Photoionization detector with ignition failure alarm system

Abstract

The invention relates to a photo ionization (PID) detector with a firing failure alarm system. The PID detector comprises an ultraviolet (UV) lamp, a sensing electrode, an ignition electrode, a driver, an ignition failure alarm circuit and a processor. The firing failure alarm circuit is operable to detect the absence of ultraviolet radiation emitted by the ultraviolet lamp after the driver attempts to ignite the ultraviolet lamp, and to alert the ultraviolet lamp when the driver attempts to ignite the ultraviolet lamp and detects the absence of ultraviolet radiation emitted by the ultraviolet lamp after the driver attempts to ignite the ultraviolet lamp. An abnormally violent, human-perceivable, high-low oscillation of the reported target analyte concentration is generated.

Description

Technical Field

[0001] The present disclosure relates at least to photoionization detectors. Background Art

[0002] Photoionization detector (PID) sensors use high-energy ultraviolet (UV) radiation emitted by a UV lamp to break molecules (usually volatile organic molecules) into positively charged ions and free electrons. When the target analyte enters the detector, it is bombarded by high-energy ultraviolet (UV) photons. The target analyte absorbs the UV light, resulting in the ejection of electrons and the formation of positively charged ions. The positively charged ions are sensed by the anode / cathode arrangement within the detector and produce an electric current whose amplitude is proportional to the positively charged ions produced (i.e., the greater the concentration of the target analyte in the sample entering the detector, the more positively charged ions are produced, resulting in a greater current). The current is amplified and displayed on an ammeter, or converted to the concentration of the target molecule by an algorithm or lookup table and displayed digitally.

[0003] UV lamps are ignited by introducing an electrical discharge into the lamp's gaseous contents (usually krypton) via a driver and a pair of ignition electrodes. However, not every ignition attempt is successful. Under various conditions and for a variety of reasons, including lamp aging, loss of the lamp's gaseous contents, and cold ambient conditions, ignition failures are a constant and increasing possibility.

[0004] Ignition reliability can be increased by exposing the gas contents of the UV lamp to electromagnetic radiation of blue wavelengths prior to the ignition attempt, typically by using a blue LED capable of emitting electromagnetic radiation with a wavelength comprised between 400 and 500 nm. Blue wavelength electromagnetic radiation can ionize a small number of gas molecules within the lamp, thereby increasing the chances of achieving ignition (particularly at low temperatures). While effective as an ignition aid, the use of an ignition aid light source such as a blue LED is not always effective and has the disadvantage of significantly reducing the useful life of a battery-powered PID sensor because the ignition aid light source remains on and consumes power throughout the test.

[0005] In a PID sensor, if a UV lamp ignition failure cannot be identified, then continuing the test even if the lamp fails to ignite can result in lost time and can even lead to erroneous and potentially dangerous readings when the ignition failure remains unnoticed and a reading of 0% of the target analyte is considered accurate. Therefore, it is desirable to know when an ignition attempt has failed. This is particularly true when the PID sensor is used in situations where timely reporting of potentially dangerous concentrations of the target analyte is a safety requirement.

[0006] Known methods for alerting users to ignition failures detect ignition failures and report them as low or zero target analyte concentrations. However, this approach is unsuitable and unreliable when PID sensors are used to measure low or ultra-low target analyte concentrations and / or when higher target analyte concentrations are expected to be encountered only occasionally, with low or near-zero concentrations encountered in the interim between these events. Users will always be unable to distinguish between a report of ignition failure and a report that the target analyte concentration is actually low or zero.

[0007] Therefore, a reliable means is needed to detect and unambiguously report a failed attempt to ignite the UV lamp in a PID sensor. It is further desirable to achieve such detection without deviating from the conventional three terminals used with PID sensors, one for input voltage, a second for ground, and a third for transmitting an output signal proportional to the sensed concentration of the target analyte. It is further desirable to achieve such detection even when electromagnetic radiation from an ignition-assist light source is observed, and it is even more desirable to achieve detection only when an ignition failure is detected, accompanied by activation of the ignition-assist light source. Summary of the Invention

[0008] The present invention is a photoionization (PID) detector with an ignition failure alarm system. The PID detector includes (i) an ultraviolet (UV) lamp, (ii) a sensing electrode, (iii) an ignition electrode, (iv) a driver, (v) an ignition failure alarm circuit, and (vi) a processor, each of which is described in detail below.

