Automated Zero-Order Calibration of Photoionization Detectors

Abstract

A method for detecting gas using a photoionization detector (PID) system. The method includes: determining, by a controller, a zero level of the photoionization detector using ambient air inflow when an ultraviolet lamp is in an off state; storing, by the controller, the zero level in a memory of the photoionization detector system, sampling, by the controller, an output of a detector electrode of the photoionization detector when the ultraviolet lamp is in an on state; and comparing the output of the detector electrode to the stored zero level to determine whether a threshold concentration of gas is present; wherein the photoionization detector system senses an external temperature and algorithmically adapts the stored zero level based on changes in the sensed external temperature.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] No.

[0003] STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0004] not applicable.

[0005] References to Microfilm Appendix

[0006] not applicable. Background Art

[0007] A photoionization detector (PID) employs a lamp to emit photons which ionize the gas near the detector electrodes. An electric field is established between the electrode plates by an applied voltage bias. The electric field causes the ionized particles to move to one or the other plate, thereby establishing a current between the electrodes. This current can be processed to extract an indication of the presence of gas. For example, a PID can be used to detect the presence and / or concentration of volatile organic compounds (VOCs) that may pose a threat to humans. Summary of the invention

[0008] In an embodiment, a method for detecting gas using a photoionization detector (PID) system is disclosed. The method includes: energizing the photoionization detector; turning off, by a controller of the photoionization detector system, an ultraviolet lamp of the photoionization detector and keeping it off during a zero calibration process; flowing ambient air from an ambient environment through a detector electrode of the photoionization detector by a fan of the photoionization detector system; processing, by the controller, an output of the detector electrode to determine a zero level of the photoionization detector; and storing, by the controller, the zero level in a memory of the photoionization detector system, wherein the photoionization detector in a detection mode compares the output of the detector electrode with the zero level to determine whether a threshold concentration of gas is present.

[0009] In another embodiment, a photoionization detector (PID) system is disclosed. The photoionization detector includes: a detector electrode, outputting 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 controller, communicatively coupled to the output signal of the detector electrode and to a control input of the lamp driver, outputting an indication of gas detection based on the output signal of the detector electrode and based on a zero calibration level stored in the photoionization detector system; and a zero calibration application, stored in a memory of the photoionization detector system. When executed by the controller, the zero calibration application turns off the ultraviolet lamp of the photoionization detector system during a zero calibration process, processes the output signal of the detector electrode while ambient air from the surrounding environment flows through the detector electrode to determine a zero level of the photoionization detector system, and stores the zero level in the photoionization detector system.

[0010] In yet another embodiment, a method for detecting the presence of a gas by a photoionization detector (PID) system is disclosed. The method includes: energizing the photoionization detector; turning off, by a controller of the photoionization detector system, an ultraviolet lamp of the photoionization detector during a zero calibration process; flowing ambient air from the surrounding environment through a detector electrode of the photoionization detector by a fan of the photoionization detector system; processing, by the controller, an output of the detector electrode to determine a zero level of the photoionization detector; and storing, by the controller, the zero level in a memory of the photoionization detector system, wherein the photoionization detector system compares the output of the detector electrode to the zero level in a detection mode to determine whether a threshold concentration of gas is present. The method also includes: periodically turning on and off, by the controller, the ultraviolet lamp after storing the zero level; analyzing, by the controller, a sampling of the output of the detector electrode after storing the zero level; determining, by the controller, a gas concentration based on the stored zero level and based on an analysis of the output of the detector electrode after storing the zero level; and outputting, by the controller, a gas detection indication based on the determination of the gas concentration.

[0011]

[0011] These and other features will become more clearly understood from the following detailed description taken in conjunction with the accompanying drawings and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] For a more complete understanding of the present disclosure, reference is now made to the following brief description, which is read in conjunction with the accompanying drawings and detailed description, wherein like reference numerals represent like parts.

[0013] Figure 1 is a block diagram of a photoionization detector system according to an embodiment of the present disclosure.

[0014] Figure 2 is a flowchart of a method according to an embodiment of the present disclosure.

[0015] Figure 3 is a flow chart of another method according to an embodiment of the present disclosure.

[0016] Figure 4 is a block diagram of a system according to an embodiment of the present disclosure.

[0017] Figure 5 is a diagram of a portion of a photoionization detector according to an embodiment of the present disclosure.

