JP3342266B2 - Method and apparatus for detecting disconnection of light source in infrared gas analyzer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for detecting disconnection of a light source in an infrared gas analyzer having an infrared light source whose pulse width is controlled.

[0002]

2. Description of the Related Art The above-mentioned infrared gas analyzer measures a specific gas by utilizing the fact that the gas absorbs infrared light in a specific wavelength range. High strength is required. For this purpose, conventionally, a light shielding plate is provided in an infrared light source of an infrared gas analyzer, and the intensity of infrared light from the infrared light source is adjusted by the amount of light shielding.

The infrared light source is often formed by a filament. If the infrared light source is broken, an abnormal value is generated in the measurement result. Therefore, conventionally, it has been necessary for the measurer to determine the disconnection of the infrared light source by observing the abnormality of the measurement result, visually confirm the disconnection of the light source filament by himself, and replace the light source filament.

Alternatively, a circuit as shown in FIG. 3 is conceivable as a method of automatically determining the break of the filament of the infrared light source. In FIG. 3, reference numeral 21 denotes an infrared light source of the infrared gas analyzer, 22 denotes a power supply, R denotes a resistor having a small resistance value interposed in a power supply line 23 between the infrared light source 21 and the power supply 22, and V denotes a resistance. This is a voltmeter provided in parallel with the resistor R.

By monitoring the voltage drop across the resistor R with a voltmeter V, the current flowing through the resistor R and the infrared light source 21 can be measured. By determining the disconnection of the external light source 21, a disconnection occurrence alarm (not shown) is sounded.

[0006]

However, in the above-described method for visually confirming the disconnection of the infrared light source, the determination is made not only when an abnormal analysis result is output from the infrared gas analyzer, but also in this case. A great deal of experienced experience was required to recognize that the abnormality in the measured value was due to the disconnection of the infrared light source.

When an electric circuit for judging the disconnection of the light source is provided as shown in FIG. 3, since the current measuring resistor R is connected in series to the infrared light source 21, the resistance is changed depending on the ambient temperature. The resistance value of R changes, and the voltage applied to the infrared light source 21 changes. Since the temperature of infrared light fluctuates due to the resistance R, an error occurs in the measured value. Further, since it is necessary to insert the resistor R in the circuit of the infrared light source 21, the circuit design is changed,
This was the cause of the high cost.

The present invention has been made in view of such circumstances, and it is possible to cut a light source filament of an infrared light source used in an infrared gas analyzer or the like without affecting analysis accuracy. It is an object of the present invention to provide a method and an apparatus for detecting a disconnection of a light source in an infrared gas analyzer for reliably determining.

[0009]

That is, the present invention relates to an infrared gas analyzer provided with an infrared light source whose light amount is adjusted by a pulse width-modulated voltage, wherein the infrared light source is simply
By being connected to the stable multivibrator, the power supply voltage supplied to the infrared light source is input to the monostable multivibrator having a circuit constant equal to or longer than the period of the voltage pulse,
The infrared light source is opened due to the disconnection, the power supply voltage does not fluctuate in pulse, and the disconnection of the infrared light source is determined by changing the output of the monostable multivibrator.

A DC power supply, an infrared light source for irradiating the cell, a transistor connected between the output of the DC power supply and the infrared light source, and a power supply voltage applied to the infrared light source having a pulse width. A pulse width modulation control unit that outputs a control signal to be modulated to the transistor, wherein the infrared gas analyzer has a circuit constant equal to or longer than the period of the voltage pulse, and the infrared light source is connected to the transistor, A monostable multivibrator that outputs a disconnection detection signal of the infrared light source when the infrared light source is opened due to disconnection and the power supply voltage does not fluctuate.

By setting the circuit constant of the monostable multivibrator to be at least twice as long as the period of the voltage pulse, even if the power supply pulse generating circuit misses one voltage pulse, this skipping occurs. The one pulse does not cause the monostable multivibrator to determine the break of the filament. That is, the reliability of the disconnection determination by the monostable multivibrator can be increased.

[0012]

FIG. 1 shows an example of a light source disconnection detecting device in an infrared gas analyzer of the present invention. An example of a method for detecting disconnection of the light source in the infrared gas analyzer will be described below with reference to FIG.

In FIG. 1, reference numeral 1 denotes an infrared gas analyzer,
2 is a DC power supply that outputs a constant voltage of, for example, 5 V;
Is the F that each source terminal is connected to this DC power supply.
Reference numerals ET, 5, 6 denote infrared light sources connected to the drain terminals of the FETs 3, 4, respectively, and reference numeral 7 denotes a chopper for optically blocking infrared light from the infrared light sources 5, 6. Reference numerals 8 and 9 denote cells for transmitting infrared light from the infrared light sources 5 and 6 through the chopper 7, respectively. A reference gas is sealed in the cell 8, and a sample gas S is stored in the cell 9. Supplied.

