JPS5912132B2 - A device that detects the presence of a specific substance in a gas stream - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for detecting the presence of specific substances in a gas stream using chemical test strips.

It is generally known to utilize the coloring of chemical test strips to determine the presence of component gases or air in gases or gas mixtures. Known devices such as U.S. Pat. No. 4,023,930 issued May 17, 1972;
U.S. Patent No. 4,032,29, issued June 28,
The device disclosed in No. 7 uses a lamp as a light source to illuminate a test strip placed in a measuring chamber in which the gas to be monitored is circulated, and the test strip is colored by exposure to the gas. A light detection device, such as a photocell, is used to detect the increase in light absorption of the test strip.

All known devices only provide a non-linear output that indicates the cumulative amount of gas that has reacted with the test strip according to the Bougerand Lambert power law for absorption of light. These devices are usually arranged to issue an alarm when a predetermined amount of the gas to be detected is reached. No device is yet known which indicates the concentration of the gas to be monitored instantaneously as the gas passes through the device. Another disadvantage of the known device is that it does not have an automatic zeroing device before reading and therefore has to be manually adjusted.

Yet another drawback of the known device is that it does not compensate for lamp aging and voltage fluctuations.

A further disadvantage of existing devices is that the tape is heated by the lamp, which usually serves as a light source, which in turn affects the accuracy of the coloring of the tape, especially at the end of the measuring cycle. The object of the invention is therefore to obtain a device substantially free from the above-mentioned disadvantages, and more particularly to obtain an instantaneous indication of the concentration of the substance to be monitored.

The apparatus according to the invention comprises: a detection chamber for receiving a test strip which becomes colored upon contact with a specific substance in a gas present in the chamber; a device for generating a beam of light and directing it onto the test strip disposed within the detection chamber; a photodetection device responsive to the degree of coloration that the test strip receives upon exposure to a particular substance in the gas stream; an amplifier connected to the photodetection device to obtain an output voltage proportional to the coloration of the test strip; and a device connected to the amplifier to obtain an output signal that is an instantaneous indication of the concentration of the substance being monitored. This device has a light splitting device that divides the beam into two beams, one facing the test paper in the detection chamber and the other facing the Machihen optical density filter, and responds to the transmittance of this variable optical density filter. It is preferable to include a second light flux detection device.

An amplifier (hereinafter referred to as a photocell amplifier) is responsive to the two flux detection devices to provide an output that is a function of the ratio of the light detected by the two flux detection devices and is independent of changes in the intensity of the light source. . It is also preferred to include an automatic zeroing device for resetting the output of the photocell amplifier to zero before taking measurements.

A device for obtaining an output signal which is an instantaneous value of the concentration of the substance to be monitored includes a signal conditioning circuit connected to a photocell amplifier and a photocell to obtain an output which is a proportional function of the cumulative amount of the substance that has reacted with the drug test strip. It is preferred to have a differentiator connected to the output of the amplifier to derive the instantaneous concentration of the substance.

Such a signal conditioning circuit is an operational amplifier whose output is connected to the input of a photocell amplifier, and receives positive feedback from the output of the photocell amplifier so that its output is linearly connected to the input of the photocell amplifier. An operational amplifier may be provided to cause the change in direction. The differentiation of the linear output of the photocell amplifier will thereby give an instantaneous indication of the concentration of the substance being detected. Preferably, a low pass filter is connected to the output of the photocell amplifier to remove noise components in the output signal.

Preferably, the device also has a decomposition compensation device connecting the photoelectric amplifier to the differentiating device to compensate for the normal decomposition of the material reacted with the drug test strip. To prevent the heat generated by the lamp that acts as a light source from adversely affecting the test paper,
A thermal filter is preferably installed in the optical path between the lamp and the beam splitter. It is also preferable to provide a filter in the light beam before the light beam splitter to allow light of a predetermined wavelength to pass through.

This filter may be an interference filter or an optical glass filter. The use of selective filters is important to maintain high sensitivity in detecting specific colorations. Test strips usually have an elongated shape with a predetermined length suitable for multiple readings.

