Improvements in or relating to photoionisation detectors

Abstract

This disclosure provides a self-test photoionization detector for determining the concentration of a gaseous compound. The photoionization detector has a gas ionization chamber for receiving the gaseous compound and an ultraviolet lamp configured to ionize the gaseous compound within the gas ionization chamber. An output sensor is configured to generate an output electrical signal related to the ion current within the gas ionization chamber. A control unit is configured to generate a control electrical signal for driving the ultraviolet lamp, and to increase or decrease the control electrical signal. In the absence of the control electrical signal or in the presence of any change in the control electrical signal with respect to the output electrical signal or any change in the output electrical signal, a user alarm electrical signal is provided.

Description

Technical Field

[0001] This invention relates to improvements of photoionization detectors or improvements related to photoionization detectors, and more specifically, to photoionization detectors with self-testing capabilities. Background Technology

[0002] A photoionization detector (PID) is a device used to measure the concentration of gaseous compounds, such as volatile organic compounds (VOCs), and other types of gases, some of which are explosive, corrosive, or toxic. In typical applications, such as health and safety applications, PIDs monitor the presence of toxic substances in breathable air. PIDs typically produce an output in the form of a voltage, which corresponds to the concentration of the detected compound.

[0003] If a PID is used in a safety application, it must be regularly maintained and tested to verify its performance. If a component within the PID fails, the output (i.e., voltage) may indicate an incorrect concentration of gaseous compounds or indicate that there are no gaseous compounds at all. This poses a risk to the PID user, as they may be exposed to harmful gaseous compounds without the PID detecting it.

[0004] A PID controller capable of self-testing its entire signal chain (which can be periodically executed by the PID itself) increases the confidence of the output, such as the reported concentration of gaseous compounds, and can extend maintenance intervals. Furthermore, performing self-tests regularly improves safety by reducing the risk of failure, for example, in industrial plants.

[0005] It is against this backdrop that the present invention came into being. Summary of the Invention

[0006] In a first aspect of the invention, a self-test photoionization detector for determining the concentration of a gaseous compound is provided, the self-test photoionization detector comprising: A gas ionization chamber for receiving the gaseous compound; An ultraviolet lamp, the ultraviolet lamp being configured to ionize the gaseous compound in the gas ionization chamber; An output sensor, configured to generate an output electrical signal related to the ion current within the gas ionization chamber; and The control unit is configured to generate a control electrical signal for driving an ultraviolet lamp, increase or decrease the control electrical signal, and provide a user alarm electrical signal when there is no correlation between the control electrical signal or any change in the control electrical signal and the output electrical signal or any change in the output electrical signal.

[0007] In a second aspect of the invention, a method is provided for self-testing a photoionization detector configured to determine the concentration of a gaseous compound, the method comprising the steps of: A control electrical signal is generated, which is configured to drive an ultraviolet lamp to ionize the gaseous compound in the gas ionization chamber of the photoionization detector; Measure the ion current in the gas ionization chamber; Generates an output electrical signal related to the measured ion current; Increase or decrease the control electrical signal; and A user alarm signal is generated when there is no correlation between the control signal or any change in the control signal and the output signal or any change in the output signal.

[0008] The invention will now be described in further and more specific terms with reference to the accompanying drawings. Attached Figure Description

[0009] Figure 1 A simplified block diagram of a photoionization detector (PID) is shown; Figure 2 A photoionization detector (PID) with self-test capability is shown; Figure 3a and Figure 3b Past examples of self-tests for amplitude and timing correlation are shown respectively, where the correlation coefficient is at least 0.7; and Figure 4a and Figure 4b Examples of self-test failures for amplitude and timing correlation are shown separately, where the correlation coefficient is at least 0.7 and there is no correlation for amplitude correlation. Detailed Implementation

[0010] In a first aspect of the invention, a self-test photoionization detector for determining the concentration of a gaseous compound is provided, the self-test photoionization detector comprising: A gas ionization chamber for receiving the gaseous compound; An ultraviolet lamp, the ultraviolet lamp being configured to ionize the gaseous compound in the gas ionization chamber; An output sensor, configured to generate an output electrical signal related to the ion current within the gas ionization chamber; and The control unit is configured to generate a control electrical signal for driving an ultraviolet lamp, increase or decrease the control electrical signal, and provide a user alarm electrical signal when there is no correlation between the control electrical signal or any change in the control electrical signal and the output electrical signal or any change in the output electrical signal.

[0011] The control signal is the UV lamp intensity control signal. Therefore, when the PID operates correctly, the control signal is related to the output signal because the UV lamp intensity control signal is related to the ion current and the concentration of gaseous compounds.

[0012] The output sensor can be a sensing electrode.

[0013] The output electrical signal may include voltage. A PID controller operates correctly when there is a correlation between the control signal and the output electrical signal. A correlation can exist if the correlation coefficient is at least 0.5 and preferably at least 0.7. However, any correlation coefficient can be used. For example, the correlation coefficient can be at least 0.5, at least 0.55, at least 0.6, at least 0.65, at least 0.7, at least 0.75, at least 0.8, at least 0.85, at least 0.9, or at least 0.95. The correlation coefficient has amplitude and time components. Therefore, in order to separately confirm the correlation between the control signal or any change in the control signal and the output electrical signal, there must be a correlation between any increase and / or decrease in the control signal and the amplitude and time components of any subsequent increase and / or decrease in the output electrical signal.

[0014] In some embodiments, the correlation between the control electrical signal and the output electrical signal can be proportional.

