Patent ID: 12255583

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Nomenclature TableREF. NO.DESCRIPTION100Photoionization Detector Sensor110Housing119Sample Retention Chamber1191Sample Intake Port1192Sample Venting Port120UV Lamp121First Ignition Electrode122Second Ignition Electrode130Sensing Electrodes1301First Sensing Electrode or Anode1302Second Sensing Electrode or Cathode140Amplifier150Processor200Driver for UV LampATarget AnalyteCCapacitorLInductorQ1First TransistorQ2Second TransistorRbPrimary Bias ResistorRtPositive Temperature Coefficient ResistorS1Current Signal from Sensing ElectrodesS2Signal from AmplifierT1First TransformerVbSeparate Supply VoltageVinPrimary Circuit Supply Voltage
Construction

Referring toFIG.3, a first aspect of the invention is a temperature compensating and output adjustable ultraviolet lamp driver200for supplying an alternating current signal to the ultraviolet lamp120effective to light the ultraviolet lamp120. Still referring toFIG.3, a second aspect of the invention is a photoionization detector sensor100equipped with a lamp driver200in accordance with the first aspect of the invention.

Referring toFIG.1, photoionization detector sensors100have an ultraviolet (UV) lamp120for ionizing target analyte A within a sample, a pair of sensing electrodes130(i.e., an anode1301and a cathode1302) for detecting the ions and generating a first electrical current signal S1proportional to the concentration of target analyte A within the sample, and an amplifier140in electrical communication with the electrodes130for receiving the generated first electrical current signal S1and amplifying and converting the first electrical current signal S1to a second voltage electrical signal S2. These components are generally retained within a housing110that defines a sample retention chamber119positioned to receive UV radiation emitted by the UV lamp120upon excitation of the lamp120and having a sample intake port1191and optionally a sample venting port1192.

Photoionization detector sensors100are employed in instruments that typically include a processor150for receiving the amplified electronic signal S2, converting the value of the amplified electronic signal S2to a concentration of target analyte A in the sample based upon an algorithm or a lookup table, and displaying or otherwise reporting the concentration.

Referring toFIGS.1and2, an alternating current signal is commonly supplied to a pair of ignition electrodes121and122positioned on opposite sides of an ultraviolet lamp120by an oscillator driving a primary side of a transformer T1wherein the oscillator includes a pair of transistors Q1and Q2configured to operate out-of-phase feeding the primary side of the transformer T1. A common oscillator is a Baxandall oscillator such as depicted inFIG.2. The Baxandall oscillator includes a circuit supply voltage Vin. biased via a biasing resistor Rbprior to reaching the pair of transistors Q1and Q2with a feedback loop provided to keep the pair of transistors Q1and Q2operating out-of-phase. The Baxandall oscillator further includes an inductor L and a capacitor C as depicted inFIG.2.

Referring toFIG.3, the driver200of the invention provides a temperature compensated and output adjustable alternating current signal to the ultraviolet lamp120. The driver200is essentially a modified Baxandall oscillator wherein direct current is supplied from both a first variable voltage supply circuit Vin, and a second fixed voltage supply circuit Vb, characterized in that the direct current supplied by the first variable voltage supply circuit Vinis not biased via a biasing resistor Rbprior to reaching the pair of transistors Q1and Q2while the direct current supplied by the second fixed voltage supply circuit Vbis biased through a series of a positive temperature coefficient resistor Rtsuch as a positive temperature coefficient silicon resistor, and a primary bias resistor Rbprior to reaching the transistors Q1and Q2. As with the Baxandall oscillator, the driver200in accordance with the invention further includes an inductor L and a capacitor C as depicted inFIG.3.

Configuration of the oscillator in accordance with the invention with the positive temperature coefficient resistor Rtallows for constant bias to transistors Q1and Q2independent of the oscillator's variable input voltage Vinand temperature changes. The resistance of Rtwill 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. Rtand Rbcan 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.

The photoionization detector sensor100equipped with a driver200in accordance with the invention is particularly adapted to detect and quantify the concentration of volatile organic compounds in a sample.

Factory Standardization

Output from a photoionization detector sensor100equipped with a driver200in 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 sensor100to detect target analyte A in a standardizing sample to create an electrical signal S2having a test value, wherein the standardizing sample has a known concentration of the target analyte A and is expected to generate an electrical signal S2of known anticipated value, (B) comparing the test value and the anticipated value, and (C) standardizing output of the photoionization detector sensor100by adjusting the voltage supplied to the driver200by the first variable voltage supply circuit Vinso that future reported values will more closely approximate actual values.