Patent Description:
Photoionization detectors (PIDs) are handheld, portable gas detectors used to measure volatile organic compounds (VOCs), such as benzene, and other organic gases by ionizing environmental gases and measuring the generated electrons. They can produce instantaneous readings and can operate continuously, which make them useful when monitoring for health and safety in military, industrial, and confined working facilities. However, since PID sensors are capable of creating current levels down to the femtoampere range proportional to the concentration of an ionized gas being measured, galvanic currents that arise in the presence of electrolytes bridging two conductors comprised of different materials are a potential source of error in PID sensors and, therefore, limit the sensitivity of the detector. More specifically, a galvanic current can arise when two electrodes, each comprised of a different metal having different galvanic potentials, are bridged by an electrolyte. When galvanic currents arise, they can create errors in the readout by showing either higher or lower readings.

Current art has focused on cleanliness of the materials to minimize the effect of stray currents and the formation of electrolytes in humid environments. However, better protective features are needed that provide protection from extraneous galvanic currents and allow for a more accurate and sensitive detector that is capable of use in more extreme (i.e., humid) environments. Examples of the current art include: United States patent application <CIT>, which discloses an electrode stack assembly for a PID including an air-gapped multi-layer electrode structure that assists in preventing leak current leaking across layers; United States patent application <CIT>, which discloses a plug-in photoionization sensor for detecting volatile organic compounds in organic air; and United States patent application <CIT>, which discloses a low profile PID.

The invention provides a photoionization detector sensor as claimed in claim <NUM>, a photoionization detector as claimed in claim <NUM>, and a method of using the photoionization detector as claimed in claim <NUM>. Preferred features are recited in the dependent claims appended hereto. The present disclosure relates to a photoionization detector sensor having conductors with unique geometry that reduces or prevents galvanic currents.

The present disclosure relates to a photoionization detector sensor (PID sensor) having conductors with unique geometry that reduces or prevents galvanic currents. Various embodiments of the PID sensor will be described in detail with reference to the drawings, wherein like reference numerals represent like parts and assemblies throughout the several views. Reference to various embodiments does not limit the scope of the PID sensor disclosed herein. Additionally, any examples set forth in this specification are not intended to be limiting and merely set forth some of the many possible embodiments for the PID sensor. It is understood that various omissions and substitutions of equivalents are contemplated as circumstances may suggest or render expedient, but these are intended to cover applications or embodiments without departing from the scope of the appended claims. Also, it is to be understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting.

<FIG> illustrate various views of an example of a photoionization detector according to the present disclosure. <FIG> is a schematic of a photoionization detector. <FIG> is an exploded view of a prior art photoionization detector. <FIG> is a top view of a prior art photoionization detector sensor of the detector of <FIG>. <FIG> is a schematic top view of a photoionization detector sensor according to the present disclosure. <FIG> is a schematic bottom view of the photoionization detector sensor of <FIG> is a schematic view of prior art photoionization detector sensor electrodes. <FIG> is a schematic view of the photoionization detector sensor electrodes according to the present disclosure.

Some embodiments of PIDs disclosed herein include a sensor having two or more electrodes, a gas discharge lamp, and an amplifier connected to one of the two or more electrodes. The two or more electrodes of the PID sensor can be comprised of a collector electrode, a bias electrode, a grounding electrode, and combinations thereof (ex: a collector electrode and a grounding electrode). The bias electrode and the collector electrode can support an electrostatic field. The grounding electrode can establish a low impedance path back to a supply source to facilitate the operation of the device by intercepting currents that may arise between the bias and collector electrodes (often configured as a guard trace) as well as establish a stable voltage to ground during operation.