[0015] The absence of correlation between the control electrical signal or any change in the control electrical signal and the output electrical signal or any change in the output electrical signal can be defined as a correlation coefficient less than 0, less than 0.1, less than 0.15, less than 0.2, less than 0.25, less than 0.3, less than 0.35, less than 0.4, less than 0.45, less than 0.5, less than 0.55, less than 0.6, less than 0.65, or less than 0.7. The absence of said correlation is indicated by the absence of correlation between any increase and / or decrease in the control electrical signal and one or both of the amplitude and time components of any subsequent increase and / or decrease in the output electrical signal.

[0016] A self-test photoionization detector (PID) determines whether a device is functioning correctly. Specifically, a positive PID self-test confirms the absence of defects in the PID signal chain, indicating that the self-test PID is working properly. More specifically, the self-test PID self-tests the propagation of the control signal through the entire signal chain of the self-test PID, verifying that all components of the photoionization detector are operating correctly. This prevents inaccurate or misleading readings from the self-test PID that could endanger the user. For example, gaseous compounds can be volatile organic compounds (VOCs). By determining whether the self-test PID is functioning correctly, the user can accurately and confidently determine the risks associated with, for example, VOCs in a given environment.

[0017] The output electrical signal can be displayed on an external device. The external device can be a mobile device, such as a light-emitting diode (LED), telephone, laptop, or tablet. In some embodiments, the output can be displayed by a self-test photoionization detector. For example, the self-test photoionization detector may include an output module configured to receive the output electrical signal and display the output.

[0018] The self-test photoionization detector may include a UV lamp driver. The UV lamp driver can be configured to power the UV lamp by supplying current to it. The current can be alternating current (AC) or direct current (DC). A control signal is sent to the UV lamp driver. Increasing or decreasing the control signal proportionally increases or decreases the current supplied to the UV lamp by the UV lamp driver, which ultimately proportionally increases or decreases the output signal when the PID controller is operating correctly.

[0019] The self-test photoionization detector may also include an output electrical signal amplifier, which is configured to amplify the output electrical signal or any variation of the output electrical signal.

[0020] The user alarm electrical signal can be configured to generate at least one of an audible user alarm and a visible user alarm. For example, a user alarm may include a written message, numbers, symbols, colored lights, or pictures. The numbers may be voltages. The voltage may be low, such as 10 mV, where the output electrical signal or amplified output electrical signal is at least 50 mV. The indicated voltage may indicate a self-test PID failure. Alternatively or additionally, the user alarm electrical signal is configured to generate an audible alarm, such as a ringing or buzzing noise.

[0021] User alarm electrical signals can be configured to be received by external devices. The external device can generate a user alarm upon receiving the user alarm electrical signal. The user alarm can be audible and / or visible. The user alarm may include a voltage reading indicating the concentration of gaseous compounds in the gas ionization chamber. The external device can be a mobile device, such as a light-emitting diode (LED), telephone, laptop, or tablet. The external device can be connected to the self-test PID via a wired and / or wireless connection, such as Wi-Fi.

[0022] The self-test photoionization detector may also include a UV lamp intensity sensor configured to measure the intensity of the UV lamp. The UV lamp intensity sensor can generate a UV lamp intensity electrical signal indicating the measured intensity of the UV lamp. The UV lamp intensity sensor can then send the measured UV lamp intensity to a control unit. This can be used to determine whether the UV lamp is operating correctly.

[0023] Ultraviolet lamp intensity sensors can be sensing resistors, infrared photodiodes, infrared phototransistors, pyroelectric sensors, semiconductor nanowires, or Hall effect sensors.

[0024] A sensing resistor measures the current passing through a UV lamp. The sensing resistor comprises a known resistor. The voltage across the sensing resistor is related to or can be proportional to the control signal. Therefore, the current in the UV lamp can be measured. When the self-test PID operates correctly, the current in the UV lamp is related to or can be proportional to the UV lamp intensity, the control signal, and the output signal.

[0025] An infrared photodiode or infrared phototransistor is configured to measure the intensity of infrared light generated by an ultraviolet lamp. When the self-test PID operates correctly, the intensity of the infrared light generated by the ultraviolet lamp is related to or can be proportional to the intensity of the ultraviolet light generated by the ultraviolet lamp, the control signal, and the output signal.

[0026] The Hall effect sensor is configured to convert the magnetic field generated by the current within the UV lamp into a voltage. Furthermore, when the self-test PID operates correctly, the current (and voltage) in the UV lamp is related to or can be proportional to the intensity of the UV light produced by the UV lamp, the control signal, and the output signal.

[0027] Gaseous compounds may be selected from the group consisting of: acetone, ammonia, benzene, butadiene, dichloromethane, ethanol, ethyl acetate, ethylbenzene, ethylene, ethylene glycol, ethylene oxide, isopropanol, jet fuel, kerosene, butanone, methanethiol, propylene, styrene, toluene, trichloroethylene, volatile organic compounds, vinyl chloride, vinylene carbonate, xylene, aromatic hydrocarbons, alkenes, bromides, iodides, sulfides, hydrogen sulfide, thiols, organic amines, trimethylamine, aniline, ketones, benzophenone, acetophenone, cycloacetone, cyclohexanone, cyclobutanone, ethers, diethyl ether, dimethyl ether, tetrahydrofuran, dioxane, esters, acrylates, methyl acrylate, ethyl acrylate, butyl acrylate, acrylic acid, 2-ethylhexyl acrylate, methacrylic acid, methyl methacrylate, aldehydes, formaldehyde, acetaldehyde, vinyl alcohol, alcohols, methanol, ethanol, propanol, alkanes, methane, ethane, propane, butane, and phosphine. In a second aspect of the invention, a method is provided for self-testing a photoionization detector configured to determine the concentration of a gaseous compound, the method comprising the steps of: A control electrical signal is generated, which is configured to drive an ultraviolet lamp to ionize the gaseous compound in the gas ionization chamber of the photoionization detector; Measure the ion current in the gas ionization chamber; Generates an output electrical signal related to the measured ion current; Increase or decrease the control electrical signal; and A user alarm signal is generated when there is no correlation between the control signal or any change in the control signal and the output signal or any change in the output signal.

