AU603816B2 - Improvements in psychrometer sample chambers - Google Patents

Description

4.3. AUSTRALIA jL 60381 I RP/oo/01 I 603 816 PATENTS ACT COMPLETE

SPECIFICATION

(ORIGINAL)

FOR CFFICE USE -r cf Short Title: Int. Cl: Application Number: Lodged: Complete Specification-Lodged Accepted Lapsed Published Priority: 4 44 Related Art: 41 I I .a met~nmcn als fr Name of Applicant: Address of Applicant: Actual Inventor: Address for Service: TO BE COMPLETED BY APPLICANT NIGEL STUART BEAL 29 Kimba Street, Chapel Hill, Q. 4069 Nigel Stuart Beal 29 Kimba Street, Chapel Hill, Q. 4069 Complete Specification for the invention entitled: Improvements in psychrometer sample chamber s The following statement is a full description of this invention, including the best method of performing it known to me:- Note: The description is to be typed in double spacing, pica type face, in an area not exceeding 250 mm in depth and 160 mm in width, on tough white paper of good quality and it is to be inserted inside this form.

14599/78- L Printed by C. J. THOMPSON, Commonwealth Government Printer, Canberra 1

REFERENCES

United States Patent 3,739,629 E C Campbell FIELD OF INVENTION This invention relates to certain improvements in the design of psychrometer sample chambers used for the measurement of the moisture potential of soil and other substances.

In particular, the invention relates to psychrometer sample chambers which may be used in 10 environments in which the ambient temperature is not «o i o precisely controlled,in the laboratory or in the field.

BACKGROUND TO INVENTION Commonly, the psychrometric temperature measurements are r*r. made by means of thermocouple junctions located in the air space of the measurement chamber. The necessary 00 6 00 "wet bulb" can be achieved by peltier cooling causing condensation on at least one thermocouple junction in the measurement chamber.

AlteLnatively, as is already known, the wet bulb may be formed by the direct application of a droplet of water (or other fluid whose vapour potential is to be measured) onto the thermocouple junction, in which case Sa second thermocouple junction is usually required to -1provide the necessary "dry bulb" reference.

For the succes-ful operation of these devices, the sample substance, the internal surfaces of the sample chamber, the proximate (upper) ends of the thermocouple wires, the air in the sample chambers and the sample carrier must be as nearly as possible at the same -temperature.

Isothermal conditions are most readily and rapidly attained when there is good thermal conductivity between the'above-described elements. Such conductivity ensures that any initial temperature disequilibrium is rapidly dissipated. Good thermal conductivity also ensures that any heat flows from the exterior result in minimal temperature disequilibrium between the various o o Coo 9 elements of the device.

o 0 o In a previous psychrometric sample chamber, the o 00 oproximate (upper) ends of the thermocouple wires and intermediate connectors are attached to a subassembly within the body of the sample chamber. Sealing of the sample chamber is achieved by movement of the subassembly within the body of the chamber.

o S. The necessary sliding fit results in limited thermal conductivity between the subassembly and the remainder of the device.

The objects of this invention are to improve the *a04 thermal conductivity between the proximate (upper) ends of the thermocouple wires and the remainder of the device; to improve the thermal conductivity between the I. :i .urreir~x~ i i-i- sample carrier and the remainder of the device; to allow access to at least one thermocouple junction to allow its use as a wet loop psychrometer; and to simplify the construction of the device with consequent reduction in cost of manufacture.

THE INVENTION The invention resides in the combination of having the proximate (upper) ends of the thermocouple wire mechanically and thermally bonded to the entirety of the device body, together with the method of loading and sealing an essentially monolithic sample carrier in Oo0 the device by means of a screw thread formed on the o0 0 outside of the sample carrier.

o 0 The thermal and mechanical bonding of the thermocouple o0 wire ends may be achieved by any effective combination o Ot of mechanical or adhesive connections that will minimise the thermal resistance between the proximate (upper) ends of the thermocouple wires and the $tat remainder of the device body, whilst maintaining the 4144 S0necessary electrical isolation of the connections to at least one wire of the thermocouple wire pair or pairs.

It is necessary to the invention that the 0 sample carrier be engaged into the device by means of a screw thread formed on the outside of the sample carrier. The intimate and extensive surface area of

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contact afforded by the mating threads provides the F. I-3necessary thermal conductivity between the sample carrier and the remainder of the device.