[0009] The UV lamp, when ignited, is operable to emit UV radiation effective to ionize a target analyte (such as a volatile organic solvent within a sample). The sensing electrode is operable to detect the presence of the ionized target analyte within the sample and generate a true value electrical signal having a value proportional to the concentration of the target analyte within the sample. The ignition electrode is operable to ignite the UV lamp. The driver provides an ignition current to the ignition electrode, theoretically effectively igniting the UV lamp. The ignition failure alarm circuit is operable to (A) detect the absence of UV radiation emitted by the UV lamp after the driver attempts to ignite the UV lamp, and (B) generate a secondary electrical signal having alternating high and low values ​​when the driver detects the absence of UV radiation emitted by the UV lamp after the driver attempts to ignite the UV lamp. The processor is operable to receive the true value electrical signal and the alternating high and low value secondary signal and generate a human-perceivable ignition failure indication upon receipt of the secondary signal.

[0010] A photoionization (PID) detector may include a housing defining a sample retention chamber for enclosing a sample to be tested by the photoionization (PID) detector.

[0011] The sensing electrodes may be an anode-cathode pair.

[0012] The human-perceptible indication of ignition failure generated by the processor may be a human-perceptible oscillation in the reported target analyte concentration.

[0013] In a preferred embodiment, the photoionization (PID) detector also includes a selectively activatable ignition auxiliary light source different from the ultraviolet lamp, which is used to emit electromagnetic radiation, and the electromagnetic radiation is ineffective for detectably ionizing the target analyte in the sample; and the ignition failure alarm system is a circuit that can be operated to (A) detect the absence of ultraviolet radiation emitted by the ultraviolet lamp after the driver attempts to ignite the ultraviolet lamp, (B) when the driver attempts to ignite the ultraviolet lamp, detect the absence of ultraviolet radiation emitted by the ultraviolet lamp, oscillate the power supply of the ignition auxiliary light source between the light-on state and the light-off state, (C) detect the on and off state of the ignition auxiliary light source over time, and (D) generate a light-on electrical signal having a value when the ignition auxiliary light source is turned on, and generate a light-off electrical signal having a value different from the value of the light-on electrical signal when the ignition auxiliary light source is turned off, thereby generating a set of secondary electrical signals oscillating high and low values.

[0014] In more detail, the ignition failure alarm circuit may include (i) a photodiode, (ii) a transimpedance amplifier, (iii) a low-pass filter, and (iv) a hysteresis comparator, each described in detail below.

[0015] The photodiode is operable to (A) periodically detect the presence and absence of radiation emitted by at least one of the UV lamp or the ignition auxiliary light source after the driver attempts to ignite the UV lamp, and (B) periodically generate an ON current signal when the presence of UV radiation emitted by at least one of the UV lamp and the ignition auxiliary light source is detected, and otherwise bypass the generation of the ON signal.

[0016] The transimpedance amplifier is in electrical communication with the photodiode and is operable to receive each ON current signal and convert it into an ON voltage signal, and to bypass generation of the ON voltage signal when no ON current signal is received.

[0017] A low-pass filter electrically connected between the transimpedance amplifier, the ignition auxiliary light source and the processor has a time constant (e.g., between 0.1 and 10 Hz, preferably between about 0.5 and 5 Hz) for receiving each ON voltage signal and providing a timed passage of each ON voltage signal according to the time constant.

[0018] The comparator is electrically connected to the low-pass filter and is used to (A) receive each ON voltage signal and generate a first electrical output when each ON voltage signal is received, and the first electrical output can be operated to turn off the ignition auxiliary light source and transmit a low-value secondary electrical signal to the processor; and (B) generate a second electrical output when no ON voltage signal is received, and the second electrical output can be used to turn on the ignition auxiliary light source and transmit a high-value secondary electrical signal to the processor. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a schematic diagram of one embodiment of a typical photoionization detector (PID) sensor with an ignition auxiliary lamp.

[0020] Figure 2 is a circuit diagram of a PID sensor with an ignition failure warning system according to one embodiment of the present invention.

[0021] Figure 3 is a generalized flow chart for the operation of a typical photoionization detector (PID) sensor with an ignition assist lamp equipped with an ignition failure warning system according to the present invention. DETAILED DESCRIPTION

[0022] definition

[0023] As used herein, including the claims, the terms "high value" and "low value," when used to modify the noun "secondary electrical signal," are relative terms that refer to higher and lower values ​​relative to each other, wherein the "high value" has a value greater than the "low value." The terms "high value" and "low value" do not indicate any specific numerical value or any specific difference (i.e., Δ) between the "high value" and the "low value."

