Measuring and testing – Volume or rate of flow – System
Patent
1995-05-02
1999-02-09
Chilcot, Richard
Measuring and testing
Volume or rate of flow
System
7320411, G01F 700
Patent
active
058697586
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to the measurement of the flow rate of a medium flowing through a channel, more particularly, to a method and apparatus for measuring flow rate utilizing a number of measurement sites in the channel and measuring the temperature of the liquid at the measurement site to determine the flow rate based on a predetermined rule.
DESCRIPTION OF THE PRIOR ART
A method of the above mentioned type is disclosed by EP-A-0269823. This prior art document does not disclose the type of sensor or detection means used. The detection means is connected in a voltage divider. During second periods a measuring current is fed through the whole voltage divider and from a node of the voltage divider a signal is derived which represents an electrical parameter which is dependent on the temperature of the detection means. This signal is supplied to a number of comparators, which each receive in addition a different threshold voltage. The threshold voltages are selected in advance such that they are related in a specific manner according to one or more equations, a number of which being dependent on the number of comparators, and dependent on a supposed exponential development of the cooling of the detection means. Starting at the beginning of each second period each comparator will therefore provide a pulse and the pulses from the comparators will have different durations. From the times between trailing edges of said pulses, which times each correspond to a specific temperature of the detection means, a flow rate value is determined. Though the document discloses the use of several detection means with identical or different characteristics, the document does not disclose anything about the locations of the detection means and nothing about the flow characteristics at said locations.
DE-A-3210888 discloses a method for measuring the flow rate of a medium, which includes the use of a flow channel having measurement sites with different flow velocities for any flow rate at a time. At each measurement site a heat supply member is arranged and a small distance downstream therefrom a temperature sensor is arranged. The heat supply members are suitable to transfer heat from it to the medium in response to an electric current pulse received from a pulse generator. The time which elapses between feeding a heating current pulse to a heat supply member of a measuring site and the receiving of a measurement signal from the temperature sensor of the site is a measure used for determining a flow rate value. The different measurement sites with different flow velocities are used to select a measurement of the flow rate with the highest accuracy.
US-A-4653321 discloses a method for measuring the flow rate of a medium including the use of at least two flow channels of different sizes, each containing a thermally sensitive resistance element, such as a thermistor. Each flow channel is provided with an orifice which is important for accurate correlation and measurement because the orifice reduces the sensitivity of the calibration of the system to variances in the system. The temperature sensor in each channel is positioned just downstream of the orifice. Some flow channels are provided with valves which are electrically connected to and operated by an electronic controller. The output of a sensor is supplied to an associated bridge circuit, which then supply the electronic controller with the desired flow rate information or with electrical information from which that information can be calculated by the electronic controller. Dependent on the flow rate the electronic controller opens or closes one or more of the valves to provide a wide measurement range of flow rates. Each bridge is connected to a differential amplifier, of which the output is connected to a supply node of the bridge thus providing feed back to the bridge. The sensor continuously receives an electrical current from the output of the amplifier. Said current is dependent on the temperature of the sensor, which temperature is
REFERENCES:
patent: 4483200 (1984-11-01), Togawa et al.
patent: 4653321 (1987-03-01), Cunningham
patent: 4770037 (1988-09-01), Noir et al.
patent: 4821568 (1989-04-01), Kiske
patent: 4969357 (1990-11-01), Mickler
patent: 5460040 (1995-10-01), Tada et al.
Jan. 1984 NTS Tech. Notes.
Artis Jewel V.
Chilcot Richard
GAScontrol b.v.
Jaskiewicz Edmund M.
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