[0028] When a PID controller operates correctly, changing the control signal will cause a change in the ion current within the gas ionization chamber, thus affecting the output signal. Therefore, changing the control signal can be used to verify whether the PID controller is working correctly.

[0029] The photoionization detector can be the self-testing photoionization detector of the first aspect of this invention.

[0030] The method may also include a step of generating an output based on an output electrical signal. The output may correspond to the concentration of gaseous compounds in the gas ionization chamber. The output may include a voltage. The voltage may be proportional to the ion current in the gas ionization chamber. The output may be displayed on an external device. The external device may be a mobile device, such as a light-emitting diode (LED), a telephone, a laptop, or a tablet.

[0031] The output electrical signal may include voltage. A PID controller operates correctly when there is a correlation between the control signal and the output electrical signal. A correlation can exist if the correlation coefficient is at least 0.5 and preferably at least 0.7. However, any correlation coefficient can be used. For example, the correlation coefficient can be at least 0.5, at least 0.55, at least 0.6, at least 0.65, at least 0.7, at least 0.75, at least 0.8, at least 0.85, at least 0.9, or at least 0.95. The correlation coefficient has amplitude and time components. Therefore, in order to separately confirm the correlation between the control signal or any change in the control signal and the output electrical signal, there must be a correlation between any increase and / or decrease in the control signal and the amplitude and time components of any subsequent increase and / or decrease in the output electrical signal.

[0032] In some embodiments, the correlation between the control electrical signal and the output electrical signal can be proportional.

[0033] The absence of correlation between the control electrical signal or any change in the control electrical signal and the output electrical signal or any change in the output electrical signal can be defined as a correlation coefficient less than 0, less than 0.1, less than 0.15, less than 0.2, less than 0.25, less than 0.3, less than 0.35, less than 0.4, less than 0.45, less than 0.5, less than 0.55, less than 0.6, less than 0.65, or less than 0.7. The absence of said correlation is indicated by the absence of correlation between any increase and / or decrease in the control electrical signal and one or both of the amplitude and time components of any subsequent increase and / or decrease in the output electrical signal.

[0034] The self-test method can be automated. For example, each step within the self-test method can be performed automatically without user input. Therefore, the self-test method can be executed within the photoionization detector itself as part of its functionality. Alternatively or additionally, the self-test method can be performed upon user request.

[0035] The self-test method can be performed periodically. In other words, the self-test method can be repeated periodically. For example, the self-test method might be performed every minute. However, any time period can be used. For example, the self-test method can be performed every 1 second, 10 seconds, 30 seconds, 60 seconds, 2 minutes, 5 minutes, 10 minutes, 30 minutes, 1 hour, 8 hours, or 24 hours. Alternatively or additionally, the self-test method can be performed during the startup of the photoionization detector.

[0036] The method may further include the following steps: measuring the intensity of the ultraviolet lamp by measuring the current or voltage across the sensing resistor, measuring the intensity of the infrared light generated by the ultraviolet lamp, or using a Hall effect sensor to convert the magnetic field generated by the current in the ultraviolet lamp into a Hall effect voltage.

[0037] The current within a UV lamp can be measured using a sensing resistor. The current or voltage across the sensing resistor is related to or proportional to the intensity of the UV light. The intensity of the infrared light produced by a UV lamp can be measured using an infrared diode or an infrared phototransistor. The intensity of the infrared light produced by a UV lamp is related to or proportional to the intensity of the UV light produced by the same UV lamp.

[0038] The control signal can be amplified or decreased for a period of less than one second. This period of less than one second allows the self-test to be measured by the PID user as a small VOC fluctuation, or even unnoticed by the user. This is because the UV lamp intensity changes by only 1% or 2%, and this change lasts for less than one second. Therefore, the output signal, or the amplified output signal, changes by only 1% or 2% within a period of less than one second, which is a measurable change by the control unit. This fluctuation in the output signal caused by the self-test may appear similar to the naturally occurring VOC fluctuations on the PID output.

[0039] The method may also include the following steps: amplifying the output electrical signal or any change in the output electrical signal.

[0040] The method may further include the steps of: determining the variance of the measured ion current; and increasing or decreasing the control signal only when the variance is below a predetermined threshold level. Fluctuations in the concentration of gaseous compounds or increased humidity in the ionization chamber (206), especially when combined with strong winds, can cause variations in the output signal and may interfere with self-test results, as these fluctuations may unintentionally mimic the pattern of the control unit (209) increasing and decreasing the control signal to control the expected intensity of the UV lamp. Therefore, such variance can be measured before performing the self-test method. This allows the control unit to determine whether to use a first type of step change, a second type of step change, or no step change in the control signal.

