The present invention relates to a calibrator for temperature sensor and more particularly it relates to a calibration system for temperature sensor and method thereof for stable and accurate calibration of temperature sensors at low temperature range of -100°C to 40°C.
Background and prior art of the invention
In the world, the industrialization goes at a peak and performs most important role in the economy. There are many types of industries and they used different types of machines. All machines require different types of parts for best performance of the machine and in all type of machine all quantity is measured by the different types of measuring instruments and sensors to achieve proper operation, performance and stability of machine. Time, size, distance, speed, direction, weight, volume, temperature, pressure, force, sound, light, energy- these are among the physical properties for which humans have developed accurate measures, without which we could not live our normal daily lives.
Through measurement, the value of an unknown parameter has been obtained through the measuring instrument. However this measured value cannot be the actual or true value. If the measured value is very close to the true value, it can call it to be a very accurate measuring system. But before using the measured data for further use, one must have some idea how accurate is the measured data.
The accuracy of even the most precise and most sensitive measurement instrument or measuring system can deteriorate through wear, aging and environmental influences. Besides, for maintaining the accuracy the readings of the measuring instrument are frequently to be compared and adjusted with the reading of another standard instrument. This process is known as “calibration”.
As focuses on the physical quantity measurement, the temperature plays most important role. The term “temperature” defines an intensity of heat present in a substance or object, especially as expressed according to a comparative scale and shown by a temperature measuring instruments. The temperature is the most significant and important parameter, and therefore the precision temperature measurement is essential in electrical power, automotive & material processing industries, and widely in all aspects of aviation, aerospace, weapons, ships and civil research in production and testing. Since long time, various kinds of temperature measuring instruments/devices are being utilizing for temperature measurement i.e. thermocouples, thermistors, resistance temperature detector (RTD), pyrometer, Longmuir probes (for electron temperature of plasma), platinum resistance thermometers (PRT), sheath-protected resistance thermometer (SPRT), infrared and other common temperature sensors.
The sensor calibration is a method of improving the sensor performance by removing structural errors in sensor outputs. The structural errors are differences between a sensor’s expected output and its measured output, which shows up consistently every time a new measurement is taken. The temperature sensor calibrations are used in instruments which are designed for measuring of temperature.
There are many temperature calibrators which calibrate the temperature sensor. However, in conventional temperature calibrator has a limit in generating a low temperature and it is difficult to obtain constant temperature with in shorter time. Further, conventional temperature calibrator only having particular range of calibrator in heating temperature or cooling temperature and it does not able to perform both temperature ranges. The resistance temperature sensors are calibrated by the conventional calibration method of fixed point verification and formula indexing. The drawbacks and disadvantages associated with the said conventional calibration method include a large deviation of the calibration results from the actual value and low reliability which can not meet the needs of model tasks.
It is desired to invent an ultra-low temperature calibrator that can be carried, is compact, lightweight, and can perform stable and highly accurate temperature control, achieve the temperature ranges at shorter time and able to perform in both temperature range i.e heating temperature and cooling temperature range .
Hence, it is desperately needed to invent an ultra cool temperature calibrator for calibrating the temperature sensor that overcomes the difficulties as described above.
Object of the invention
The main object of the present invention is to provide an ultra cool temperature calibrator for temperature sensor and method thereof.
Another object of the present invention is to provide an ultra cool temperature calibrator which provides low temperature range -100°C to 40°C.
Yet another object of the present invention is to provide a calibration system for temperature sensor and method thereof which can be used as calibrator for calibration of RTD, SPRT, thermocouples and other temperature probes at very low temperatures.
Further object of the present invention is to provide an ultra cool temperature calibrator that can able to operate dual mode, cooling and heating mode as required to user.
Another object of the present invention is to provide an ultra cool temperature calibrator that can be portable and easy to use.
Yet another object of the present invention is to provide an ultra cool temperature calibrator having higher efficiency.
Further object of the present invention is to provide an ultra cool temperature calibrator which is highly stable and accurate.
Another object of the present invention is to provide an ultra cool temperature calibrator which provides low temperature at minimum time.
Still another object of the present invention is to provide an ultra cool temperature calibrator that provides automatic adjustable and controllable temperature.
Another object of the present invention is to provide an ultra cool temperature calibrator which can overcome the drawbacks and shortcomings of the conventional calibration system for temperature sensors.
Summary of the Invention
An ultra cool temperature calibrator comprises an insulated body formed with controlling chamber accommodate a FPSC (free piston sterling cooler having a tip and mounted on an anti-vibration rubber. An electrically and thermally conductive block is coaxially disposed on the tip of the FPSC. A controlling sensor (6) is mounted with the conductive block and said sensor is electrically connected to a controlling chamber which having a PID controller. Said conductive block is wrapped with a silicon rubber heater on outer surface that defining a heating furnace. A Teflon block is mounted on the conductive block to prevent from thermal energy loss. The present invention provides high stability, radial uniformity of temperature and takes minimum time to reach the set value of temperature.