As illustrated in <FIG>, a gas discharge lamp <NUM> can ionize molecules of interest <NUM> to create ionized molecules <NUM> and electrons <NUM>. More specifically, when a UV light source in the gas discharge lamp <NUM> is activated, it can ionize environmental gases and create ionized molecules <NUM> and electrons <NUM>. The ionized molecules <NUM> can be collectable by a bias electrode <NUM>, and the electrons <NUM> can be collectable by the collector electrode <NUM>. The collector electrode <NUM> can be connected to the amplifier <NUM>, which can be a high gain transimpedance amplifier that measures the electrons <NUM> generated from the ionized gas. When the gas <NUM> is ionized, the electrons <NUM> produced can be accelerated to the collector electrode <NUM> by the electrostatic field developed between the bias <NUM> and the collector <NUM> electrodes. The results can be sent from the amplifier to a display/record <NUM> for observance by a user.

Generally, the PID can have components that are contained within a cylindrical housing, as illustrated by the prior art PID <NUM> in <FIG>. More specifically, the cylindrical housing can include a sensor body <NUM> with a cap <NUM>, wherein the sensor body and cap contain a gas discharge lamp <NUM> (having a UV light source), a sensor <NUM>, a spacer <NUM>, a filter cloth <NUM>, and a filter <NUM>. The components can be stacked on top of one another, as illustrated in <FIG>, and the gas discharge lamp <NUM> and sensor <NUM> can be placed adjacent to one another.

As mentioned briefly above, the sensor includes two or more electrodes such as, but not limited to, a bias electrode, a collector electrode, and a grounding electrode. The electrodes <NUM>, <NUM>, <NUM> can be approximately circular and can be positioned in line with each other, as illustrated in <FIG>. In some embodiments, electrode <NUM> can be a bias electrode, electrode <NUM> can be a grounding electrode, and electrode <NUM> can be a collector electrode. Even though the PID in <FIG> and the details of the PID sensor in 2b are prior art, their components and layout can remain consistent with the PID and sensor described herein. More specifically, as illustrated in <FIG>, similar to PID sensor <NUM> from <FIG>, the grounding electrode <NUM> on the PID sensor <NUM> can be positioned between the bias electrode <NUM> and the collector electrode <NUM>.

Prior art electrodes <NUM>, <NUM> and <NUM>, as illustrated in <FIG>, and <NUM>, <NUM>, such as those illustrated in <FIG>, are approximately circular. Since a voltage differential between bias and collector electrodes can typically be tens or hundreds of volts, a third electrode, a grounding electrode, can be employed to block surface conduction currents that may arise between the bias and collector electrodes. Illustrated in <FIG> is a collector electrode <NUM> and a grounding electrode <NUM>. The collector <NUM> and grounding <NUM> electrodes each include respective feed-thru pins <NUM>, <NUM> that are electrically connected. Typical materials used in the PID include gold-plated features and tin-containing solders. Solder may be placed over the feed-thru pins <NUM>, <NUM> and may further cover portions of the inner traces <NUM>, <NUM> such that the appearance of each electrode is that of an inner trace with solder on top of it.

Unfortunately, if the collector electrode and the grounding electrode are made from metals that are significantly far apart on the galvanic series, a weak battery can result when bridged by a conductive medium. Since the materials used in a PID include gold-plated features and tin-containing solders, these metals, when bridged by a conductive medium, can produce electrochemical voltages in the range of several hundred millivolts. This voltage can appear between the grounding electrode and the collector electrode, which can then feed into the transimpedance amplifier. This stray voltage can drive the transimpedance amplifier in either a positive or negative direction depending on which metal type is connected to the collector electrode and which type is connected to the grounding electrode.

More specifically, and again referring to <FIG>, in order for a voltage to develop, if an electrolyte is present and two conductive materials of different galvanic potentials are present (for example, a first metal used for the inner trace and a second metal used for the solder), then moisture combined with surface contamination can create a weak electrolyte that bridges the solder on one electrode with the inner trace on a second electrode, therefore potentially resulting in a voltage leading to errors in the VOC measurement. If, however, an electrolyte bridges two identical metals, there will be no voltage developed because both metals have the same galvanic potential. Therefore, one solution to reduce errors in the VOC measurement is to use only one metal type throughout the detector or use only metals that lie close together galvanically. Unfortunately, this may not always be achievable in practical designs.