It is therefore usually arranged to be intermittently supplied to the detection chamber to take a series of measurements. Therefore, it is preferable that the device for advancing the test strip is equipped with a motor.
. For advancing the paper, the measuring chamber is divided into two sections, one of which is preferably movable by a suitable mechanism connected to a motor for advancing the paper.
The device is equipped with a programming device which sequentially activates the motor for short periods of time to advance the tape, then activates the automatic zeroing device at short time intervals to zero the device and finally supplies the gas flow to the measurement chamber. Preferably, the pump is activated. The variable optical density filter may be a disk whose transmission may vary over a range responsive to the range of typical drug test strips.

Such a disc may be mounted on the shaft of a servo motor driven by the automatic zeroing device described above. The variable optical density filter may alternatively have an elongated shape with a predetermined length that is advanced by a linear servo motor. The automatic zeroing device includes an operational amplifier connected to the output of the photocell amplifier and a switch device responsive to a programming device to connect the operational amplifier and the servo motor. Thus, during the automatic zero adjustment time, the servo motor is operated to set the output of the photoelectric amplifier to zero.
The photocell amplifier has a first transistor in series with its inverting input terminal.
A photodetector is connected, and a second photodetector is connected across the inverting input terminal and the output terminal of the photodetector, the output being a function of the ratio of the light detected by the two photodetectors, regardless of the intensity of the light source. an operational amplifier for automatically adjusting the gain of the photocell amplifier; a summing network for comparing the output of the operational amplifier with a reference source; and an inverter connected to the output of the summing network for providing the output signal of the photocell amplifier. It has The invention is disclosed with reference to preferred embodiments illustrated in the accompanying drawings. Referring to FIG. 1, a measurement chamber made up of two compartments 12, 14 is illustrated.

The compartment 12 is movable by a motor 18 as indicated by arrow A so that a drug test strip 16 can be advanced through the chamber. Movement of compartment 12 is completely controlled by motor 18 through conventional coupling mechanisms (not shown). A gas stream containing the substance to be detected is supplied through an inlet 20 in chamber section 12 by means of a suitable pump (not shown) to chamber section 14.
Exit through exit 22 located at An O-ring or other suitable device (not shown) is located between the two sections of the chamber to ensure sealing of the chamber during measurements. The portion of the test strip in the measuring chamber is illuminated by a light beam generated by a lamp 24 serving as a light source.

This light flux is transmitted to the plano-convex lens 2 located just in front of the aperture plate 30.
6,28. An image of the light flux passing through the apertured plate 30 is formed on the test strip 16 and the variable optical density filter 36 by the achromatic lens 32 and the light flux splitter 34 . Various optical arrangements may be used to form this image. For example, the distance between the aperture plate and the achromatic lens may be twice the focal length f of this lens. Similarly, the sum of the distance between this achromatic lens and the beam splitter and the distance between the beam splitter and the test paper or the distance between the beam splitter and the variable optical density filter is 2.
It may be adjusted equal to f. As is well known, achromatic lenses are used to prevent chromatic aberration. The end of the chamber section 14 is closed by a transparent plate 31 to allow the passage of the light beam. Thermal filter 38 connects light source 24 and lens 2
6.28 to prevent the heat from the lamp from affecting the moisture content of the test paper.

This has been found to have a significant impact on the reading accuracy, especially at the end of the measurement period as the test strip gradually dries out due to the heat generated by the lamp. Of course, the thermal filter can be placed anywhere between the light source and the beam splitter. It can be either an interference filter or an optical filter, but the filter 40 is installed in front of the beam splitter to pass colors of predetermined wavelengths. Make it.

For example, if the coloration to be observed in the test is yellow, use a blue filter. It is very important to place a filter before the beam splitter so that it affects the two photocells equally. The use of selective filters is important to maintain high sensitivity in detecting specific colorations. Test paper 1
The light passing through the transparent plate 44 in the chamber section 12
It is detected by a photoelectric cell 42 provided behind the camera.

