AL5002 Ultra Fast Carbon Monoxide (CO) analyzer

Front view of a AL5002 ultra-fast CO-monitor. The instruments is operated by a touch-screen in the front panel or remotely via RS232.

General description

The AL5002 is an ultra fast carbon monoxide (CO) monitor with an unique sensitivity below 1ppb (parts per billion). The AL5002 is specially designed for the application in air-planes, where a high time reolution results in a high spatial resolution. The detection of CO is based on a VUV-fluorimetry, employing the excitation of CO at 150nm. This method combines a high sensitivity with high selectivity and is linear from 1ppb to 100 ppm. The AL5002 is widely used in remote research stations like in Antarctica, on research ships and air-crafts, where very low detection limits, high sensitivity, fast response, high temperature stability, low zero drift and a huge linearity range is required. The excitation light is generated by a cw-CO2 resonance lamp, which needs only a low maintenance. A monochromator unit, using dielectric mirrors, filters out the VUV from the lamp's spectrum. The fluorescence light in the wavelength range between 160 nm and 190 nm is detected by a VUV sensitive photomultiplier followed by a fast counter. The basic principle is described in detail by Gerbig et al. [1]. 
The AL5002 calibrates within minutes, using only a low amount of calibration gas and an in-built zero gas source. The calibration procedure is fully automatic and can be scheduled in custom-set time intervals. The gas concentration is displayed in real time and can be logged via a standard RS-232 interface e.g. by SqeezeDat. Contrary to the AL5001, the AL5002 is equipped with a hard disk for internal data storage for stand-alone operation.
The instrument is rugged and designed for field campaigns in rough environment, as well as for laboratory applications. The standard version requires 24V DC power supply as it is commonly available on aircrafts.

[1]  C. Gerbig, S. Schmitgen, D. Kley, A. Volz-Thomas, K. Dewey, D. Haaks, An improved fast-response vacuum-UV resonance fluorescence CO instrument, J. Geophys. Res. 104 D1 (1999) 1699

Technical details

The instrument consists of a resonance CO2-lamp excited by a RF discharge, an optical filter for selection of the appropriate wavelength interval around 150 nm, and a fluorescence chamber. The emission of the lamp is collimated within the optical filter to a parallel beam of 150 nm light, using off-axis parabola and dielectrical mirrors. The VUV-light is then focused into the fluorimeter chamber, where the fluorescence from CO is viewed at right angles by a VUV-sensitive photomultiplier (PMT) with Suprasil pre-optics. The dielectric mirrors in the parallel part of the light beam, provide the spectral band path (bandwidth of ~10 nm full width at half maximum (FWHM) at approximately 150 nm). The optical filter is continuously flushed with dry N2 (purity of 6.0 and filtered to compress organic substances) which is necessary to avoid absorption of radiation in the Schumann-Runge continuum of molecular oxygen and from impurities, in particular CO. This only requires a flow of ca. 35 ml/min N2 since the volume is very small. The optical filter housing is made from Al covered with a black coating for reduction of stray light. The air is vented into the fluormeter chamber, which is connected to an external vacuum pump at the end of the light trap and at the PMT flange, in order to provide a well-defined air flow. A pressure sensor and a electrically driven dosing valve stabilize the pressure and the air flow through the cell. 

Requirements  

  • Vacuum pump: membrane pump or scroll pump (recommended)
  • Gas purifier for the monochromator gas (N2 – 6N)
  • Lamp gas: 0.25% CO2 – 4N5 in Argon – 6N
  • Monochromator gas: N2 – 6N
  • Calibration gas: ~1ppm CO in artificial air

Features of the instrument

  • Provides absolute concentrations for carbon monoxide (CO).
  • Designed to be used for CO monitoring where very fast measurements and very low detection limits are required.
  • Fully automated operation using 166 MHz Pentium CPU.
  • Internal data storage on hard drive.
  • RS232 interface to external PC.
  • USB interface for data access.
  • Fully automatic calibration using external CO standard within minutes.
  • Rugged and simple to use.
  • Control of instrument and data display on large touchscreen.
  • Linearity range (pulse counting): 0 to 100 ppm.
  • Detection limit: 
    • < 1.5ppb (integration time 1s) .
    • < 0.8 ppb (integration time 10s).
  • Rise and fall time (10 to 90 %): 0.1 s (ultra fast version with scroll pump) 1.5 s (fast version with membrane pump).
  • Weight: < 22 kg.
  • Power supply: 24 VDC (aircraft version).
  • 110/220 VAC with adapter.

    Linearity Test

    The fluorimetric detection of carbon Monoxide (CO) is linear over several orders of magnitude.This was tested by the Eidgenössische Materialprüfungs- & Forschungsanstalt in Dübendorf, Switzerland. The data presented below is from two correlation tests run with two different calibrations for high and low levels, respectively. The result shows an excellent linearity of the Aero-Laser CO-analyzer family.

    Linearity test of the instrument by the Eidgenössische Materialprüfungs- & Forschungsanstalt (EMPA), Switzerland.