[0018] Figure 6 is a graphical representation of waveforms according to an embodiment of the present disclosure.

[0019] Figure 7 is a flowchart of a method according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0020] First, it should be understood that although illustrative implementations of one or more embodiments are described below, the disclosed systems and methods may be implemented using any number of techniques, whether currently known or not yet in existence. The present disclosure should in no way be limited to the illustrative implementations, drawings, and techniques described below, but may be modified within the scope of the appended claims and their full scope of equivalents.

[0021] The present disclosure teaches a photoionization detector (PID) that performs zero-level calibration without using a dedicated gas but instead simply using ambient air (regardless of what gases the ambient air may contain at the time). This contrasts with known methods that require a dedicated source of calibration gas (such as nitrogen). Providing calibration gas can be expensive and complicates the process of calibrating the PID. The PID disclosed herein can be provided in the form factor of a handheld device that can be carried by workers in potentially hazardous work environments where hazardous gases such as benzene, toluene, gasoline, fuel oil, diesel fuel or other volatile organic compounds (VOCs) may pose a hazard to workers. These environments may include, but are not limited to, refineries, chemical plants, manufacturing plants, etc. In some cases, the PID of the present disclosure can be installed separately from humans in various parts of the infrastructure and can be coupled to a monitoring system in a communicative manner.

[0022] The operating principle of the PID is to radiate ultraviolet light onto a gas stream that comes from the environment near a pair of electrically biased electrodes. If VOCs are present, the ultraviolet gas will ionize some of the VOC gas, collecting the ions at one or the other electrode to produce a current that can be amplified and filtered and analyzed to determine the current magnitude representing the VOC concentration. The greater the current, the greater the VOC concentration. The zero level can be determined during calibration and stored in the processor or memory of the PID. When detecting the VOC concentration, the current level is compared to the stored zero level to determine the gas concentration.

[0023] Prior art methods of performing a zero calibration require providing a gas that does not ionize in response to irradiation with ultraviolet light and therefore does not provide incremental current in the electrodes. The present disclosure teaches turning off the ultraviolet lamp while performing a zero calibration. When doing so, there is essentially no incremental current caused by ionization in the electrodes. Even though VOCs may be present, since the ultraviolet lamp is turned off, the VOCs will not be ionized and there is almost no incremental current. This provides the desired conditions for determining the current level that exists when no ions are present. The process may be similar to determining a tare weight to measure the weight in a container - subtracting the weight of the container from the combined weight of the container and the contents of the container to determine the weight of the contents alone.

[0024] Now turn to Figure 1, a photoionization detector (PID) system 1 is described. In an embodiment, the PID system 1 includes a controller 2, a photoionization detector 4, a fan 6, a battery 8 or an external power source, a visual display 10, and an input device 12. The photoionization detector system 1 can be similar in some aspects to the following reference Figure 4 , Figure 5 , Figure 6 and Figure 7 The PID system 100 described herein focuses on the zero-order calibration aspects of the PID system 1; the following focuses on the components of the PID system 100 and their functions after the zero-order is determined.

[0025] Gas from the surrounding environment is drawn through the photoionization detector 4 by the fan 6. During the zero calibration, the UV lamp in the photoionization detector 4 is turned off, and therefore any gas (e.g., any VOC) present in the inflowing air is not ionized because there is no UV radiation to ionize the gas molecules. The electrical output of the photoionization detector 4 is measured or sampled by the controller 2 during this zero calibration process (i.e., when the UV lamp is turned off), and the zero level is stored in the controller 2 and / or in a memory coupled to the controller 2 in a communicative manner. In an embodiment, the zero level can be a count associated with the zero level. In an embodiment, the zero level can be a digital value output by an analog-to-digital converter of the photoionization detector 4. The PID system 1 can be powered by a battery 8 or by an external power source (i.e., in this case, the PID system 1 is not a handheld device, but is coupled to infrastructure in a refinery or manufacturing plant). The visual display 10 can provide visual feedback when the zero calibration process has begun and when the zero calibration process has been completed.

[0026] The zero level may be determined by keeping the UV light in the photoionization detector 4 off throughout the duration of the zero level determination process. Alternatively, in an embodiment, the UV light may be turned off and on at a predefined on duty cycle, and the electrical output of the photoionization detector 4 may be captured when the UV light is off (e.g., after the UV light has been off long enough so that deionization has been substantially completed). The captured output of the photoionization detector 4 is then used to determine the zero level.

