JP2710115B2 - Optical gas concentration measurement device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an optical gas concentration measuring device for measuring the concentration of a specific gas contained in the atmosphere or the like based on the refractive index of the gas.
More specifically, the present invention relates to a calibration technique for adjusting an interference fringe caused by a difference in refractive index between a reference gas and a measured gas to a reference position.

(Prior Art) An optical gas concentration measuring device is a first type in which a reference gas flows.
And a second cell into which the gas to be measured flows,
By passing light from the same light source through these cells, interference fringes are generated due to the difference in gas density, and the amount of movement of specific fringes is detected as a change in output level by a photoelectric detector. Have been.

(Problems to be Solved by the Invention) In such an apparatus, since the generation position of the specific interference fringe with respect to the gas of the reference concentration greatly affects the measurement accuracy, the optical path difference between the light source and the detector is usually different. An optical member for adjustment, for example, an optical wedge is inserted, and the optical wedge is moved by an adjusting member such as a screw using an inspection jig so that the interference fringe becomes a reference position.

However, there is a problem that not only the calibration result is caused due to the manual operation, but the calibration result is caused to vary from individual to individual, and the reliability is deteriorated. In addition, the calibration cycle is lengthened and the reliability of the measurement result is reduced.

The present invention has been made in view of such a problem, and an object of the present invention is to provide a novel optical gas concentration measurement device that can automatically perform calibration without manual operation.

(Means for Solving the Problems) In order to solve such a problem, in the present invention,
A light beam from the same light source is incident on a first optical cell into which a gas to be measured flows and a second optical cell into which a gas having a known refractive index flows, and the difference between the refractive indices of the two gases is determined by interference fringes. In a gas concentration measuring device that converts an amount of movement into an electric signal by photoelectric detection means, an optical path difference correction means inserted in an optical path inserted in an optical path of the optical cell, and a driving mechanism for driving the optical path difference correction means Means for detecting that the optical path difference correction means has reached the initial position, and means for detecting the optical path difference correction means from two extreme values of a signal from the photoelectric detector which changes with movement in one direction from the initial position. Span calculating means for determining an appropriate measurement range, span setting means for setting a span based on data from the span calculating means, output from the span calculating means corresponding to gas introduced into the optical cell during calibration. When the optical path difference correction member moves in the other direction, the output from the reference value setting means and the output from the span setting means are compared with each other, and when the optical path difference correction member agrees, the optical path difference correction member is set. And a means for injecting the same gas into the two optical cells at the start of calibration.

(Action) The upper limit and the lower limit of the measurement range are determined based on the two extreme values of the detector output, and the optical path difference correction member is set to the reference value specified by the determined range, thereby obtaining the light emitting element. Of output levels due to aging of the sensor and detectors, and contamination of optical components, etc., and the output level over time due to contamination and deterioration of the optical system can be corrected without the need for special calibration jigs or human intervention. Fluctuations can be automatically corrected.

(Embodiment) Therefore, the details of the present invention will be described below based on an illustrated embodiment.

FIG. 1 shows an embodiment of the present invention. In the figure, reference numerals 1 and 2 denote optical cells into which a gas to be measured and a reference gas respectively flow, which are arranged so that their optical axes are parallel. The light from the light source 4 is incident through a parallel light beam generating member 3 such as a prism.

On the emission side, a converging member 6 is disposed to face through an optical path difference correcting member 5 described later, and is configured to detect the position of the interference fringe generated here as a level change of the photoelectric detector 7.

5 is an optical path difference correction member as described above, and as shown in FIG. 2, a glass section 22, 23 having a rectangular cross section is formed at a fixed angle θ on an axis 21 rotated by a lever 20 with an optical path interval 1 therebetween. At least one is fixed by a screw 24 so as to be relatively movable around the axis, and the pulse motor 8 is
Thus, the shaft 21 is rotated. 9 is
When the optical path difference correction member 5 is retracted to the initial position set outside the measurement range by the position detection switch, the position detection plate
It is located at the position activated by 10.

