Products

Multi-technology products.

The Company's two principal product lines address ambient air quality, which is monitored by fixed-site units and by wearable monitors, respectively, each deploying the multi-technology approach, which is the core signature of the Company’s products.

Governments and administrations in many parts of the world are turning to the monitoring of street-level air pollution in cities, with wireless transmission of real time analytical data to nominated control centres, in an attempt to keep this health threat in check.

The Atmospheric Sensors unit for fixed site monitoring deploy four electrochemical sensors, an NDIR sensor for carbon dioxide, a particle monitor, relative humidity monitoring and temperature measurement. Data can be stored locally and can be transmitted to a central management site.

In many circumstances a wearable air quality monitoring system that also makes use of a complementary range of sensing technologies will be the optimum way to provide a reliable information set: Electrochemical, NDIR, and metal oxide sensors can all be included in the system.

Wearable air quality monitors

See also 'Product Brochures'.

Metal oxide sensor products.

ASL metal oxide sensors give early warning of the accumulation of atmospheric components that pose either toxic or fire hazards but also allow for energy economy through on-demand use of ventilation systems.

We take the use of metal oxide gas sensors to a new level of both sensitivity and selectivity through an elegant approach to sensor management and signal processing and our system opens the door to new applications. 
ASL has developed the technology to advance the capabilities of metal oxide gas monitoring to hitherto unachievable levels. In the past semiconductor gas sensors have proved useful in a limited range of applications in the detection of flammable and/or toxic gases in the environment.  Although such devices are inherently robust and inexpensive their wider application has been precluded by poor selectivity between analyte gases in some cases and by inadequate sensitivity in others.
 In the ASL system sensors based on purpose-designed materials formulations are supported by advanced control and read-out electronics that overcome such limitations in both sensitivity and selectivity.

The response of a metal oxide sensor to any particular gas is temperature-dependent. If the sensor is not maintained at the correct temperature for that combination of sensing material and the specific gas being sensed then the sensitivity is degraded, as shown in Figure 1.

Figure 1 – The response (dR/Ro) of a sensor to 5 ppm of hydrogen sulfide in air is a maximum at 322°C. The signal is greatly reduced at higher and lower temperatures.

In order for the sensor to be held accurately at the correct temperature the heater track resistance of the device must be calibrated and the heater driver system must be able to hold it at the correct value regardless of any outside influence (cooling effects of gas flow etc.). The digital temperature control system in ASL units responds very fast to control temperature within 1°C, as shown in Figure 2.

Figure 2 – Speed of response and precision of temperature control are greatly enhanced by the ASL digital system.

ASL sensor management systems enable the wider use of semiconductor gas sensors by the introduction of three measures that, together, enhance the selectivity and sensitivity of such sensors far beyond the capability of semiconductor gas sensor systems that are currently available:

1. A digital sensor management system is used that gives far greater precision and stability of sensor operating temperature than is possible with the conventional analogue approach.
2. New high-sensitivity semiconductor materials with sharp temperature peaks of maximum response are used. The materials are of both n- and p-types and thus can be used in n-/p- pairs to aid discrimination.
3. The sensors are interrogated with AC so that their impedance is evaluated and the extra response information that is available in the imaginary component (Figure 3) is thus made available without the high expense of a frequency response analyser.

Figure 3 – The temperature of peak response of the imaginary component of the impedance (at 300 Hz) to 5 ppm hydrogen sulfide is at a higher temperature than that for the resistance response (Figure 1).

All three technology developments have been confirmed separately and integrated together in a low-cost implementation that will have broad market appeal as it allows metal oxides sensors to be used in far more demanding applications (monitoring and control) than has been possible in the past. Responses monitored with the system are clean and stable (Figure 4) and will allow a very high degree of sensitivity.

Figure 4 – Response of the resistance of a sensor to alternating pulses of 20 ppm and 5 ppm hydrogen sulfide.