Brief description of the drawing
Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the present embodiment when taken in conjunction with the accompanying drawings.
Fig. 1shows the cross sectional side view of ultra cool temperature calibrator according to the present invention
Fig. 2 shows the prospective view of assembly of calibrator box of ultra cool temperature calibrator according to the present invention.
Fig. 3 shows the prospective view of assembly of Teflon block of ultra cool temperature calibrator according to the present invention.
Fig. 4 shows the cross sectional and front view of the Teflon block of ultra cool temperature calibrator according to the present invention.
Fig. 5 shows the prospective view of the Teflon block of ultra cool temperature calibrator according to the present invention.
Fig. 6 is a graphical representation of experimental readings of temperature stability at 0°C of ultra cool temperature calibrator according to the present invention.
Fig. 7 is a graphical representation of experimental readings of temperature stability at -50°C of ultra cool temperature calibrator according to the present invention.
Fig. 8 is a graphical representation of experimental readings of temperature stability at -100°C of ultra cool temperature calibrator according to the present invention.
Fig. 9 is a graphical representation of experimental readings of temperature of cooling time of ultra cool temperature calibrator for reach from 0°C to -100°C according to the present invention.
Fig. 10 is a graphical representation of experimental readings of temperature of heating time of ultra cool temperature calibrator for reach from -100°C to 0°C according to the present invention.
Detailed description of the invention