[0041] The magnitude of the change in the control signal depends on the magnitude of the change in the compound concentration within the gas ionization chamber over a specific time period. For example, if the variance is below a first threshold level (TL1), a first type of step change in the control signal can be used. If the variance is above the first threshold level (TL1) but below a second threshold level (TL2), a second, larger type of step change in the control signal can be used. The first type of step change (SC1) can have a value of 1% of the current intensity of the UV lamp. The second type of step change (SC2) can have a value of 2% of the current intensity of the UV lamp. However, other types of step change values ​​can be used. For example, a step change of up to 5% of the current intensity of the UV lamp can be used for the first type of step change and / or the second type of step change. Therefore, when performing a self-test, the output signal can change the current intensity of the UV lamp by up to 5%, which corresponds to a change of up to 5% in the ion current within the gas ionization chamber for a specific gas compound.

[0042] Figure 1 A simplified block diagram of a photoionization detector (PID) (100) is shown. The PID (100) includes a UV lamp driver (102), a UV lamp (103), two electrodes (cathode 105, anode 107), a gas ionization chamber (106), and an output signal amplifier (108). The PID (100) can be connected to an output module (111). The output module (111) can be external to the PID. The output module (111) can display the output generated by the PID.

[0043] The PID is configured to detect compound (110). The compound is in gaseous form. The gaseous compound (110) may be a volatile organic compound (VOC). The gaseous compound (110) enters the gas ionization chamber (106) by diffusion or by pumping into the gas ionization chamber (106).

[0044] The UV lamp (103) can be powered by a lamp driver (102). The UV lamp driver (102) can be integrated with the UV lamp (103). The UV lamp (103) ionizes the gaseous compound (110) present in the gas ionization chamber (106) into positive ions and electrons, thereby generating an ion current in the electric field between the cathode (105) and the anode (107). The ion current generated in the gas ionization chamber (106) is measured. The anode (107) can be a signal electrode. The signal electrode can be configured to generate an output electrical signal. When the PID operates correctly, the output electrical signal is correlated with the concentration of the gaseous compound in the gas ionization chamber (106). Therefore, the ion current generates the output electrical signal. The output electrical signal can be amplified by an amplifier (108). The raw or amplified output electrical signal can be sent to an output module (111). The output module (111) displays the output. The output can indicate the concentration of the compound in the ionization chamber (106). For example, the output can include a voltage. The voltage can be up to 3 volts (V). The output (e.g., voltage) can be related to the concentration of compound (110) in the ionization chamber (106). More specifically, the output (e.g., voltage) can be proportional to the concentration of compound (110) in the ionization chamber (106).

[0045] Failure of any component within the PID (such as the UV lamp driver (102), UV lamp (103), electrodes (105, 107), output electrical signal amplifier (108), and / or electrical contacts with any of the aforementioned components) can disrupt the PID function. Therefore, each component in the PID must function correctly to generate an accurate output. When a compound is actually present, component failure can result in an output indicating the absence of a compound (e.g., VOCs).

[0046] For example, if the UV lamp (103) fails, the compound (110) cannot be ionized due to the lack of ionizing UV photons in the chamber (106). If the UV lamp driver (102) malfunctions, the UV lamp (103) will operate incorrectly. If the amplifier (108) fails, the ion current (or signal) for ionizing the compound (110) will not be amplified correctly, and the output may indicate an incorrect compound concentration or the complete absence of the specific compound. This poses a risk to PID users who may be exposed to explosive or toxic atmospheres that cannot be detected by the PID (100). In such cases, the compound may be present at dangerous concentrations, potentially endangering the safety of nearby personnel and facilities.

[0047] Figure 2 A block diagram (200) of a photoionization detector (PID) with self-test capability is shown. The PID (200) self-test function is configured to self-test the integrity of its entire signal chain (i.e., from the control electrical signal to the output electrical signal).

[0048] The signal chain of the PID (200) includes two sub-circuits. The first sub-circuit is the UV lamp sub-circuit. The UV lamp sub-circuit includes a UV lamp intensity control line (201), a UV lamp driver (202), a UV lamp (203), and a UV lamp intensity sensor (204). The UV lamp driver (202) and the UV lamp (203) can be integrated. The UV lamp intensity sensor (204) is configured to measure the intensity of the UV lamp (203). The UV lamp intensity sensor (204) can be a Hall effect sensor, a sensing resistor, an infrared photodiode, and / or a phototransistor. The UV lamp intensity sensor (204) generates an ultraviolet (UV) lamp intensity electrical signal. The UV lamp intensity electrical signal is sent to the control unit (209).

[0049] The second sub-circuit is an amplifier sub-circuit. The amplifier sub-circuit includes a first electrode (205), a gas ionization chamber (206), and a second electrode (207). The first electrode (205) is a cathode. The second electrode (207) is an anode. Additionally, the second electrode (207) is a signal electrode. The signal electrode is configured to generate an output electrical signal. When the PID operates correctly, the output electrical signal corresponds to the concentration of the gaseous compound within the gas ionization chamber (206). The second sub-circuit may also include an output electrical signal amplifier (208).

[0050] The functions of these two sub-circuits are synchronized by a control unit (209), which controls the intensity of the UV lamp (203) in the UV lamp sub-circuit and the voltage at the first electrode (205) in the amplifier sub-circuit. The control unit (209) can also monitor any outputs of these two sub-circuits, such as output electrical signals, amplified output electrical signals, and / or UV lamp intensity electrical signals.