Reference numeral 15 denotes a calibration device which receives commands from the external switch 16 and the keyboard 18, and an embodiment of the calibration device will be described in detail below with reference to FIG.

Reference numeral 30 denotes a pulse generating circuit which, when a calibration command signal is inputted from the calibration command circuit 41, moves the optical path difference correcting member 5 in the direction of the initial position S (FIG. 5) and the position detecting switch 9
The signal is inverted in the first direction when the signal from the comparator 39 is input, and when the signal exceeds the second extreme value, and the pulse output is stopped when the signal from the comparison circuit 39 is input, and the optical path difference correcting member is stopped. 5 is stopped.

Numeral 32 denotes a first extremum detection circuit, which outputs a signal when the optical path difference correction member 5 returns from the initial position and the output of the detector 7 shows the first extremum, in this embodiment, the extremum, The pulse from the pulse generation circuit 30 is output to operate the pulse motor 8, and at the same time, the output of the detector 7, that is, the minimum value, is stored in the first extreme value storage circuit 33. 34
Is a second extreme value detection circuit, which outputs a second extreme value, in this embodiment, a maximum value, by the movement of the optical path difference correction member 5,
This is detected and a signal is output to stop the operation of the pulse generation circuit 30. At this time, the output of the detector 7
That is, the maximum value is stored in the second extreme value storage circuit 34. Reference numeral 37 denotes a span operation circuit which reads data from the first and second extreme value storage circuits 33 and 34 and has a relatively high linearity in the output between the extreme values, for example, 8.5% of the maximum value and 91.
The level of 5% is calculated, and one is set as the lower limit of the span, and the other is set as the upper limit, and the level difference between the upper limit and the lower limit is calculated so as to correspond to the gas concentration. This is set as the density.

Reference numeral 39 denotes a comparison circuit which is used when the output from the span setting circuit 38 matches a value from a reference value setting circuit 40, which will be described later, or within the upper / lower limit value calculated by the span calculation circuit 37. When the value coincides with the designated one, the operation of the pulse generation circuit 30 is stopped and the movement of the optical path difference correction member 5 is stopped.

Reference numeral 40 denotes the reference value setting circuit described above.
When measuring the calorific value of the gas, enter the calorific value of the reference gas as an absolute value or a relative value, and when not using the reference gas, specify one of the upper and lower limits calculated by the span calculation circuit 37 It is configured to be. Reference numeral 41 in the figure denotes a calibration command circuit that outputs a calibration signal using a calibration command button or a built-in timer.

Next, the operation of the device configured as described above will be described based on the flowchart shown in FIG.

One of the cells 2 is connected to the reference gas source 14 and the other cell 1 is connected to the measured gas inlet 19 via the first solenoid valve 12 and to the second cell 1.
Is connected to the reference gas source 14 via the solenoid valve 13 of FIG.

When the connection is completed, the first solenoid valve 12 is opened, and the second solenoid valve 13 is closed to start the measurement operation. The interference fringes move in proportion to the concentration difference from the gas, that is, the difference in the refractive index, is converted into an electric signal by the photoelectric detector 7, and is measured by the measuring circuit as the concentration difference from the reference gas.

On the other hand, when calibration is required, when the external switch 16 is operated or a calibration command signal is output by a timer signal of the calibration command circuit 41, the first solenoid valve 12 is closed, and the second solenoid valve 13 is closed. Is opened and the reference gas source is
From 14 the reference gas flows. Simultaneously pulse generation circuit 30
Is to output a pulse signal and operate the pulse motor 8 to move the optical path difference correcting member 5 in one direction, in this embodiment, in the direction in which the output level decreases (a path in FIG. 5), and to set the minimum point. Pass through and move in the same direction. When the initial position S is reached in this way, an initial position reaching signal is output from the position detection switch 9. The pulse generating circuit 30 receives this signal and rotates the pulse motor 8 in the reverse direction.
The optical path difference correction member 5 is moved in the direction of the minimum value that has just passed. When the detector 7 outputs the first extreme value, in this embodiment, the minimal value, the first minimal value detection circuit 32 outputs a signal,
The output level of the detector 7, that is, the minimum value, is stored in the first minimum value storage circuit 33.