PARTICULAR EMBODIMENT OF INVENTION A particular example of the invention is described hereunder with reference to the accompanying drawings in which:- Figure 1 is a vertical section through the centre line of the device.

Figure 2 is a plan section through the device at the level of stainless steel insert 0900 0 oo and 0 0. Figure 3 is a plan view of the sample carrier (13) and sample substance (12).

In these figures:aoo Item 1 is a solid aluminium cap piece; Item 2 is the aluminium upper body; Item 3 is the aluminium lower body; 0I Items 4 are socket head cap screws joining the lower body to the'upper body; Items 5 are the electrical lead wires which are soldered to the intermediate connectors A The lead wires pass around an anular groove in the top of the upper body before exiting from it.

Item 6 is aluminium-filled epoxy resin filling the space between the intermediate connectors and the upper body Item 7 is one of two copper intermediate connectors; Item 8 is an anular, stainless steel insert which has an interference fit within the upper body Item 9 is a polytetrafluoethylene insert which is an interference fit within the ,stainless steel insert Item 10 is a synthetic rubber 0-ring; S* c Item 11 is a thermocouple wire pair and i thermocouple junction; t Item 12 is the sample substance which fills the cavity in the top of the sample carrier (13); 1 4' Item 13 is the brass sample carrier which is threaded to mate with the the lower body The sample carrier is engaged in the lower body by means of an allen key tool which fits in the recess in the bottom of the carrier; and Items 14 are socket head cap screws which join the cap piece and the upper body /U A-N The operation required in loading a sample into the sample chamber is as follows.

The sample substance (12) is loaded into' the sample carrier (13).

The carrier (13) is fitted to the end of an allen key and screwed into the lower body of the sample chamber device and brought up against the O-ring thus sealing the chamber.

The allen key is then removed.

0 10 The electrical operation of the device is identical to previous thermocouple sample 0° I chamber devices.

0 a The intermediate connectors are a manufacturing convenience. These connectors are only an extension of the lead wires and may be dispensed with. In which case the lead wire should be directly connected with the thermocouple wires and the distal ends of the lead wires and/or the upper ends of the thermocouple wires should be thermally bonded to the device body.

The aluminium-filled epoxy resin infill is a, convenient means of providing thermal bonding -6-

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and electrical insulation between the intermediate connectors (if provided) and the body of the device.

However, other electrical insulating materials may be adopted provided the thickness of material between the connectors and the body of the device is proportioned so as to maintain good thermal conductivity through the electrical insulating material.

The polytetrafluoethylene insert is an extension of the electrical insulation surrounding the intermediate connectors and is a manufacturing convenience. The insert may be diminished or dispensed with.

r 4 t' I t ilt The stainless steel insert forms part of the inner surface of the measurement space and as such, affords a 4. 'degree of corrosion resistance. However, alternative materials may be adopted or the insert may be dispensed with, leaving the upper surface of the measurement space to be formed by the material of the upper body.

4 4 The synthetic rubber O-ring (10) is a convenient means 20 by which an air-tight seal may be effected between the sample carrier and the remainder of the measurement S space.

The device body may, for manufacturing convenience, be 'subdivided .into two or more parts and -7i t t9 te 4 S4 e t I It isI t St 4 6 4 ES which are fastened together, provided that good thermal conductivity is obtained between the various parts of the device body. The device body may be conveniently manufactured from aluminium. However, other materials, metallic or non-metallic, may be used, provided the material has good thermal conductivity.

The sample carrier (13) may be manufactured from materials other than brass provided that the material has good thermal conductivity. Alternatively, part or all of the sample carrier may be plated or coated with another material to confer a higher degree of corrosion resistance if required.

CE 1 -8- 4 r 4 it 4 44 i 4 4 44

Claims (3)

1. A thermocouple psyr-hrometer sample chamber in which the proximate (upper) ends of the thermocouple wires are rigidly and thermally bonded, either directly or through intermediate elements, to the entire body of the sample chamber; and in which a substantially monolithic sample carrier is loaded and sealed into the chamber by the operation of a screw thread formed on the outside of the sample carrier.

2. An apparatus as defined in Claim 1 in which part or the whole of the sample carrier is plated or coated with another material.

3. A thermocouple psychrometer sample chamber substantially as hereinbefore described with reference to the example and accompanying description. /VG6 S7097 S+ PP11C N7