How to Measure Gases with NIRONE Sensors?

Gases are typically colorless and therefore invisible to the eye. Some gases may have noticeable odours or smells, even at extremely low concentrations, but although the nose can sniff the gases, the brain functions so that it starts to filter out that annoying signal, and it is filtered out, leaving you to keep breathing that gas, thinking that the source of the smell is gone. But in most cases, gases are undetectable without special gas measurement instruments.

Unlike solids and liquids, the interactions between gas molecules only have a negligible effect on the spectra. This makes the calibration of gas IR measurement systems easy, assuming that you have the equipment and calibration gases at hand.

Setup for Gas Sample Cell Measurements

In this setup, sample gases flow into the cell for measurement, after which they flow out. Sampling can be done with a small pump, which samples the gas from a stream, the environment, and so on.

This setup is a closed system. The advantages are that the gases are not in direct contact with the light source and the spectral module. This will restrict harmful and possibly reactive, hot and humid gases from entering the critical components of the system. As any NIR light source, when turned on, is a potential ignition source, this is usually the best choice for ATEX environments.

The gas sample cells can be quite expensive and will bring added weight to the systems, but on the other hand, the sample cells can also be heated to measure hot and humid gases without condensation.

Required equipment:

  • NIRONE Sensor
  • Light source
  • Collimating/focusing optics
  • Measurement computer
  • Possibly a closed gas-tight cabinet, where the optical bench can be installed
Figure: Setup for Gas Sample Cell Measurements
Setup for Gas Sample Cell Measurements

A typical setup consists of a gas sample cell with Swagelok connectors for gas input and output, a NIRONE Sensor, and a separate light source. The gas measurement and analysis are controlled by an on-site computer, and further data analysis and gathering, as well as system status display, are integrated to a cloud service.

Setup for In-situ Measurements

In this setup, sample gases flow through an open air path of several centimeters. The gas sampling path is defined by the beam of light travelling from the light source to the spectral module.

Required equipment:

  • NIRONE Sensor
  • Light source
  • Collimating/focusing optics
  • Measurement computer
  • Possibly a closed gas-tight cabinet, where the optical bench can be installed
Figure: Setup for In-situ Measurements
Setup for In-situ Measurements

A typical setup consists of a NIRONE Sensor, a separate light source, and focusing optics. No separate gas cell is needed in this setup.

Suitable Gas Applications

See below for a list of suitable gas applications:

  • Anything with high concentration of hydrocarbon gases, and also water vapor, carbon monoxide CO, and carbon dioxide CO2
  • The NIRONE sensors may be used to detect hydrocarbons (especially C1-C5 alkanes such as methane, ethane, propane, etc.)
    • Liquified Natural Gas (LNG) applications
    • Oil industry
    • Biogas industry
Table 1. Gases with Different Sensor Versions
Sample Type NIRONE S1.7 NIRONE S2.0 NIRONE S2.2 Typical Concentrations1
Hydrocarbon gases CxHy Yes Yes Yes, at least somewhat useful Minimum 500 - 2000 ppm and higher, up to 100 vol-% (1 000 000 ppm)
Carbon monoxide CO Yes (1567 nm, weak) Yes (1567 nm, weak) No 1000 ppm to 100 vol-%
Carbon dioxide CO2 Yes (1400 nm) Yes (1600 nm) Yes (2008 nm) 1000 ppm to 100 vol-%
Water vapor Yes (1380 nm) Yes (1870 nm) Yes (1870 nm) 1000 ppm to 100 vol-%

The units are:

  • 1 ppm = 1 part-per-million
  • 1 vol-% = 1 volume percent = 10 000 ppm

Unsuitable Gas Applications

See below for a list of unsuitable gas applications:

  • Container fumigant measurements. These applications have too low gas concentrations.
  • Most atmospheric emissions from industrial processes, such as AMS/CEMS-type requirements for continuous emissions monitoring. These applications have too low gas concentrations, and require certified instruments.
  • Anything with low ppm/ppb/ppt-detection requirements.
  • Indoor air quality, as we cannot measure:
    • Radon.
    • Second-hand smoke.
    • Pollen/spores/toxins in the air in ppm/ppb/ppt.
    • Carbon monoxide in low enough concentrations, in the low ppm range, up to 100 / 150 ppm.
1 40 cm path length, atmospheric pressure