Further, when the optical path difference correction member 5 continues to move and the second extreme value, that is, the maximum value in this embodiment, is output from the detector 7, the second extreme value detection circuit 34 detects this and detects this maximum value as the second maximum value. 2 is stored in the extreme value storage circuit 36.

The pulse generation circuit 30 stops when the optical path difference correction member 5 has passed the second extreme value by a predetermined step. The span calculation circuit 37 calculates the data stored in the first and second extreme value storage circuits 33 and 36, that is, the minimum value L1 and the maximum value of the signal from the photoelectric detector 7 calculated so as to correspond to the gas concentration. The value L2 and the movement amount n of the optical path difference correction member are read, 8.5% of the difference between the maximum value and the minimum value, and 91.5% of the value are obtained, and the value obtained by adding the minimum value to these values is calculated. The two values are defined as a lower limit L1 'and an upper limit L2', respectively, and a value per step between the upper and lower limits is calculated, and the span is adjusted by a span setting circuit 38 based on these values. Let them do it. As a result, the span is set irrespective of fluctuations in the detector output due to deterioration or contamination of the optical member.

When the span adjustment is completed, the pulse generation circuit 30
A pulse of the opposite phase is output to rotate the pulse motor 8 in reverse,
The optical path difference correction member 5 is moved toward the initial position S after passing the local maximum value.

The comparison circuit 39 compares the output from the span setting circuit 38 with the signal from the reference value setting circuit in the course of the movement of the optical path difference adjusting member 5, and outputs a signal when the two coincide with each other to output the pulse generation circuit 30. Stop the operation of.

As a result, the optical correction member 5 is specified by the reference value setting circuit 40 in a state where the output change caused by the deterioration or contamination of the light emitting element 4, the detector 7, and the cells 1 and 2 has been corrected. It will be set to the value.

FIGS. 6 (a) to 6 (c) show an embodiment around the cell of the apparatus to which the present invention is applied.
Reference numerals 0 and 51 denote an entrance prism and an exit prism respectively arranged in the optical axis direction of the measurement cell 52 and the reference cell 53.The measurement cell 52 and the reference cell 53 are arranged in the axial direction. A measurement optical path leading to the photoelectric detector is formed. In this optical path, in this embodiment, the outgoing light side of the cell and the outgoing prism
A shaft rotatable by the rod 20 shown in FIG.
An optical path adjusting member 5 is provided, which is provided at a right angle to the optical axis and has glass plates 22 and 23 attached to the lower part thereof so as to face the cells 52 and 53.

Reference numeral 60 denotes an operating rod, which is connected to a pulse motor 61 via a train wheel 62, and is attached to a substrate 63 so as to move in the axial direction in proportion to the rotation of the pulse motor 61, and the rod 20 has a spring at its tip. 64, and a detection plate 68 for initial position detection is attached to the rear end via a long groove so that the position can be adjusted by screws 69, 69, and a position detection switch 70 is arranged opposite to this. It is configured.

By the way, in this embodiment, an example has been described in which the gas concentration is optically measured. However, an optical gas calorific value measuring apparatus that positively utilizes that the refractive index of the gas correlates with the calorific value is described. That is, as shown in FIG. 7, a gas inlet is connected to the fuel gas supply pipe G, and a cylinder 70 filled with a gas having a known calorific value is connected to the reference gas inlet. It is apparent that the same effect is obtained even when applied to an optical gas calorific value measuring device that detects a difference in the refractive index of gas and finally converts and detects the calorific value by the calorific value conversion circuit 71. .

In this embodiment, the point of occurrence of the extreme value is set as the initial position, and the upper and lower limits of the measurement range are determined by the number of drive steps of the pulse motor from here, but the initial position setting member, in this embodiment, the switch Obviously, the same operation can be obtained even if the position where the signal is output is set as the initial position and the upper and lower limits are determined by the number of steps from this position.

