Measuring and testing – Volume or rate of flow – By measuring electrical or magnetic properties
Patent
1997-06-06
1999-05-25
Chilcot, Richard
Measuring and testing
Volume or rate of flow
By measuring electrical or magnetic properties
G01F 160
Patent
active
059071036
ABSTRACT:
Instrumentation amplifier arrangements (10, 10') of electromagnetic flowmeters are disclosed which permit reliable conditioning of the measuring-electrode signals without an increase in coil current even if solids-loaded fluids are measured. The flowmeter has a measuring tube (1) with at least two measuring electrodes (3, 2) and a ground electrode (4) as well as a coil arrangement (5) for producing a magnetic field. A first variant of the instrumentation amplifier arrangement comprises two preamplifiers (11, 12) each connected to a respective one of the two measuring electrodes (3, 2) and followed by a respective ana-log-to-digital converter (13, 14). A clock generator (18) supplies the analog-to-digital converters (13, 14) with a sampling signal whose frequency is greater than approximately 1 kHz. The analog-to-digital converters (13, 14) are followed by a subtractor (17). A second variant comprises two preamplifiers (11', 12') each connected to a respective one of the two measuring electrodes, an analog-to-digital converter (13') connected directly to the output of one (11') of the preamplifiers (11', 12'), a differential stage (19) following the preamplifiers, and an analog-to-digital converter (20) following the differential stage (19). The analog-to-digital converters (13', 20) are followed by a subtractor (17').
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Sanderson, M.L., Principles and Practice of Electromagnetic Flow Measurement, Mar., 1991, 1207a Journal A, Antwerp, Belgium, pp. 19-26.
Chilcot Richard
Endress & Hauser Flowtec AG
Thompson Jewel
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