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Delta F Moisture Sensing Technology

The Delta F 700 Series analyzers use TDLAS technology to measure moisture in gases. TDLAS is a spectroscopic technique that utilizes a diode laser as its light source. TDLAS has advantages over other techniques because the moisture sample only comes in contact with a few optical components that are made from very robust materials. It works according to the fundamental principle of Beer's law, therefore, the reading is stable over time and does not even require calibration.

Tunable Diode Laser Absorption Spectroscopy (TDLAS)


Beer's Law is:

  • I is the measurement of beam intensity when tuned to the absorbing wavelength of moisture
  • is the reference measurement or beam intensity when tuned away from the moisture absorbing wavelength
  • S is the fundamental absorption line strength and is a fixed constant
  • L is the path length of the beam through the sample and is a fixed constant
  • N is the number of water molecules contained in the beam path passing through the sample

Other spectroscopic techniques that follow Beer's Law take the reference measurement, Iš, by sending the light beam through a different optical path and generally, utilize a second detector. By rapidly tuning the laser, Delta F's TDLAS technology uses a single light source, a single light path and a single detector and, therefore, does not require any recalibration.

In spectroscopy, a longer path length is one way to achieve more sensitivity. Inside the Herriott Cell, the laser is reflected back and forth numerous times by mirrors inside the measuring cell. By making multiple passes, this increases the laser path length to achieve extremely high sensitivity. Delta F's TDLAS technology offers a robust and simple optical design with the sample and reference measured with a single laser source and a single detector.

Using Lasers for Unmatched Accuracy and Reliability
  • Drift Free Operation: Combination of self-correcting optics and the laser line locking onto the water peak removes all possibility of significant drift.
  • High Accuracy/Low Maintenance: Based on Beer's Law, the measurement requires no field span calibration.
  • Unparalleled Performance: Spectroscopy allows sub-ppb level readings instantly! Other measurement techniques with solid surfaces require lengthy adsorption and desorption times.
  • Increased Capabilities: When packaged with the NanoTrace II Oxygen Analyzer, you can easily make both oxygen and moisture measurements from a single unit.

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