Similarly, light passing through the variable optical density filter 36 is transmitted to a photocell 46 located behind the variable optical density filter 36.
detected by. It will be appreciated that other light detection devices responsive to light passing through or reflected from test strips or variable optical density filters are also contemplated. photoelectric cell 42,
46 is a variable impedance device connected to the circuit of a suitable photocell amplifier 48 which is proportional to the coloration of the test strip and which also compensates for changes in light source intensity caused by, for example, lamp aging and lamp voltage variations. 2 regardless of change
provides an output that is a direct ratio of the light detected by one photocell. An example of such an amplifier is illustrated in FIG. Details will be disclosed later. Now assume that when the transmittance of the variable optical density filter 36 matches that of the test strip (without flowing gas into the measurement chamber), the impedances of the photocells 42 and 46 are equal and the output of the photocell amplifier is zero. This zero volt output indicates a condition referred to as a permeability value of 1 before the gas to be monitored is supplied to the measurement chamber. Before supplying the gas to be monitored through the chamber, if the transmission of the possible optical density filter does not exactly match that of the test strip, the photocell 46 has a different impedance than the photocell 42 and the photocell amplifier 48 The output of will not be zero. Such output is provided to an auto-reset servo amplifier 50, previously referred to as an auto-zero device. The output of the servo amplifier is provided to a servo motor 54 which drives a variable optical density filter 36 under the control of a programmer 52. Thus, before supplying gas to the measuring chamber, when the output of the photocell amplifier is not zero, the servo motor 54 forces the dynamically variable optical density filter 36 so that the transmission of the variable optical density filter matches that of the test strip. , thereby automatically returning the amplifier output to zero. The programming device 52 controls the motor 18 and servo motor 5 according to the sequence shown in FIG.
4 and a conventional timing device to drive a gas pump (not shown). For example, if the predetermined time interval is 20
If it is seconds, the motor 18 is operating during this time and the chamber 1
Open 0 and advance the tape. This motor then stops and the chamber closes. Servo amplifier 50 is then connected to servo motor 54 to provide automatic zero output adjustment of amplifier 48. It is believed that a time interval of 1-10 seconds is sufficient to make this adjustment. The servo motor 54 is then deenergized and the pump controlling gas delivery to the measurement chamber is operated to begin the measurement cycle. This measurement cycle is repeated until the permeability through the test strip reaches a condition of 0.5 or, if the sample gas does not contain a sufficient amount of the substance to be detected, at predetermined intervals, e.g. 2 to 8 hours. Preferably, it is carried out for a period of time. During the measurement period, in the presence of the substance to be detected, such as hydrogen arsenide (arsine) in the air, a test strip impregnated with, for example, mercury bromide will gradually change from white to yellow.

When illuminated with blue light (using a blue filter), this color change will reduce the transparency of the paper and the impedance of photocell 42 will increase. However, photocell 4
6's impedance will remain unchanged. This increases the output of the photocell amplifier to a value that is responsive to the cumulative amount of hydrogen arsenide that has reacted with the test strip. The curve in Figure 3 shows the permeability of the chemical test strip as a function of the amount of hydrogen arsenide (μ9) reacted with the test strip. This curve is not linear due to Boger's and Lambert's power laws for light absorption, and without compensation, the output of the photocell amplifier is also not linear. As will be disclosed in more detail hereinafter, it is an object of the present invention to differentiate the output signal of the photocell amplifier by means of a suitable differentiator 56 to obtain an instantaneous indication of the concentration of the substance reacted with the test strip; The concentration may be indicated on a display, for example block 58.
However, since the output of the photocell amplifier is not linear, differentiation of such output will not give an indication of the true concentration of material reacted with the test strip. In order for the amplifier 48 to produce a linear output, the present invention includes a signal conditioning circuit 60 connected to the output of the photocell amplifier so that the transmission of the chemical test strip is We propose to compensate for the non-linearity. An example of a signal conditioning circuit is disclosed in detail in the description of FIG. 4 below. Referring now to FIG. 4, photocell amplifier 48, auto-reset servo amplifier 50. An example of a circuit diagram is provided which includes a differentiator 56, a signal conditioning circuit 60 and also a low pass filter 62 and a decomposition compensator 64. The photocell amplifier is an operational amplifier 0P1
have.