Reference numerals 10 and 11 denote interference filters arranged on the other end sides of the cells 8 and 9, respectively.
A condenser microphone type detector that detects infrared light passing through 0 and 11 is a preamplifier that amplifies the output of the detector 12.

A pulse width modulation control unit (PWM modulation control unit) 14 outputs a pulse width modulation control signal for pulse width modulation (PWM modulation) of the power supply voltage supplied to the infrared light sources 5 and 6 to the gate terminals of the FETs 3 and 4. And 15 are temperature adjusting circuits for adjusting the temperatures of the FETs 3 and 4 to, for example, 55 ° C. in order to stabilize the operation of the FETs 3 and 4.

According to the infrared gas analyzer 1, since the infrared light sources 5 and 6 are PWM-modulated, the voltage supplied to the infrared light sources 5 and 6 can be changed by changing the duty of the voltage pulse. By changing the size, the infrared light source 5,
6 can be adjusted freely, and by irradiating the optimum light amount for infrared gas analysis, the analysis accuracy of the infrared gas analyzer 1 can be improved.

The present invention provides a disconnection detecting method capable of reliably detecting disconnection of the light source filaments of the infrared light sources 5 and 6 without affecting the analysis accuracy of the infrared gas analyzer 1. The following disconnection detection device is used as a very simplified configuration for implementing the detection method.

Reference numeral 16 denotes a monostable multivibrator,
The input terminals of the monostable multivibrator 16 are connected to the respective points P ₁ and P ₂ on the power supply lines to the light sources 5 and 6 so that the output voltage V _{O of the} FETs 3 and 4 is monostable. Input to vibrator 16. That is, the monostable multivibrator 16 detects a voltage signal supplied to each of the light sources 5 and 6, and determines whether or not the power supply voltage V _O changes in pulses. Accordingly, the output of the monostable multivibrator 16 is a disconnection detection signal S ₁₆ of each light source 5,6.

FIG. 2 shows the monostable multivibrator 16.
5 is a time chart showing a relationship between a signal input to the mono-stable multivibrator 16 and a signal output from the monostable multivibrator 16. FIG. 2 shows a time chart of a PWM modulation signal, a power supply voltage, and a disconnection detection signal for controlling the infrared light source 5 and describes a disconnection determination method.
Is also the same method, and a detailed description thereof will be omitted.

In FIG. 2, S ₁₄ is a PWM modulation controller 1
The PWM modulation signal V _O output from 4 is an output voltage (voltage pulse) from the FET 3 controlled by the PWM modulation signal S ₁₄ . S ₁₆ is the disconnection detection signal outputted from the monostable multivibrator 16. In other words, the duty of the PWM modulation signal S ₁₄ and the voltage pulse V _O is adjusted to adjust the power supplied so that the infrared light source 5 emits constant infrared light in accordance with the state of the infrared light source 5. are PWM modulated at a period T _P.

As shown in FIG. 2, the circuit constant T _M of the monostable multivibrator 16 (this circuit constant is a fixed time from when the monostable multivibrator 16 becomes unstable until it returns to the original state). to say, the monostable multivibrator 16 in which is determined by constant of the circuit included therein) is 2.5 times the period T _P of pulses of the PWM modulated signal S _14. Therefore, the output signal of the monostable multivibrator 16 remains at the Hi level as long as the power supply voltage V _O changes in pulses.

At a certain time T, the infrared light source 5
Is disconnected. The PWM modulation signal S ₁₄ outputted from the PWM modulation control unit 14, as before disconnection occurred and outputs a PWM modulated signal S _14. However, after the infrared light source 5 is disconnected, the output terminal of the FET 3 is open, so that the output voltage of the FET 3 remains at 5 V, and the pulse does not fluctuate. Therefore, since the voltage pulse is not input to the monostable multivibrator 16, from the rising time of the last voltage pulse before a disconnection occurs, T _M seconds after the disconnection detection signal S ₁₆ has the infrared light source 5 becomes Low level Detects disconnection. And
By sounding the wire breakage alarm by an unillustrated alarm generating apparatus in accordance with the fall of the disconnection detection signal S _16, it is possible to inform the filament breakage of the infrared light source to the subject.

