Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Reexamination Certificate
2001-10-26
2004-06-08
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
C250S340000, C250S372000
Reexamination Certificate
active
06747276
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a convenient and inexpensive analytical apparatus for determining the concentration of an interesting component in a sample without interference from coexistent components by measuring the light absorption of the interesting component.
More particularly, the present invention relates to the convenient and inexpensive analytical apparatus which is realized by the procedures of:
preparing an interference filter that has means for scanning a transmission wavelength periodically;
detecting a change in the intensity of light whose wavelengths are scanned by the interference filter and which transmit through the sample; and
determining a concentration of the interesting component by periodically examining the detected electric signal.
2. Description of the Related Art
It is well-known to detect an interesting component in a sample or to determine its concentration by measuring the light absorption of the interesting component. The simplest known method is to measure intensity changes of a monochromatic light transmitting through the sample in which the interesting component absorbing the monochromatic light is contained. For instance, an ultraviolet absorption photometer for monitoring water quality is well-known. This photometer utilizes a phenomenon in which an organic waste in water absorbs light of 253.7 nm from a mercury lamp, and the photometer consists of a light source, a sample cell, a detector and an amplifier. By this method, which is referred to as a single beam method, there often exists a measuring error because an interfering value due to a change in the intensity of the light source is not able to be distinguished from a measured value due to the light absorption of the organic waste.
There exists a double beam method which removes this defect of the single beam method. In the double beam method, a beam from a light source splits into two beams in which one of the beams is for a sensing beam and the other beam is for a reference beam, and the measured value is obtained as the difference or ratio between the intensities of these two beams. The intensity change of the sensing beam is standardized by the intensity of the reference beam. By adopting the double beam method, a change in the intensity of the light source does not affect the measured results.
Double wavelength spectrometry is another method which does not affect the measured results due to a change in the intensity of the light source. In this method, two different monochromatic beams are alternately transmitted through or reflected on a sample, and the absorption intensity of an interesting component in the sample is obtained by measuring the difference or ratio between the intensities of the two monochromatic beams. A wavelength of the one monochromatic beam for reference is selected separately from an absorption wavelength of the interesting component, and a wavelength of the other monochromatic beam for sensing is equal to the absorption wavelength of the interesting component. The intensity change of the monochromatic beam for sensing is standardized by the intensity of the monochromatic beam for reference. Therefore, this method does not have a measuring error due to a change in the intensity of the light source.
As the present invention is aimed at developing an apparatus which does not have a measuring error due to a change in the intensity of the light source, like the double wavelength spectrometry method described above, a prior art method that is one kind of the double wavelength spectrometry will now be explained with reference to FIG.
1
.
FIG. 1
is a block diagram of a filter correlation infrared analyzer in which an infrared beam
121
radiated from an infrared source
101
is transmitted through a sample cell
102
. An infrared beam
122
, which is transmitted from the sample cell
102
, is transmitted to a modulator
103
. The sample cell
102
is a pipe in which infrared transmission windows are disposed on both ends thereof and which includes an inlet and an outlet on the near places from the both ends. An interesting component in a sample gas flowing through the sample cell absorbs infrared of a specific wavelength, and the infrared beam
122
transmitted through the sample cell
102
loses the energy at the specific wavelength. The modulator
103
is a rotating disk with filters mounted thereon, where one of the filters is a sensing filter
104
whose maximum transmission wavelength is equal to the specific wavelength absorbed by the interesting component, and the other filter is a reference filter
105
whose maximum transmission wavelength is different from the specific wavelength. By rotating the modulator, the filters periodically cross the infrared beam
122
transmitted through the sample cell
102
. The infrared beam
122
transmitted through the sample cell
120
is modulated by the beam being transmitted through the sensing filter
104
and the reference filter
105
alternately. The modulated infrared beam
123
is focused on an infrared sensor
108
by a focusing lens
107
, and the modulated infrared beam
123
is detected as an electric signal. The detected electric signal is amplified by a head amplifier
110
, and is then output to a synchronous rectifier
111
. On the other hand, a synchronous signal detector
106
detects a synchronous signal of the modulator
103
, and transmits the synchronous signal to a phase adjuster
109
. The phase adjuster
109
adjusts the synchronous signal and outputs the signal in the synchronous rectifier
111
. The synchronous rectifier
111
rectifies the electric signal synchronizing with the synchronous signal, and thereby obtains a measured signal corresponding to the concentration of the interesting component in the sample.
By more careful consideration, the gaseous or liquid samples contain many coexisting components with the interesting component. Some of the components interfere with analyzing the interesting component, such as water vapor in the case of analyzing nitrogen mono-oxide in flue gas and water or electrolytes in water in the case of analyzing glucose dissolved in water.
Details of the interference caused by the coexisting components will be described with reference to
FIG. 2. A
spectrum of interfering components
152
has no peak at an absorption wavelength of the interesting component
153
but tails over it. Even if the slope of the tailing is small, the tailing often causes fatal errors in the analysis results because of an increasing concentration of the interfering components. The double wavelength spectrometry often has a problem in that the tailing of spectrum of the interfering components causes fatal errors in the analysis results even if the reference wavelength
154
is selected near the absorption wavelength of the interesting component
153
.
Accordingly, an objective of the present invention is to provide an analyzing apparatus which removes the interference caused by the tailing spectrum of the interfering components, and which determines an exact concentration of the interesting component by measuring the light absorption of the interesting component. It is a further object of the present invention to provide a convenient and inexpensive analyzing apparatus capable of measuring interesting components in a manner that is neither destructive nor invasive to a person.
SUMMARY OF THE INVENTION
The present invention provides an interference filter transmission wavelength scanning photometer for determining the concentration of an interesting component in a sample without interference from the coexistent components by measuring the light absorption of the interesting component.
The photometer of the present invention comprises a light source, an interference filter operable to scan a transmission wavelength periodically, an infrared sensor, and a zero cross detector.
The photometer of the present invention can determine the concentration of an interesting component in a sample without interference from coexisting compone
Hannaher Constantine
Moran Timothy
Wenderoth , Lind & Ponack, L.L.P.
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