[0027] The worker can use the input device 12 (e.g., a keypad or other input device) to initiate the zero calibration process at the beginning of the workday, at the beginning of the workweek, or on some other schedule. The visual display 10 can also provide an alarm for the presence of hazardous gases (e.g., the presence of VOCs). The visual display 10 can provide an indication of the gas concentration, such as quantified as parts per billion (ppb) or parts per million (ppm). When the gas concentration exceeds a predefined concentration threshold, the visual display 10 and / or an audible alarm (not shown) can provide a warning alarm. For example, a red indication can flash on the visual display 10 and / or an alarm can sound. In an embodiment, the PID system 1 can also include a vibrator (not shown) that can vibrate to convey an alarm to the worker in a high noise work environment, where the worker may miss the audible alarm.

[0028] The zero calibration process can be performed for a duration of about 1 minute, for a duration of about 5 minutes, for a duration of about 15 minutes, for a duration of about 1 hour, for a duration of about 4 hours, for a duration of about 12 hours, for a duration of about 24 hours, or for a duration that is intermediate between any two of these durations.

[0029] The determination of the gas concentration implemented by the controller 2 may be performed as follows:

[0030] Gas concentration = Sensitivity x (Count gas -Count zero ) Formula 1

[0031] Where Count zero is the stored zero level, and where Count gas is the value of the level or count of the sensed gas sensed by the photoionization detector during gas sensing. As discussed further below, Count gas The value of the level or count of the sensed gas may be determined shortly after the UV lamp has been turned off. As discussed further below, the UV lamp may be periodically turned off and on, rather than being left on continuously, to save and extend battery power. For example, the UV lamp may be on at a duty cycle of less than 10%. For example, the UV lamp may be on at a duty cycle of less than 2%. A reduction in the UV lamp's on duty cycle may also extend the life of the UV lamp and slow the deposition rate of polymer deposited on the UV lamp and / or lamp window. In an embodiment, the UV lamp may be a vacuum ultraviolet (VUV) lamp.

[0032] By performing a zeroing process, the effects of ambient temperature changes can be easily adapted by the PID system 1. For example, when moving from a first working area with a first ambient temperature to a second working area with a second ambient temperature, a worker can initiate a zeroing process of the PID system 1. Alternatively, the PID system 1 can sense the external temperature and algorithmically adapt the value of the zero level Count accordingly based on the sensed external temperature. zero .

[0033] Now turn to Figure 2 , a method 50 for detecting gas using a photoionization detector system 1 is described. At box 52, the photoionization detector is powered on. At box 54, the ultraviolet lamp of the photoionization detector is turned off and remains off during the zero calibration process. Alternatively, the photoionization detector is alternately turned on and off at an on duty cycle of less than 50%, less than 10%, or less than 2% of the period of the on-off cycle cycle. At box 56, ambient air flows from the surrounding environment through the detector electrode of the photoionization detector by the fan of the photoionization detector. At box 58, the output of the detector electrode is processed to determine the zero level of the photoionization detector. The output of the detector electrode is sampled at a time when the ultraviolet light is turned off (e.g., a predefined duration after the ultraviolet light is turned off) to allow most of the ionized gas molecules to deionize. At box 60, the zero level is stored in the memory of the photoionization detector system 1, wherein the photoionization detector system 1 in the detection mode compares the output of the detector electrode with the zero level to determine whether there is a threshold concentration of gas. In an embodiment, the process of method 50 is performed each time the photoionization detector system 1 is powered on. In an embodiment, the processes of method 50 may also be initiated and performed in response to user input using input device 12, such as when a user moves from a first working environment to a second working environment (eg, from an indoor working environment to an outdoor working environment).

[0034] Now turn to Figure 3 , a method 70 for detecting the presence of gas by a photoionization detector system 1 is described. At box 72, the photoionization detector is powered on. At box 74, the ultraviolet lamp of the photoionization detector is turned off by the controller of the photoionization detector system 1 and is kept off during the zero calibration process. Alternatively, the photoionization detector is alternately turned off and on, wherein the on duty cycle is less than 50%, less than 10% or less than 2% of the on-off cycle cycle period. At box 76, ambient air from the surrounding environment flows through the detector electrode of the photoionization detector by the fan of the photoionization detector system 1. At box 78, the output of the detector electrode is processed by the controller to determine the zero level of the photoionization detector. The output of the detector electrode is sampled at a time when the ultraviolet light is turned off (e.g., a predefined duration after the ultraviolet light is turned off) to allow most of the ionized gas molecules to deionize.

