Measuring and testing – Volume or rate of flow – Thermal type
Patent
1990-10-31
1992-06-09
Goldstein, Herbert
Measuring and testing
Volume or rate of flow
Thermal type
7320417, G01F 168
Patent
active
051196743
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a flowmeter comprising a thermocouple and a current source for causing a temperature difference between the two junctions of the thermocouple, and wherein the thermocouple is electrically communicating with the current source through a controlled switch alternately closing and breaking a current, and wherein a control input on the controlled switch is connected to a control device also controlling a measureing circuit, which on its input port receives a signal representing the e.m.f. of the thermocouple during the periods of time where the current from the current source to the thermocouple has been interrupted by the controlled switch.
BACKGROUND ART
U.S. Pat. No. 3,485,099 discloses a fluid flow responsive apparatus comprising a thermocouple having both its junctions in the fluid, and means for periodically heating one of the junctions. An output circuit responds to the thermocouple EMF produced between the heating periods. The thermocouple EMF depends on the rate of flow of the loss of heat at the heated junction and depends thus on the rate of flow of the fluid. Similar apparatuses are disclosed in DE-A No. 1,928,228, DE-A No. 1,648,006, U.S. Pat. No. 1,996,943, and U.S. Pat. No. 4,240,441. Typically the flowmeters comprise a probe including one or two thermocouples and a heating coil and reference means connected through a cable to associated electronic equipment including a current source, a control means, switching means, and measuring means.
Especially the medical industry presents a demand for very small probes and connecting cables to the flowmeters. All the known systems require several electrically conducting wires between the probe of the flowmeter and the associated electronic. Typically eight conductors are used in a connecting cable between a probe and the electronic equipment, as the heating coil, a reference means, and an active sensor all need connections including connections to the ground. In addition a demand has arisen for a diminution and preferably a complete omission of a supply of heat.
DISCLOSURE OF INVENTION
The object of the present invention is to provide a flowmeter comprising a particularly small probe with only two electrical conductors, and in particular a probe capable of measuring the blood flow in the cardiovascular system.
The flowmeter according to the invention is characterised in that the current source and the hot and the cold junction of said thermocouple all are connectable in series by the control device through the same two conductors also connected to the measuring circuit, and wherein the current source is a dc-source.
Due to the Seeback-effect the thermocouple acts per se as both a heating and a cooling member because one junction of the thermocouple is heated by the dc-current from the current source simultaneously with the other junction of said thermocouple being correspondingly cooled, whereby a temperature difference between the two junctions develops. During the periods of time where the controlled switch has interrupted the current from the current source, the thermocouple supplies a voltage representing the temperature difference caused. As the resulting temperature difference simultaneously depends on the flow velocity in the surroundings of the thermocouple, the output voltage of the thermocouple can be used for determining the flow velocity. The controlled switch renders it possible to use the same two wires for the supply of dc-current and consequently for the heating of the thermocouple as well as while the switch is interrupted for transferring the measurement signal. In this manner a probe with only two electrical conductors is obtained which allows production of a very small probe. An additional advantage of the above probe is that the net supply of heat to the observed fluid is zero.
According to a preferred embodiment of the invention the measuring circuit comprises an amplifier and/or a sample and hold circuit, and that the control device is a timer circuit.
According to a second emb
REFERENCES:
patent: 1996943 (1929-12-01), Wile
patent: 2540822 (1951-02-01), Hastings
patent: 2745283 (1956-05-01), Hastings
patent: 3485099 (1969-12-01), Collins
patent: 3564916 (1971-02-01), Collins
patent: 4240441 (1980-12-01), Khalil
patent: 4848147 (1989-07-01), Bailey et al.
LandOfFree
Flowmeter does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Flowmeter, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Flowmeter will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1796543