[0024] Glossary

[0025]

[0026]

[0027]

[0028] Generalized functional description

[0029] Usually refer to Figure 3 , the ignition failure alarm circuit 160 provides a human-perceivable alarm that an attempt to ignite the ultraviolet (UV) lamp 120 has failed and further ignition attempts are required.

[0030] In further detail, when the ignition failure alarm circuit 160 detects an unignited UV lamp 120, the ignition failure alarm circuit 160 activates the ignition auxiliary light source 180 and generates and reports a human-perceptible high PID signal output 1601 upon detecting emission of light from the ignition auxiliary light source 180. After a delay (e.g., 0.5 to 2 seconds) selected to allow reporting of changes in the PID signal output between the high value 1601 and the low value 1602 at a human-perceptible rate, the ignition failure alarm circuit 160 deactivates the ignition auxiliary light source 180 and generates a low PID signal output 1602 upon no detection of emission of light from the ignition auxiliary light source 180. If the UV lamp 120 remains unignited, the activation and deactivation cycle of the ignition auxiliary light source 180 repeats, with the output of the PID signal and the human-perceptible reporting of continued oscillations between the high value 1601 and the low value 1602. When the UV lamp 120 is ignited, the ignition failure alarm circuit 160 deactivates the ignition auxiliary light source 180, releases the PID signal output line 147 to operate normally, and reports a true value PID signal output S proportional to the concentration of the target analyte A in the sample S being tested. True .

[0031] structure

[0032] refer to Figure 1-2 The present invention relates to a photoionization detector (PID) sensor 100 having an ignition failure alarm circuit 160 for indicating that a driver 150 has failed to ignite an ultraviolet (UV) lamp 120.

[0033] refer to Figure 1 The photoionization detector (PID) sensor 100 has an ultraviolet (UV) lamp 120 for ionizing a target analyte A in a sample S, a pair of ignition electrodes 130 (1301 and 1302) for igniting a plasma in the UV lamp 120, and a PID current signal S for detecting the ionized target analyte A and generating a true PID current signal S proportional to the concentration of the target analyte A in the sample S. True The sensing electrodes 140 (i.e., the anode 1401 and the cathode 1402) are connected to the sensing electrodes 140. The sensing signal amplifier 145 is usually electrically connected to the sensing electrodes 140 and is used to receive the generated true value PID current signal S True , the signal S True Amplify and convert the signal S True These components are typically retained within housing 110, which defines a sample holding chamber 119 positioned to receive the UV radiation emitted by UV lamp 120 when lamp 120 is energized, and having a sample inlet 1191 and an optional sample outlet 1192.

[0034] The photoionization detector (PID) sensor 100 is used in an instrument that typically includes a processor 170 for receiving an amplified and converted true value PID current signal S True , and converts the signal value into the concentration of the target analyte A in the sample S according to an algorithm or a lookup table, and displays or otherwise reports the target analyte concentration in the sample S.

[0035] refer to Figure 1 and Figure 2 , typically an AC current is provided from a power input terminal (unnumbered) through a driver 150 to a pair of ignition electrodes 1301 and 1302 located on opposite sides of the UV lamp 120, for igniting the plasma (typically krypton) retained in the UV lamp 120 and thereby starting to emit ionizing UV radiation from the UV lamp 120.

[0036] refer to Figure 2 The ignition failure alarm circuit 160 alerts the user of the photoionization detector (PID) sensor 100 of an ignition failure by generating and displaying an oscillating signal output of the target analyte concentration, wherein the signal output is preferably a low frequency of about 0.1 to 10 Hz, preferably about 0.5 to 5 Hz, and most preferably about 1 Hz, which is perceptible to humans and oscillates preferably between zero scale and full scale, and preferably along the same frequency as the frequency used to convert the true value PID signal S True The same output terminal that is transmitted to the processor 170 is transmitted to the processor 170, thereby reporting an alarm as an abnormally violent human-perceivable oscillation of the reported concentration of the target analyte A. The ignition failure alarm circuit 160 can be powered by the same power input terminal as the power input terminal used to power the ignition electrode 130. In a specific embodiment, the PID sensor 100 includes an ignition auxiliary light source 180, and the ignition failure alarm circuit 160 also controls the activation and deactivation of the ignition auxiliary light source 180.