[0035] At box 80, the zero level is stored by the controller in a memory of the photoionization detector system 1, wherein the photoionization detector system 1 in a detection mode compares the output of the detector electrode to the zero level to determine whether a threshold concentration of gas is present. At box 82, after the zero level is stored, the ultraviolet lamp is periodically turned on and off by the controller. In an embodiment, the photoionization detector is alternately turned off and on, wherein the turn-on duty cycle is less than 50%, less than 10%, or less than 2% of the on-off cycle cycle period. At box 84, after the zero level is stored, the controller analyzes the output of the detector electrode. At box 86, the controller determines the gas concentration based on the stored zero level and based on the analysis of the output of the detector electrode after the zero level is stored. At box 88, the controller outputs a gas detection indication based on the determination of the gas concentration. For example, the visual display 10 may indicate a gas concentration in parts per billion (ppb) or parts per million (ppm). Alternatively, if the gas concentration exceeds a predefined alarm threshold, the photoionization detector system 1 may present an alarm, such as a visual alarm on the visual display 10, an audible alarm, and / or a vibration alarm.

[0036] In an embodiment, the lamp driver is turned on and off by the controller to turn the PID lamp on and off. The PID lamp is turned on for a relatively short operating time, such as 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 off and on by the controller, thereby achieving signal sampling, conditioning, and signal output to the controller to determine an indication of the presence or absence of gas. The controller will only turn on the signal conditioning circuit after the PID lamp driver (and therefore the PID lamp) is turned off. Since the PID lamp driver and / or the PID lamp generate 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 entering the signal conditioning circuit. Due to the presence of less electrical noise, the filtering time constant of the signal conditioning circuit can be significantly reduced, thereby increasing the response time of the PID.

[0037] Now turn to Figure 4 , describes a PID system 100. In an embodiment, the PID system 100 may be substantially similar to the above reference Figure 1 , Figure 2 and Figure 3PID system 1 described. In an embodiment, PID 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. Controller 102 may 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. Lamp driver 104 is configured to provide power to UV lamp 106 and / or excite UV lamp 106 to emit UV light. In an embodiment, UV lamp 106 may be associated with a window (not shown) through which UV light emitted by UV lamp 106 passes before radiating the vicinity of electrode 108. Electrode 108 may include at least two parallel electrode plates, which are provided with a stable direct current (DC) bias voltage.

[0038] When the UV lamp 106 is turned on, the UV light emitted by the UV lamp 106 ionizes the gas near the electrode 108 (if present), and the electric field between the plates of the electrode 108 induces a current that is proportional to the presence of ionized gas molecules. Note that when the UV lamp 106 is turned off, the ionization process stops but the gas molecules that have been ionized do not immediately de-ionize, so if gas is present (for example, if volatile organic compounds (VOCs) are present), the current can continue between the plates of 108 for some time after the UV lamp 106 is turned off. When the UV lamp 106 is turned on, the UV lamp 106 and / or the lamp driver 104 introduce electrical noise into the PID. When the UV lamp 106 and the lamp driver 104 are turned off by the controller 102, this source of electrical noise is eliminated.

[0039] The controller 102 turns the lamp driver 104 on and off via the first control signal 103. In an embodiment, the controller 102 turns the lamp driver 104 on and off periodically and at an on duty cycle of less than 10%. As understood by those skilled in the art, a duty cycle is a representation of the amount of time that something is turned on and off, usually expressed as a percentage. As an example, if the period is 1 second (S), a 10% on duty cycle will cause the lamp driver 104 to be turned on for approximately 100 milliseconds (mS) and turned off for approximately 900mS in each 1S period. In another example, if the period is 1 second, a 1% on duty cycle will cause the lamp driver 104 to be turned on for approximately 10mS and turned off for approximately 990mS in each 1S period. As another example, if the period is 100mS, a 10% on duty cycle will cause the lamp driver 104 to be turned on for approximately 10mS and turned off for approximately 90mS in each 100mS period. In another example, if the period is 100 mS, a 1% on duty cycle will cause the lamp driver 104 to be on for approximately 1 mS and off for approximately 99 mS in each period of 100 mS.