Before explaining the present invention in detail, it is to be understood that the invention is not limited in its application to the details of the construction and arrangement of parts illustrated in the accompany drawings. The invention is capable of other embodiments, as depicted in different figures as described above and of being practiced or carried out in a variety of ways. It is to be understood that the phraseology and terminology employed herein is for the purpose of description and not of limitation.
Before explaining the present invention, it is to be noted that the term “PID Controller” is a proportional integral derivative controller which continuously calculates an error value {e(t)} as a difference between the desired set-point value (SP) and a measured variable present value (PV) and applies a correction based on proportional, integral and derivative terms. Further, it is to be understood that the term “RTD” refers to a resistance temperature detector which contains an electrical resistance source, the resistance of which changes depending on temperature of the element itself.
Referring to Fig.1, Fig. 2 and Fig.3, an ultra cool temperature calibrator according to the present invention comprises an insulated body (1) formed with controlling chamber (7) and accommodates a FPSC (free piston sterling cooler) (2)having a tip (3); Said FPSC mounted on an anti-vibration rubber (4). An electrically and thermally conductive block (5) is coaxially disposed on the tip (3) of the FPSC (2). A controlling sensor (6) being mounted on outer surface of the conductive block (5) and said sensor (6) is electrically connected through electrical cables to a controlling chamber (7) which having a self-tuned PID controller (8).Further, Said conductive block (5) in combination of the controlling sensor (6) is wrapped with a silicon rubber heater (9)on outer surface that defining a heating furnace. Said Silicon rubber heater (9) is electrically connected with the PID controller (8) through a solid state relay. A Teflon block (10) is mounted on the conductive block (5) to prevent from thermal energy loss. An electrically driven fan (11) is mounted on the insulated body (1) for cooling the internal circuits of the controller chamber and Communication port of FPSC (not shown in figure).
The FPSC (2) offers ultra cool temperature range from -100°C to 0°C and heating temperature 0°C to 40° for calibration of the temperature sensors like thermocouples, thermistors, resistance temperature detector (RTD), pyrometer, Longmuir probes (for electron temperature of plasma), platinum resistance thermometers (PRT), sheath-protected resistance thermometer (SPRT), infrared and other common temperature sensors.
The FPSC (2) is a Stirling heat pump that uses a small amount of helium gas as a heat transport medium. The FPSC (2) has two major moving parts (i.e. piston and displacer) that oscillate in a linear motion along the same axis within a single cylinder which is installed in a stainless steel casing. The piston repeatedly compresses and expands the helium gas to cool the tip (3) (cold head) of the extended part of the casing. By fixing a thermal load or secondary heat transport mechanism to the tip (3)(cold head), the FPSC (2) can be used to cool an object down to a temperature between -50°C and -80°C within several minutes at an ambient temperature condition of 25°C. The anti-vibration rubber (4) is provided at the below of the FPSC (2) and resist from the vibration.
As shown in Fig. 2 and Fig. 4, on the tip (3) of the FPSC (Free piston stirling cooler) (2), the conductive block (5) disposed such that there is no air gap between the tip (3) and the conductive block (5). Said conductive block (5) having property of highly thermal conductive and highly electrically conductive and said conductive block (5) preferably, but not limited to, made from aluminium material. The conductive block (5) having longitudinal boreholes (H) extended up to the inner partial length of the conductive block (5) in which temperature sensor being inserted. The conductive block (5) is provided with the controlling sensor (6) which senses the temperature and provide to the PID controller (8) for controlling to required temperature. Said controlling sensor (6) preferably, but not limited to, is RTD (resistance temperature detector).
Referring to Fig. 3, the silicon rubber heater (9) is excellent source for uniform heat especially on challenging shapes and applications with flexibility or vibration. It plays an important role in temperature controlling, because of fast cooling and heating. It has also an advantage of better calibration result in any harsh environmental condition. Said silicon rubber heater (9) is wrapped at the outer side of the conductive block (5) and insulated with nitrile sheet. The silicon rubber heater (9) is electrically connected to the PID controller (8) through the solid state relay and is operated by the solid state relay through the PID controller (8) and provides heating temperature to the conductive block (5) and stabilizes particular temperature. While the temperature required below the ambient temperature, the silicon rubber heater (9) stabilizes particular cooling temperature and temperature requirement above the ambient temperature, the silicon rubber heater (9) provides the heating up to certain level of the temperature. It has an advantage of fine controlling, which helps in using the present calibrator in temperature range from (-100°C) to (40°C).
Referring Fig. 3 and Fig. 5, the Teflon block (10)is mounted on the combination of the conductive block (5) and the silicon rubber heater (9). The Teflon block (10) having high thermal stability and low thermal conductivity gives excellent temperature insulation to the conductive block (5). Longitudinal wells (W1, W2, W3and W4) are formed on the Teflon block (10) which aligned with the respective boreholes (H) of the conductive block (5).The temperature sensor probes are inserted in the longitudinal Wells (W1, W2, W3 and W4) such that the lower end of the temperature sensor probe inserts in calibration block through respective holes.
