JP2003098153A - Photoionization detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an photoionization detector in which lowering of sensitivity can be suppressed. SOLUTION: An photoionization detector comprising a detection chamber provided with a translucent window and an applying electrode and introducing or discharging a measuring fluid, a lamp for irradiating the detection chamber with UV-rays of short wavelength through the translucent window, a circuit for exciting the lamp, a circuit for applying a voltage to the applying electrode, and a circuit for detecting a measurement signal from the applying electrode is further provided with an on/off valve provided in the detection chamber in order to introduce or discharge the measuring fluid, a circuit for holding an output signal from the detection circuit, and a synchronization circuit for delivering a drive signal intermittently to the on/off valve and the exciting circuit every predetermined time and delivering a signal for holding the output value upon elapsing a specified time after lamp excitation to the hold circuit.

Description

Description: BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a photoionization detector capable of reducing a decrease in sensitivity. 2. Description of the Related Art FIG. 2 is an explanatory view of the configuration of a conventional example generally used conventionally. In the drawing, reference numeral 1 denotes a detection chamber provided with a light transmitting window 2 and an application electrode 3, and into which a measurement fluid FL is introduced and discharged. Reference numeral 4 denotes a lamp for irradiating the detection chamber 1 with ultraviolet light having a short wavelength through the light transmitting window 2. Reference numeral 5 denotes an excitation circuit that excites the lamp 4. Reference numeral 6 denotes an application circuit for applying a voltage to the application electrode 3. Reference numeral 7 denotes a detection circuit that detects a measurement signal from the application electrode 3. In the above configuration, the measurement fluid FL is discharged after being introduced into the detection chamber 1. The detection chamber 1 has a lamp 4 for generating ultraviolet light of a short wavelength and an application electrode 3. The introduced measurement fluid FL is ionized by the lamp 4 by ultraviolet light irradiated through the light transmitting window 2. Is captured by the application electrode 3. [0005] Ionization by ultraviolet rays has a selectivity depending on whether the energy of the wavelength exceeds the ionization energy of each substance. Therefore, as an effective detector for detecting a specific substance, an organic compound in the air is used. It is used for detection and gas chromatograph detector. [0006] However, in such an apparatus, various chemical species are generated because ultraviolet rays having a short wavelength are used. Some of them have high oxidizing and reactive properties such as ozone and radicals.
The light-transmitting window 2 and the electrode portion 3 are contaminated by products generated by polymerization and other chemical reactions in the inside, and the sensitivity is changed. An object of the present invention is to solve the above-mentioned problems and to provide a photoionization detector capable of reducing a decrease in sensitivity. In order to achieve the above object, according to the present invention, in a photoionization detector according to the present invention, a light transmitting window and an application electrode are provided, and a measurement fluid is provided. A detection chamber that is introduced and discharged, a lamp that irradiates the detection chamber with short-wavelength ultraviolet rays through the light-transmitting window, an excitation circuit that excites the lamp, an application circuit that applies a voltage to the application electrode, A photoionization detector comprising: a detection circuit for detecting a measurement signal from the application electrode; an open / close valve provided in the detection chamber for introducing and discharging the measurement fluid; and a hold circuit for holding an output signal from the detection circuit. When,
A synchronization circuit that intermittently sends a drive signal to the on-off valve and the excitation circuit at predetermined time intervals and sends a hold signal to hold the output signal value after a predetermined time after the lamp excitation to the hold circuit. It is characterized by. The present invention will be described below in detail with reference to the drawings. FIG. 1 is an explanatory diagram of a main part of an embodiment of the present invention, and FIG. 2 is an explanatory diagram of the operation of FIG. In the figure, the configuration of the same symbol as FIG. 3 represents the same function. Hereinafter, only differences from FIG. 3 will be described. In FIG. 1, reference numeral 11 denotes an on-off valve provided in the detection chamber 1 for introducing and discharging the measurement fluid FL. 12
Is a hold circuit for holding an output signal from the detection circuit 7. 13 intermittently sends a drive signal to the on-off valve 11 and the excitation circuit 5 every predetermined time,
This is a synchronous circuit for sending a hold signal for holding an output signal value after a predetermined time after the lamp 4 is excited. In the above configuration, the measurement fluid FL is introduced at regular intervals by opening the on-off valve 11 by the synchronous circuit 13. The excitation circuit 5 is also operated by the synchronization circuit 13 so as to excite the lamp 4 at regular intervals. The signal obtained by the detection circuit 7 is held by the signal from the synchronizing circuit 13 at a value after a certain period of time when the ramp 4 is excited. FIG. 2 shows the on / off valve 11, the excitation of the lamp 4, the operation of the hold circuit 12, the signal of the detection circuit 7, and the output signal S.
4 shows a time chart of out. As a result, by intermittently operating the ramp 4 and retaining the measuring fluid FL in synchronism therewith, compared to the case where the measuring fluid FL is continuously introduced,
By suppressing generation of a substance that causes a decrease in the sensitivity of the photoionization detector, a photoionization detector capable of reducing a change in sensitivity can be obtained. It is to be noted that the above description has shown only specific preferred embodiments for the purpose of explanation and illustration of the present invention. Therefore, the present invention is not limited to the above-described embodiment, but includes many more changes and modifications without departing from the spirit thereof. As described above, according to the first aspect of the present invention,
According to the above, the following effects are obtained. Installed in the detection chamber,
An on-off valve for introducing and discharging the measurement fluid, a hold circuit for holding an output signal from the detection circuit, and a drive signal intermittently sent to the on-off valve and the excitation circuit at predetermined time intervals, and a predetermined time for lamp excitation to the hold circuit. And a synchronous circuit for transmitting a hold signal for holding a subsequent output signal value. Therefore, the intermittent operation of the ramp and the retention of the measuring fluid in synchronism with it cause a decrease in the sensitivity of the photoionization detector compared to the case where the measuring fluid is continuously introduced. By suppressing the generation of such a substance, a photoionization detector capable of reducing a change in sensitivity can be obtained. Therefore, according to the present invention, it is possible to realize a photoionization detector capable of reducing a decrease in sensitivity.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory diagram of a main part configuration of an embodiment of the present invention. FIG. 2 is an operation explanatory diagram of FIG. 1; FIG. 3 is an explanatory diagram of a configuration of a main part of a conventional example generally used in the related art. [Description of Signs] 1 Detection chamber 2 Translucent window 3 Applied electrode 4 Lamp 5 Excitation circuit 6 Applied circuit 7 Detection circuit 11 Open / close valve 12 Hold circuit 13 Synchronous circuit FL Measurement fluid Sout Output signal

Claims (1)

Claims: 1. A detection chamber provided with a light-transmitting window and an application electrode, through which a measurement fluid is introduced and discharged, and a short-wavelength ultraviolet ray is irradiated to the detection chamber through the light-transmitting window. A photoionization detector including a lamp, an excitation circuit for exciting the lamp, an application circuit for applying a voltage to the application electrode, and a detection circuit for detecting a measurement signal from the application electrode; provided in the detection chamber. An on-off valve for introducing and discharging the measurement fluid, a hold circuit for holding an output signal from the detection circuit, and intermittently sending a drive signal to the on-off valve and the excitation circuit at predetermined time intervals to the hold circuit. A synchronous circuit for transmitting a hold signal for holding the output signal value after a predetermined time after the lamp excitation.