Low power photoionization detector (PID)

Abstract

A photoionization detector is disclosed. The photoionization detector includes a detector electrode that outputs a signal, an ultraviolet lamp, a lamp driver that is communicatively coupled to the ultraviolet lamp and configured to turn the ultraviolet lamp on and off in response to a control input, and a controller that is communicatively coupled to the output signal of the detector electrode and the control input of the lamp driver, outputs an indication of a gas detection based on the output signal of the detector electrode, and turns the lamp driver on and off with an on-duty cycle that is less than 10%.

Description

[0001] Cross-reference to related applications

[0002] none.

[0003] Regarding federal funding

[0004] A brief description of the research or development

[0005] not applicable.

[0006] References to microfilm attachments

[0007] not applicable. Background Technology

[0008] Photoionization detectors (PIDs) use lamps to emit photons that ionize gas near the detector electrodes. An electric field is established between the plates of these electrodes by applying an external voltage. This electric field causes ionized particles to move to one or more plates, thus establishing a current between the electrodes. This current can be processed to extract an indication of the presence of the gas. For example, PIDs can be used to detect the presence and / or concentration of volatile organic compounds (VOCs), which can pose a threat to humans. Summary of the Invention

[0009] In one embodiment, a photoionization detector is disclosed. The photoionization detector includes: a detector electrode for outputting a signal; a UV lamp; a lamp driver communicatively coupled to the UV lamp and configured to turn the UV lamp on and off in response to a control input; and a controller communicatively coupled to the output signal of the detector electrode and the control input of the lamp driver, outputting an indication of gas detection based on the output signal of the detector electrode, and turning the lamp driver on and off with an on-duty cycle of less than 10%.

[0010] In another embodiment, a method for detecting the presence of a gas using a photoionization detector is disclosed. The method includes periodically switching an ultraviolet lamp on and off by a controller, wherein the on-duty cycle is less than 10%; sampling the output of a detector electrode when the ultraviolet lamp is off; analyzing the sampled output of the detector electrode by the controller; and outputting a gas detection indication by the controller based on the analysis of the sampled output of the detector electrode.

[0011] In yet another embodiment, a photoionization detector is disclosed. The photoionization detector includes a detector electrode that outputs a signal, an ultraviolet lamp, a lamp driver communicatively coupled to the ultraviolet lamp and configured to turn the ultraviolet lamp on and off in response to a control input, a filter that receives the signal output by the detector electrode and outputs a filtered detector electrode signal, wherein the filter has a time constant of less than 50 milliseconds (mS), and a controller communicatively coupled to the filtered detector signal output by the filter and the control input of the lamp driver, outputs an indication of a gas detection based on the filtered detector electrode signal output by the filter, and turns the lamp driver on and off.

[0012] These and other features and characteristics will become more apparent upon consideration of the following detailed description with reference to the accompanying drawings, all of which form a part of this specification. BRIEF DESCRIPTION OF DRAWINGS

[0013] For a more complete understanding of the present disclosure, reference is now made to the following brief description of the drawings and the detailed description, in which like reference numerals represent like parts, and in which:

[0014] Figure 1 is a block diagram of a system according to an embodiment of the present disclosure.

[0015] Figure 2 is an illustration of a portion of a photoionization detector according to an embodiment of the present disclosure.

[0016] Figure 3 is an illustration of a waveform according to an embodiment of the present disclosure.

[0017] Figure 4 is a flowchart of a method according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0018] It should be understood that, although the following teaches exemplary implementations of one or more embodiments, any number of techniques, whether currently known or not, can be used to implement the disclosed systems and methods. The present disclosure should in no way be limited to the illustrative implementations, drawing and techniques illustrated below, but can be modified in various ways within the scope of the appended claims and their equivalents.