Among of temperature sensor inserted in the longitudinal Wells (W1, W2, W3 and W4), one temperature sensor is a “Master temperature sensor” and the rest of the temperature sensors are the “temperature sensor under calibration” (sensor to be calibrated).
The master temperature sensor can be define as the temperature sensor which having very low value of error, high accuracy and high precision compare to the other temperature sensor. The temperature sensors under calibration are the sensors which are calibrated using the ultra cool temperature calibrator.
Referring back to Fig. 1, the PID controller (8) in accordance with the controlling chamber (7) is connected to the controlling sensor (6) being configured for controlling the temperature of silicon rubber heater (9)and in-house temperature of the FPSC (2); the solid state relay being configured for varying power to the silicon rubber heater (9) to maintain a requisite temperature according to the set-point temperature of the PID controller (8). An up-down key is also provided in the PID controller (8) for setting and changing of set-point temperature in the PID controller (8) for calibration of the temperature sensors in the range of -100°C to 40°C. Said PID controller (8), solid state relay and a communication port of FPSC (12) are to be interconnected into the controlling chamber (7). The controlling chamber (7) and all components thereof are powered by an input supply voltage/power.
The ultra cool temperature calibrator for temperature sensor provides the minimum heating and cooling time to achieve the set-point temperature of the calibrator.
After installation of calibrator for temperature sensors as illustrated in Fig.1 to Fig.9; the calibration process according to the present invention comprises the following steps:
connecting of a controlling chamber (7) to a power supply source and providing an input supply power/voltage to a self-tuned PID controller (8)and a communication port of FPSC (not shown);
inserting a master temperature sensor probe in a well (W1) and temperature sensor under calibration in the wells (W2, W3 and W4) of a Teflon block (10).
setting of set-point temperature between -100°C to 40°C in the self tuned PID controller (8) by using an up-down key (not shown in figure) for calibration of the temperature sensors under calibration probe (in temperature range of -100°C to 40°C) that are disposed into the Wells (W2,W3 and W4);
starting a FPSC (free piston sterling cooler) (2) and generating cooling temperature on a tip (3) of the FPSC (2) and transmitting the temperature of the tip (3) through conduction to a conductive block (5).
generating heating temperature by a silicon rubber heater (9)and transmitting the temperature of the silicon rubber heater (9) through conduction to the conductive block (5).
stabilizing the temperature of the conductive block (5) in cooling temperature (-100°C to up to ambient temperature) or heating temperature (ambient temperature to up to 40°C) of the conductive block (5).
decreasing or increasing temperature gradually from the ambient temperature according to setting of temperature in step (III), the temperature of the master temperature sensor (disposed into the longitudinal well W1) reaches near to the set-point temperature;
allowing of temperature stabilization of the master temperature sensor probe (disposed into well W1) and the temperature sensor under calibration (disposed into the well W2,W3 and W4) until the present value (PV) gets equal to the set value (SV) of the set-point temperature;
after temperature stabilization in step (VIII), recording of readings of the master temperature sensor probe and the temperature sensor under calibration, when the master temperature sensor probe and the temperature sensor under calibration are thermally stable at or near the set-point temperature;
comparing the readings of the master temperature sensor probe with the readings of the temperature sensor under calibration obtained in step (IX), and thereafter finding out the error by comparison method.
The ultra cool temperature calibrator further provides the radial temperature uniformity. The radial temperature uniformity refers to the temperature differences of the temperature in Wells (W1, W2, W3 and W4). This temperature non uniformity is strongly influenced by the difference between the aluminium block temperature and ambient temperature.
After installation of calibrator, the radial temperature uniformity testing process according to the present invention comprises the following steps:
connecting a controlling chamber (7) to a power supply source and providing an input supply power/voltage to a self-tuned PID controller (8) and a communication port of FPSC;
inserting two master temperature sensor probe (P1,P2) in each different Wells (W1,W2) respectively of the ultra cool temperature calibrator;
setting of set-point temperature between -100°C to 40°C in the self tuned PID controller (8) by using an up-down key (not shown in figure);
generating cooling and heating temperature of a conductive block (5) using combination of a FPSC (2) and a silicon rubber heater (9) according to the set-point of the temperature in step (iii);
decreasing or increasing temperature in gradually from the ambient temperature according to the setting of temperature in step (iii);
allowing of temperature stabilization of the master temperature sensor probe (P1) (disposed into well W1) and the master temperature sensor probe (P2) (disposed into well W2) until the present value (PV) gets equal to the set value (SV) of the set-point temperature;
measuring and recording the temperature of the well
(W1,W2) by the master temperature sensor probe (P1,P2) inserted in step (ii);
interchanging the master temperature sensor probe (P1,P2)and inserted in said well (W2,W1) respectively;
allowing of temperature stabilization of the master temperature sensor probe (P1) (disposed into well W2) and the master temperature sensor probe (P2) (disposed into well W1) until the present value (PV) gets equal to the set value (SV) of the set-point temperature;
measuring and recording the temperature of said well (W1, W2) by temperature sensor probe (P2,P1) respectively;
calculating the difference of the temperature measured in step (vii) and step (x);
repeating the step (ii-xi) for radial temperature uniformity testing of well (W3,W4) accordingly;