[0040] The filter 112 and the analog-to-digital converter 116 may be considered as signal conditioning circuits. In an embodiment, some or all functions of the signal conditioning may be performed in the controller 102. For example, the controller 102 may perform digital filtering on the input from the analog-to-digital converter 116. The filter 112 and the analog-to-digital converter 116 may be turned on and off by the controller 102. The filter 112 and / or the analog-to-digital converter 116 may be turned on and off by the controller 102 (e.g., via the second control signal 111) at an on duty cycle of less than 1%. In an embodiment, the controller 102 turns on the filter 112 and / or the analog-to-digital converter 116 after the lamp driver 104 and the UV lamp 106 are turned off. In an embodiment, the filter 112 remains on continuously, and the analog-to-digital converter 116 is turned on after the lamp driver 104 and the UV lamp 106 have been turned off.

[0041] In an embodiment, the controller 102 turns on the analog-to-digital converter 116 a predefined time delay after the lamp driver 104 and the UV lamp 106 have been turned off. In an embodiment, the predefined time delay is related to the time constant of the filter 112, for example, the predefined time delay is one time constant of the filter 112, two times the time constant of the filter 112, or some other duration. As known to those skilled in the art, the time constant of a filter is the time it takes for the filter to reach a threshold portion of its final output value in response to an input value. In an embodiment, the time constant of the filter 112 may be less than 50mS. In an embodiment, the time constant of the filter 112 may be less than 5mS. In an embodiment, the time constant of the filter 112 may be less than 1mS. By turning on the analog-to-digital converter 116 after the lamp driver 104 and the UV lamp 106 are turned off, the noise generated by the lamp driver 104 and the UV lamp 106 can be kept out of the signal conditioning circuit and the time constant of the filter 112 can be reduced, thereby producing a faster response in the signal conditioning circuit. The electrode 108 outputs a detector electrode signal 110, which is input to the filter 112. The filter 112 outputs a filtered detector electrode signal 114, which is input to an analog-to-digital converter 116. The analog-to-digital converter 116 outputs a digital signal 118 to the controller 102.

[0042] Prior art PIDs can leave the UV lamp on continuously. By turning on the UV lamp 106 for a shortened portion of time, for example, 1 / 10 of the amount of time, the power load on the battery 132 that provides power to the PID system 100 can be reduced and the battery life cycle (or recharge cycle) can be extended. In addition, by turning on the UV lamp 106 for a shortened portion of time, the life of the UV lamp 106 can be extended before it burns out. In addition, when the UV lamp 106 is turned on in the presence of VOCs, some polymers may be formed during ionization, and these polymers may be deposited and accumulated on the UV lamp 106 and / or on the window of the UV lamp. The deposition of polymers on the UV lamp 106 and / or the window of the UV lamp may degrade the performance of the UV lamp 106.

[0043] When the controller 102 detects the presence of gas, it can output a gas detection alarm or signal 120. The signal 120 can cause an output device 122 of the PID system 100 to present an indication, such as to a human being associated with the PID system 100. For example, the PID system 100 can be a personal portable photoionization detector carried by a worker in an environment that may expose the worker to VOC hazards. The output device 122 can include an audible alarm device 124 and / or a visual alarm device 126. In an embodiment, the PID 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 a record to the memory 130, such as a periodic log entry that records the gas detection level indexed by time. For example, such a log entry may be useful and / or necessary for auditing the safety of the work environment.

[0044] Now turn to Figure 5 , describes further details of the PID system 100. In an embodiment, the filter 112 may 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 may be configured in accordance with the embodiment of the present invention. Figure 5 The method may be implemented in a manner other than that shown in .