Therefore, in the present disclosure, the geometry of the electrodes (i.e., conductors) has been designed to minimize the areas where metals of different electrochemical potentials can be bridged by an electrolyte. Specifically, as illustrated in <FIG>, areas where solder is present on the electrodes <NUM>, <NUM>, such as the feed-thru pins <NUM>, <NUM> and inner traces <NUM>, <NUM>, are surrounded by outer traces <NUM>, <NUM> made of a chosen material (for example, gold-plated copper). Therefore, the electrode pattern restricts solder to the inner traces <NUM>, <NUM> and feed-thru pins <NUM>, <NUM>. Therefore, if or when an electrolyte develops between the electrodes <NUM>, <NUM>, it can bridge the outer traces <NUM>, <NUM> first. As long as the surrounding outer traces <NUM>, <NUM> are comprised of the same material (or are comprised of materials lying close galvanically) for any set of electrodes <NUM>, <NUM> on the sensor, any galvanic effects can be minimized even in the presence of a conducting electrolyte. Therefore, if the solder remains inside the inner traces <NUM>, <NUM>, the chance of mixed metals becoming electrically bridged by a conductive electrolyte is reduced. Even if the electrolyte bridges all the way to the inner traces <NUM>, <NUM> and comes in contact with the solder, a voltage can develop but will be reduced due to the larger area of the ring electrode relative to the solder area. This improved geometry and architecture removes the limitation of using only the same materials or materials lying close galvanically in order to reduce errors in the VOC measurement. Further, it allows for PID sensors to have less variation in their measurements and also allows for production of higher gain sensors than have been previously feasible. Lastly, the improvement results in a sensor that is less sensitive to atmospheric variation and allows for use of PIDs in the environmental monitoring station market.

As mentioned above, the PID sensor includes at least two electrodes <NUM>, <NUM>, each having a feed-thru pin <NUM>, <NUM>, an inner trace <NUM>, <NUM> surrounding each feed-thru pin, an outer trace <NUM>, <NUM> surrounding each inner trace, a channel <NUM>, <NUM> between each inner trace and outer trace, and a bridge <NUM>, <NUM> connecting each outer trace with each inner trace. The outer traces <NUM>, <NUM> on both electrodes are comprised of the same material. The channel <NUM>, <NUM> can be comprised of a different material than the outer <NUM>, <NUM> and inner traces <NUM>, <NUM>.

More specifically, the at least two electrodes are a collector electrode <NUM> and a grounding electrode <NUM> that are located adjacent to one another, as illustrated in <FIG>. The electrodes <NUM>, <NUM> can be approximately circular and the feed-thru pins <NUM>, <NUM> for each electrode can be approximately centered, as illustrated in <FIG>. The feed-thru pins can be comprised of materials such as bronze, brass, copper, beryllium-copper, stainless steel, which can be plated with, Nickel, Gold, Silver, Platinum, Tin-lead, and Tin-silver. Surrounding the feed-thru pins <NUM>, <NUM> can be an inner trace <NUM>, <NUM>. The inner trace <NUM>, <NUM> on each electrode <NUM>, <NUM> can be circular and can be comprised of materials such as gold-plating (for example, gold-plated copper, silver-plated copper, tin-silver plated copper, and tin-lead plated copper). Each feed-thru pin <NUM>, <NUM> can be soldered in place in a central portion of the inner traces <NUM>, <NUM>. The solder can surround the feed-thru pins <NUM>, <NUM> and cover at least a portion of their respective inner traces <NUM>, <NUM>.

Surrounding each inner trace <NUM>, <NUM> of electrodes <NUM>, <NUM> there is a channel <NUM>, <NUM>. This channel <NUM>, <NUM> can be circular or annular and can be comprised of a hydrophobic material such as, but not limited to, polytetrafluoroethylene (i.e., Teflon). In some cases, the channel <NUM>, <NUM> can be comprised of the same material as the sensor plate <NUM> that the sensor materials are all connected to. Therefore, in manufacture, it can simply be a gap between the inner traces <NUM>, <NUM> and the outer traces <NUM>, <NUM>. In other cases, the channel can be an additional material placed onto the sensor plate <NUM> and between the inner trace <NUM>, <NUM> and outer traces <NUM>, <NUM>.