The radial uniformity of two wells can be determined by following formula:

Radialuniformity (X)=((P1W1-P1W2)+(P2W1-P2W2))/2
Where,
X = Radial Uniformity
P1W1 = Temperature of Well-1 measured by sensor probe 1
P1W2 = Temperature of Well-2 measured by sensor probe 1
P2W1 = Temperature of Well-1 measured by sensor probe 2
P2W2 = Temperature of Well-2 measured by sensor probe 2

The present invention provides the ultra cool temperature calibrator which is ease of portability and offers the temperature range from -100°C to 40°C. The present invention is highly stable, accurate and provides uniform temperature radially. The present invention provides the cooling as well as heating temperature to the temperature sensor probe for calibration.

The ultra cool temperature calibrator provides desire temperature of heating and cooling at minimum time. The present invention provides the minimum cooling and heating time as shown in Fig.9 and Fig.10.

After installation of calibrator, the process of testing the time to reach temperature of wells (W1. W2, W3 and W4) to set value of an ultra cool temperature calibrator comprising following steps:
connecting a controlling chamber (7) to a power supply source and providing an input supply power/voltage to a self-tuned PID controller (8) and a communication port of FPSC;
inserting master temperature sensor probe (P1) in any of the Wells (W1,W2, W3 and W4) of the Teflon block (10);
setting of set-point temperature between -100°C to 40°C in the PID controller (8) by using an up-down key;
generating cooling and heating temperature of a conductive block (5) using combination of a FPSC (2) and a silicon rubber heater (9) according to the set-point of the temperature in step (c);
decreasing or increasing temperature in gradually from the ambient temperature according to the setting of temperature in step (c);
reaching the temperature to the present value (PV) of master sensor equal to the set value (SV) of the set-point temperature in step (c);
reading and recording the temperature measured by the master temperature sensor probe ( disposed into well ) at interval of 5 minutes from step (c) to step (f).
calculating time taken by the ultra cool temperature calibrator to reach the set value of the temperature in step (c).

The present invention is illustrated more in details in the following experimental examples. The example describes and demonstrates the embodiments within the scope of the present invention. This example is given solely for the purpose of illustration and is not to be construed as limitations of the present invention, as many variations thereof are possible without departing from spirit and scope.
Experiment: 1
In the first experiment, the radial uniformity of ultra cool temperature calibrator by master temperature sensor probes was carried out at set-point temperature of -100°C, in which the temperature of -100°C was set in the self-tuned PID controller (8). The master temperature sensor probe RTD 1 and RTD 2 was inserted in the Well-1 and Well-3 respectively. The reading of the both sensor probe were gradually thermally stabilized until the temperature of the sensor probe was reached to or near the set-point temperature. After that, the master temperature sensor probe RTD 1 and RTD 2 was inserted in the Well-3 and Well-1 respectively. The reading of the both sensor probe were gradually thermally stabilized until the temperature of the sensor probe was reached to or near the set-point temperature. Then, the readings of temperature of the both temperature sensor probe were recorded that have been illustrated in below Table 1. To check the uniformity of temperature calibrator, said readings of the temperature sensors ware found out by the formula method.
Table 1
Temp (Deg C) Sensor Well 1 Well 3
-100 RTD 1 -100.44 -100.41

RTD 2 -100.45 -100.44
Radial Uniformity : +/-0.020

Experiment: 2
In the second experiment, the radial uniformity of ultra cool temperature calibrator by temperature sensor probes was carried out at set-point temperature of -50°C, in which the temperature of -50°C was set in the self-tuned PID controller (8). The master temperature sensor probe RTD 1 and RTD 2 was inserted in the Well-1 and Well-3 respectively. The reading of the both sensor probe were gradually thermally stabilized until the temperature of the sensor probe was reached to or near the set-point temperature. After that, the master temperature sensor probe RTD 1 and RTD 2 was inserted in the Well-3 and Well-1 respectively. The reading of the both sensor probe were gradually thermally stabilized until the temperature of the sensor probe was reached to or near the set-point temperature. Then, the readings of temperature of the both master temperature sensor probe were recorded that have been illustrated in below Table 2. To check the uniformity of temperature calibrator, said readings of the temperature sensors ware found out by the formula method.
Table 2
Temp (Deg C) Sensor Well 1 Well 3
-50 RTD 1 -50.664 -50.635

RTD 2 -50.641 -50.650
Radial Uniformity : +/-0.019

Experiment: 3
In the third experiment, the radial uniformity of ultra cool temperature calibrator by temperature sensor probes was carried out at set-point temperature of 0°C, in which the temperature of 0°C was set in the self-tuned PID controller (8). The master temperature sensor probe RTD 1 and RTD 2 was inserted in the Well-1 and Well-3 respectively. The reading of the both sensor probe were gradually thermally stabilized until the temperature of the sensor probe was reached to or near the set-point temperature. After that, the master temperature sensor probe RTD 1 and RTD 2 was inserted in the Well-3 and Well-1 respectively. The reading of the both sensor probe were gradually thermally stabilized until the temperature of the sensor probe was reached to or near the set-point temperature. Then, the readings of temperature of the both master temperature sensor probe were recorded that have been illustrated in below Table 3. To check the uniformity of temperature calibrator, said readings of the temperature sensors ware found out by the formula method.
Table 3
Temp (Deg C) Sensor Well 1 Well 3
0 RTD 1 0.409 0.386

RTD 2 0.375 0.398
Radial Uniformity : +/-0.011

Experiment: 4
In the fourth experiment, the stability of ultra cool temperature calibrator by temperature sensor probes was carried out at set-point temperature of 0°C in which the temperature of 0°C was set in the self-tuned PID controller (8). Thereafter, the master temperature sensor and heating furnace were gradually thermally stabilized until the temperature of master temperature sensor reached to or near the set-point temperature. Then, the readings of temperature of the master temperature sensor were recorded at regular interval of 5 minutes that have been illustrated in below Table 4. To check the stability of the ultra cool temperature calibrator, said readings of the master temperature sensor were compared with the set temperature of the ultra cool temperature calibrator and error was found out by the comparison method. Graphical representation of said readings of temperature of master temperature sensor with respect to timeframe of 5 minutes at set-point temperature of 0°C is shown in Fig.6.