[0051] The UV lamp subcircuit is configured to generate UV light of a desired intensity in the gas ionization chamber (206). The desired intensity is controlled by a control unit (209). The control unit (209) generates a control electrical signal for driving the UV lamp (203) via a UV lamp intensity control line (201). The control electrical signal sends a signal to the lamp driver (202) to drive the UV lamp (203). The UV light generated by the UV lamp (203) ionizes the gaseous compounds (210) in the gas ionization chamber (206). The control unit (209) can change the control electrical signal, for example, by using pulse width modulation (PWM). The UV lamp driver (202) can generate an alternating current (AC) voltage or a direct current (DC) voltage for the UV lamp (203) proportional to the control electrical signal. A UV lamp intensity sensor (204) is configured to determine the actual intensity of the UV light generated by the UV lamp (203). The UV lamp intensity sensor (204) can send a UV lamp intensity electrical signal corresponding to the measured intensity of UV light to the control unit (209), wherein the measurement is a direct UV light measurement or an indirect infrared (IR) light measurement of the UV lamp.

[0052] The control unit (209) can compare the control electrical signal with the UV lamp intensity electrical signal. The control unit can generate a user alarm electrical signal when there is no correlation between the control electrical signal and the UV lamp intensity electrical signal.

[0053] An amplifier subcircuit generates an ion current in the gas ionization chamber (206). The ion current flows between the cathode (205) and the anode (207). When the PID operates correctly, the ion current is correlated with a control signal from the UV lamp intensity control line (201). The correlation can be proportional. The anode (207) generates an output signal. The output signal is correlated with the ion current generated in the gas ionization chamber (206) and / or the concentration of compounds in the gas ionization chamber. An output signal amplifier (208) amplifies the output signal. The output signal can be displayed as a voltage by the output module (211). Therefore, the output signal can be used to generate an output. The output signal can also be fed back to the control unit (209).

[0054] When the output electrical signal is fed back to the control unit (209), the control unit (209) can compare the control electrical signal with the output electrical signal. Then, the control unit can generate a user alarm electrical signal if there is no correlation between the control electrical signal and the output electrical signal.

[0055] The control unit (209) instructs the UV lamp (203) to generate UV light by sending a control signal along the UV lamp intensity control line (201). This determines the expected intensity of the UV lamp (203). For example, the control signal may include a 30% duty cycle PWM. However, any PWM duty cycle can be used. The actual UV light intensity of the UV lamp (203) is monitored by a UV lamp intensity sensor (204). The UV lamp intensity sensor (204) may send a UV lamp intensity signal to the control unit (209) indicating the actual intensity of the UV light.

[0056] Fluctuations in the concentration of gaseous compounds or increased humidity in the ionization chamber (206), especially when combined with strong winds, can cause variations in the output electrical signal and may interfere with self-test results. This is because these fluctuations may unintentionally mimic the behavior of the step-change signal pattern used by the control unit (209) during self-testing to control the expected intensity of the UV lamp. Therefore, this variance is measured before performing the self-test. This allows the control unit to determine whether to use a first type of step change, a second type of step change, or no step change in the control electrical signal.

[0057] Once the UV lamp (203) is operational, the control unit (209) determines the variance of the measured ion current and / or the output electrical signal. This variance can be determined over a defined time period and / or can be continuously monitored. In some embodiments, the variance is determined by measuring changes in the ion current within the gas ionization chamber (206). The defined time period can be 1 second. However, the defined time period can be 0.1, 0.5, 1, 2, or 5 seconds. In some embodiments, the defined time period can be 5 seconds or more.

[0058] If the variance is below a first threshold level (TL1), a first type of step change in the amplitude of the control signal can be used. If the variance is above the first threshold level (TL1) but below a second threshold level (TL2), a second type of step change in the amplitude of the control signal can be used. The first type of step change (SC1) can have a value of 1% of the current intensity of the UV lamp. The second type of step change (SC2) can have a value of 2% of the current intensity of the UV lamp. When the PID operates correctly, the current intensity of the UV lamp (203) corresponds to the current control signal.

[0059] The variance of the output electrical signal (or the ion current within the gas ionization chamber (206)) can be measured before each self-test is performed, allowing the control unit (209) to determine whether to use a first-type step change (SC1) or a second-type step change (SC2) in the control electrical signal during the self-test. If the variance exceeds a second threshold level (TL2), the self-test may not be performed due to strong fluctuations in the output electrical signal, which could interfere with the accuracy of the self-test.

[0060] If a first-type step change (SC1) is to be used, the control unit (209) adjusts the UV lamp intensity by introducing a first-type step change (SC1) into the control electrical signal. For example, the control unit (209) can adjust the PWM duty cycle from 30% to 31%. After 1 second, the control unit (209) can change the PWM duty cycle back from 31% to 30%. This causes the UV lamp driver (202) to temporarily (i.e., for 1 second) generate a slightly higher AC or DC voltage for the UV lamp (203), which temporarily increases the current through the UV lamp (203). The intensity of the UV light in the chamber (206) also temporarily increases. The increase in UV light flux affects the ion current between the anode (207) and cathode (205) in the chamber (206). Therefore, in use, if the PID is working properly, the ion current flowing through the anode (207) and fed back to the control unit (209) in the form of an output electrical signal also temporarily increases. In some embodiments, the ion current flowing through the anode (207) is amplified by an amplifier (208) and fed back to the control unit (209) as an amplified output electrical signal. In other words, if the PID operates correctly, the (amplified) ion current flowing through the anode (207) will be correlated with the (amplified) output electrical signal. The control unit (209) then determines the effect of the step changes in the control signal by examining the output electrical signal or the amplified output electrical signal. If all parts of the signal chain are functioning correctly, the control unit will recognize the output electrical signal or the amplified output electrical signal as the correct response to the step changes in the control signal propagating throughout the signal chain.

