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Establishment of the Encoded Photometric (EP-IR) Spectrometer's Ability to Detect the Lowest Possible Level of Moisture

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Figure 1: Calibration Fitting

Figure 2: Calibration Linearity

Problem Statement

The race for a system that can detect the lowest possible level of moisture is seemingly everlasting. As the race continues we have begun to explore the options of using an EP-IR spectrometer coupled with DID Photonics Integrated IR Source 4 Runner.

Experimental Equipment

The EP-IR spectrometer is vibration insensitive and runs on the basis of an encoded disk with 128 channels. The spectrograph used in the spectrometer is a compact short path that operates on a TE cooled detector in the mid IR range. The integrated IR Source 4Runner used for the experiment has a 6m path length, is constructed of stainless steel, has laminar gas flow, and a high energy throughput of about 40%. For more information regarding the system used to conduct this experiment, please refer to the CIC Photonics specification sheet for the EP-IRGAS LPA. For information solely on the EP-IR spectrometer, please contact Aspectrics (manufacturer of the EP-IR spectrometer).

EP_IRGAS LPA Experiment

To ensure that moisture from the atmosphere is not permeating through to the cell and skewing the true moisture levels being produced by the moisture generator, the system was set up in a cabinet enclosure and was purged for over three days prior to beginning experiments.

A calibration was generated using the Aspectrics Chemobuilder software program. The software is designed to generate and validate calibrations files that function on the quantification algorithm based on the PCR (principle components regression) method. Chemobuilder can automatically calculate PCR parameters based on calibrated spectra.

The data used to create the calibration were collected in three concentration increments (1.4ppm, 2.8ppm, 0.713ppm). The graph in Figure 1 shows the calibration fitting of the calibrated spectrum. It can be seen that the data is fitting quite well to the calibration generated based on the initial points collected from the system.


The EP-IRGAS LPA offers a feasible solution for moisture detection of 75ppb. This sensitivity correlates to an average standard error of 50ppb and an integration time of 20 minutes.

Figure 2 depicts the calibration linearity of these parameters for the EP-IRGAS LPA. It demonstrates that the average concentrations for each of the three sets of runs were linear, and that they were remaining fairly close to the target concentrations.

It must be noted that with an integration tie of 40 seconds the moisture sensitivity decreases to about 500ppb with a standard error of around 240ppb.

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