• C20
  • C100

gas sensing technology


technology used

Circuit Board 3

key features

  • High speed
  • Real time sensing
  • Low power consumption – typically 100mW (Spec dependent)
  • High accuracy
  • High poison resistance & long term stability
  • Various voltages available from 3.3v to 5.5v
  • 20mm package

Benefits

  • Wide range of applications
  • Low cost
  • Low power consumption, suitable for battery and portable applications

Technolgies Used

There are two types of gas sensors commonly available for monitoring CO2 concentrations in air, i.e., non-dispersive infrared (NDIR) and solid electrolyte sensor types. Non-dispersive infrared sensors have performance advantages in terms of long-term stability, accuracy, and power consumption for CO2 measurement. Hence, NDIR sensors are the most widely used for the real-time measurement of carbon dioxide. Solid electrolyte types have cost advantages, but the product performance is not good enough to allow their use in any but the least demanding applications.

The NDIR method is an optical method of detecting gases. This relies on the fact that many gases absorb specific wavelengths of infra-red light.

It is possible to calculate the gas concentration by passing light through a defined length and measuring how much light is absorbed at the specific wavelength absorbed by the gas. For CO2 the used wavelength is 4.26um.

MID INFRA RED LIGHT EMITTING DIODE/PHOTODIODE TECHNOLOGY

Wafer

Using unique photonics technology GSS has produced light emitting diodes (LED) sources and Photodiode (PD) detectors operating at the mid-infrared wavelengths of interest in gas detection. The technology is based on Indium Aluminium Antimonide, and the spectral characteristics of both source and detector can be tuned by altering the aluminium content.

LED

This technology produces LED's and detectors which are tuned to absorption wavelength of CO2, used as a pair, the bandwidth of the combined system is so narrow optical filtering is not required. This simplifies the optical design and significantly reduces cost.

ADVANTAGES OF MID INFRA-RED LIGHT EMITTING DIODE AND PHOTODIODE TECHNOLOGY

Typical NDIR sensors use incandescent sources (essentially light bulbs) and pyroelectric detectors. The GSS sensor replaces these elements with the matched LED and PD pair.

There are a number of important advantages in using solid state (LED/PD) technology in place of incandescent sources:

SPEED OF RESPONSE

LED's can be pulsed very rapidly and the gas sensing signal can be detected very rapidly. The GSS LED is currently pulsed at 500Hz, but in principle can be pulsed at much higher frequencies.

This allows the sensor to detect rapid changes in gas concentrations and to make individual measurements in less than 500mS.

The speed of response is important in safety alarm applications, and in applications with rapid change – fitness, processing industries etc.

LOW POWER

The LED in the GSS C20 sensor is typically running only 5% of the time resulting in relatively low power. Future designs will capitalise more on this feature and are expected to have power levels at least ten times lower than the existing design.

Low power is of great interest to manufacturers of portable equipment. If power levels can be reduced further (which looks possible), there are also potential high volume applications in battery powered fixed infrastructure for building control.

OPTICAL FILTER

Existing sensors require wavelength filters to measure only the wavelengths of interest. These filters are complex multilayered optical structures and are prone to manufacturing variations. The restricted bandwidth of the GSS LED and PD means that no additional optical filter is required. The optical assembly consists simply of the LED, a mirror and the PD, with no fine tuning or mechanical adjustment required.

LOW COST AND HIGH VOLUME

The LED and PD are well suited to high volume manufacturing at low cost. The fabrication uses standard, scaleable wafer processing techniques, the optical elements are injection moulded, the electronics are standard and the assembly is simple.

PRESSURISED ENVIRONMENTS

There are a number of niche applications – diving, sub sea systems, hyperbaric chambers – in which sensors are subjected to high pressure and helium concentrations. GSS LED technology has been tested to 40 atmosphere of pressure and continued to function without being affected by helium ingress – a problem for incandescent sources.