[0019] The present disclosure presents a low power photoionization detector (PID). The PID presented herein achieves a number of advantages, including extended battery life due to less power demand on the battery, extended life of the PID lamp, reduced degradation of the PID lamp due to polymer deposition on the PID lamp and / or the PID lamp window, and faster response time due to the use of a significantly faster filter. The lamp driver is turned on and off by the controller, thereby turning on and off the PID lamp. The PID lamp is turned on for a relatively short duty cycle, e.g., less than 10% of the time. This reduces the power load on the battery. In addition, this extends the life of the PID lamp and reduces the rate of polymer deposition on the PID lamp and / or the PID lamp window. The signal conditioning circuit that receives the output of the PID sensor and / or the PID electrode is turned on and off by the controller, thereby enabling signal sampling, conditioning, and output of the signal to the controller for determination of an indication of the presence or absence of a gas. The controller only turns on the signal conditioning circuit after the PID lamp driver (and the PID lamp) is turned off. Because the PID lamp driver and / or the PID lamp creates electrical noise in the PID when turned on, sampling and signal conditioning when the PID lamp driver and the PID lamp are turned off reduces the noise that enters the signal conditioning circuit. Because there is less electrical noise, the filter time constant of the signal conditioning circuit can be significantly reduced, thereby increasing the response time of the PID.

[0020] Turning now to Figure 1 , a system 100 is described. In one embodiment, the system 100 includes a controller 102, a lamp driver 104, an ultraviolet (UV) lamp 106, an electrode 108, a filter 112, and an analog-to-digital converter 116. The controller 102 can be a microcontroller, an application specific integrated circuit (ASIC), a programmable logic device (PLD), a field programmable gate array (FPGA), or some other logic processor. The lamp driver 104 is configured to provide power and / or to stimulate the ultraviolet lamp 106 to emit ultraviolet light. In one embodiment, the ultraviolet lamp 106 can be associated with a window (not shown) through which the ultraviolet light emitted by the ultraviolet lamp 106 passes before impinging on the electrode 108 in the vicinity of the electrode 108. The electrode 108 can include at least two parallel plates of an electrode to which a steady direct current (DC) bias voltage is provided.

[0021] When the ultraviolet lamp 106 is on, the ultraviolet light emitted by the ultraviolet lamp 106 ionizes the gas (if present) near the electrodes 108, and the electric field between the plates of the electrodes 108 causes a current that is proportional to the presence of ionized gas molecules. It should be noted that when the ultraviolet lamp 106 is off, the ionization process stops, but the ionized gas molecules do not immediately de-ionize, such that the electric current between the plates of the electrodes 108 can persist for some time after the ultraviolet lamp 106 is turned off (if gas is present (e.g., if volatile organic compounds [VOCs] are present)). When the ultraviolet lamp 106 is on, the ultraviolet lamp 106 and / or the lamp driver 104 cause electrical noise into the PID. When the ultraviolet lamp 106 and the lamp driver 104 are turned off by the controller 102, this source of electrical noise is eliminated.

[0022] The controller 102 turns the lamp driver 104 on and off via the first control signal 103. In one embodiment, the controller 102 periodically turns the lamp driver 104 on and off with an on-duty cycle of less than 10%. As understood by one skilled in the art, a duty cycle is a representation of the amount of on-time versus off-time, typically expressed as a percentage. As one example, if the period is 1 second (S), a 10% on-duty cycle would turn the lamp driver 104 on for about 100 milliseconds (mS) and off for about 900 mS in each 1 S period. In another example, if the period is 1 second, a 1% on-duty cycle would turn the lamp driver 104 on for about 10 mS and off for about 990 mS in each 1 S period. As another example, if the period is 100 mS, a 10% on-duty cycle would turn the lamp driver 104 on for about 10 mS and off for about 90 mS in each 100 mS period. In another example, if the period is 100 mS, a 1% on-duty cycle would turn the lamp driver 104 on for about 1 mS and off for about 99 mS in each 100 mS period.

[0023] The filter 112 and the analog-to-digital converter 116 can be considered signal conditioning circuitry. In one embodiment, some or all of the functions of signal conditioning can be performed in the controller 102. For example, the controller 102 can perform digital filtering on the input from the analog-to-digital converter 116. The filter 112 and the analog-to-digital converter 116 can be turned on and off by the controller 102. The filter 112 and / or the analog-to-digital converter 116 can be turned on and off by the controller 102 (e.g., by the second control signal 111) with an on-duty cycle of less than 1%. In one embodiment, the controller 102 turns the filter 112 and / or the analog-to-digital converter 116 on only after the lamp driver 104 and the ultraviolet lamp 106 have been turned off. In one embodiment, the filter 112 is left continuously on, and the analog-to-digital converter 116 is turned on only after the lamp driver 104 and the ultraviolet lamp 106 have been turned off.

