Measuring and testing – Instrument proving or calibrating – Fluid pressure
Patent
1997-03-24
1998-11-24
Raevis, Robert
Measuring and testing
Instrument proving or calibrating
Fluid pressure
G01L 2700
Patent
active
058410171
ABSTRACT:
In a photo-acoustic gas sensor having a measuring cell, a lamp, a photo-diode, a gas-permeable diaphragm and a microphone, a device is included for monitoring the gas-permeable diaphragm and the microphone. The device is operated in an explosion-proof manner. Intentionally, for diagnostic purposes, an artificial pressure modulation is generated in the measuring cell. The pressure modulation is converted by the microphone into electrical monitoring signals which are amplified by an amplifier circuit and assigned to preset ranges by a microprocessor, for determining the functional condition of the diaphragm and the microphone, and of microphone sensitivity. Depending on the range assigned to the monitoring signal, an output signal is generated indicating a fault in the microphone and/or the diaphragm. In the event of long-term drift in microphone sensitivity, a calibration is performed in which gas concentration values are re-calculated and stored in an EEPROM. A heater wire can be used, for modulated heating to generate the pressure modulation.
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Applied Physics Letters, Bd. 31, Nr. 11, 1, Dec. 1977, New York, US, Seiten 728-730, XP002011370. Murphy J C et al: "The Photothermophone, A Device For Absulute Calibration of Photoacoustic Spectrometers", Seite 729, linke Spalte, Zeile--rechte Spalte, Zeile 1: Abbildung 1.
Baraket Mourad
Feltre Mauro
Forster Martin
Lenggenhager Rene
Portmann Andreas
Cerberus AG
Raevis Robert
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