The inverting terminal of this amplifier 0P1 is connected to the photosensitive resistor R1 (
1) to a positive voltage source (supplied by a signal conditioning circuit 60, hereinafter disclosed). The non-inverting terminal of this operational amplifier is grounded. Photoresistor R2 (photocell 46 in FIG. 1) is connected to the operational amplifier feedback loop between the inverting terminal and the output terminal of the operational amplifier. Variable optical density filter 3
6 matches that of the test strip (without flowing gas into the measurement chamber), then R1 = R2 and the output of the operational amplifier is the reciprocal of the voltage applied to R1. operational amplifier 0
The output of R1 is supplied to the inverting input terminal of the operational amplifier 0P2, with one terminal connected to the reference source V+REF and the second terminal connected to the inverter 0P2.
Under conditions of transparency 1.0, the reference voltage +REF is applied to the inverting input of inverter 0P2, acting as an inverter through the first resistor R3 of the summing network, which includes a second resistor R4 connected to the inverting input terminal of P2. O volts are selected to be applied to the terminal, so that an output voltage VO-0 appears at its output. A resistor R5 is connected between the output terminal and the inverting input terminal of the inverter 0P2 and determines the gain of the inverter in a known manner. The non-inverting input terminal of the operational amplifier is grounded. When the transmission of the variable optical density filter 36 does not match that of the test strip (before supplying gas to the chamber), impedance R2 (photocell 46) has a different value than impedance R1 (photocell 42), and the operational amplifier The outputs of 0P1 and inverter 0P2 are not O.

This output is fed through resistor R6 to the inverting input terminal of operational amplifier 0P3, which acts as a comparator. The non-inverting input terminal of operational amplifier 0P3 is grounded. resistor R7
is connected between the inverting input terminal of the operational amplifier and its output and determines the gain of the operational amplifier in a known manner.
The non-inverting input terminal of operational amplifier 0P3 is grounded.
Contacts (RL-1) of relay RL operated by output programming device 52 (see Figure 1) of operational amplifier 0P3
is applied to the servo motor 54 (see FIG. 1) through the servo motor 54 (see FIG. 1). Operational amplifier 0P3 is the auto-reset servo amplifier 50 of FIG. Variable optical density filter 3 in one direction or another depending on polarity
Rotate 6. The output Vd of the operational amplifier 0P2 of the photocell amplifier can also be applied directly to the differentiator 56;
In practice, this output has a substantial amount of undesirable noise, so it is connected to operational amplifier 0P4 and resistor R
8, R9 capacitors Cl, C2 and a conventional secondary filter network.

Resistors R8 and R9 are connected in series between the output terminal of operational amplifier 0P2 and the non-inverting input terminal of operational amplifier 0P4. Capacitor C1 is connected between the non-inverting input terminal of operational amplifier 0P4 and ground;
2 is connected between the common point of resistors R8 and R9 and the output terminal of the operational amplifier. The inverting input terminal of this operational amplifier is connected to its output terminal. Resistor R8, R9
The values of capacitors Cl and C2 are determined by the cut-off frequency of the low-pass filter. In order to remove noise components satisfactorily, it is preferable to set the cutoff frequency in the range of 0.1 to 2 Hz. The output of operational amplifier 0P2 is
Operational amplifier 0P5 and resistors RlO, Rll, Rl2
is also applied to a signal conditioning circuit 60 (FIG. 1) that includes.

Resistor RlO has a terminal connected to reference voltage V-REF and a terminal connected to the inverting input terminal of operational amplifier 0P5. Resistor Rll is a variable resistor connected between the inverting input terminal of operational amplifier 0P5 and the output terminal of operational amplifier 0P2. Resistor Rl2 is a conventional feedback resistor connected between the output terminal of operational amplifier 0P5 and the inverting terminal of that amplifier. The purpose of the signal conditioning circuit is to compensate for the non-linear transmittance of the drug test strip as shown in FIG. If this non-linearity is not compensated for, the differentiator 56 will not give an accurate indication of the instantaneous concentration of the substance being monitored as it reacts with the drug paper. Referring to FIG. 4, the use of signal conditioning circuit 60 in the feedback loop of a photovoltaic cell amplifier causes the amplifier to produce a voltage output VO having the following characteristics.

As shown in FIG. 5, a number of curves were obtained for various values of K using mercury bromide as a chemical test strip to detect hydrogen arsenide.

The curve closest to linearity is the curve with K=0.5. Such a curve is linear up to point B, which responds to a transmission value of T-0.5. In fact, in order to produce a linear output, a known constant concentration of the substance to be detected is continuously reacted with a chemical test strip, and the gain of the operational amplifier determined by the variable resistor R1l is used to obtain a linear lamp output. change up to.

