Moisture measuring apparatus

• US 4,655,076 A
• Filed: 01/23/1984
• Issued: 04/07/1987
• Est. Priority Date: 01/23/1984
• Status: Expired due to Term

• Current Assignee: Tyco Electronics Corporation (TE Connectivity Ltd. (United Kingdom))
• Original Assignee: Raychem Limited (TE Connectivity Limited)
• Inventors: Lion, Roger D., Weihe, Gary R.
• Primary Examiner(s): Frankfort, Charles
• Assistant Examiner(s): Will, Thomas B.
• Application Number:
  US06/573,230
• Time in Patent Office: 1,170 Days
• Field of Search: 73/73, 73/76, 73/337, 340/602, 340/604, 340/620, 239/63
• US Class Current: 73/73
• CPC Class Codes: G01N 19/10 Measuring moisture content, e.g. by measuring change in length of hygroscopic filament; Hygrometers

Abstract

An apparatus for measuring the moisture content of soil includes a chamber having a water-swellable material in the chamber, the chamber being sized so that the water-swellable material can swell to its fully swollen state, with the external resistance, if any, against the swelling being substantially constant. The device includes a device for transmitting water to the water-swellable material so that it is in equilibrium with the environment. A sensor responsive to the volume of the water-swellable material is provided to indicate the water content of the environment exterior of the apparatus. The preferred sensor is a magnet moveable by the water-swellable material and a Hall effect sensing device.

Claims

1. An apparatus for measuring humidity comprising:

(a) a rigid, porous, cylindrical substrate, the substrate being capable of passing water therethrough;

(b) a tube of water-swellable polymer in contact with the cylindrical substrate, the water-swellable polymer having a fully swollen volume when in its fully swollen state in equilibrium with water at least about 2 times its dry volume, said tube and substrate being substantially completely contained in a chamber, the volume of the chamber being sufficiently large to accomodate the tube in its fully swollen state; and

(c) sensing means responsive to the volume of the water-swellable polymer for producing a signal that varies with the water content of the environment exterior to the chamber.

2. The apparatus of claim 1 in which the substrate is a porous ceramic material.

3. The apparatus of claim 1 in which the substrate is tubular.

4. The apparatus of claim 3 including a water wicking material in the interior of the tubular substrate.

5. The apparatus of claim 1 wherein (a), (b) and (c) are arranged such that the external resistance, if any, to swelling of the water-swellable polymer remains substantially constant as the water-swellable polymer swells to its fully swollen state.

6. The apparatus of claim 1 including sensing means responsive to the volume of the water-swellable polymer for producing a signal proportional to the water content of the environment around the water-swellable polymer.

7. The apparatus of claim 1 which the water-swellable polymer is shrunk into contact with the cylindrical substrate.