TEMPERATURE COMPENSATING ADJUSTABLE ULTRAVIOLET LAMP DRIVER CIRCUIT AND PHOTOIONIZATION DETECTOR EMPLOYING THE DRIVER CIRCUIT

Abstract

A photoionization detector sensor equipped with a temperature compensating and output adjustable ultraviolet lamp driver for supplying an alternating current signal to the ultraviolet lamp effective to light the ultraviolet lamp with direct current supplied from both a first variable voltage supply circuit and a second temperature sensitive fixed voltage supply circuit, and method of standardizing output of the photoionization detector sensor by adjusting the voltage supplied to the driver by the first variable voltage supply circuit so that future reported values will more closely approximate actual values.

Claims

1. A temperature compensating and output adjustable ultraviolet lamp driver for supplying an alternating current signal to the ultraviolet lamp effective to light the ultraviolet lamp, the driver comprising an oscillator driving a primary side of a transformer wherein the oscillator includes a pair of transistors configured to operate out-of-phase feeding the primary side of the transformer with (i) direct current from a first variable voltage supply circuit, and (ii) direct current from a second fixed voltage supply circuit, characterized in that the direct current from the second fixed voltage supply circuit is biased through a series of a positive temperature coefficient resistor and a primary bias resistor prior to reaching the transistors.

2. The temperature compensating and output adjustable ultraviolet lamp driver of claim 1 wherein out-of-phase operation of the pair of transistors is maintained via a feedback signal from the primary side of the transformer.

3. The temperature compensating and output adjustable ultraviolet lamp driver of claim 1 wherein the transformer is a step-up transformer.

4. The temperature compensating and output adjustable ultraviolet lamp driver of claim 1 wherein the oscillator is a modified Baxandall oscillator.

5. A photoionization detector sensor having (i) an ultraviolet lamp operable for ionizing a target analyte within a sample, (ii) ignition electrodes for generating target analyte ionizing ultraviolet radiation within the lamp, (iii) sensing electrodes for detecting the presence of ionized target analyte within the sample and generating a current signal proportional to the concentration of target analyte within the sample, and (iv) a driver in accordance with claim 1 in electrical communication with the ignition electrodes.

6. The photoionization detector sensor of claim 5 wherein the ultraviolet lamp is operable for ionizing a volatile organic compound target analyte.

7. A photoionization detector sensor having (i) a housing defining a sample retention chamber, (ii) an ultraviolet lamp operable for ionizing a target analyte within the sample retention chamber, (iii) ignition electrodes for generating target analyte ionizing ultraviolet radiation within the lamp, (iv) an anode-cathode pair for detecting the presence of ionized target analyte within the sample retention chamber and generating a current proportional to the concentration of target analyte within the sample retention chamber, and (v) a driver in accordance with claim 1 in electrical communication with the ignition electrodes.

8. The photoionization detector sensor of claim 7 wherein the ultraviolet lamp is operable for ionizing a volatile organic compound target analyte.

9. A method of standardizing output of a photoionization detector sensor in accordance with claim 5 so that reported values of target analyte concentration in a target analyte containing test sample will more closely approximate actual values of target analyte concentration in the target analyte containing test sample, comprising the steps of (A) activating the photoionization detector sensor to detect target analyte in a standardizing sample to create an electrical signal having a test value, wherein the standardizing sample has a known concentration of the target analyte and is expected to generate an electrical signal of known anticipated value, (B) comparing the test value and the anticipated value, and (C) standardizing output of the photoionization detector sensor by adjusting the voltage supplied to the driver by the first variable voltage supply circuit so that future reported values will more closely approximate actual values.

10. A method of standardizing output of a photoionization detector sensor in accordance with claim 7 so that reported values of target analyte concentration in a target analyte containing test sample will more closely approximate actual values of target analyte concentration in the target analyte containing test sample, comprising the steps of (A) activating the photoionization detector sensor to detect target analyte in a standardizing sample to create an electrical signal having a test value, wherein the standardizing sample has a known concentration of the target analyte and is expected to generate an electrical signal of known anticipated value, (B) comparing the test value and the anticipated value, and (C) standardizing output of the photoionization detector sensor by adjusting the voltage supplied to the driver by the first variable voltage supply circuit so that future reported values will more closely approximate actual values.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIG. 1 is a schematic view of one embodiment of a typical PID sensor.

[0013] FIG. 2 is a circuit diagram of an exemplary prior art Baxandall oscillator supplying an AC signal to an UV lamp.

[0014] FIG. 3 is a circuit diagram of one embodiment of an UV lamp driver in accordance with the invention supplying an AC signal to an UV lamp.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

[0015]

TABLE-US-00001 Nomenclature Table REF. NO. DESCRIPTION 100 Photoionization Detector Sensor 110 Housing 119 Sample Retention Chamber 119.sub.1 Sample Intake Port 119.sub.2 Sample Venting Port 120 UV Lamp 121 First Ignition Electrode 122 Second Ignition Electrode 130 Sensing Electrodes 130.sub.1 First Sensing Electrode or Anode 130.sub.2 Second Sensing Electrode or Cathode 140 Amplifier 150 Processor 200 Driver for UV Lamp A Target Analyte C Capacitor L Inductor Q.sub.1 First Transistor Q.sub.2 Second Transistor R.sub.b Primary Bias Resistor R.sub.t Positive Temperature Coefficient Resistor S.sub.1 Current Signal from Sensing Electrodes S.sub.2 Signal from Amplifier T.sub.1 First Transformer V.sub.b Separate Supply Voltage V.sub.in Primary Circuit Supply Voltage

Construction

[0016] Referring to FIG. 3, a first aspect of the invention is a temperature compensating and output adjustable ultraviolet lamp driver 200 for supplying an alternating current signal to the ultraviolet lamp 120 effective to light the ultraviolet lamp 120. Still referring to FIG. 3, a second aspect of the invention is a photoionization detector sensor 100 equipped with a lamp driver 200 in accordance with the first aspect of the invention.