The output of operational amplifier 0P4 is connected to operational amplifier 0P6 and resistor R.
I3 and a differentiator circuit containing capacitor C3.

Resistor 13 is connected to the inverting input terminal and output terminal of operational amplifier 0P6. The non-inverting terminal of this operational amplifier is grounded. Furthermore, the differentiator 56 has a resistor R14 connected in series with the capacitor C3 and a capacitor C4 directly across the resistor R13. Resistor Rl4 and capacitor C4 further act as a low-pass filter to remove noise components. The ratio of Rl3 to Rl4 must be 100 or more. Similarly, C3 is 100 of the value of C4
It needs to be double or more. The colored areas on the chemical test paper will degrade or fade to some extent over time.

It is therefore preferable to compensate for this decomposition. A compensation circuit having resistors Rl5 and Rl7 and a variable resistor Rl7 is therefore provided. Resistors Rl5 and Rl7 are voltage dividers that send a fraction of VO to operational amplifier 0 through Rl6.
Provided to the non-inverting input terminal of P6. The value of Rl6 is Rl3
is the same as the value of V and is determined by the ratio of Rl5 and Rl7
A portion of O appears at the output of the operational amplifier with opposite polarity. The compensation circuit is regulated by stopping the gas circulation after it is observed that the test strip has developed a color. Without this compensation, the output of the differentiator will normally drop below zero as a result of discoloration of the test strip due to decomposition.
Adjust the variable resistor Rl7 to return the output voltage of the differentiator to zero. Although the invention has been disclosed with reference to a preferred embodiment, it will be understood that various modifications may be made to the same without departing from the scope of the claims.

For example, the signal conditioning circuit could take on other types of circuits than those described above. In order to straighten the curve in Figure 3 and make it linear, this linear function can be differentiated using a simple differentiation circuit in order to obtain an indication of the instantaneous concentration of the gas that reacted with the test paper. A known exponential function calculator connected between the two may also be used. Other types of automatic zeroing circuits could also be used. Other devices may also be planned to compensate for lamp aging and voltage fluctuations. Other types of photocells, amplifiers, low pass filters, decomposition compensators and differentiators can also be used.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a device according to the invention. FIG. 2 is a sequence diagram produced by the programming device.
FIG. 3 shows the permeability of a drug test strip as a function of the amount of substance reacted with the drug test strip. FIG. 4 is a circuit diagram of the electrical elements of the device shown in FIG. FIG. 5 shows the output of the photocell amplifier as a function of the amount of material reacted with the drug test strip at various temperatures under nonlinear conditions. 10...
...Photodetection chamber, 16...Drug test paper,
18...Motor, 24...Light source, 26
, 38... flat, convex lens, 30...
Aperture plate, 32...Achromatic lens, 34...
- Luminous flux splitting device, 36... Variable optical density filter, 38... Heat filter, 40... Filter, 42, 46... Photoelectric cell, 54...・・・
···Servomotor.

Claims (1)