In this embodiment, the output level of the detector 7 is detected to move the optical path difference correction member to a predetermined position. However, the number of drive pulses from the reference position to the pulse motor is counted. Using the position detecting means, the optical path difference correction member is set to correspond to the count value indicating the detector level value to be set or the data of the position detecting means. Obviously,

Furthermore, in the present invention, the initial position is set on the minimum side, but the initial position is provided on the maximum side, and the level measurement of the measurement range limit is performed by moving from the maximum side to the minimum side,
It is apparent that the same effect is obtained even when the setting to the initial position is performed while moving from the minimum value side to the maximum value side.

Further, in this embodiment, the reference gas is injected into the two optical cells. However, it is obvious that the same effect can be obtained by using the gas to be measured or air.

(Effects) As described above, in the present invention, a light beam from the same light source is made incident on the first optical cell into which the measurement gas flows, and into the second optical cell into which the gas having a known refractive index flows. In a gas concentration measuring device for converting a difference in refractive index between different types of gases into an electric signal by photoelectric detection means as a movement amount of an interference fringe, an optical path difference correction means inserted in an optical path inserted in an optical path of an optical cell; A drive mechanism for driving the correction means,
A means for detecting that the optical path difference correcting means has reached the initial position, and an appropriate measuring range based on two extreme values of the signal from the photoelectric detector which change with movement in one direction from the initial position. Calculating means, a span setting means for setting a span based on data from the span calculating means, a reference value for setting a measured value to be output from the span calculating means corresponding to a gas introduced into the optical cell at the time of calibration. When the setting means and the optical path difference correction member move in the other direction, the output from the reference value setting means and the output from the span setting means are compared and the comparison means stops the movement of the optical path difference correction member at the time of coincidence. Since a means for injecting the same gas into the two optical cells is provided, the upper and lower limits of the measurement range are determined based on the two extreme values of the detector output, and the determined range is used. By setting the optical path difference correction member to the specified reference value, it is possible to correct output level fluctuations caused by aging of light emitting elements and detectors and contamination of optical members, etc. It is possible to automatically correct fluctuations in the output level over time due to contamination or deterioration of the optical system without the need for Can be calibrated.

[Brief description of the drawings]

FIG. 1 is a structural view of an apparatus showing an embodiment of the present invention, and FIGS. 2 (a) and 2 (b) are a side view and a front view, respectively, showing an embodiment of an optical path difference correcting member in the apparatus. 4 is a block diagram showing an embodiment of the calibration circuit in the above-mentioned apparatus, FIGS. 4 and 5 are flowcharts and explanatory diagrams showing the operation of the above-mentioned apparatus, respectively, and FIGS. FIG. 7 is a block diagram showing another embodiment of the present invention. FIG. 7 is a top view, a front view, and a rear view showing the vicinity of an optical path difference correcting mechanism. 1, 2, cell 3, light beam splitting member 4, light source 5, converging member 6, optical path difference correcting member 7, photoelectric detector 8, cam 9, position switch 10 Position detector plate 12, 13 Gas switching stop valve 14 Reference gas source

Claims (1)

(57) [Claims] 1. A first optical cell into which a gas to be measured flows,
A light beam from the same light source is incident on a second optical cell into which a gas having a known refractive index flows, and the difference between the refractive indices of the two types of gases is converted into an electric signal by a photoelectric detection unit as the amount of movement of interference fringes. In the gas concentration measurement device, optical path difference correction means inserted in the optical path inserted in the optical path of the optical cell,
A drive mechanism for driving the optical path difference correction means, a means for detecting that the optical path difference correction means has reached the initial position, and a photoelectric mechanism which changes as the optical path difference correction means moves from the initial position to one direction. Span calculating means for determining an appropriate measurement range from two extreme values of a signal from a detector, span setting means for setting a span based on data from the span calculating means, corresponding to gas introduced into the optical cell during calibration Reference value setting means for setting a measurement value to be output from the span calculation means, and when the optical path difference correction member moves in the other direction, the output from the reference value setting means and the output from the span setting means are compared. An optical gas concentration measuring device comprising: comparing means for stopping the movement of the optical path difference correction member at the time of coincidence; and means for injecting the same gas into the two optical cells at the start of calibration.