[0061] As described above, a first type of step change (SC1) can be used in the control signal, and one second after the start of the self-test, the control signal can be reduced back from 31% to 30% of the PWM duty cycle in the step change. This reduces the expected intensity of the UV light in the chamber (206), and therefore the output signal should change accordingly.

[0062] The control unit (209) then monitors any changes in the output electrical signal (or amplified output electrical signal) and identifies them as correct self-test behavior if they are correlated with the provided control electrical signal. The correlation can be calculated over a defined time period. In this case, the defined time period is 1 second. However, any time period can be used. For example, the time period can be 0.1 seconds, 0.2 seconds, 0.3 seconds, 0.5 seconds, 0.75 seconds, 1 second, 2 seconds, or more than two seconds. Therefore, the correlation can include two components. The two components can be a time component and an amplitude component. The time component is affected by hysteresis in the circuit. In other words, the amplitude of the step change in the output electrical signal and the time at which the step change in the output electrical signal occur must both be correlated with the amplitude of the step change in the control electrical signal and the time at which the step change in the control electrical signal occurs. If the step change in the output electrical signal is correlated with the step change in the control electrical signal, the control unit (209) determines the self-test as successful (or passed). If the step changes of the output electrical signal cannot be correlated with the step changes of the control electrical signal, the integrity of the signal chain may be compromised, and the self-test will fail.

[0063] If the amplitude correlation coefficient is at least 0.5, preferably greater than at least 0.7, then a correlation can exist between the amplitude of the control signal and the amplitude of the output signal. However, any amplitude correlation coefficient can be used. For example, the amplitude correlation coefficient can be greater than at least 0.5, at least 0.55, at least 0.6, at least 0.65, at least 0.7, at least 0.75, at least 0.8, at least 0.85, at least 0.9, or at least 0.95.

[0064] Similarly, if the timing correlation coefficient is at least 0.5, preferably at least 0.7, then a correlation can exist between the timing of the control signal and the timing of the output signal. However, any timing correlation coefficient can be used. For example, the timing correlation coefficient can be at least 0.5, at least 0.55, at least 0.6, at least 0.65, at least 0.7, at least 0.75, at least 0.8, at least 0.85, at least 0.9, or at least 0.95. Generally, the timing correlation coefficient is greater than the amplitude correlation coefficient.

[0065] The following examples are provided purely for understanding amplitude and timing dependencies and do not reflect any actual self-test PIDs. See Table 1 below and... Figure 3a and Figure 3b In the example provided, a correlation coefficient of at least 0.7 between the two correlations is considered a pass for the self-test. The voltage correlation coefficient is 0.866 and the time correlation coefficient is 0.999; for this example, a pass for the self-test indicates that both correlation coefficients are greater than 0.7.

[0066] Table 1: Examples of successful self-tests for amplitude and timing correlation, where the correlation coefficient between the two correlations must be at least 0.7. (Voltage correlation coefficient is 0.866, time correlation coefficient is 0.999).

[0067]

[0068] Another example illustrates the lack of magnitude correlation, but see Table 2 below and Figure 4a and Figure 4b The documentation provides acceptable timing correlations, where a correlation coefficient of at least 0.7 between two correlations is considered a pass for the self-test. A voltage correlation coefficient of -0.423 and a time correlation coefficient of 0.999, for this example, indicate a self-test failure due to the absence of voltage correlation, i.e., a voltage correlation coefficient below 0.7.

[0069] Table 2: Examples of self-test failures for amplitude and timing correlation, where the correlation coefficient between the two correlations must be at least 0.7. (Voltage correlation coefficient is -0.423, time correlation coefficient is 0.999).

[0070]

[0071] The previously described example considered the first type of step change (SC1) pattern. However, PID self-testing can be performed using various step change patterns. The first type of step change pattern (SC1) can be denoted as "+1, -1", meaning that the step change first increases the PWM of the control signal by one unit (from 30% to 31%), and then, after a defined time period, decreases it by one unit (from 31% to 30%). However, other possible step change patterns include '-1, +1', '+1, -2, +1', '-1, +2, -1', etc. In each of these cases, the control unit (209) can be programmed to generate the step change of the control signal. The control unit (209) can also be programmed to use an appropriate time period between the step changes of the control signal.

[0072] If the self-test is activated using the second type of step change (SC2), the signal pattern can have a larger amplitude, as they may need to be identifiable when there are large fluctuations in compound concentration or due to high humidity in the ionization chamber (206). For example, a '+2, -2' step change could be used, meaning that the PWM step change of the control electrical signal first increases by two units (i.e., from 30% to 32%), and then, after a defined time period, decreases by two units (i.e., from 32% to 30%).

[0073] The self-test function can be repeated multiple times. This can increase the confidence of the test results. For example, fluctuations in the concentration of compounds in the ionization chamber (206) or increased humidity, especially if combined with strong winds, can interfere with the self-test results because these fluctuations may unexpectedly mimic the behavior of the step-change signal pattern used by the control unit (209) to control the expected intensity of the UV lamp. Therefore, in some of the aforementioned situations, the correlation made by the control unit (209) may be inaccurate. Thus, multiple consecutive successful self-tests can be used to indicate that the self-test has passed. Similarly, multiple consecutive unsuccessful self-tests can be used to indicate that the self-test has failed. The user alarm electrical signal can be configured to reflect multiple test results. If consecutive self-test results (i.e., correlations) show conflicting results, such as "pass, then fail, then pass," the self-test can continue until multiple consecutive test results have the same result.

