Kathryn M Howard

US Patent:

55023800, Mar 26, 1996

Filed:

Apr 28, 1994

Appl. No.:

8/234182

Inventors:

Fred C. Sittler - Victoria MN
Kathryn M. Howard - Chanhassen MN

Assignee:

Rosemount Inc. - Eden Prairie MN

International Classification:

G01B 714
G01R 3306
H03M 122
G01D 534

US Classification:

32420721

Abstract:

A magnet mounted on a moving stem or rotary member of a valve generates magnetic flux over part of a stationary member of the valve which has an uniquely patterned set of magnetoresistive sense resistors and three reference resistors (the sensor) disposed thereon. The distance between two adjacent patterns can be equally spaced, or can be compressed for valves with non-linear characteristics in order to achieve increased resolution over a specific portion of the valve travel. Other embodiments can use a light source, beta radiation or neutron radiation as the source of flux, the pattern for each embodiment's sensor having some material responsive and some unresponsive to the flux. The sensor can provide feedback representative of position in a valve positioner, or functions as the position sensor in a position transmitter. Reference resistors provide a first signal representative of the resistance of a sense resistor in the absence of the flux and a second signal representative of the additive resistance of a sense resistor which is caused by the flux. An A/D circuit connected to the sense resistors differences the sensed resistance of each sense resistor with the first signal to calculate a referenced additive resistance and then ratios the difference with the second signal, weights the ratio by an appropriate weighting function and sums the referenced additive resistance for each of the sense resistors to provide the position sensor output.