Measuring and testing – Instrument proving or calibrating – Volume of flow – speed of flow – volume rate of flow – or mass...
Patent
1995-09-11
1997-03-25
Raevis, Robert
Measuring and testing
Instrument proving or calibrating
Volume of flow, speed of flow, volume rate of flow, or mass...
F16K 1900
Patent
active
056146558
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a gas mixing devices in general and more particularly to improved apparatus for calibrating gas analyzers comprised of a plurality of critical nozzles which have their outputs connected to a mixing chamber.
Known gas mixing devices, also called gas distributors, use eleven or eight critical nozzles to obtain eleven or seventeen different concentrations or selectively variable proportions. At a specific input gas pressure, because of a special shaping of their outlet ports, these nozzles provide a constant gas passage that remains dependent only on the opening cross-section. Nozzles of this type require precision manufacturing and exact measuring.
Because of this last requirement there is a need to increase the ratio between the number of selectively variable proportions and the number of critical nozzles required for this purpose, so that one can make do with a smaller number of critical nozzles.
SUMMARY OF THE INVENTION
This need is fulfilled in accordance with the present invention by providing a plurality of critical nozzles having their outputs connected to a mixing chamber with the cross-sections of each critical nozzles increasing in the proportion of 1:2 from one to the next, and permitting each critical nozzle to receive either a test gas or a zero gas.
The present invention makes it possible to reduce the number of required critical nozzles at least by half and to give the gas mixing device a considerably more compact design.
In accordance with the illustrated embodiment a valve having two inlets capable of being alternatively opened is placed upstream from each critical nozzle. A remotely controllable, electromagnetic actuation of the valves is provided. The valves may be provided with a position transducer. In the illustrated embodiment, four nozzles, whose cross-sections are in proportions of 1:2:4:8, are provided. The nozzle with the largest cross-section is arranged opposite the output of the mixing chamber. Furthermore, as illustrated, a microprocessor is provided as a control computer to activate the valves, as well as to monitor and regulate the gas pressures. The microprocessor is provided with a communication line leading to a host computer superordinate to said microprocessor.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a gas mixing device in an arrangement for the computer-supported calibration of a gas analyzer.
FIG. 2 is a block diagram of the gas mixing device according to the present invention.
DETAILED DESCRIPTION
In FIG. 1 a gas mixing device or distributor 1, which is integrated in a generally known arrangement for the computer-supported calibration of a gas analyzer 2 is shown. A so-called zero gas N, also denoted as carrier gas or diluent gas, as well as the test gas P, also called a calibration gas, are supplied via piping to the gas mixing device. The gas distributor 1 and the gas analyzer 2 each have an interface, as a rule a serial interface, together with corresponding communication lines K1 or K2 leading to a host computer 3. The gas analyzer 2 is calibrated by means of a program, which is loaded in the working storage of the computer 3 and which prescribes to the gas distributor 1 discrete concentrations of test gas and zero gas, one after another, for the gas mixture G to be supplied to the analyzer 2. Then, for every adjustment of the gas mixture, it logs the concentration value measured by the analyzer 2. The purpose of such a calibration is determining the correlation valid for a given measuring device between the measured value specified by it and the correct value of the measurable parameter, which is adjusted as a standard measure by means of the gas distributor 1.
In the block diagram of the gas distributor according to the present invention in accordance with FIG. 2, a mixing chamber 4 is shown, in which the gas streams flowing through the nozzles D1, D2, D4 and D8 mix and emerge as a gas mixture G out of the gas distributor 1. The nozzles D1 through D8 are supposed to be so-called critical
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AMEC AG Wangen, Switzerland, Comtomer Information, May 14, 1987.
Technisches Messen 59 (1992) 2, R. Oldenbourg Verlag: Rechnergest utzte Kalibrierung von Gasanalyseger aten (Computer-aided Calibration of Gas Analyers), A. Slemeyer et al.
Raevis Robert
Siemens Aktiengesellschaft
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