Systems and methods for improving detection accuracy in electronic trace detectors

Inventors

Shaw, Bradley Douglas • Rogers, William • Romanov, Vladimir • Maines, Adam Justin

Assignees

Rapiscan Systems Inc

Abstract

Embodiments of the present specification provide methods and systems for maintaining accuracy and precision of calibration for a detector. The methods and systems include reducing the humidity of an internal calibration assembly by directing flow path of dry air periodically through the internal calibration assembly.

Core Innovation

The invention relates to reducing humidity within an internal calibration chamber of a trace detection system, where the trace detection system comprises a first pump, a dryer, a desorber, a detector, and an internal calibration assembly defined by a housing. The internal calibration assembly includes a first valve, a second valve, and a calibrant source positioned within the housing. The disclosed approach directs dry air to the desorber without flow communication with the calibrant source in a first mode, and directs the dry air through the calibrant source to the desorber in a second mode.

Humidity increase is identified as causing non-uniform drift-time peak shifts and calibration inaccuracy in the trace detection system. The disclosure explains that leaks and permeation lead to humidity build-up, and that controlling humidity within the internal calibration chamber improves drift-time calibration accuracy and reproducibility. The disclosure describes forming dry air by operating the first pump to direct air through the dryer.

In the first mode of operation, the first valve is placed in a first state so that the dry air is directed to the desorber without being in flow communication with the calibrant source. In the second mode of operation, the first valve is placed in a second state so that the dry air is directed through the second valve and the calibrant source to the desorber. The disclosure further describes controller operation of the trace detection system in the first mode and the second mode, and maintaining quantitative humidity targets in terms of dry air relative humidity and internal calibration relative humidity.

The disclosure also describes maintaining low humidity using periodic internal calibration chamber purge concepts, including regular intervals for placing the system in the second mode, and observing humidity build-up without purging. Documented observations include reduced calibration standard deviation with reduced internal calibration assembly relative humidity, and drift-time peak behavior described as peak shifting/quenching with increasing relative humidity. The disclosure further describes detecting relative humidity via dopant peak disappearance and provides example measurements using a Bruker spectrometer.

Claims Coverage

The partial claims content provides two independent claims: one method claim and one system claim. Across these independent claims, the core inventive coverage centers on (1) operating a pump with a dryer to form dry air and (2) using first and second valve states to either bypass or route flow through a calibrant source to a desorber, thereby reducing humidity within an internal calibration chamber.

Together, the independent claims cover a humidity-reduction strategy for trace detection internal calibration by forming dry air with a dryer and pump, then selectively switching valve states to bypass the calibrant source in a first mode or to route dry air through the calibrant source via the second valve in a second mode before reaching the desorber.

Stated Advantages

Documented Applications