[0037] Usually refer to Figure 3 as well as Figure 2In the embodiment of the present invention described in

[15] , the ignition failure alarm circuit 160 includes a photodiode 162 capable of detecting the visible output from the ignited UV lamp 120. The photodiode 162 transmits an electrical signal to a transimpedance amplifier (TIA) 164, where the electrical signal is converted to a voltage. The electrical signal then passes through a low-pass filter or RC network 166 having a time constant of approximately 0.1 to 10 Hz, preferably approximately 0.5 to 5 Hz, and most preferably approximately 1 Hz, before being transmitted to a comparator 168. The RC network 166 determines the oscillation rate. The hysteresis of the comparator 168 is adjusted so that it generates and outputs either a high voltage or a low voltage, depending on whether the input voltage from the comparator 168 is above or below a threshold value, which is selected to be between the values ​​when the ignition auxiliary light source 180 is activated and the values ​​when the ignition auxiliary light source 180 is deactivated. As long as the voltage input to the comparator 168 is high (i.e., the UV lamp 120 is ignited), the output of the comparator 168 remains low. When the ultraviolet lamp 120 is disabled, the voltage input to the comparator 168 will decay to a low value and eventually to zero, thereby enabling the output of the comparator 168 to transition from a low value to a high value, thereby turning on the ignition auxiliary light source 180 and enabling the signal output to a high value through the isolation diode 169.

[0038] The photodiode 162 is exposed to electromagnetic radiation emitted by the ignition-assist light source 180. Thus, when the ignition-assist light source 180 is activated (turned on), the photodiode 162 detects the electromagnetic radiation emitted by the ignition-assist light source 180, resulting in a high voltage input to the comparator 168, which in turn pulls the voltage output from the comparator 168 low and deactivates (turns off) the ignition-assist light source 180. This creates an optically coupled relaxation oscillator whose time base is determined by the product of the resistance and capacitance of the RC network 166.

[0039] Properly setting hysteresis on comparator 168 will result in oscillation of the reported target analyte A concentration value only occurring when UV lamp 120 is not ignited and not emitting electromagnetic radiation. When UV lamp 120 is ignited and emitting electromagnetic radiation, photodiode 162 will detect the electromagnetic radiation emitted by UV lamp 120, causing photodiode 162 to transmit a high voltage input to comparator 168 via transimpedance amplifier 164 and low-pass filter 166, which in turn pulls down the voltage output from comparator 168 and deactivates (turns off) the ignition-assist light source 180. Thereafter, even if ignition-assist light source 180 is deactivated (turned off), photodiode 162 will continue to detect electromagnetic radiation emitted by UV lamp 120 and will continue to transmit a high voltage input to comparator 168 via transimpedance amplifier 164 and low-pass filter 166, which in turn maintains the voltage output from comparator 168 at a low level, thereby keeping ignition-assist light source 180 deactivated (turned off) and stopping the oscillation of the target analyte A concentration value. This saves power by turning off and keeping off the ignition auxiliary light source 180. This also pulls the isolation diode 169 low and releases the PID signal output line 147 to transmit the true value PID signal S generated by the sensing electrode 140. True .

Claims

1. A photoionization detector with an ignition failure alarm system, comprising: (a) an ultraviolet lamp operable, when ignited, to emit ultraviolet radiation effective to ionize a target analyte in the sample; (b) a sensing electrode for detecting the presence of an ionized target analyte in the sample and generating a true electrical signal having a value proportional to the concentration of the target analyte in the sample; (c) an ignition electrode for igniting the UV lamp; (d) a driver in electrical communication with the ignition electrode for providing an ignition current theoretically effective to ignite the ultraviolet lamp; (e) an ignition failure alarm circuit operable to (A) detect an absence of ultraviolet radiation emitted by the ultraviolet lamp after the driver attempts to ignite the ultraviolet lamp, and (B) generate a secondary electrical signal having alternating high and low values ​​when the driver detects an absence of ultraviolet radiation emitted by the ultraviolet lamp after the driver attempts to ignite the ultraviolet lamp, and (f) a processor configured to receive the true value electrical signal and the secondary signal having alternating high and low values, and to generate a human-perceivable ignition failure indication upon receipt of the secondary signal.

2. The photoionization detector according to claim 1, wherein When the true value electrical signal is received but the secondary signal is not received, the processor converts the true value electrical signal into a corresponding concentration of the target analyte.