[0045] Now turn to Figure 6, describing a waveform diagram 180. The first waveform 182 represents the first control signal 103 output by the controller 102 for enabling or turning on the lamp driver 104 and, therefore, turning on the UV lamp 106. The first waveform 182 is high at mark 186 and enables or turns on the lamp driver 104. The second waveform 184 represents the second control signal 111 output by the controller 102 for enabling or turning on the filter 112 and / or the analog-to-digital converter 116. The second waveform 184 is high at mark 192 and enables or turns on the filter 112. In an embodiment, the filter 112 remains on and the second control signal 111 turns the analog-to-digital converter 116 on and off itself. It should be understood that the waveform diagram 180 does not represent the entire duration of the cycle of the waveforms 182, 184. For example, if the first control signal 103 has a 1% on duty cycle, then Figure 6 The portion of the complete waveform cycle shown in may include only about 1 / 33 of the cycle. The waveform diagram 180 illustrates 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 further illustrates the timing sequence of the on interval of the first control signal 103 and the on interval of the second control signal 111.

[0046] The on interval of the first control signal 103 (and therefore the on interval of the UV lamp 106) is significantly longer than the on interval of the second control signal 111 - and therefore longer than at least the on interval of the analog-to-digital converter 116. In an embodiment, the on interval of the first control signal 103 may be at least five times the on interval of the second control signal 111. In an embodiment, the on interval of the first control signal 103 may be at least fifty times the on interval of the second control signal 111. In an embodiment, the on interval of the first control signal 103 may be at least five hundred times the on interval of the second control signal 111. In an embodiment, the first control signal 103 is on for about 10 mS (milliseconds), while the second control signal 111 may be on for about 10 μS (microseconds).

[0047] After the first control signal 103 is turned off, the second control signal 111 is turned on. In an embodiment, there is a time interval between the first control signal 103 being turned off and the second control signal 111 being turned on. For example, the first control signal 103 may be turned off at time 188, and the second control signal 111 may be turned on at time 190. The difference between time 188 and time 190 may be a predefined time interval related to a constant of the filter 112 (e.g., approximately one times the constant of the filter 112, approximately two times the constant of the filter 112, approximately three times the constant of the filter 112, or some other amount). Delaying turning on the second control signal 111 for a predefined period of time after turning off the first control signal 103 may result in excluding noise associated with the UV lamp 106 being turned on from sampling and / or capturing the output of the detector electrode signal 110, and may result in the filter 112 reaching a steady state or a stable value of the output of the detector electrode signal 110. It should be noted that it is not desirable to overly extend the predefined time period (the predefined time period between time 188 and time 190) because the ionized gas will deionize over time. Therefore, the predefined time period should be long enough to allow the filter 112 to stabilize after turning off the first control signal 103 and thus turning off the UV lamp 106 and eliminating the electrical noise it generates, while at the same time being short enough to avoid excessive deionization of the gas that was ionized when the UV lamp 106 was turned on. In conjunction with the present disclosure, those skilled in the art will readily determine a suitable time interval for the deviation between time 188 and time 190. As an example, in some embodiments, a time interval of approximately three times the time constant of the filter 112 may be suitable. As another example, in other embodiments, a time interval of approximately 1.5 times the time constant of the filter 112 may be suitable.

[0048] Now turn to Figure 7 , describing method 200. Method 200 may describe a method of using PID system 100. In an embodiment, a human may carry PID system 100 with them into a work environment to warn of the presence of hazardous gases, such as the presence of VOCs. Without limitation, VOCs may include various solvents, fuels, degreasers, plastics, heat transfer fluids, lubricants, etc. VOCs may be harmful to humans if inhaled and / or inhaled in concentrations exceeding a predefined exposure threshold. VOCs may pose an explosion or fire risk, for example when present in concentrations exceeding a predefined threshold. PID system 100 may be used to monitor industrial hygiene and safety, environmental pollution and remediation, hazardous materials disposal, ammonia detection, and refinery environments. Multiple PID systems 100 may be used in combination, each PID system 100 being tuned to a different type of gas or VOC based on the dominant wavelength of its UV lamp 106.

[0049] At block 202, the UV lamp is periodically turned on and off by the controller, wherein the on duty cycle is less than 100%. For example, the UV lamp 106 is periodically turned on and off by the controller 102. In other words, the UV lamp 106 is periodically turned on and off by the lamp driver 104, and the lamp driver 104 is periodically turned on and off by the controller 102. At block 204, when the UV lamp is off, the output of the detector electrode is sampled. The output of the detector (e.g., the detector electrode signal 110) may be sampled after a predefined period of time after the UV lamp 106 is turned off, as described above with reference to Figure 3 As further described. Sampling of the output of the detector may be performed within a relatively short period of time (e.g., within about 10 μs or about 100 μs). Sampling may be performed with an on-duty cycle of less than 1%. In an embodiment, sampling may be performed with an on-duty cycle of less than 0.01%.