[0074] If the variance of the output electrical signal is below the first threshold level (TL1), two consecutive self-tests may be required to confidently conclude that the test result has passed. However, if the variance of the output electrical signal is above the first threshold level (TL1) and below the second threshold level (TL2), three consecutive self-tests may be required to confidently conclude that the test result has passed.

[0075] If the self-test result is unsuccessful (i.e., "failed"), a user alarm electrical signal generates a user alarm configured to indicate the unsuccessful result. In some embodiments, the user alarm may include a voltage reading. The voltage reading may be 10 mV, wherein a voltage reading higher than 50 mV indicates a valid compound concentration level. In some embodiments, the output may be a digital line (e.g., a COM interface). In such an embodiment, the output module can stream the unsuccessful result to the user via this communication line.

[0076] If the self-test fails, the PID can perform additional internal tests to identify the part of the signal chain that caused the fault. Information about the faulty part can be included in a user alarm. For example, a diagnostic sensor can be used to verify the function of a specific component. If the diagnostic sensor detects that a component is not functioning correctly, it can generate a diagnostic alarm electrical signal. This signal may lead to the generation of a diagnostic alarm. The diagnostic alarm can be generated by the PID and / or a remote device connected to it. A UV lamp intensity sensor (204) can be a diagnostic sensor.

[0077] After generating a user alarm signal (and / or a diagnostic alarm signal), the PID continues self-testing in a self-recovering manner. If multiple consecutive self-test results are successful after generating the user alarm signal (and / or a diagnostic alarm signal), the PID resumes normal operation. For example, the user alarm signal (and / or diagnostic alarm signal) can be stopped. Alternatively or additionally, a second user alarm signal can be generated. The second user alarm signal can be configured to notify the user of a successful result.

[0078] Self-tests can be performed automatically. For example, a self-test can be performed during PID power-up. Alternatively or additionally, self-tests can be performed on demand. For example, a self-test can be performed during maintenance or when requested by the user. Self-tests can also be performed periodically, such as once per minute. However, any time interval can be used, such as 1 second, 30 seconds, 1 minute, 5 minutes, 10 minutes, or an hour interval. In such embodiments, the PID periodically verifies that the output electrical signal contains accurate information.

[0079] In some embodiments, reference Figure 2 The described PID can be used as a reference. Figure 1 The described simple PID operation (i.e., without self-test features). In this case, the control unit (209) can be configured to keep the control electrical signal constant without introducing step changes.

[0080] Although the use of ultraviolet lamps has been described, other forms of ionizing radiation sources (with appropriate drivers and intensity sensors where applicable) can be used.

[0081] As mentioned above, pulse width modulation (PWM) can be used to change the control signal for self-testing, but it can also be used to extend the lifespan of ionizing radiation sources such as ultraviolet lamps.

[0082] In view of this disclosure, various other aspects and embodiments of the invention will be apparent to those skilled in the art. The term “and / or” as used herein should be considered as a specific disclosure of each of two specified features or components, with or without the other. For example, “A and / or B” should be considered as a specific disclosure of (i) A, (ii) B, and (iii) each of A and B, as each is set forth separately herein.

[0083] Unless the context otherwise requires, the description and definition of the features set forth above are not limited to any particular aspect or embodiment of the invention, and are equally applicable to all aspects and embodiments described. Those skilled in the art will further understand that although the invention has been described by way of example with reference to several embodiments, the invention is not limited to the disclosed embodiments, and alternative embodiments can be constructed without departing from the scope of the invention as defined in the appended claims.

Claims

1. A self-test photoionization detector for determining the concentration of a gaseous compound, the photoionization detector comprising: A gas ionization chamber for receiving the gaseous compound; An ultraviolet lamp, the ultraviolet lamp being configured to ionize the gaseous compound in the gas ionization chamber; An output sensor is configured to generate an output electrical signal related to the ion current in the gas ionization chamber; as well as The control unit is configured to generate a control electrical signal for driving the ultraviolet lamp, increase or decrease the control electrical signal, and provide a user alarm electrical signal when there is no correlation between the control electrical signal or any change in the control electrical signal and the output electrical signal or any change in the output electrical signal.

2. The self-test photoionization detector according to claim 1 further includes an output electrical signal amplifier, the output electrical signal amplifier being configured to amplify the output electrical signal or any variation thereof.

3. The self-test photoionization detector according to claim 1 or claim 2, wherein, The user alarm electrical signal is configured to generate at least one of an audible user alarm and a visible user alarm.

4. The self-test photoionization detector according to any one of the preceding claims, wherein, The user alarm electrical signal is configured to be received by an external device.

5. The self-test photoionization detector according to any one of the preceding claims further includes an ultraviolet lamp intensity sensor, the ultraviolet lamp intensity sensor being configured to measure the intensity of the ultraviolet lamp.

6. The self-test photoionization detector according to claim 5, wherein, The ultraviolet lamp intensity sensor is a sensing resistor, an infrared photodiode, an infrared phototransistor, a pyroelectric sensor, a semiconductor nanowire, or a Hall effect sensor.

7. The self-test photoionization detector according to any one of the preceding claims, wherein, The gaseous compounds are selected from the group consisting of: acetone, ammonia, benzene, butadiene, dichloromethane, ethanol, ethyl acetate, ethylbenzene, ethylene, ethylene glycol, ethylene oxide, isopropanol, jet fuel, kerosene, butanone, methanethiol, propylene, styrene, toluene, trichloroethylene, volatile organic compounds, vinyl chloride, vinylene carbonate, xylene, aromatic hydrocarbons, alkenes, bromides, iodides, sulfides, hydrogen sulfide, thiols, organic amines, trimethylamine, aniline, ketones, benzophenone, acetophenone, cycloacetone, cyclohexanone, cyclobutanone, ethers, diethyl ether, dimethyl ether, tetrahydrofuran, dioxane, esters, acrylates, methyl acrylate, ethyl acrylate, butyl acrylate, acrylic acid, 2-ethylhexyl acrylate, methacrylic acid, methyl methacrylate, aldehydes, formaldehyde, acetaldehyde, vinyl alcohol, alcohols, methanol, ethanol, propanol, alkanes, methane, ethane, propane, butane, and phosphine.

