction path and a second introduction path, and
the flow rate switching mechanism comprises:
a first flow rate regulating part provided in the first introduction path to regulate the flow rate
of the fluid to a first flow rate;
a second flow rate regulating part provided in the second introduction path to regulate the flow
15 rate of the fluid to a second flow rate that is a larger flow rate than the first flow rate;
a flow path switching part that switches a flow path to be connected to the detector between
the first introduction path and the second introduction path; and
a switching control part that compares the concentration obtained by the detector with a
predetermined threshold value to control the flow path switching part.
20
3. The fluid analysis apparatus as claimed in claim 2, further comprising
an amplifier that amplifies a detection signal obtained by the detector.
4. The fluid analysis apparatus as claimed in claim 3, further comprising
25 a calculation part that calculates the concentration by on a basis of concentration conversion
corresponding to the flow rate of the fluid, calculating an output signal resulting from the amplification
by the amplifier.
5. The fluid analysis apparatus as claimed in claim 4,
16
the fluid analysis apparatus making a detection response on a side of the second introduction
path slower than a detection response on a side of the first introduction path.
6. The fluid analysis apparatus as claimed in claim 4, wherein
5 the calculation part is one adapted to perform the concentration conversion by taking a moving
average of the output signal and makes an averaging time for an output signal obtained at the first flow
rate shorter than an averaging time for an output signal obtained at the second flow rate.
7. The fluid analysis apparatus as claimed in claim 1, wherein
10 the fluid is exhaust gas discharged from an internal combustion engine.
8. The fluid analysis apparatus as claimed in claim 7,
the fluid analysis apparatus being one mounted in a vehicle to analyze the exhaust gas.
15 9. A fluid analysis method using a fluid analysis apparatus comprising a detector for measuring
concentration of a measurement target component contained in fluid and an introduction path connected
to the detector to introduce the fluid into the detector,
the fluid analysis method, depending on the concentration of the measurement target
component, switching a flow rate of the fluid to be introduced into the detector.