Table 4
Sr. No. Time
(Min) Set-Point Temperature/or
Temperature of calibrator (°C) Temperature of Master temperature sensor
(°C)
1 5 0 -0.648
2 10 0 -0.648
3 15 0 -0.648
4 20 0 -0.641
5 25 0 -0.648
6 30 0 -0.656
7 35 0 -0.648
8 40 0 -0.641
9 45 0 -0.648
10 50 0 -0.648
11 55 0 -0.648

Experiment: 5
In the fifth experiment, the stability of ultra cool temperature calibrator by temperature sensor probes was carried out at set-point temperature of -50°C in which the temperature of -50°C was set in the self-tuned PID controller (8). Thereafter, the master temperature sensor and calibrator were gradually thermally stabilized until the temperature of master temperature sensor reached to or near the set-point temperature. Then, the readings of temperature of the master temperature sensor were recorded at regular interval of 5 minutes that have been illustrated in below Table 5. To check the stability of the ultra cool temperature calibrator, said readings of the master temperature sensor were compared with the set temperature of the ultra cool temperature calibrator and error was found out by the comparison method. Graphical representation of said readings of temperature of master temperature sensor with respect to timeframe of 5 minutes at set-point temperature of -50°C is shown in Fig.7.

Table 5
Sr. No. Time
(Min) Set-Point Temperature/or
Temperature of calibrator (°C) Temperature of Master temperature sensor
(°C)
1 5 -50 -49.93
2 10 -50 -49.93
3 15 -50 -49.93
4 20 -50 -49.938
5 25 -50 -49.93
6 30 -50 -49.93
7 35 -50 -49.93
8 40 -50 -49.93
9 45 -50 -49.93
10 50 -50 -49.93
11 55 -50 -49.93

Experiment: 6
In the sixth experiment, the stability of ultra cool temperature calibrator by temperature sensor probes was carried out at set-point temperature of -100°C, in which the temperature of -100°C was set in the self-tuned PID controller (8). Thereafter, the master temperature sensor and calibrator were gradually thermally stabilized until the temperature of master temperature sensor reached to or near the set-point temperature. Then, the readings of temperature of the master temperature sensor were recorded at regular interval of 5 minutes that have been illustrated in below Table 6. To check the stability of the ultra cool temperature calibrator, said readings of the master temperature sensor were compared with the set temperature of the ultra cool temperature calibrator and error was found out by the comparison method. Graphical representation of said readings of temperature of master temperature sensor with respect to timeframe of 5 minutes at set-point temperature of -100°C is shown in Fig.8.
Table 6
Sr. No. Time
(Min) Set-Point Temperature/or
Temperature of calibrator (°C) Temperature of Master temperature sensor
(°C)
1 5 -100 -100.01
2 10 -100 -100.02
3 15 -100 -100.03
4 20 -100 -100.04
5 25 -100 -100.02
6 30 -100 -100.03
7 35 -100 -100.02
8 40 -100 -100.01
9 45 -100 -100.01
10 50 -100 -100.02
11 55 -100 -100.01

Experiment: 7
In the seventh experiment, the cooling time of ultra cool temperature calibrators was carried out for reach the set-point temperature of -100°C from 0°C, in which the temperature of -100°C was set in the self-tuned PID controller (8). The readings of temperature of the master temperature sensor were recorded at regular interval of 5 minutes that have been illustrated in below Table 7. Graphical representation of said readings of temperature of master temperature sensor with respect to timeframe of 5 minutes at set-point temperature of -100°C is shown in Fig. 9.
Table 7
Sr. No. Time
(Min) Temperature of Master temperature sensor
(°C)
1 5 -0.961
2 10 -8.195
3 15 -27.336
4 20 -49.344
5 25 -66.039
6 30 -77.773
7 35 -86.906
8 40 -93.859
9 45 -98.938
10 50 -102.51