Further, the PWM modulation signal S ₁₄ outputted from the PWM modulation control unit 14, which changes its duty by the state of the infrared light source 5, sometimes, two previous pulse disconnection occurs, as in the three previous pulse interval, it will be missing one time pulse, the interval of the voltage pulse which may become 2T _P. However,
As already described in detail, since in this example has a circuit constant T _M of the monostable multivibrator 16 to 2.5 times the period T _P of the voltage pulse, the variation of the PWM signal S _14, disconnection detection Is not inadvertently notified.

The monostable multivibrator 16
_May be further increased to further suppress occurrence of the erroneous recognition. Conversely, the response of the monostable multivibrator 16 may be improved by setting the circuit constant T _M to about one time the period T _P.

Further, in this embodiment, an infrared gas analyzer having two cells and two infrared light sources, in which a reference gas is sealed in one cell, has been described. Is not limited to this, for example, an infrared gas analyzer that alternately supplies a sample gas and a reference gas at constant intervals,
It is needless to say that the present invention can be applied to an infrared gas analyzer having one cell and one infrared light source.

In this embodiment, an FET is used as an example of a transistor for performing PWM modulation. However, the present invention is not limited to this, and it goes without saying that various transistors such as a power transistor may be used. .

[0027]

As described above, according to the present invention,
With a very simple configuration in which a pulse of a PWM-modulated power supply voltage is input to a monostable multivibrator, disconnection of an infrared light source can be determined by the presence or absence of voltage fluctuation, and a current detection resistor is provided as in the conventional case. Since there is no need,
There is no adverse effect on the power supplied to the infrared light source. That is, disconnection of the infrared light source can be reliably and automatically determined without lowering the analysis accuracy of the infrared gas analyzer.

Further, the disconnection detection method of the present invention only monitors the power supply voltage of the infrared light source. There is no need to change the control circuit of the external light source or disassemble the infrared light source. In addition, since the reference for disconnection detection is whether or not there is a pulse fluctuation in the voltage, the power supply voltage can be applied to any magnitude.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a light source disconnection detection device in an infrared gas analyzer of the present invention.

FIG. 2 is a time chart showing the operation of the infrared gas analyzer.

FIG. 3 is a circuit diagram illustrating an example of a general light source disconnection detection device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Infrared gas analyzer, 2 ... DC power supply, 3,4 ... Transistor, 5,6 ... Infrared light source, 8,9 ... Cell, 14 ... Pulse width modulation control part, 16 ... Monostable multivibrator,
S ₁₄ ... pulse width modulation control signal, S ₁₆ ... disconnection detection signal, T
_M : circuit constant, T _P : period of voltage pulse, V _O : voltage pulse.

Continuation of front page (56) References JP-A-4-331493 (JP, A) JP-A-5-346999 (JP, A) JP-A-57-36386 (JP, A) JP-A-54-139591 (JP) , A) Japanese Utility Model Application Hei 3-2244 (JP, U) Japanese Utility Model Application Hei 4-94837 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 21/00-21/01 G01N 21/17-21/61 Practical file (PATOLIS) Patent file (PATOLIS)

Claims (5)

(57) [Claims] 1. An infrared gas analyzer having an infrared light source whose light intensity is adjusted by a pulse width modulated voltage,
The infrared light source is connected to a monostable multivibrator
By inputting the power supply voltage supplied to the infrared light source to a monostable multivibrator having a circuit constant equal to or longer than the period of the voltage pulse, the infrared light source becomes open due to disconnection and the power supply voltage does not fluctuate in pulse. A method for detecting a disconnection of a light source in an infrared gas analyzer, wherein the disconnection of an infrared light source is determined based on a change in the output of the monostable multivibrator. 2. The method for detecting disconnection of a light source in an infrared gas analyzer according to claim 1, wherein the circuit constant of the monostable multivibrator is at least twice the period of the voltage pulse. 3. A DC power supply, an infrared light source for irradiating a cell, a transistor connected between the output of the DC power supply and the infrared light source, and a power supply voltage applied to the infrared light source having a pulse width. A pulse width modulation control unit that outputs a control signal to be modulated to a transistor, the infrared gas analysis device having a circuit constant equal to or longer than the period of the voltage pulse,
When the infrared light source is connected, the output voltage of the transistor is input, and the infrared light source is opened due to the disconnection, and the power supply voltage does not fluctuate in pulse. A disconnection detection device for a light source in an infrared gas analyzer, wherein a monostable multivibrator is provided. 4. The apparatus for detecting disconnection of a light source in an infrared gas analyzer according to claim 3, wherein the circuit constant of the monostable multivibrator is at least twice the period of the voltage pulse. 5. An apparatus for detecting disconnection of a light source in an infrared gas analyzer according to claim 3, wherein the transistor is an FET.