Surrounding each channel <NUM>, <NUM> of electrodes <NUM>, <NUM> is an outer trace <NUM>, <NUM>. The outer trace <NUM>, <NUM> can be circular or annular and is comprised of the same material as the inner trace <NUM>, <NUM> such as gold-plating (for example, gold-plated copper (for example, gold-plated copper, silver-plated copper, tin-silver plated copper, and tin-lead plated copper). It can have a similar thickness as the exposed portion of the inner traces <NUM>, <NUM>, as illustrated in <FIG>. Alternatively, it can be thinner or thicker than the inner traces <NUM>, <NUM>. As with the inner traces <NUM>, <NUM>, the feed-thru pins <NUM>, <NUM> can be centered on the outer traces <NUM>, <NUM>. Therefore, in one embodiment, the inner traces <NUM>, <NUM>, channels <NUM>, <NUM>, and outer traces <NUM>, <NUM> can be a series of rings that are centered on one another, as illustrated in <FIG>, and the thru-pins <NUM>, <NUM> can be centered within this series of rings. Alternatively, the inner traces, channels, and outer traces may be solid circular pieces that are centered and stacked on top of one another with the feed-thru pins penetrating through all layers.

In general, the greater the space between all electrodes the better, however practical design constraints will limit what can be achieved. The relative sizes of the outer and inner traces and the channels between can impact the effectiveness of the galvanic blocking pattern. Since solder on the outer ring would connect mixed metals and would diminish the effectiveness of the galvanic blocking pattern, the channels can be wide enough such that easy soldering of the feed-thru pin can occur without getting solder on the outer ring. The bridge going from the inner trace to the outer trace (explained in more detail below) should be as narrow as allowed by the manufacturing process creating the patterns. The radius of the inner trace need only be large enough to permit a good solder attachment to the feed-thru pin.

Connecting the inner traces <NUM>, <NUM> to the outer traces <NUM>, <NUM> on electrodes <NUM>, <NUM> are the bridges <NUM>, <NUM>. Bridges <NUM>, <NUM> can be a straight portion of material that connect on a first end to inner traces <NUM>, <NUM> and on a second end to outer traces <NUM>, <NUM>. They may have the same width as inner traces <NUM>, <NUM>, the same width as outer traces <NUM>, <NUM>, or a different width than either. The bridges <NUM>, <NUM> are comprised as the same material as the inner traces <NUM>, <NUM> and the outer traces <NUM>, <NUM> (for example, gold-plated copper, silver-plated copper, tin-silver plated copper, and tin-lead plated copper ). Further, the inner traces <NUM>, <NUM>, outer traces <NUM>, <NUM>, and bridges <NUM>, <NUM> can all be on the same horizontal plane such that they are all positioned relatively flat on the sensor plate <NUM>. The orientation of bridges <NUM>, <NUM> on the collector electrode <NUM> and grounding electrode <NUM>, respectively, can be symmetrical, mirrored, or any other configuration.

More specifically, in some embodiments, each electrode <NUM>, <NUM> can have at least a first side and a second side. The bridge <NUM> on the collector electrode <NUM> can be on the first side of the collector electrode, the grounding electrode <NUM> can be nearest the second side of the collector electrode, and the second side of the collector electrode can be opposite the first side of the collector electrode. Further, the bridge <NUM> on the grounding electrode <NUM> can be on a first side of the grounding electrode, the collector electrode <NUM> can be nearest the second side of the grounding electrode, and the second side of the grounding electrode can be opposite the first side of the grounding electrode. This "mirror" configuration of the collector electrode <NUM> and grounding electrode <NUM> can be seen in <FIG>, wherein the first side of the collector electrode <NUM> is a left side and the first side of the grounding electrode <NUM> is a right side (i.e., the bridges are on opposite sides). However, the electrodes are not limited to this left-right configuration, and, in some cases, the bridges may be otherwise mirrored on opposite ends (for example, top and bottom, right and left, or opposite corners) or the bridges may both be on the same side such that they are symmetrical (for example, both bridges are on the top, left, right or bottom) of their respective electrodes. In other embodiments, the bridges can be randomly placed such that they do not have a clear symmetrical or mirrored configuration relative to each other.

Whereas, in the prior art, the inner trace has a connection line <NUM>, <NUM>, in the current disclosure, the connection line <NUM>, <NUM> is instead paired to outer traces <NUM>, <NUM> for each electrode <NUM>, <NUM>. In some cases, the connection line may be a continuation of the respective bridge, as illustrated by the middle, grounding electrode in <FIG> that is positioned between the bias electrode and the collector electrode. In other cases, the connection line may be separate from the bridge on the electrode, as illustrated by the rightmost collector electrode in <FIG>. For example, one or more of the connection lines <NUM>, <NUM> may be positioned <NUM> degrees away from the bridges <NUM>, <NUM>, as illustrated in <FIG>.

In use, a photoionization detector with the improved geometry and architecture for the sensor electrodes can be used by activating a gas discharge lamp and reading an output of the amplifier. The gas discharge lamp can have a UV light source and can ionize molecules of interest to create ionized molecules and electrons. The ionized molecules can be collected by a bias electrode <NUM> on a sensor <NUM>, and the electrons can be collected by a collector electrode <NUM> on the sensor, wherein the collector electrode can further be connected to an amplifier. A grounding electrode <NUM> on the sensor can be located between the bias electrode <NUM> and the collector electrode <NUM>. The collector electrode <NUM> and the grounding electrode <NUM> can each include a feed-thru pin <NUM>, <NUM>, an inner trace <NUM>, <NUM> surrounding the feed-thru pin, an outer trace <NUM>, <NUM> surrounding the inner trace, a channel <NUM>, <NUM> between the inner trace and outer trace, and a bridge <NUM>, <NUM> connecting the outer trace with the inner trace. According to the present invention, the trace <NUM>, <NUM> on both electrodes is comprised of the same material. Further, the channel <NUM>, <NUM> can be comprised of a different material than the outer trace <NUM>, <NUM> and the inner trace <NUM>, <NUM>.

Claim 1:
A photoionization detector sensor (<NUM>), the photoionization detector sensor (<NUM>) comprising:
at least two electrodes including a collector electrode (<NUM>) and a grounding electrode (<NUM>), wherein each electrode includes
a feed-thru pin (<NUM>, <NUM>),
an inner trace (<NUM>, <NUM>) surrounding the feed-thru pin (<NUM>, <NUM>),
an outer trace ring (<NUM>, <NUM>) surrounding the inner trace (<NUM>, <NUM>), wherein the outer trace ring (<NUM>, <NUM>) on each electrode (<NUM>, <NUM>) is comprised of the same material,
a channel (<NUM>, <NUM>) between the inner trace (<NUM>, <NUM>) and the outer trace ring (<NUM>, <NUM>), wherein the channel (<NUM>, <NUM>) is comprised of a different material than the outer trace ring (<NUM>, <NUM>) and the inner trace (<NUM>, <NUM>), and
a bridge (<NUM>, <NUM>) connecting the outer trace ring (<NUM>, <NUM>) with the inner trace (<NUM>, <NUM>),
wherein the inner trace (<NUM>, <NUM>), the outer trace ring (<NUM>, <NUM>), and the bridge (<NUM>, <NUM>) are comprised of the same material,
wherein the feed-thru pin (<NUM>, <NUM>) is centered within the outer trace ring (<NUM>, <NUM>), and
wherein the bridge (<NUM>) on the collector electrode (<NUM>) is on an opposite side compared to the bridge (<NUM>) on the grounding electrode (<NUM>).