Experiment: 8
In the eighth experiment, the heating time of ultra cool temperature calibrators was carried out for reach the set-point temperature of 0°C from -100°C,in which the temperature of 0°C was set in the self-tuned PID controller (8) when temperature of the ultra cool temperature calibrator was -100°C. The readings of temperature of the master temperature sensor were recorded at regular interval of 5 minutes that have been illustrated in below Table 8. Graphical representation of said readings of temperature of master temperature sensor with respect to timeframe of 5 minutes at set-point temperature of 0°C is shown in Fig.10.
Table 8
Sr. No. Time
(Min) Temperature of Master temperature sensor
(°C)
1 5 -100.2
2 10 -88.422
3 15 -76.617
4 20 -66.359
5 25 -57.391
6 30 -49.508
7 35 -42.648
8 40 -36.453
9 45 -30.781
10 50 -25.695
11 55 -21.18
Further, the silicon rubber heater (9) employed in the calibrator of the present invention is flexible that can be fixed around circular surface of the conductive block (5), which helps in maintaining uniform temperature distribution of the conductive block (5).

The invention has been explained in relation to specific embodiment. It is inferred that the foregoing description is only illustrative of the present invention and it is not intended that the invention be limited or restrictive thereto. Many other specific embodiments of the present invention will be apparent to one skilled in the art from the foregoing disclosure. All substitution, alterations and modification of the present invention which come within the scope of the following claims are to which the present invention is readily susceptible without departing from the spirit of the invention. The scope of the invention should therefore be determined not with reference to the above description but should be determined with reference to appended claims along with full scope of equivalents to which such claims are entitled.

Reference numerals
1 Insulated body
2 FPSC (Free Piston Stirling Cooler)
3 Tip
4 Anti-vibration Rubber
5 Conductive block
6 Controlling sensor
7 Controlling chamber
8 PID controller
9 Silicon rubber heater
10 Teflon block
11 Fan
H. Longitudinal borehole of Conductive block
W1. Well 1 of ultra cool temperature calibrator
W2. Well 2 of ultra cool temperature calibrator
W3. Well 3 of ultra cool temperature calibrator
W4. Well 4 of ultra cool temperature calibrator

We claim:

1. An ultra cool temperature calibrator comprises;
an insulated body (1) formed with a controlling chamber (7)and accommodate a FPSC (Free piston sterling cooler) (2) mounted on an anti-vibration rubber (4);said FPSC (2) having a tip (3);
Characterized in that,
an electrically and thermally conductive block (5)coaxially disposed on the tip (3) of the FPSC (2) and having longitudinal boreholes (H) extend up to an inner partial length of said conductive block (5);
said controlling chamber (7) accommodates a PID controller (8) with an up down key electrically connected with a controlling sensor (6); said controlling sensor (6) mounted with the conductive block (5);
a silicon rubber heater (9) wrapped on outer surface of the combination of said conductive block (5) and the controlling sensor (6); said silicon rubber heater (9)electrically connected through electrical cables to the PID controller (8) via solid state relay;
a Teflon block (10)is mounted on the combination of said conductive block (5) and the silicon rubber heater (9) and having longitudinal wells (W1,W2,W3 and W4) aligned with the respective boreholes (H) of the conductive block (5);
Wherein one of the borehole of the longitudinal wells (W1, W2, W3 and W4) receive the master sensor and rest of the longitudinal wells (W1, W2, W3 and W4) receive the temperature sensors under calibration.

2. The ultra cool temperature calibrator as claimed in claim 1, wherein the conductive block (5) is made of the aluminium material.

3. The ultra cool temperature calibrator as claimed in claim 1, wherein the silicon rubber heater (9) is insulated with nitrile sheet and operated by the solid state relay through the PID controller (8).

4. The ultra cool temperature calibrator as claimed in claim 1, wherein the controlling sensor (6) is RTD (resistance temperature detector) sensor.

5. The ultra cool temperature calibrator as claimed in claim 1, wherein the conductive block (5) is mounted on the tip (3) such that there is no any air gap between the tip (3) and conductive block (5).

6. The ultra cool temperature calibrator as claimed in claim 1, an electrically driven fan (11) mounted on the insulated body (1) for cooling of internal circuits of the controlling chamber (7) and a communication port of FPSC;

7. The ultra cool temperature calibrator as claimed in claim 1, wherein the combination of FPSC (2) and silicon rubber heater (9) provide the heating temperature up to 40°C and cooling temperature up to -100°C.

