Measuring and testing – Gas analysis
Reexamination Certificate
1999-07-01
2001-09-18
Williams, Hezron (Department: 2856)
Measuring and testing
Gas analysis
C073S001060
Reexamination Certificate
active
06289718
ABSTRACT:
BACKGROUND OF THE INVENTION
U.S. Pat. No. 4,833,909 discloses an apparatus for detecting a gaseous componet in air. The apparatus includes a measuring chamber through which a throughflow can take place from a gas inlet to a gas outlet. The gas sample to be investigated is guided through a sample intake line to the gas inlet of the measuring chamber. A pressure is built up in the sample intake line at the inflow end by means of a throttle and this pressure is detected by a pressure sensor. The pressure measurement signal supplied by the pressure sensor is an index for the velocity of the gas flow within the gas sample intake line. A value proportional to the gas volume can be determined by a time integration of the pressure measurement signal.
Arrangements are known wherein a measurement value is needed for calibration purposes and this measurement value is proportional to the ambient pressure. Test gases from pressure cylinders are used for the calibration and these test gases are fed into the measuring apparatus to be checked. Generally, the test gas concentration is indicated in ppm or volume percent on the pressure cylinders and the test gas concentration is thereby independent of pressure. The concentration indication on the pressure cylinders and the value supplied by the measurement apparatus are only coincident for the ambient pressure at which the measuring apparatus was adjusted with this test gas. With changes of the ambient pressure, a difference arises which must be corrected. An arrangement for correcting the ambient pressure influence is disclosed in U.S. Pat. No. 5,400,637.
SUMMARY OF THE INVENTION
It is an object of the invention to improve an arrangement of the kind described above so that a sample intake line can be detected wherein there is no flow.
The arrangement of the invention is for detecting a gaseous component in a gas flow. The arrangement includes: a measuring chamber wherein the gaseous component of the gas flow is measured; a sample intake line for conducting the gas flow into the measuring chamber; a flow throttle mounted in the intake line; a pressure sensor for detecting the pressure in the sample intake line upstream of the flow throttle and for generating a pressure measurement signal indicative of the pressure in the sample intake line; and, a flow detector mounted along the sample intake line for generating a zero signal when there is a nonflow in the sample intake pipe and a nonzero signal when there is a gas flow in the sample intake line.
The advantage of the invention is essentially that a static gas flow can be detected with the flow detector mounted in the sample intake line and the pressure sensor, which is present, can be used to detect the velocity of the gas flow within the sample intake line as well as to determine the absolute ambient pressure.
The flow detector is advantageously configured as a hot wire anemometer. The cooling of the hot wire is an index for the presence of a gas flow. As an alternative to a hot wire anemometer, a measuring system can be used wherein a flexible tongue is deflected which is located in the gas flow.
It is especially advantageous to use a switching device which is operatively connected to the flow detector. With this switching device, a switching connection to a first evaluation path is established when a flow zero signal is present. The evaluation path forms, from the pressure measurement signal, a first pressure signal, which is proportional to the ambient pressure. Insofar as the flow detector supplies a value other than zero, a switching connection to a second evaluation path is established by the switchover device. The second evaluation path then determines, from the pressure measurement signal, a quantity proportional to the velocity of the gas flow in the sample intake line. The switchover device and the evaluation paths can be configured as discrete components or even in the form of software modules in a microprocessor.
The arrangement according to the invention is especially advantageous as a breath alcohol measuring apparatus wherein a calibration with a test gas mixture must be carried out at specific intervals.
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Drager Sicherheitstechnik GmbH
Garber Charles D.
Ottesen Walter
Williams Hezron
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