8. A method for self-testing a photoionization detector, the photoionization detector being configured to determine the concentration of a gaseous compound, the method comprising the steps of: A control electrical signal is generated, which is configured to drive an ultraviolet lamp to ionize the gaseous compound in the gas ionization chamber of the photoionization detector; Measure the ion current in the gas ionization chamber; Generates an output electrical signal related to the measured ion current; Increase or decrease the control electrical signal; as well as A user alarm signal is generated when there is no correlation between the control signal or any change in the control signal and the output signal or any change in the output signal.

9. The method according to claim 8, wherein, The self-testing method is performed automatically.

10. The method according to claim 8 or claim 9, wherein, The self-testing method is performed periodically.

11. The method according to any one of claims 8 to 10, further comprising the following step: The intensity of the ultraviolet lamp is measured by measuring the current or voltage across a sensing resistor, measuring the intensity of the infrared light generated by the ultraviolet lamp, or using a Hall effect sensor to convert the magnetic field generated by the current in the ultraviolet lamp into a Hall effect voltage.

12. The method according to any one of claims 8 to 11, wherein, The control electrical signal is increased or decreased for a period of less than 1 second.

13. The method according to any one of claims 8 to 12, further comprising the following step: Amplify the output electrical signal or any change in the output electrical signal.

14. The method according to any one of claims 8 to 13, further comprising the following step: Determine the variance of the measured ion current; and The control signal is increased or decreased only when the variance is below a predetermined threshold level.

15. A self-test photoionization detector for determining the concentration of a gaseous compound, the photoionization detector comprising: A gas ionization chamber for receiving the gaseous compound; An ionizing radiation source configured to ionize the gaseous compound within the gas ionization chamber; An output sensor is configured to generate an output electrical signal related to the ion current in the gas ionization chamber; as well as The control unit is configured to generate a control electrical signal for driving the ionizing radiation source, increase or decrease the control electrical signal, and provide a user alarm electrical signal when there is no correlation between the control electrical signal or any change in the control electrical signal and the output electrical signal or any change in the output electrical signal.

16. The self-test photoionization detector according to claim 15, wherein, The ionizing radiation source includes an ultraviolet lamp.

17. The self-test photoionization detector according to claim 15 or 16, further comprising an output electrical signal amplifier configured to amplify the output electrical signal or any variation thereof.

18. The self-test photoionization detector according to any one of claims 15 to 17, wherein, The user alarm electrical signal is configured to generate at least one of an audible user alarm and a visible user alarm.

19. The self-test photoionization detector according to any one of claims 15 to 18, wherein, The user alarm electrical signal is configured to be received by an external device.

20. The self-test photoionization detector according to any one of claims 15 to 19, wherein, The gaseous compounds are selected from the group consisting of: acetone, ammonia, benzene, butadiene, dichloromethane, ethanol, ethyl acetate, ethylbenzene, ethylene, ethylene glycol, ethylene oxide, isopropanol, jet fuel, kerosene, butanone, methanethiol, propylene, styrene, toluene, trichloroethylene, volatile organic compounds, vinyl chloride, vinylene carbonate, xylene, aromatic hydrocarbons, alkenes, bromides, iodides, sulfides, hydrogen sulfide, thiols, organic amines, trimethylamine, aniline, ketones, benzophenone, acetophenone, cycloacetone, cyclohexanone, cyclobutanone, ethers, diethyl ether, dimethyl ether, tetrahydrofuran, dioxane, esters, acrylates, methyl acrylate, ethyl acrylate, butyl acrylate, acrylic acid, 2-ethylhexyl acrylate, methacrylic acid, methyl methacrylate, aldehydes, formaldehyde, acetaldehyde, vinyl alcohol, alcohols, methanol, ethanol, propanol, alkanes, methane, ethane, propane, butane, and phosphine.

21. A method for self-testing a photoionization detector, the photoionization detector being configured to determine the concentration of a gaseous compound, the method comprising the steps of: A control electrical signal is generated, the control electrical signal being configured to drive an ionizing radiation source to ionize the gaseous compound in the gas ionization chamber of the photoionization detector; Measure the ion current in the gas ionization chamber; Generates an output electrical signal related to the measured ion current; Increase or decrease the control electrical signal; as well as A user alarm signal is generated when there is no correlation between the control signal or any change in the control signal and the output signal or any change in the output signal.

22. The method according to claim 21, wherein, The ionizing radiation source includes an ultraviolet lamp.

23. The method according to claim 21 or claim 22, wherein, The self-testing method is performed automatically.

24. The method according to any one of claims 21 to 23, wherein, The self-testing method is performed periodically.

25. The method according to any one of claims 21 to 24, wherein, The control electrical signal is increased or decreased for a period of less than 1 second.

26. The method according to any one of claims 21 to 25, further comprising the step of: Amplify the output electrical signal or any change in the output electrical signal.

27. The method according to any one of claims 21 to 26, further comprising the step of: Determine the variance of the measured ion current; and The control signal is increased or decreased only when the variance is below a predetermined threshold level.

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