[0024] In one embodiment, the analog-to-digital converter 116 is turned on by the controller 102 a predetermined time delay after the lamp driver 104 and the ultraviolet lamp 106 have been turned off. In one embodiment, the predetermined time delay is related to a time constant of the filter 112, for example the predetermined time delay is one time constant of the filter 112, two time constants of the filter 112, or some other duration. As known to those skilled in the art, a time constant of a filter is the time for the filter to reach a threshold portion of its final output value in response to an input value. In one embodiment, the time constant of the filter 112 can be less than 50 mS. In one embodiment, the time constant of the filter 112 can be less than 5 mS. In one embodiment, the time constant of the filter 112 can be less than 1 mS. By turning on the analog-to-digital converter 116 after the lamp driver 104 and the ultraviolet lamp 106 are turned off, the noise generated by the lamp driver 104 and the ultraviolet lamp 106 can be substantially kept out of the signal conditioning circuit and the time constant of the filter 112 can be reduced, resulting in a faster response in the signal conditioning circuit. The electrode 108 outputs a detector electrode signal 110 that is input to the filter 112. The filter 112 outputs a filtered detector electrode signal 114 that is input to the analog-to-digital converter 116. The analog-to-digital converter 116 outputs a digital signal 118 to the controller 102.

[0025] Prior art PIDs can keep the ultraviolet lamp continuously on. By turning the ultraviolet lamp 106 on for a reduced portion of time, for example for 1 / 10 of the amount of time, the power load on the battery 132 that provides power to the system 100 can be reduced and the battery life cycle (or recharge cycle) can be extended. Additionally, by turning the ultraviolet lamp 106 on for a reduced portion of time, the life of the ultraviolet lamp 106 can be extended before the ultraviolet lamp burns out. Furthermore, when the ultraviolet lamp 106 is turned on in the presence of VOCs, some polymers can be formed during ionization and these polymers can deposit and accumulate on the ultraviolet lamp 106 and / or the window of the ultraviolet lamp. The deposition of polymers on the ultraviolet lamp 106 and / or the window of the ultraviolet lamp can degrade the performance of the ultraviolet lamp 106.

[0026] When the controller 102 detects the presence of gas, it can output a gas detection alert or signal 120. This signal 120 can cause a presentation of an indication by an output device 122 of the system 100, for example, to a human associated with the system 100. For example, the system 100 can be a personal portable photoionization detector carried by a worker into an environment that can expose the worker to VOC hazards. The output device 122 can include an audible alert device 124 and / or a visual alert device 126. In one embodiment, the system 100 also includes a microprocessor 128 that receives the signal 120 and provides a control signal to the output device 122. The microprocessor 128 can also write records to a memory 130, for example, time-stamped periodic log entries of gas detection levels. For example, such log entries can be used and / or prescribed for auditing the safety of a work environment.

[0027] Turning now to Figure 2 , more details of the system 100 are described. In one embodiment, the filter 112 can include an amplifier 160 that increases the amplitude of the detector electrode signal 110. In an embodiment, the filter 112 also includes a first resistor 162, a second resistor 164, and a capacitor 166. It should be understood that the filter 112 can be implemented differently than shown. Figure 2

[0028] Turning now to Figure 3 , a waveform diagram 180 is described. A first waveform 182 represents the first control signal 103 output by the controller 102 to enable or turn on the lamp driver 104, thereby turning on the ultraviolet lamp 106. The first waveform 182 is higher at a label 186, and the lamp driver 104 is enabled or turned on. A second waveform 184 represents the second control signal 111 output by the controller 102 to enable or turn on the filter 112 and / or the analog-to-digital converter 116. The second waveform 184 is higher at a label 192, and the filter 112 is enabled or turned on. In one embodiment, the filter 112 remains on, and the second control signal 111 turns on and off the analog-to-digital converter 116 alone. It should be understood that the waveform diagram 180 does not represent the entire duration of the period of the waveforms 182, 184. For example, if the first control signal 103 has a 1% on duty cycle, the portion of the full waveform period shown can only represent about 1 / 33 of a period. The waveform diagram 180 shows the relationship between the duration of the on interval of the first control signal 103 and the duration of the on interval of the second control signal 111. The waveform diagram 180 also shows the timing of the on interval of the first control signal 103 and the on interval of the second control signal 111. Figure 3

[0029] ​​The on interval of the first control signal 103 (and thus of the ultraviolet lamp 106) is significantly longer than the on interval of the second control signal 111 (and thus of at least the analog-to-digital converter 116). In one embodiment, the on interval of the first control signal 103 can be at least five times the on interval of the second control signal 111. In one embodiment, the on interval of the first control signal 103 can be at least fifty times the on interval of the second control signal 111. In one embodiment, the on interval of the first control signal 103 can be at least five hundred times the on interval of the second control signal 111. In one embodiment, the first control signal 103 can be on for about 10 mS (milliseconds) and the second control signal 111 can be on for about 10 µS (microseconds).