3. The photoionization detector of claim 1, wherein the true-value electrical signal and the secondary electrical signal are transmitted to the processor as indistinguishable signals through a common output terminal.

4. The photoionization detector of claim 1, wherein the ignition electrode and the ignition failure alarm circuit are powered by a common power input terminal.

5. The photoionization detector of claim 1 , wherein high and low secondary electrical signals are reported by the processor as high and low concentrations of the target analyte, respectively, resulting in unusually large, human-perceivable oscillations in the reported target analyte concentration.

6. The photoionization detector of claim 5, wherein the oscillation frequency is between 0.1 and 10 Hz.

7. The photoionization detector of claim 5, wherein the oscillation frequency is between 0.5 and 5 Hz.

8. The photoionization detector of claim 1, wherein the ultraviolet lamp is operable to ionize a volatile organic compound target analyte.

9. The photoionization detector of claim 1 , further comprising an ignition assist feature, wherein a selectively activatable ignition assist light source, when turned on, emits electromagnetic radiation having a wavelength comprised between 400 and 500 nm and directs the electromagnetic radiation toward the ultraviolet lamp to assist ignition of the ultraviolet lamp by the ignition electrode.

10. The photoionization detector of claim 9, wherein the ignition failure alarm circuit is further operable to, upon detecting the presence of ultraviolet radiation emitted by the ultraviolet lamp after an attempt to ignite the ultraviolet lamp, shut down a selectively activatable ignition auxiliary light source until at least a subsequent attempt to ignite the ultraviolet lamp using the ignition electrode.

11. The photoionization detector of claim 1 , wherein the ignition failure alarm circuit comprises: (a) a photodiode operable to (A) periodically detect the presence and absence of radiation emitted by at least one of the ultraviolet lamp or the ignition-assist light source after the driver attempts to ignite the ultraviolet lamp, and (B) periodically generate an ON current signal when the presence of ultraviolet radiation emitted by at least one of the ultraviolet lamp and the ignition-assist light source is detected, and otherwise bypass generation of the ON signal; (b) a transimpedance amplifier in electrical communication with the photodiode, configured to receive each ON current signal and convert it into an ON voltage signal, and to bypass generation of the ON voltage signal when no ON current signal is received; (c) a low-pass filter having a time constant of 0.1 to 10 Hz in electrical communication between the transimpedance amplifier, the ignition auxiliary light source, and the processor, for receiving each ON voltage signal and providing a timed passage of each ON voltage signal according to the time constant; and (d) a hysteresis comparator electrically connected to the low-pass filter, for receiving each ON voltage signal and generating a first electrical output when each ON voltage signal is received, wherein the first electrical output is operable to turn off the ignition auxiliary light source and transmit a low-value secondary electrical signal to the processor, and generating a second electrical output when no ON voltage signal is received, wherein the second electrical output is operable to turn on the ignition auxiliary light source and transmit a high-value secondary electrical signal to the processor.

12. The photoionization detector of claim 1 , further comprising a housing defining a sample retention chamber, and wherein the ultraviolet lamp, when ignited, is operable to emit ultraviolet radiation effective to ionize a target analyte in a sample retained in the sample retention chamber.

13. The photoionization detector of claim 12, wherein the sensing electrodes are an anode-cathode pair for detecting the presence of a target analyte ionized in the sample holding chamber.

14. The photoionization detector of claim 1 , further comprising a selectively activatable ignition auxiliary light source different from the ultraviolet lamp, the ignition auxiliary light source configured to emit electromagnetic radiation that is ineffective for detectably ionizing a target analyte in the sample, wherein: The ignition failure alarm circuit is capable of operating to generate a secondary electrical signal alternating between high and low values ​​when it is detected that the ultraviolet radiation emitted by the ultraviolet lamp does not exist after the driver attempts to ignite the ultraviolet lamp by performing the following operations: (i) after the driver attempts to ignite the ultraviolet lamp, when it is detected that the ultraviolet radiation emitted by the ultraviolet lamp does not exist, oscillating power is supplied to the ignition auxiliary light source between the light-on state and the light-off state, (ii) detecting the on-off state of the ignition auxiliary light source over time, and (iii) generating a light-on electrical signal having a value when the ignition auxiliary light source is turned on, and generating a light-off electrical signal having a value different from the value of the light-on electrical signal when the ignition auxiliary light source is turned off, thereby generating a set of oscillating high and low value secondary electrical signals.

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