IMS CAD: An Updated Surveillance Tool And Its Critical Issues In Tropical Environment

Abstract

This paper describes varieties of IMS tubes used in Chemical Agent Detector (CAD) and their behavior in tropical climatic conditions like India. Using in-house Environment test set-up, a comparative study of detectors procured from three different OEMs have been studied at progressively high humid environment at constant temperature. Closed loop IMS Detector ( Model –GDA-P) used by BEL has much less influence of humidity over low end one, though all types of detectors suffer from longer warm-up time at high humidity( ~80% and above).

As a way-out, a pump driven air filter based mounting system as housing station is introduced for BEL Detector. This system, by providing 24x7 dry clean air to its reaction chamber, make detector capable for ready usages at any site. Mounting system further is also fitted with facility for external alarm at customer chosen distance (50-1000 M) as well as live data communication in command control station.

Key words: IMS tube, CWA, CBRNI.

Introduction

Globally, clandestine activities by non-state actors have been spilled over from border, isolated site to urban, densely populated areas. In Asian country this type of secessionist activities has been more or less a daily event. Thus, CBRN threat is an ongoing reality in India. The designing of Equipment for fast threat anticipation for surveillance, mitigation purpose has become a matter of challenge to global OEMs, so in India and BEL. However, among CBRN threats, Chemical Agent is most accessible.

So, surveillance against Chemical threat is of paramount importance for Military and Disaster Management Forces. In light of this, R&D Establishments have shifted its focus for development of Analytical methods and device that can rapidly detect toxic chemical agents with alarm. Consequently, CAD as portable (hand-held) device or fixed with other network like integrated security and surveillance system is considered as one of indispensible Deliverables. Therefore, present study concentrates on Ion Mobility Spectrometry (IMS) process, advantages of IMS-CAD and some issues while tested in tropical environment condition. IMS Detector is found to be a proven, most widely used sensor device meant for fast detection of CW Agent /TIC hazards at ppm level (1,2). However, there are several issues of IMS-CAD often masked or deliberately not highlighted by OEMs especially trial and test report executed in tropical environment.

IMS Detector And Its Process

IMS detectors have been in use worldwide (in millions, more than fifty lacs) thus most studied and proven than other detection technology which are still thousand in numbers.

IMS process shown above (Fig. 1) is mainly divided in two compartments: reaction region where CWA and TIC compounds are ionized; and other is measurement cell where ions are made to travel under the influence of Electric field. Faster drifting time to reach Detector/Faraday plate for uncontaminated smaller sized ions that recognized against their recorded spectra. In other words, CWA agents after being ionized and detected in terms of Time Of Flight (TOF) principle and their spectrum matched with recorded spectra stored in the library. IMS detector provides very low detection limit (ppm/ppb level), much below lethal concentration, and short response times. Now-a-days, because of up gradation of technology like the state of the art measuring cell, highly sophisticated software, chemical agents can be detected in the time range, millisecond to less than minute.

Further, suitable Dopants (3) like ammonia used in measurement cell that can neutralize interfering positive ions due to its higher proton affinity and prevent its reaching detector plate and thereby reduce false alarm.