[0030] The second control signal 111 can be on after the first control signal 103 is off. In one embodiment, there is a time interval between the first control signal 103 being off and the second control signal 111 being on. For example, the first control signal 103 can be off at time 188 and the second control signal 111 can be on at time 190. The difference between time 188 and time 190 can be a predetermined time interval related to a constant of the filter 112, such as about one time constant of the filter 112, about two time constants of the filter 112, about three time constants of the filter 112, or some other number.

[0031] Turning now to FIG. 2, a method 200 is described. The method 200 can describe a method of using the system 100. In one embodiment, a human can carry the system 100 into a work environment to warn of the presence of a hazardous gas, such as to warn of the presence of VOCs. VOCs can include various solvents, fuels, degreasers, plastics, heat transfer fluids, lubricants, and other substances, but are not limited thereto. VOCs can be harmful to humans when inhaled and / or at concentrations that exceed a predetermined exposure threshold. VOCs can pose a risk of explosion or ignition, such as when present at concentrations that exceed a predetermined threshold. The system 100 can be used for industrial hygiene and safety, environmental pollution and remediation, hazardous material handling, ammonia detection, and refinery environments. Multiple systems 100 can be used in combination, each tuned to suit a different kind of gas or VOC based on the dominant wavelength of its UV lamp 106.

[0032] Turning now to Figure 4 , a method 200 is described. The method 200 can describe a method of using the system 100. In one embodiment, a human can carry the system 100 into a work environment to warn of the presence of a hazardous gas, such as to warn of the presence of VOCs. VOCs can include various solvents, fuels, degreasers, plastics, heat transfer fluids, lubricants, and other substances, but are not limited thereto. VOCs can be harmful to humans when inhaled and / or at concentrations that exceed a predetermined exposure threshold. VOCs can pose a risk of explosion or ignition, such as when present at concentrations that exceed a predetermined threshold. The system 100 can be used for industrial hygiene and safety, environmental pollution and remediation, hazardous material handling, ammonia detection, and refinery environments. Multiple systems 100 can be used in combination, each tuned to suit a different kind of gas or VOC based on the dominant wavelength of its UV lamp 106.

[0033] At block 202, the controller periodically turns on and off the ultraviolet lamp, with an on-duty cycle less than 10%. For example, the controller 102 periodically turns on and off the ultraviolet lamp 106. In other words, the lamp driver 104 periodically turns on and off the ultraviolet lamp 106, and the controller 102 periodically turns on and off the lamp driver 104. At block 204, the output of the detector electrode is sampled while the ultraviolet lamp is off. The output of the detector (e.g., the detector electrode signal 110) can be sampled after a predetermined period of time after the ultraviolet lamp 106 is turned off, as described above with reference to FIG. 1. In one embodiment, the output of the detector can be sampled while the ultraviolet lamp is off. In one embodiment, the output of the detector can be sampled while the ultraviolet lamp is off and the ultraviolet lamp is not emitting ultraviolet light. In one embodiment, the output of the detector can be sampled while the ultraviolet lamp is off and the ultraviolet lamp is not emitting ultraviolet light and the ultraviolet lamp is not powered. In one embodiment, the output of the detector can be sampled while the ultraviolet lamp is off and the ultraviolet lamp is not emitting ultraviolet light and the ultraviolet lamp is not powered and the ultraviolet lamp is not powered by the lamp driver 104. Figure 3 The output of the detector can be sampled over a relatively short period of time (e.g., within about 10 µS or within about 100 µS). The sampling can be performed with an on-duty cycle less than 1%. In one embodiment, the sampling can be performed with an on-duty cycle less than 0.01%.