[Scope of Claims] 1. (a) A detection chamber for receiving a test strip that becomes colored when it comes into contact with a specific substance in a gas stream circulating therethrough;
(b) a light source; (c) a device responsive to the light source that generates a luminous flux and directs the luminous flux toward a test strip located within the detection chamber;
a luminous flux detection device that responds to the degree to which a test paper in the detection chamber is colored by exposure to a specific substance in the gas flow;
(e) an amplifier connected to the luminous flux detection device and providing an output signal proportional to the coloration of the test strip, the test strip being stationary during a measurement cycle, and an amplifier that is in contact with the test strip being detected; A signal conditioning circuit is connected to the amplifier for providing an output signal that is a linear function of the cumulative amount of the substance, and in response to the linear output signal provides an output instantaneously indicating the concentration of the substance in the gas stream. A device for detecting the presence of a specific substance in a gas flow, characterized by comprising a differentiating device for extracting the substance. 2. The signal conditioning circuit is connected to the input of the amplifier and includes positive feedback from the output of the amplifier for varying the input of the amplifier in a direction that linearizes the output of the amplifier, thereby making the output of the amplifier linear. A circuit according to claim 1, characterized in that the differential of the linear output of the amplifier provides an instantaneous indication of the concentration of the substance to be detected. Device to detect. 3 (a) a detection chamber for receiving a test strip that becomes colored when it comes into contact with a specified substance in a gas stream circulating therethrough;
(b) a light source; (c) a device responsive to the light source that generates a luminous flux and directs the luminous flux toward a test strip located within the detection chamber;
a luminous flux detection device that responds to the degree to which a test paper in the detection chamber is colored by exposure to a specific substance in the gas flow;
(e) an amplifier connected to the luminous flux detection device and providing an output signal proportional to the coloration of the test strip, the test strip being stationary during a measurement cycle, and an amplifier that is in contact with the test strip being detected; A signal conditioning circuit is connected to the amplifier for providing an output signal that is a linear function of the cumulative amount of the substance, and in response to the linear output signal provides an output instantaneously indicating the concentration of the substance in the gas stream. In a device for detecting the presence of a specific substance in a gas stream, the light beam is directed towards a test strip located in the detection chamber and towards a variable optical density filter in a device for detecting the presence of a specific substance in a gas stream, which is provided with a differentiating device for extracting the light beam. a beam splitting device that splits the directed beam into two separate beams;
a second light flux detection device connected to the amplifier and responsive to the transmittance of the variable optical density filter; an operational amplifier connected to the output of the amplifier; and a second beam detection device responsive to the operational amplifier and connected to the variable optical density filter. an automatic zeroing device including a servomotor for resetting the output of the amplifier to zero before making a measurement. 4 (a) a detection chamber for receiving a test strip that becomes colored when it comes into contact with a specified substance in a gas stream circulating therethrough;
(b) a light source; (c) a device responsive to the light source that generates a luminous flux and directs the luminous flux toward a tape-shaped test strip located within the detection chamber; and (d) a test strip located within the detection chamber. (e) an amplifier connected to the light flux detection device and providing an output signal proportional to the coloration of the test strip; encompasses,
During the measurement cycle the test strip is stationary and a signal conditioning circuit is connected to the amplifier for providing an output signal that is a linear function of the cumulative amount of substance to be detected that has come into contact with the test strip; a differentiator for producing an output instantaneously indicating the concentration of the substance in the gas stream in response to a signal; a light flux and a variable optical density filter for directing said light flux towards a test strip located within said detection chamber; a beam splitting device for splitting the beam into two separate beams with a beam directed toward the amplifier; a second beam detection device connected to the amplifier and responsive to the transmittance of the variable optical density filter; a gas flow comprising an operational amplifier connected thereto and an automatic zeroing device including a servomotor responsive to the operational amplifier and connected to the variable optical density filter to reset the output of the amplifier to zero before making a measurement; The apparatus further includes a motor for intermittently advancing a predetermined length of the tape test strip through the chamber, and first energizing the motor for a predetermined time interval to detect the presence of a specific substance in the chamber. a programming device operative to advance a tape test strip, then energize the automatic zeroing device for a second predetermined time interval to reset the amplifier to zero output, and finally initiate a measurement cycle. A device for detecting said presence, characterized in that: 5 (a) a detection chamber for receiving a test strip which becomes colored when it comes into contact with a specified substance in a gas stream circulating therethrough;
(b) a light source; (c) a device responsive to the light source that generates a luminous flux and directs the luminous flux toward a test strip located within the detection chamber;
a luminous flux detection device that responds to the extent to which a test paper in the detection chamber is colored by exposure to a specific substance in the gas flow;
(e) an amplifier connected to the luminous flux detection device and providing an output signal proportional to the coloration of the test strip, the test strip being stationary during a measurement cycle, and an amplifier that is in contact with the test strip being detected; A signal conditioning circuit is connected to the amplifier for providing an output signal that is a linear function of the cumulative amount of the substance, and in response to the linear output signal provides an output instantaneously indicating the concentration of the substance in the gas stream. In a device for detecting the presence of a specific substance in a gas stream, which is equipped with a differentiator for extracting the substance, a decomposition compensation device connects the amplifier to the differentiator to compensate for slight decomposition of the substance that has reacted with the test strip. A device for detecting said presence, characterized in that said device comprises: