This invention relates generally to the field of thermometry, and more particularly therein to methodologies and apparatuses for calibration of temperature sensing devices by comparison method.
Specifically, an isolated embodiment of the present invention disclosed in this paper outlines the construction and operation of an inventive system including an isothermal chamber in which stable reference temperatures are provisioned whereby a master thermocouple may be accurately maintained for comparative calibration of another thermocouple or like temperature sensing device.
Definitions and interpretations
Before undertaking the detailed description of the invention below, it may be advantageous to set forth definitions of certain words or phrases used throughout this patent document: the terms "include" and "comprise," as well as derivatives thereof, mean inclusion without limitation; the term "or" is inclusive, meaning and/or; the phrases "associated with" and "associated therewith," as well as derivatives thereof, may mean to include, be included within, interconnect, with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term "PRT" refers platinum resistance thermometer; "RTD" refers resistance temperature detector; "ISO" refers International Organization for Standardization; "Ml" refers Mineral Insulated heating element; "UUC" refers Unit which is the temperature sensor under calibration; "MCB: refers miniature circuit breaker.

Background of the invention and description of related art
It is a well known fact that critical capacity of all temperature sensing devices inevitably alters with increasing age of components and equipment, mechanical strains occasioned by usage, changes in atmosphere of the working environment and so on. This is termed as drift, which squarely affects both accuracy and precision of the temperature sensing devices and hence makes research or production processes error-prone. Replacement of said temperature sensing devices is not an option as it only adds to costs and integration overages. It would therefore be advantageous to have some means of correction or offset bias which allows long-term accurate temperature measurement using existing temperature sensing devices.
Industry today is imposed with aggravated and stringent demands with respect to measuring accuracy and quality assurance as per statutory manufacturing and process standards such as ISO and so on. For this, it is decisive that any temperature sensing devices implemented are maintained for impeccable as well as reproducible measurement of temperature.
Scheduled re-calibration of existing temperature sensing devices is the only solution to the issue voiced above, for which it is extremely critical to have very accurate yet cost-effective methodologies and their implementing apparatuses for calibration of said temperature sensing devices. To put simply, re-calibration of any temperature sensing device involves comparing it to a known standard preferably maintained by certified laboratories according to national and international standards. It would be hence desirable to have some means for re-calibration of existing temperature sensing devices which can be procured by the industry instead of arranging logistics of said temperature sensing devices to and fro from said certified laboratories.
Prior art, to the extent surveyed, lists some scattered attempts to address the issues mentioned hereinabove. For example, dry-block calibrators which typically include an enclosure in which means for altering temperature are housed around an elongated cavity in which the temperature sensing devices may be received for calibration. Liquid-based temperature calibrators are equally popular, the operations of which are based on having a recess or bath filled with a liquid which serves for immersion of the temperature sensing devices may be received for calibration.

Examples of prior art temperature calibrators working on either of the technologies referred in the preceding paragraph may be observed in US2299867A (assigned to Western Electric Co Inc), US6709152B1 (issued to Ole Einar Bronlund), FR2590981A1 (assigned to Electricite De France), US3370454A (assigned to Tenney Engineering Inc). However, the apparatuses disclosed in these references tend to be heavy, space-demanding, and expensive besides not lending favorably to portable use, besides enjoining the following drawbacks-
In case of liquid bath calibrators-Continuous agitation is needed for homogeneous temperature distribution Immersion liquid has to be changed for different temperature ranges Immersion liquid bath is prone to spills which can be extremely damaging, especially at high temperatures
Immersion liquid needs to be removed from the system and separately transported or procured locally at site of use of the system
In case of dry block calibrators-Heat transfer is slow and inefficient at times due to dependency on natural convection, resulting in temperature differences at different depths in the bore for receiving the temperature sensor to be calibrated
Sensitive to varying thermal capacity in the temperature sensors to be calibrated
Requires repeated and through cleaning of block and bore for optimal performance
Mandates a large mass and weight in the calibrator block, besides also a liner filled with temperature conductive contacting fluid.
Thus, the need to have improved temperature calibrating systems yet survives. State-of-art therefore, does not list a single effective solution embracing all considerations mentioned hereinabove, thus preserving an acute necessity-to-invent for the present inventor/s who, as result of focused research, has come up with novel solutions for resolving all needs once and for all. Work of the presently named inventor/s, specifically directed against the technical problems recited hereinabove and currently part of the public domain including earlier filed patent applications, is neither expressly nor impliedly admitted as prior art against the present disclosures.

A better understanding of the objects, advantages, features, properties and relationships of the present invention will be obtained from the following detailed description which sets forth an illustrative yet-preferred embodiment.
Objectives of the present invention
The present invention is identified in addressing at least all major deficiencies of art discussed in the foregoing section by effectively addressing the objectives stated under, of which:
It is a primary objective to provide a standard temperature reference system which provides very stable temperature nearing to its controlled / configured point against which temperature sensing systems / devices can be calibrated.
It is another objective further to the aforesaid objective(s) that the standard temperature reference system so provided allows precise electronic or digital control for quick regulation over desired reference temperature achieved and maintained within said system.
It is another objective further to the aforesaid objective(s) that the standard temperature reference system so provided requires minimal time for reaching working temperatures.
It is another objective further to the aforesaid objective(s) that the standard temperature reference system so provided is capable of working with different liquid media.
It is another objective further to the aforesaid objective(s) that the standard temperature reference system so provided is robust, portable but not unduly bulky, technically complex, or expensive.
It is another objective further to the aforesaid objective(s) that the standard temperature reference system so provided is not space demanding and expensive to procure and operate nor has an overt energy demand.

It is another objective further to the aforesaid objective(s) that the standard temperature reference system so provided has marked simplicity and no environmental impact even across long term use.
5 It is another objective further to the aforesaid objective(s) that the standard temperature reference system so provided is easy to operate, and requires minimal if not none, involvement or skills on part of the user.
The manner in which the above objectives are achieved, together with other objects 10 and advantages which will become subsequently apparent, reside in the detailed description set forth below in reference to the accompanying drawings and furthermore specifically outlined in the independent claims. Other advantageous embodiments of the invention are specified in the dependent claims.
15 Summary / Statement of the present invention
The following simplified summary provides a basic overview of some aspects of the present technology. This summary is not an extensive overview. It is not intended to identify key or critical elements or to delineate the scope of this technology. This Summary is not intended to be used as an aid in determining the scope of the
20 claimed subject matter. Its purpose is to present some simplified concepts related to the technology before the more detailed description presented below.
For the achievement of the above-mentioned objectives, the present invention is directed at establishment of a relatively portable, inexpensive yet efficient apparatus
25 for calibration of temperature sensing devices, which has extended field of use by allowing a user to calibrate a wide spectrum of temperature sensors. An improved liquid bath calibrator is disclosed herein in which characteristically, methanol is used as the immersion liquid, and a PT-100 RTD is employed for controlling temperature. Required reference temperature is provisioned with combinatorial action of a MI
30 heater element power to which is varied via a solid-state relay, and an electric fan disposed under the heating chamber for cooling the heater. A PID controller is employed for precise maintenance of required reference temperature. A cascade (agitated) compressed refrigerant gas system is provided for removal of excess heat from the system.
35
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Attention of the reader is now requested to the drawings and detailed description to follow which narrate a preferred embodiment of the present invention and such other ways in which principles of the invention may be employed without parting from the essence of the invention claimed herein. 5
Brief description of drawings
The present invention is described below in connection with an exemplary
embodiment with reference to the accompanying drawings, wherein:
10 FIGURE 1 is a photograph of the liquid bath temperature calibrator system of the present invention.
FIGURE 2 is a schematic representation of mechanical assembly of components constituting the liquid bath temperature calibrator system of FIGURE 1. 15
FIGURE 3 is a schematic representation of electrical assembly of components constituting the liquid bath temperature calibrator system of FIGURE 1.
FIGURE 4 is a block diagram showing electrical interface of the liquid bath 20 temperature calibrator system of FIGURE 1.
FIGURE 5 is a screenshot of a computer screen showing the software-implemented user interface including a graph plot area for visualization of the user while using the liquid bath temperature calibrator system of FIGURE 1. 25
FIGURE 6 is an inset of the screenshot at FIGURE 5 showing a field index to be filled in by the user to connect the liquid bath temperature calibrator system of FIGURE 1 to a computer, and thereby being ready for use.
30 FIGURE 7 is an inset of the screenshot at FIGURE 5 showing another field index to be filled in by the user to initialize the liquid bath temperature calibrator system of FIGURE 1 for use.
FIGURE 8 is a graph showing a plot of temperature versus time, as arranged during 35 operations of the liquid bath temperature calibrator system of FIGURE 1.
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FIGURE 9 is an exploded schematic representation of the assembly of components constituting the liquid bath temperature calibrator system of FIGURE 1.
FIGURE 10 is a right-side cross sectional view of the liquid bath temperature 5 calibrator system of FIGURE 1.
FIGURE 11 is a left-side cross sectional view of the liquid bath temperature calibrator system of FIGURE 1.
10 FIGURE 12 is a photograph of the heating chamber included in the liquid bath temperature calibrator system of FIGURE 1.
FIGURE 13 is a cross sectional view of the heating / working chamber of the liquid bath temperature calibrator system of FIGURE 1. 15
FIGURE 14 is a schematic representation of connections of the RTD at controller port as per assembly shown in FIGURE 2 and FIGURE 3.
FIGURE 15 is a photograph showing connections of the RTD at controller port as per 20 assembly shown in FIGURE 2 and FIGURE 3.
FIGURE 16 is a schematic representation of the filter / drier assembly with capillary system included in the liquid bath temperature calibrator system of FIGURE 1.
25 FIGURE 17 is a circuit diagram showing cascade connection for refrigerant calibration included in the liquid bath temperature calibrator system of FIGURE 1.
The above drawings are illustrative of particular examples of the present invention but are not intended to limit the scope thereof. The drawings are not to scale (unless so 30 stated) and are intended for use solely in conjunction with their explanations in the following detailed description. In above drawings, wherever possible, the same references and symbols have been used throughout to refer to the same or similar parts.
35 Though numbering has been introduced to demarcate reference to specific components in relation to such references being made in different sections of this
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specification, all components are not shown or numbered in each drawing to avoid obscuring the invention proposed.
Detailed description 5 Principally, general purpose of the present invention is to assess disabilities and shortcomings inherent to known systems comprising state of the art and develop new systems incorporating all available advantages of known art and none of its disadvantages.
10 Accordingly, the disclosures herein are directed towards achievement of an effective liquid bath temperature calibrator system having an isothermal enclosure with a controlled temperature-stable liquid bath that may be used advantageously over dry block furnaces as a standard temperature reference, and so thereby as a calibration system for temperature sensing devices such as resistance thermometers to calibrate
15 thermocouple (contact type sensors) against a master sensor RTD within the range of -80 to 50 °C.
The invention recited herein discloses nuances including construction and operation of a system designed for allowing precise temperature calibration of a resistance 20 thermometer by comparison to a master resistance thermometer maintained in an isothermal enclosure housing a controlled temperature-stable liquid bath.
Construction of the liquid bath temperature calibrator system proposed herein is intended to encompass various embodiments, among which a few are explained 25 below with reference to certain examples that illustrate generically the manner in which principles of the present invention may be employed. The accompanying FIGURE 1 is a photograph showing external front-side view of the liquid bath temperature calibrator system.
30 Mechanical and electrical connections of the internal assembly of the liquid bath temperature calibrator system shown at FIGURE 1 are depicted at FIGURE 2 and FIGURE 3 respectively. FIGURE 9 is an exploded view, and FIGURES 10 and 11 further are left and right side cross sectional views of the assembly comprising the liquid bath temperature calibrator system proposed herein. As seen from these
35 drawings, the liquid bath temperature calibrator system proposed herein comprises
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an inner chamber, and an outer chamber, and furthermore the components listed at Table 1 below.

Component Make / Technical Specifications
1) Compressors (1) and (2) Emersion make/ COMPRESSOR MODEL: KCN422LAL-B330H.; Voltage 230 V,50 Hz,1 Phase
2) Condenser 14''X14''X 4 ROW.
3) Heat exchanger Product Type: BL14 8601015320PP,MAX Design Temperature: -195/200,
4) Copper coils 3/8 inch
5) Drier Eliminator Filter Drier, Model NO:023Z5035, Max. Working Pressure [bar] 46 bar, Inlet connection size [mm]:6 mm, Net volume [l] 0.051 L
6) Filter / drier Eliminator Filter Drier, Model NO:023Z5035, TYPE: DML-032 Weight: 0.2 Kg
7) Heating chamber 200(H)X325(W)X162(D)
8) Sub zero meter Sub Zero Meter,Model No: Sz-7510-P, Relay 8(3) A / 250V AC
9) Axial Fan Axial Fan Rexnord Make, Model NO: REC-4E-300, 230V AC
10) Rectifier Bridge Rectifier (O/P=12 VDC)
11) Refrigerant R-23, R-404
12) MCB MCB 25 Ampere Double Pole
13) DC motor P.M. D.C Motor Microtech Make Watt-20 Dcv-12 Speed-1500 Rpm
14) Transformer Transformer 30 VA, 230 TO 12 V CONTROL
15) SSR SSR, make-unison, model-(801 ZDA 48 5001) (50 Amp); INPUT (4-32 VDC) (4-16 mA) (INSUL 4KV, PIV 1200) OUTPUT 24-480 VAC
5 Table 1
Accordingly, it follows that above mentioned components are assembled in a final form embodying the liquid bath temperature calibrator system identified in comprising at the outset, a hollow cylindrical container (shown in FIGURE 12) of a suitable
Page 10 of 39

material, for example stainless steel is provided for serving as an as an isothermal chamber therein defining a temperature-controlled bath of the liquid in which the master / reference PT-100 RTD and a UUC can be immersed for comparative calibration according to the protocol mentioned later in this paper. The working 5 chamber / container shown at FIGURE 12 is of sufficient depth so as to allow proper thermal contact between the temperature sensors, and methanol (homogenous bath, in which methanol is made to circulate in said chamber continuously). Working chamber is placed in the liquid bath. The master / reference RTD serves to sense temperature of the working chamber and give output to controller as will be described 10 later in this document.
According to another aspect of the present invention explained herein with general reference to the accompanying FIGURES 2, 3, 9, and 17, the liquid bath temperature calibrator system proposed herein includes a heating chamber wherein an MI heating
15 element is disposed for heating contents (liquid) of the container. A solid-state relay is used for controlling power to said heating element. For dissipation of heat from the heating chamber, an electric axial fan is provided in proximity of the heating chamber, particularly behind the condenser (to be described later in this document) for serving as an exhaust for heat, thereby cooling the heating chamber.
20
Additionally, the heating chamber is jacketed with a vapour compression refrigeration system having a supply of cooling media (R-23 and R-404 gases commonly used for refrigeration, which are azeotropic HFC refrigerant gas with zero ozone layer depletion) continuously flowing through with copper piping with SS (stainless steel)
25 plating). To explain further, this cooling assembly is of cascade type having compressed CFC-free refrigerant gas circulated about said heating chamber for cooling the heating element and cooling media when required or when the liquid bath temperature calibrator system is decommissioned from use. As can be visualized from FIGURE 12 (dimensions depicted in FIGURE 13), methanol is placed in this
30 working chamber having construction, features and working as described earlier in this paper.
The CFC-free refrigerant gas mentioned above is pumped around the heating
chamber, via a jacket surrounding said heating chamber, or pipes wrapped around
35 said heating chamber, by help of two compressors (visible in FIGURES 10 and 11),
which are filled with said CFC-free refrigerant gas at particular pressure at 10 PSI for
Page 11 of 39

compressor 1 and 5 PSI for compressor 2. Compressor cools the cooling tubes of the compressor, so as to enable working temperatures up to -80oC. Pressure and temperature of the refrigerant are raised so as to be above ambient condensing temperature of the CFC-free refrigerant gas. 5
Furthermore as can be seen from the accompanying FIGURES 2, 3, 9, and 17 the CFC-free refrigerant gas mentioned above is cooled, and heat imbibed by it, by help of a condenser wherein said CFC-free refrigerant gas changes state from a vapour to a liquid. The condenser is connected, via piping, in line between the two compressors
10 1 and 2. Free terminal of first compressor is piped to a plate-type heat exchanger while free terminal of the second compressor is piped with working chamber (specific reference to FIGURE 17), thereby constituting the loop for circulation of the CFC-free refrigerant gas. The plate-type heat exchanger is selected having plates made of stainless steel (AISI 304, 316), titanium or aluminum. Working chamber where
15 methanol is placed at the top side of the of the liquid bath temperature calibrator system proposed herein is shown in FIGURE 13.
The reader shall appreciate that wherever possible, all piping for circulation of the cooling media is made from copper. Accordingly, a copper coil is provisioned with a
20 capillary expansion device such that low-pressure side of the refrigerant system introduced above is able to hold entire charge of the CFC-free refrigerant gas. When compressor stops, the refrigerant therefore migrates to the cold, low-pressure side. The low-pressure side may further be equipped with a liquid separator, which acts as a receiver, just before the compressor. In this assembly, low-pressure side of the
25 refrigerant system is provided with a capillary expansion device to make it capable of holding the whole refrigerant charge. When the compressor stops, the refrigerant migrates to the cold, low-pressure side. Capillary connects with working chamber to hold the whole refrigerant system
30 Furthermore as seen generally in FIGURES 16 and 17, an expansion valve is provisioned for ensuring that a sufficient mass flow of refrigerant can pass while maintaining a stable and reasonable superheating for regulation of the evaporator. Said expansion valve is expanded when temperature and pressure in the working chamber are more than intended / desired / designed for. Evaporation temperature
35 for refrigerant is influenced by the operation of the expansion valve due to the change of superheating and mass flow. Said expansion valve is placed between compressor
Page 12 of 39

and sub-zero meter. According to pressure in compressor and temperature in the calibrator the valve expands or compresses. With increasing of temperature and pressure the expansion valve expands and with decreasing of temperature and pressure the valve pore size compresses. This valve works only on according to 5 compressor gas pressure and calibrator temperature so no other values are required for it. It’s pore / bore size is adjustable according to temperature and pressure.
As referred in the foregoing paragraph and generally referring the accompanying FIGURES 2 and 3, a sub-zero meter is used as a switch. Said sub-zero meter is
10 connected, at one end, with the reference / master RTD and at other end with an ABB make contactor (contactor is placed between compressor 2 and sub zero meter). . Main working of contactor is that it receive command from sub -zero meter, when sub-zero meter shows the reading -10 deg c then the contactor will be turn ON. When temperature reaches at the set temperature, the reference / master RTD senses the
15 temperature and causes the contactor to assume an ON state (which is otherwise resting in OFF state). In ON condition, command is given to the second compressor which is connected with the working chamber. This command is given to the second compressor which is connected to working chamber (which is surrounded with copper tube with R-23 gas and R-404 gas flowing through it).
20
As mentioned in the foregoing text and generally referring the accompanying FIGURES 2 and 3, a solid-state relay is used for controlling power to said heating element, so that a required reference temperature can be obtained and maintained in the liquid batch. Actuation of the solid-state relay, fan, and the vapour compression
25 refrigeration system is under control logic embedded in a digital self tuned PID Controller housed on-board the liquid bath temperature calibrator system.
The PID Controller (eurotherm controller 3216) of which the basic connections of RTD at controller port are shown in FIGURES 14 and 15, is included in the system 30 assembly herein as an indicator and connected, via terminals V+, V-, VI to the master / reference RTD (which works as controlling sensor) and positive and negative terminals to the solid-state relay.
For homogenous temperature across the volume of liquid (methanol) held in the
35 working chamber bath, said liquid is continually agitated and hence uniformly
circulated by means of a stirrer. The stirrer is made of stainless steel with diameter
Page 13 of 39

8mm and length 120mm. This stirrer is rotated at 1500 rpm by means of a DC motor. Rectifier gives command to motor and stirrer for rotation as mentioned above. Here, the rectifier is connected with a transformer and DC motor for taking input from transformer and give output to DC motor. (At the time when the system proposed 5 herein is switched ON, the transformer converts 230V AC to 12V and then gives output to rectifier. Rectifier then converts 12V AC into pure DC and gives output to DC motor. After receiving command from rectifier, DC motor starts to thereby rotate the stirrer at 1500 rpm speed)
10 According to another aspect of the present invention, the liquid in working chamber is selected to be a non-electrically conductive but heat-transferring medium, particularly methanol. The reader shall appreciate further, that the master / reference RTD is pre-calibrated by an independent laboratory traceable to National and / or international standards.
15
According to another aspect of the present invention, a filter / drier is a critical component (to protect refrigeration and air-conditioning systems from harmful chemical reactions and from abrasive impurities resulting from moisture, acids, and solid particles) equipped with a capillary system. The filter drier must be capable of
20 keeping the capillary tube clean and free flowing. Any other particles dust remove by filter. Two filters are used basically in the circuit. The drier is suitably sized to suit the system as it can act as a receiver for liquid refrigerant, not a good feature for a critical charge system. By this assembly, basically air is compressed in the compressor and forwarded for refrigeration to the condenser. Hot air at same air pressure goes to
25 condenser, which changes hot air to cold air at same pressure and wherein the filter / drier plays its part to remove dirt moisture from this air and again forwards it to expansion valve described in the foregoing narration.
It is recommended that the liquid bath temperature calibrator system proposed herein 30 is used while being placed on a well-ventilated flat surface having at least 12 inches of free space around the same in access to a suitable power supply, preferably 230 VAC ±10, 50/60 Hz utility / mains supply. A dedicated MCB is used for switching ON or OFF the electricity supply to the aforementioned circuitry.
35 External appearance of the liquid bath temperature calibrator system of the present invention can be appreciated from the accompanying FIGURE 1. As seen here, said
Page 14 of 39

liquid bath temperature calibrator system of the present invention is a compact, relatively portable unit having a user-interface disposed preferably in a manner and position readily accessible to the user. A preferred embodiment hereof prescribes an electronic panel being the user interface, with buttons / touch sensitive panel being 5 provided for interaction with the user, whereby the user may set the temperature to be maintained in the temperature-stable liquid bath system of the present invention.
According to another aspect of the present invention, operations of liquid bath temperature calibrator system disclosed herein are driven by logic embodied in a
10 bundled software, which may be installed on a personal computer in charge of the user. An RS-232 communication port is used for connecting the liquid bath temperature calibrator system for enabling thus serial communications with a personal computer. The accompanying FIGURES 5 to 8 reflect, in said order, a screenshot of a computer screen showing the software-implemented user interface
15 including a graph plot area for visualization of the user while using the liquid bath temperature calibrator system of FIGURE 1, a field index to be filled in by the user to connect the liquid bath temperature calibrator system of FIGURE 1 to a computer, and thereby being ready for use, an inset of the screenshot at FIGURE 5 showing another field index to be filled in by the user to initialize the liquid bath temperature
20 calibrator system of FIGURE 1 for use, and a graph showing a plot of temperature versus time, as arranged during operations of the liquid bath temperature calibrator system of FIGURE 1.
Industrial applicability 25 The present invention has been reduced to practice by the inventor named herein. Technical specifications of the resultant temperature-stable liquid bath system of the present invention are showcased in table 2 below.