[0017] Referring to FIG. 1, photoionization detector sensors 100 have an ultraviolet (UV) lamp 120 for ionizing target analyte A within a sample, a pair of sensing electrodes 130 (i.e., an anode 130.sub.1 and a cathode 130.sub.2) for detecting the ions and generating a first electrical current signal S.sub.1 proportional to the concentration of target analyte A within the sample, and an amplifier 140 in electrical communication with the electrodes 130 for receiving the generated first electrical current signal S.sub.1 and amplifying and converting the first electrical current signal S.sub.1 to a second voltage electrical signal S.sub.2. These components are generally retained within a housing 110 that defines a sample retention chamber 119 positioned to receive UV radiation emitted by the UV lamp 120 upon excitation of the lamp 120 and having a sample intake port 1191 and optionally a sample venting port 1192.

[0018] Photoionization detector sensors 100 are employed in instruments that typically include a processor 150 for receiving the amplified electronic signal S.sub.2, converting the value of the amplified electronic signal S.sub.2 to a concentration of target analyte A in the sample based upon an algorithm or a lookup table, and displaying or otherwise reporting the concentration.

[0019] Referring to FIGS. 1 and 2, an alternating current signal is commonly supplied to a pair of ignition electrodes 121 and 122 positioned on opposite sides of an ultraviolet lamp 120 by an oscillator driving a primary side of a transformer T.sub.1 wherein the oscillator includes a pair of transistors Q.sub.1 and Q.sub.2 configured to operate out-of-phase feeding the primary side of the transformer T.sub.1. A common oscillator is a Baxandall oscillator such as depicted in FIG. 2. The Baxandall oscillator includes a circuit supply voltage V.sub.in. biased via a biasing resistor R.sub.b prior to reaching the pair of transistors Q.sub.1 and Q.sub.2 with a feedback loop provided to keep the pair of transistors Q.sub.1 and Q.sub.2 operating out-of-phase. The Baxandall oscillator further includes an inductor L and a capacitor C as depicted in FIG. 2.

[0020] Referring to FIG. 3, the driver 200 of the invention provides a temperature compensated and output adjustable alternating current signal to the ultraviolet lamp 120. The driver 200 is essentially a modified Baxandall oscillator wherein direct current is supplied from both a first variable voltage supply circuit V.sub.in, and a second fixed voltage supply circuit V.sub.b, characterized in that the direct current supplied by the first variable voltage supply circuit V.sub.in is not biased via a biasing resistor R.sub.b prior to reaching the pair of transistors Q.sub.1 and Q.sub.2 while the direct current supplied by the second fixed voltage supply circuit V.sub.b is biased through a series of a positive temperature coefficient resistor R.sub.t such as a positive temperature coefficient silicon resistor, and a primary bias resistor R.sub.b prior to reaching the transistors Q.sub.1 and Q.sub.2. As with the Baxandall oscillator, the driver 200 in accordance with the invention further includes an inductor L and a capacitor C as depicted in FIG. 3.

[0021] Configuration of the oscillator in accordance with the invention with the positive temperature coefficient resistor R.sub.t allows for constant bias to transistors Q.sub.1 and Q.sub.2 independent of the oscillator's variable input voltage V.sub.in and temperature changes. The resistance of R.sub.t will decrease at cold temperatures (when it needs to be low) and increase at hot temperatures (when it does not need to be low), thereby assuring a higher current under cold conditions to aid starting, without unnecessary power consumption at hot temperatures. R.sub.t and R.sub.b can be selected such that the oscillator easily starts at cold temperatures without undue power consumption at the higher temperatures. Low power consumption is an important benefit because most PID sensors are battery operated.

[0022] The photoionization detector sensor 100 equipped with a driver 200 in accordance with the invention is particularly adapted to detect and quantify the concentration of volatile organic compounds in a sample.

Factory Standardization

[0023] Output from a photoionization detector sensor 100 equipped with a driver 200 in accordance with the invention may be standardized so that reported values of target analyte A concentration in a target analyte A containing test sample will more closely approximate actual values of target analyte A concentration in the target analyte A containing test sample. The method involves the steps of (A) activating the photoionization detector sensor 100 to detect target analyte A in a standardizing sample to create an electrical signal S.sub.2 having a test value, wherein the standardizing sample has a known concentration of the target analyte A and is expected to generate an electrical signal S.sub.2 of known anticipated value, (B) comparing the test value and the anticipated value, and (C) standardizing output of the photoionization detector sensor 100 by adjusting the voltage supplied to the driver 200 by the first variable voltage supply circuit V.sub.in so that future reported values will more closely approximate actual values.