Displacement measuring sensor

• US 4,170,897 A
• Filed: 04/22/1977
• Issued: 10/16/1979
• Est. Priority Date: 04/22/1977
• Status: Expired due to Term

• Current Assignee: Clarence O. Babcock
• Original Assignee: Clarence O. Babcock
• Inventors: Babcock, Clarence O.
• Primary Examiner(s): Ruehl, Charles A.
• Application Number:
  US05/790,013
• Time in Patent Office: 907 Days
• Field of Search: 73/88.5 R, 73/67.2, 73/517 AV, 73/DIG. 1, 73/581, 73/704, 177/210 FP, 84/199, 84/297 R, 84/297 S, 331/156
• US Class Current: 73/778
• CPC Class Codes: G01B 17/04 for measuring the deformation in a solid, e.g. by vibrating string
• CPC Class Codes: G01L 1/10 by measuring variations of frequency of stressed vibrating elements, e.g. of stressed strings using resistance strain gauges G01L1/22
• CPC Class Codes: Y10S 73/01 Vibration

Abstract

A tensioned helical wire for use as a displacement sensor. The sensor made of high strength piano wire is attached at its ends to two anchors which in turn are attached to or are a part of the object or objects to be tested. In the preferred embodiment the sensor has straight ends which are attached to two small anchor blocks. These blocks are then attached to the test object. The displacement range and sensitivity of the sensor can be controlled by the initial geometry selected. If an initial tension applied is small, the sensor has a very large response range that is about fifty times that of a straight wire sensor. If a large initial tension is applied, the helical shape approaches that of a straight sensor and has a displacement range only a few times that of a straight wire sensor. If the sensor has a large displacement range, the sensitivity is much less than that of a straight wire sensor and if the sensor has a small range the sensitivity is comparable to that of the straight wire sensor. When in place, a readout system can be used to pluck the wire sensor to determine its initial vibratory mode. Should a sensor length change occur, this can be interpreted as a displacement change by using calibration results obtained during the manufacture of the sensor or during the installation process. Subsequent readings made by the readout system can be used to measure on a continuing basis the resulting displacement behavior.

Claims

1. A displcement measuring device including a vibratory helical wire sensor for measuring the longitudinal displacement between two anchor points in the range of 1-15%, comprising:

(a) a wire coil of helical shape with at least one circular turn, said coil being made of material having a high yield stress and being provided with two ends to which a tensile stress of at least 10,000 p.s.i. is applied, said ends being made of the same wire as the coil, the displacement range of said sensor being 1-15% of said sensor length, said sensor having a flexibility of at least 3.4 times the flexibility of straight wire sensors, based on the same gage lengths and tensile forces applied,

(b) means for anchoring the ends of said sensor to said anchor points,

(c) plucking means for said wire, and

(d) means for reading a vibrational characteristic of the wire.

2. The measuring device of claim 1 wherein said wire is approximately 0.009 inch in diameter and said coil is 0.020-0.050 inch in diameter.

3. The measuring device of claim 1 wherein the coil contains a plurality of turns, and the flexibility of the sensor is in the range of 3.4-500 times the flexibility of straight wire sensors, based on the same gage lengths and tensile forces applied.

4. The measuring device of claim 1 wherein the ends of said sensor are straight and essentially colinear with each other and with the sensor length.

5. The measuring device of claim 1 wherein the ends of said sensor are circular, with said ends being engaged around pins which serve as said anchoring means, said pins being positioned in openings provided therefor in a test object the longitduinal displacement of which is to be measured.

6. The measuring device of claim 1 wherein said anchoring means connects the sensor ends to anchor points on two spaced objects the displacement between which is to be determined.

7. The measuring device of claim 1 wherein the ends of the sensor are anchored to a block formed with slots adjacent the ends of the block to which said sensor ends are crimped for measuring the longitudinal displacement of said block.

8. A method measuring the longitudinal displacement between anchor points of an object or objects to which a helical wire is fixedly secured, said measurement occurring after said sensor has been calibrated, said sensor comprising a wire coil of helical shape with at least one circular turn, said coil being made of material having a high yield stress and being provided with two ends to which a tensile stress of at least 10,000 p.s.i. is applied, said ends being made of the same wire as the coil, the displacement range of said sensor being 1-15% of said sensor length, said sensor having a flexibility of at least 3.4 times the flexibility of straight wire sensors, based on the same gage lengths and tensile forces applied, the method comprising the steps of:

(a) applying an elongation to the sensor that is within an elastic range for the calibration;

(b) fixedly anchoring the ends of the sensor with this elongation to said anchor points, the displacement between which is to be measured within the elastic range of the sensor;

(c) determining a vibratory mode that corresponds to said elongated fixed sensor, and

(d) converting the vibratory mode changes with time into corresponding displacement between said anchor points.