[0050] At block 206, the controller analyzes the samples 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 samples of the output of the detector electrode. It should be understood that the method 200 includes continuously repeating the processing of blocks 204, 206, and 208.

[0051] At block 210, optionally (e.g., in appropriate circumstances where a gas concentration above a predefined threshold is detected), an alarm is presented based on the gas detection indication output by the controller that the detected gas is present. The alarm may be presented by an output device 122, such as an audible alarm device 124 and / or a visual alarm device 126. In an embodiment, the method 200 may also include periodically recording the level of the detected gas to the memory 130, for example, storing a log to the memory 130.

[0052] In an embodiment, the PID system 100 can be manufactured by mechanically fixing the controller 102, the lamp driver 104, the UV 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 UV lamp 106 can be arranged on the circuit board and / or in the package so as to be close to the detector electrode 108 and radiate UV light toward the detector electrode 108. A fan and air duct can be provided in the package for directing ambient gas toward the detector electrode 108 and the UV lamp 106 when the PID system 100 is in use. The battery 132 can be assembled into the system 100 at a non-manufacturing time (e.g., by the first use by humans).

[0053] In an embodiment, a photoionization detector is disclosed. The photoionization detector may include: a detector electrode, outputting 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 output signal of the detector electrode and coupled to a control input of the lamp driver, the controller 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%. In an embodiment, the controller turns the lamp driver on and off with an on duty cycle of less than 2%. In an embodiment, the photoionization detector further includes a filter having a time constant of less than 5 milliseconds (mS), wherein the filter receives the signal output by the detector electrode and outputs a filtered detector electrode signal, wherein the controller is communicatively coupled to the output signal of the detector electrode via the filter and outputs an indication of gas detection based on the filtered detector electrode signal output by the filter. In an embodiment, the photoionization detector further comprises an analog-to-digital converter that outputs a filtered digital detector electrode signal, wherein the controller is communicatively coupled to the filtered detector electrode signal via the analog-to-digital converter and outputs an indication of gas detection based on the filtered digital 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 an on duty cycle of less than 1% and wherein the controller turns the analog-to-digital converter on when the lamp driver is turned off and turns the analog-to-digital converter off before the lamp driver is next turned on. In an embodiment, the controller turns the analog-to-digital converter on for less than 15 microseconds (μS). In an embodiment, the filter comprises an electronic amplifier.

[0054] In an embodiment, a method for detecting the presence of gas using a photoionization detector (PID) includes: periodically turning on and off an ultraviolet lamp 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, based on the analysis of the sampled output of the detector electrode, outputting a gas detection indication by the controller. In an 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 an embodiment, sampling is enabled by the controller at a duty cycle of less than 1%. In an embodiment, sampling includes analog-to-digital conversion. In an embodiment, the on duty cycle of the ultraviolet lamp is less than 2%.

[0055] In an embodiment, a photoionization detector includes: a detector electrode outputting 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 receiving the signal output by the detector electrode and outputting 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 to a control input of the lamp driver, the controller outputting an indication of gas detection based on the filtered detector electrode signal output by the filter, and turning the lamp driver on and off. In an embodiment, the filter has a time constant of less than 5 mS. In an embodiment, the controller turns the lamp driver on and off to achieve an on duty cycle of less than 10%. In an embodiment, the photoionization detector further comprises an analog-to-digital converter coupled to the filter and the controller, converting a filtered detector electrode signal from the filter into a filtered digital detector electrode signal, and outputting the filtered digital detector electrode signal to the controller, wherein the controller outputs an indication of gas detection based on the filtered digital 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 an on duty cycle of less than 1%, and wherein the controller turns the analog-to-digital converter on when the lamp driver is turned off and turns the analog-to-digital converter off before the lamp driver is next turned on.

[0056] Although several embodiments have been provided in the present disclosure, it should be understood that the disclosed systems and methods may be embodied in many other specific forms without departing from the spirit or scope of the present disclosure. The present examples are considered to be illustrative rather than restrictive, and are not intended to be limited to the details given herein. For example, various elements or components may be combined or integrated in another system, or certain features may be omitted or not implemented.