Parameter Description
1) Power requirements 230 V AC, 2.0 KW ±10, 50/60 Hz
2) Power Maximum
3) Supply Frequency 50/60 Hz
4) Temperature Range -80 to 50°C
5) Temperature resolution 0.1°C
6) Stability for different media ±0.04°C at -80°C (Methanol) ±0.07°C at 0°C (Methanol)
Page 15 of 39

±0.05°C at 50°C (Water)
7) Uniformity ±0.05°C at -80°C ±0.09°C at 0°C ±0.07°C at 50°C
8) Controlling Sensor RTD PRT(PT-100)
9) Time to reach Max. Temperature 2 Hrs
10) Operating Temperature 20 to 25°C
11) Stabilization Time 15 to 20 Min
12) Dimensions 630 (H) x 1200 (W) x 500(D) mm
13) Volume 9 Liters
14) Weight Approx 80 kg
15) Method of control Digital self tuned PID Controller
16) Computer Interface RS – 232
Table 2
The temperature-stable liquid bath system of the present invention finds utility in 5 calibration of RTD and thermocouples, having range between -80°C to 50°C with ±0.07 °C stability. Furthermore, the temperature-stable liquid bath system of the present invention is qualified in having the following salient features:
• Large Immersion depth of working chamber where RTD/ thermocouple is
placed for calibration and testing purposes
10 • High Accuracy in achieving and maintaining desired temperatures
• High Stability and Uniformity
• Wide Temperature Range
• Capable and easy-to-use PC Interface
• cooling is continuously ON
15 • Fine temperature control by heater & SSR
• compressor 1 use R-404 gas and it can cooling down to -60 oC. cascade
compressor connection we used by use plate heat exchanger to cool the gas.
Compressor 2 use R-23 gas and can cool down to -80 oC
• the system having two different and individual heating and cooling controlling
20 techniques. Cooling is done by two cascade connected compressor and the
whole mechanical system responsible for it. Heating is done by MI heater which control heating process in the working chamber and the whole electrical circuit responsible for it.
Page 16 of 39

As will be realized further, the present invention is capable of various other embodiments and that its several components and related details are capable of various alterations, all without departing from the basic concept of the present invention. Accordingly, the foregoing description will be regarded as illustrative in nature and not as restrictive in any form whatsoever. Modifications and variations of the system and apparatus described herein will be obvious to those skilled in the art. Such modifications and variations are intended to come within ambit of the present invention, which is limited only by the appended claims.
It shall be generally noted that at least a major portion of the foregoing disclosures of this patent document contains material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in files or records of the receiving Patent Office(s), but otherwise reserves all copyright rights whatsoever

WE CLAIM

An portable liquid bath temperature calibrator system for calibration of a temperature sensor, comprising-
a) a stainless steel container dimensioned of height 200mm,, 325mm width and 162mm depth, equipped with means of agitation for serving as an isothermal temperature-controlled bath of a non-electrically conductive but heat-transferring medium, particularly methanol, and thereby a uniform source of reference temperature for calibration of the temperature sensor;
b) a standard temperature sensor which when received in the methanol bath, serves to validate the reference temperature of said bath, and thereby allow a user to comparatively calibrate the temperature sensor to be calibrated;
c) means of heating, being a mineral insulated heating element power of which is controlled by a solid-state relay, connected to the methanol bath for heating the methanol contained therein to a user-defined reference temperature;
d) means of cooling, being a vapour compression refrigeration system in particular, jacketed around the methanol bath for cooling the methanol contained therein to a user-defined reference temperature;
e) means of heat dissipation, being a plate type heat exchanger rated for -195 to 200 °C, connected to the methanol bath for dissipating excess heat provided by the means of heating; and
f) means with embedded logic for controlling the means for heating, cooling and dissipation of heat so as to bring, within 15 minutes to 20 minutes, and thereafter maintain the user-defined reference temperature ranging between -80°C to 50°C for calibration of the temperature sensor.