[0034] At block 206, the controller analyzes the sample of the output of the detector electrode. For example, the controller 102 analyzes the detector electrode signal 110, at least indirectly, via the signal conditioning circuit (i.e., the filter 112 and the analog-to-digital converter 116). At block 208, the controller outputs a gas detection indication based on the analysis of the sample of the output of the detector electrode. It should be appreciated that the method 200 includes repeating the processes of blocks 204, 206, 208 on an ongoing basis.

[0035] At block 210, optionally (e.g., in appropriate circumstances where a gas concentration above a predetermined threshold is detected), an alert of the presence of the detected gas is presented based on the gas detection indication output by the controller. The alert can be presented by the output device 122 (e.g., by the audible alert device 124 and / or the visual alert device 126). In one embodiment, the method 200 can also include periodically logging the level of the detected gas to the memory 130, e.g., storing a log to the memory 130.

[0036] In one embodiment, the system 100 can be manufactured by mechanically securing the controller 102, the lamp driver 104, the ultraviolet lamp 106, the detector electrode 108, the filter 112, the analog-to-digital converter 116, the output device 122, the microprocessor 128, and / or the memory 130 to a circuit board and / or a package. Suitable wires and connections can be provided between the components. The ultraviolet lamp 106 can be disposed on the circuit board and / or within the package so as to be in proximity to the detector electrode 108 and so as to radiate ultraviolet light toward the detector electrode 108. A fan and air passageway can be disposed within the package so as to direct ambient gas toward the detector electrode 108 and the ultraviolet lamp 106 when the system 100 is in use. The battery 132 can be assembled into the system 100 at a different time than the manufacture, e.g., at a first use by a human.

[0037] In one embodiment, a photoionization detector is disclosed. The photoionization detector can include a detector electrode that outputs a signal, an ultraviolet lamp, a lamp driver communicatively coupled to the ultraviolet lamp and configured to turn the ultraviolet lamp on and off in response to a control input, and a controller communicatively coupled to the detector electrode’s output signal and the lamp driver’s control input, outputting an indication of a gas detection based on the detector electrode’s output signal, and turning the lamp driver on and off with a turn-on duty cycle of less than 10%. In one embodiment, the controller turns the lamp driver on and off with a turn-on duty cycle of less than 2%. In one embodiment, the photoionization detector further includes a filter having a time constant of less than 5 milliseconds (mS), wherein the filter receives a signal output by the detector electrode and outputs a filtered detector electrode signal, wherein the controller is communicatively coupled to the detector electrode’s output signal via the filter and outputs the indication of the gas detection based on the filtered detector electrode signal output by the filter. In one embodiment, the photoionization detector further includes an analog-to-digital converter that outputs a digital filtered detector electrode signal, wherein the controller is communicatively coupled to the filtered detector electrode signal via the analog-to-digital converter and outputs the indication of the gas detection based on the digital filtered detector electrode signal output by the analog-to-digital converter, and wherein the controller turns the analog-to-digital converter on and off to achieve a turn-on duty cycle of less than 1%, and wherein the controller turns the analog-to-digital converter on when the lamp driver is off and turns the analog-to-digital converter off before the lamp driver is turned on. In one embodiment, the controller turns the analog-to-digital converter on for less than 15 microseconds (µS). In one embodiment, the filter includes an electronic amplifier.

[0038] In one embodiment, a method of detecting the presence of a gas with a photoionization detector (PID) includes periodically turning an ultraviolet lamp on and off by a controller, wherein the turn-on duty cycle is less than 10%, sampling an output of a detector electrode while the ultraviolet lamp is off, analyzing the sampling of the detector electrode’s output by the controller, and outputting an indication of a gas detection by the controller based on the analysis of the sampling of the detector electrode’s output. In one embodiment, the method further includes filtering the output of the detector electrode by a filter having a time constant of less than 50 milliseconds (mS), wherein the filtered output of the detector electrode is sampled and provided to the controller for analysis. In one embodiment, the sampling is enabled by the controller with a duty cycle of less than 1%. In one embodiment, the sampling includes analog-to-digital conversion. In one embodiment, the turn-on duty cycle of the ultraviolet lamp is less than 2%.

