Mining Publication: A Second-Generation Remote Optical Methanometer
The theory of operation of second generation remote optical methanometer (ROM) and initial testing of the new prototype were described. The ROM operated on the principle of differential absorption of a fundamental absorption band of methane (74828) centered at 3.31 micrometers in the infrared region of the spectrum. In comparison to the previous prototypes, the new instrument replaced the two band pass differential absorption technique of measurement with a single filter gas correlation technique and a refinement of the amplifier and gating circuitry used within the unit. The results were a more accurate isolation of the methane spectral absorption band studied. A specially designed 0.4 meter diameter variable length gas mixing tunnel was constructed and instrumented with methane sampling capability to calibrate the ROM. Experiments demonstrated the ability of the detector to respond to various conditions of methane at distances as great as 12 meters. Thermal radiation generated within the instrument is the controlling factor in the drift of the output signal and therefore the reliability of the instrument. Several approaches to reduce the extraneous radiation interfering with the infrared detector were described, including the installation of a fan in the instrument and thermoelectric coolers on the detector's heat sink. The authors conclude that implementing this technology may significantly improve the safety of miners.