JP2000215990A - Method for driving incandescent lamp as gas sensor light source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably measure without being influenced by an external change, such as temperature, the lapse of time, or the like, in a measuring instrument using an incandescent lamp as a light source and measuring by detecting a light intensity from the light source. SOLUTION: In this measuring instrument, a resistance value of an incandescent lamp (a) is kept constant. In this method keeping a light emitting intensity constant by keeping the resistance value of a filament constant in a turning-on state of the incandescent lamp (a), elements having temperature variable factors, such as bridge resistor elements, an amplifier, and so on, except the filament, are used within a heat insulated space controlled at a constant temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0101]

The present invention is used in a gas sensor such as carbon dioxide.

[0092]

2. Description of the Related Art 1) Conventionally, when an incandescent lamp is used as a light source for measurement, a method of driving the incandescent lamp with a constant voltage and a constant current has been used as a method for obtaining a stable light quantity. 2) In the above-mentioned method, accurate measurement can be expected when the ambient temperature condition is constant or when the lapse of time from the start of use is short, but accurate measurement is expected when a temperature change or a temporal change occurs. Can not.

[0093]

The problem to be solved by the present invention is to obtain a stable light quantity even when a temperature change or a change with time occurs when an incandescent lamp is used as a light source for measurement.

[0093]

Means for Solving the Problems 1) An incandescent lamp emits light from the filament by increasing the temperature of the filament by energizing the filament inside. 2) It is shown by Stefan-Boltzmann's law that the amount of light emitted from the filament depends on the temperature (color temperature) of the filament. 3) Therefore, in order to make the amount of light emitted from the filament constant, the temperature (color temperature) of the filament should be kept constant.

4) In order to make the filament temperature constant, it is necessary to know the filament temperature. As a method of knowing the filament temperature, in the present invention, the resistance value of the filament was measured. This is because the filament is a metal and its resistance is determined by the resistivity and the temperature specific to the metal, so that measuring the resistance is a temperature measurement. 5) The material of the filament is mainly tungsten. The temperature change rate of the volume resistivity of tungsten is 800 ° C.
Is about 0.0011 / ° C. (1100 ppm / ° C.), and in order to keep the filament temperature constant, it is necessary to accurately detect a further change (110 ppm / ° C.) of about 1/10 of the temperature change rate. 6) In order to measure the above change, it is necessary to make the temperature characteristic of the reference resistance value zero, and an element having a temperature fluctuation factor such as an element serving as the reference resistance is operated at a constant temperature.

7) When the temperature is kept at a constant value, the heating is performed by a heater, but the heater is integrated with the substrate by using a copper foil provided as an element or a pattern printed on a certain surface of the substrate. Since the heater can be configured, it has excellent responsiveness to heating and excellent thermal efficiency.

8) On the other hand, the change in the resistance value due to the external temperature fluctuation of the incandescent lamp is about 0.005Ω / ° C. as described in 5), and the voltage value is about 2 mV / ° C. It is. In an actual circuit configuration, a temperature characteristic of about 5 μV / ° C. in terms of input is required. The low-cost general-purpose amplifier has a temperature characteristic value of about 30 μV and a temperature stability of about 0.1 ° C., which is technically difficult. 9) For this reason, the input of the amplifier that detects the fluctuation of the filament resistance value is constantly short-circuited, the output of the amplifier is controlled to be at a constant level, and the short-circuit of the amplifier input is released for a short time at the timing when the measurement is completed. A method was devised to eliminate the amplifier drift by inputting the resistance bridge output including the filament and checking the value of the fluctuation of the resistance bridge as the amplifier output and using it at the next measurement.

[Related to claim 4]

[0056]

1) When the carbon dioxide sensor is used in an ambient temperature different from the ambient temperature at the time of adjustment, the temperature of the incandescent lamp filament of the light source to be used is affected by the ambient temperature and changed, so that the light emission amount fluctuates. 2) However, since the control is performed so as to suppress the change in the light amount due to the temperature fluctuation, a stable light amount can be obtained. 3) Further, even when the resistance value of the filament fluctuates due to a change over time, control is performed so as to suppress the change in the light amount, so that a stable light amount can be obtained.

[0086]

FIG. 1 shows an embodiment.

007

According to the method of operating the incandescent lamp at a constant temperature, the amount of the incandescent lamp is stabilized. When the incandescent lamp is used in a carbon dioxide gas sensor, the temperature characteristic falls to about 2 ppm. Is driven to be a constant value, and the influence on the measured value is reduced.

[Brief description of the drawings]

FIG. 1 Example (1)

[Explanation of symbols] a Incandescent lamp b Insulation material c Amplifier
d board e copper foil pattern f _{1 to 3} bridge resistor E _L (lamp voltage)

[Explanation of Action] The variation of the filament resistance value of the incandescent lamp (a) according to the ambient temperature is determined by the bridge resistor (f).
_The lamp voltage (E _L ) is controlled so that the filament resistance value becomes constant.

FIG. 2 Example (2)

[Explanation of symbols] f _4-7 resistor i memory j _1-2
Switch l capacitor

[Explanation of Operation] In order to correct the drift of the amplifier (c) which amplifies a slight change in the lamp resistance value detected by the lamp and bridge resistors (f _1-3 ),
Normally, the switches j1 are turned off and j2 are turned on, and the amplifier output is controlled to a constant value with the input being zero. At the time of measurement, the switches j1 are turned on and j2 are turned off to amplify a slight fluctuation of the bridge and use it for lamp voltage control. The memory (i), the resistors (f6 to 7), and the capacitor (l) exclude the influence of the change in state due to the opening and closing of the switch.

Claims (4)

[Claims] 1. A method for making the amount of light emission constant by making the filament resistance value in a lighting state of an incandescent lamp constant. 2. A method for making the amount of light emission constant by making a filament resistance value in a lighting state of an incandescent lamp constant, wherein elements having temperature fluctuation factors such as a bridge resistance element and an amplifier other than the filament are fixed. A method used in an adiabatic space controlled by temperature. 3. A method of making a luminous energy constant by making a filament resistance value in a lighting state of an incandescent lamp constant, wherein an element having a temperature fluctuation factor such as a bridge resistance element or an amplifier other than the filament is fixed. A method in which a printed element or a copper foil pattern on a substrate surface is used as a heater in a system used in a heat-insulated space controlled at a temperature. 4. A method for making the amount of light emission constant by setting a filament resistance value in a lighting state of an incandescent lamp to a constant value, wherein an input of an amplifier for detecting a fluctuation in the filament resistance value is always short-circuited, and an amplifier output is kept constant. Level, release the short circuit of the amplifier input for a short time when the measurement is completed, input the resistance bridge output including the filament to the amplifier input, check the fluctuation of the resistance bridge as the amplifier output, and check the checked value. A method that eliminates the amplifier drift by storing and using it at the next measurement.