[0039] In one embodiment, the photoionization detector includes a detector electrode that outputs a signal, a UV lamp, a lamp driver communicatively coupled to the UV lamp and configured to turn the UV lamp on and off in response to a control input, a filter that receives the signal output by the detector electrode and outputs a filtered detector electrode signal, wherein the filter has a time constant less than 50 milliseconds (mS), and a controller communicatively coupled to the filtered detector signal output by the filter and the control input of the lamp driver, outputs an indication of a gas detection based on the filtered detector electrode signal output by the filter, and turns the lamp driver on and off. In one embodiment, the filter has a time constant less than 5 mS. In one embodiment, the controller turns the lamp driver on and off to achieve a less than 10% on duty cycle. In one embodiment, the photoionization detector further includes an analog-to-digital converter coupled to the filter and the controller, converts the filtered detector electrode signal from the filter to a digital filtered detector electrode signal, and outputs the digital filtered detector electrode signal to the controller, wherein the controller outputs the indication of the gas detection based on the digital filtered detector electrode signal output by the analog-to-digital converter, and wherein the controller turns the analog-to-digital converter on and off to achieve a less than 1% on duty cycle, and wherein the controller turns the analog-to-digital converter on when the lamp driver is off and turns the analog-to-digital converter off before the lamp driver is next turned on.

[0040] While several embodiments have been provided in the present disclosure, it is to be understood that the disclosed systems and methods can be embodied in many other specific forms without departing from the spirit or scope of the present disclosure. The present examples are to be considered in all respects as illustrative and not restrictive, and the scope of the disclosure is, therefore, indicated by the appended claims, rather than by the foregoing description. For example, the various elements or components can be combined or integrated in another system or certain features can be omitted or not implemented.

[0041] In addition, techniques, systems, subsystems, and methods described and illustrated in the various embodiments as discrete or separate can be combined or integrated with other systems, modules, techniques, or methods without departing from the scope of the present disclosure. Other items shown or discussed as separate from other items or each other can be implemented, for example, as integrated together with other items, and the description is not intended to require or imply that any particular items are separate or independent. Many examples of combinations, integrations, and divisions of hardware or software can be used without departing from the scope of the present disclosure. Other examples of changes, substitutions, and alterations are ascertainable by one skilled in the art and can be made without departing from the scope of the disclosure.

Claims

1. A photoionization detector, comprising: a detector electrode, the detector electrode outputting a signal; an ultraviolet lamp, the ultraviolet lamp located proximate to the detector electrode and configured to radiate ultraviolet light toward the detector electrode; a lamp driver, the lamp driver communicatively coupled to the ultraviolet lamp, wherein the lamp driver is configured to turn the ultraviolet lamp on and off in response to a control input; a filter, the filter receiving the signal output from the detector electrode and outputting a filtered detector electrode signal; an analog-to-digital converter, the analog-to-digital converter receiving the filtered detector electrode signal from the filter and outputting a digital filtered detector electrode signal; and a controller, the controller communicatively coupled to the analog-to-digital converter and to the control input of the lamp driver, wherein the controller is configured to: receive the digital filtered detector electrode signal, output an indication of gas detection based on the received digital filtered detector electrode signal, turn the analog-to-digital converter on and off to achieve a turn-on duty cycle of less than 1%, turn the analog-to-digital converter on while the lamp driver is off and turn the analog-to-digital converter off before the lamp driver is next turned on, and turn the lamp driver on and off with a turn-on duty cycle of less than 10%.

2. The photoionization detector of claim 1, wherein the controller turns the lamp driver on and off with a turn-on duty cycle of less than 2%.

3. The photoionization detector of claim 1, further comprising a filter having a time constant of less than 5 milliseconds (mS).

4. The photoionization detector of claim 3, wherein the controller is further configured to turn the analog-to-digital converter on a predetermined period of time after the lamp driver is turned off, wherein the predetermined period of time is at least equal to the time constant of the filter.

5. The photoionization detector of claim 1, wherein the controller is further configured to turn the analog-to-digital converter on for at least 15 microseconds (pS).

6. The photoionization detector of claim 1, wherein the filter comprises an electronic amplifier.

7. The photoionization detector of claim 1, further comprising a battery, the battery providing electrical energy to the lamp driver and the controller.

8. The photoionization detector of claim 1, wherein the photoionization detector is operable to detect the presence of volatile organic compounds (VOCs).

9. The photoionization detector of claim 1, wherein the photoionization detector is portable. ​

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