8. A method for calibration of temperature sensor using an ultra cool temperature calibrator comprising following steps:

I. connecting a controlling chamber (7) to a power supply source and providing an input supply power/voltage to a self-tuned PID controller (8) and a communication port of FPSC;
II. inserting a master temperature sensor probe in a well (W1) and a temperature sensor under calibration in the wells (W2, W3 and W4) of the ultra cool temperature sensor calibrator;
III. setting of set-point temperature between -100°C to 40°C in the PID controller (8) by using an up-down key for calibration of the temperature sensors under calibration probe (in temperature range of -100°C to 40°C) that are disposed into the Wells (W2,W3 and W4);
IV. starting a FPSC (free piston sterling cooler) (2) and generating cooling temperature on a tip (3) of a FPSC (2) and transmitting the temperature of the tip (3) through conduction to a conductive block (5);
V. generating heating temperature by a silicon rubber heater (9) and transmitting the temperature of the silicon rubber heater (9) through conduction to the conductive block (5);
VI. stabilizing the temperature of the conductive block (5) in cooling temperature (-100°C to up to ambient temperature) or heating temperature (ambient temperature to up to 40°C) of the conductive block (5);
VII. decreasing or increasing temperature gradually of the conductive block (5) from the ambient temperature according to setting of temperature in step (II);
VIII. allowing of temperature stabilization of the master temperature sensor (disposed into well W1) and the temperature sensor under calibration (disposed into the well W2,W3 and W4) until the present value (PV) gets equal to the set value (SV) of the set-point temperature;
IX. recording of readings of the master temperature sensor and the temperature sensor under calibration, when the master temperature sensor and the temperature sensor under calibration are thermally stable at or near the set-point temperature;
X. comparing the readings of the master temperature sensor with the readings of the sensor under calibration obtained in step (IX);
XI. finding out the error of the temperature sensor under calibration with respect to master sensor by comparison method.

9. A method for testing radial temperature uniformity of an ultra cool temperature calibrator comprising following steps:
i. connecting a controlling chamber (7) to a power supply source and providing an input supply power/voltage to a self-tuned PID controller (8) and a communication port of FPSC;
ii. inserting two master temperature sensor probe (P1,P2) in each different Wells (W1,W2) respectively of the ultra cool temperature calibrator;
iii. setting of set-point temperature between -100°C to 40°C in the PID controller (8) by using an up-down key;
iv. generating cooling and heating temperature of a conductive block (5) using combination of a FPSC (2) and a silicon rubber heater (9) according to the set-point of the temperature in step (iii);
v. decreasing or increasing temperature in gradually from the ambient temperature according to the setting of temperature in step (iii);
vi. allowing of temperature stabilization of the master temperature sensor probe (P1) (disposed into well W1) and the master temperature sensor probe (P2) (disposed into well W2) until the present value (PV) gets equal to the set value (SV) of the set-point temperature;
vii. measuring and recording the temperature of the well
(W1,W2) by the master temperature sensor probe (P1,P2) inserted in step (ii);
viii. interchanging the master temperature sensor probe (P1,P2) and inserted in said well (W2,W1) respectively;
ix. allowing of temperature stabilization of the master temperature sensor probe (P1) (disposed into well W2) and the master temperature sensor probe (P2) (disposed into well W1) until the present value (PV) gets equal to the set value (SV) of the set-point temperature;
x. measuring and recording the temperature of said well (W1, W2) by temperature sensor probe (P2,P1) respectively;
xi. calculating the difference of the temperature measured in step (vii) and step (x);
xii. repeating the step (ii-xi) for radial temperature uniformity testing of well (W3,W4) accordingly;
10. A method for testing the timing for reaching temperature to set value of an ultra cool temperature calibrator comprising following steps:
a) connecting a controlling chamber (7) to a power supply source and providing an input supply power/voltage to a self-tuned PID controller (8) and a communication port of FPSC;
b) inserting master temperature sensor probe (P1) in any of the Wells (W1,W2, W3 and W4) of the ultra cool temperature calibrator;
c) setting of set-point temperature between -100°C to 40°C in the PID controller (8) by using an up-down key;
d) generating cooling and heating temperature of a conductive block (5) using combination of a FPSC (2) and a silicon rubber heater (9) according to the set-point of the temperature in step (c);
e) decreasing or increasing temperature in gradually from the ambient temperature according to the setting of temperature in step (c);
f) reaching the temperature to the present value (PV) of master sensor equal to the set value (SV) of the set-point temperature in step (c);
g) reading and recording the temperature measured by the master temperature sensor probe ( disposed into well ) at interval of 5 minutes form step (c) to step (f);
h) calculating time taken by the ultra cool temperature calibrator to reach the set value of the temperature in step (c).