[0057] Moreover, without departing from the scope of the present disclosure, the techniques, systems, subsystems, and methods described and illustrated as discrete or separate in the various embodiments may be combined or integrated with other systems, modules, techniques, or methods. Other items shown or discussed as being directly coupled or communicating with each other may be indirectly coupled or communicating through an interface, device, or intermediate component, whether electrically, mechanically, or otherwise. Other examples of changes, substitutions, and alterations may be determined by those skilled in the art without departing from the spirit and scope disclosed herein, and other examples of changes, substitutions, and alterations may be implemented.

Claims

1. A method for detecting gas using a photoionization detector system (1, 100), comprising: When the ultraviolet lamp (106) is in an off state, the controller (2, 102) uses the inflow of ambient air to determine the zero level of the photoionization detector (4); The zero level is stored in a memory of the photoionization detector system (1, 100) by a controller (2, 102), When the ultraviolet lamp (106) is in an on state, the controller (2, 102) samples the output of the detector electrode (108) of the photoionization detector (4); as well as comparing the output of the detector electrode (108) to a stored zero level to determine if a threshold concentration of gas is present; The photoionization detector system (1, 100) senses external temperature and algorithmically adapts the stored zero level based on changes in the sensed external temperature.

2. The method of claim 1, wherein the controller (2, 102) determines that a threshold concentration of volatile organic compounds (VOCs) is present.

3. The method of claim 1, wherein after the UV lamp (106) is turned off, the filter (112) and the analog-to-digital converter (116) are turned on to output a digital signal while taking the output of the detector electrode as input.

4. The method according to claim 3, wherein the filter and the analog-to-digital converter are turned on / off by the controller (2, 102) with an on duty cycle of less than 1%.

5. The method of claim 1, after storing the zero level, turning on and off the UV lamp (106) by the controller (2, 102) with a turn-on duty cycle of less than 10%.

6. The method of claim 1, after storing the zero level, turning the UV lamp (106) on and off by the controller (2, 102) with a turn-on duty cycle of less than 2%. 7 . The method of claim 1 , further comprising displaying at least one of a visual and an audible alarm when the concentration of the gas exceeds a threshold concentration of the gas.

8. The method of claim 3, further comprising turning on the analog-to-digital converter (116) by the controller (102) a predefined time delay after the lamp driver (104) and the ultraviolet lamp (106) have been turned off.

9. The method of claim 3, wherein the filter has a time constant of less than 5 milliseconds (mS).

10. A photoionization detector system (1, 100), comprising: a lamp driver (104) communicatively coupled to the ultraviolet lamp (106) and configured to turn the ultraviolet lamp (106) on and off in response to a control input; a controller (2, 102) communicatively coupled to the output signal of the detector electrode (108) and to a control input of the lamp driver (104), A zero calibration application, stored in a memory of the photoionization detector system (1, 100), which, when executed by a controller (2, 102): processing the output signal of the detector electrode (108) to determine the zero level of the photoionization detector system (1, 100) using ambient air inflow while the ultraviolet lamp (106) is turned off; and storing the zero level in a memory of the photoionization detector system (1, 100); sampling the output of the detector electrode (108) while the ultraviolet lamp (106) is on; comparing the sampled output of the detector electrode (108) to the stored zero level to determine if a threshold concentration of gas is present; The photoionization detector system (1, 100) senses external temperature and algorithmically adapts the stored zero level based on changes in the sensed external temperature.

11. The photoionization detector system (1, 100) of claim 10, wherein after storing the zero level, the zero calibration applies turning the UV lamp (106) on and off with an on duty cycle of less than 50%.

12. The photoionization detector system (1, 100) of claim 10, wherein after storing the zero level, the zero calibration applies turning the UV lamp (106) on and off with an on duty cycle of less than 10%.

13. The photoionization detector system (1, 100) of claim 10, wherein the zero calibration application turns the UV lamp (106) on and off with an on duty cycle of less than 2%.

14. The photoionization detector system (1, 100) of claim 10, wherein the zero calibration application alternately turns the ultraviolet lamp (106) on and off during the zero calibration application process.

15. The photoionization detector system (1, 100) of claim 10, wherein the ultraviolet lamp (106) comprises a vacuum ultraviolet lamp (106).

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