Servomex’s DF-700 moisture analyzer series uses Tunable Diode Laser Spectroscopy (TDL) technology to measure trace moisture in pure gases. A spectroscopic technique that uses a diode laser as its light source, Servomex’s TDL moisture technology has a robust and simple optical design, with the sample and reference measured with a single laser source and a single detector.
TDL has advantages over other measurement techniques as the moisture sample comes only into contact with a few optical components 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 ever require calibration.
In spectroscopy, a longer path length is one way to achieve more sensitivity. In order to make a sensitive laser measurement, Servomex employs a Herriott Cell to reflect the laser back and forth numerous times, using mirrors inside the measuring cell. By making multiple passes, this increases the laser path length to achieve extremely high sensitivity.
The result is an exceptional performance capable of measuring down to sub-ppb levels, as low as an industry leading 75ppt LDL. In addition, TDL moisture sensing offers drift-free operation, high accuracy and low maintenance, achieved through self-correcting optics and laser line locking onto the water peak, removing all possibility of significant drift.