The portable liquid bath temperature calibrator system for calibration of a temperature sensor as claimed in claim 1, wherein the means of agitation provided in the stainless steel container are a stainless steel stirrer having diameter 8mm and length 120mm rotatable at 1500 RPM by means of a 20W DC motor connected to shaft of said stirrer, to thereby bring about uniformity of reference temperature throughout the liquid bath confirming to-
a) ±0.05°Cat-80°C
b) ±0.09°CatO°C
c) ±0.07°C at 50°C
The portable liquid bath temperature calibrator system for calibration of a temperature sensor as claimed in claim 1, wherein the apparatus is dimensioned to have a height of 630mm, a width of 1200 mm, and a height of 500mm.
The portable liquid bath temperature calibrator system for calibration of a temperature sensor as claimed in any one of the preceding claims, wherein the temperature sensor is selected among thermometers, thermocouples and the like.
The portable liquid bath temperature calibrator system for calibration of a temperature sensor as claimed in claim 1, wherein the vapour compression refrigeration system is one employing two serially acting 230 V,50 Hz,1 Phase compressors (1 and 2), a 14"X14"X 4 ROW condenser connected via copper piping which circulates a CFC-free refrigerant gas through said compressors (1 and 2), particularly wherein the CFC-free refrigerant gas is-
a) R-404, filled at 10 PSI in case of compressor 1
b) R-23, filled at 5 PSI in case of compressor 2
The portable liquid bath temperature calibrator system for calibration of a temperature sensor as claimed in claim 5, wherein mass flow of refrigerant gas is regulated by means of an expansion valve connected between the compressors and a switch, being a sub-zero meter in particular.
The portable liquid bath temperature calibrator system for calibration of a temperature sensor as claimed in claim 6, wherein pore size of the expansion

valve is adjustable according to temperature and pressure and requires no specific values to be set by the user.
The portable liquid bath temperature calibrator system for calibration of a temperature sensor as claimed in claims 1 and 5, wherein the means of heat dissipation is a 230V AC axial fan outfitted to the heating chamber, behind the condenser.
The portable liquid bath temperature calibrator system for calibration of a temperature sensor as claimed in claim 5, wherein the gases R-404 and R-23 are protected from harmful chemical reactions and from abrasive impurities resulting from moisture, acids, and solid particles by means of a filter / drier equipped with a capillary system.
The portable liquid bath temperature calibrator system for calibration of a temperature sensor as claimed in claim 1, wherein the means with embedded logic for controlling the means for heating, cooling and dissipation of heat are a PID controller, being a eurotherm controller 3216 in particular, of which terminals V+, V-, VI are connected to a reference RTD serving as a controlling sensor and positive and negative terminals are connected to the solid-state relay.
The portable liquid bath temperature calibrator system for calibration of a temperature sensor as claimed in claim 10, wherein the reference RTD calibrated by an independent laboratory traceable to national or international standards.
The portable liquid bath temperature calibrator system for calibration of a temperature sensor as claimed in claim 2, wherein the DC motor receives conditioned power supply through a a transformer that converts 230V AC to 12V, which output is conditioned by a rectifier that converts 12V AC received into pure DC.

The portable liquid bath temperature calibrator system for calibration of a temperature sensor as claimed in any one of the preceding claims and described substantially in the accompanying description and drawings.