1 Calibration of Thermometry Instruments

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 . Nihal. . Gunasekara. Sri Lanka. Bangladesh BEST . Programme. 2. Essential Features of Calibration. Fixed Point Calibration – Primary Level. . Primary Laboratories –NPL or NML . ID: 674947 Download Presentation

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1 Calibration of Thermometry Instruments




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Presentations text content in 1 Calibration of Thermometry Instruments

Slide1

1

Calibration of Thermometry Instruments

 Nihal GunasekaraSri Lanka

Bangladesh BEST

Programme

Slide2

2

Essential Features of Calibration

Fixed Point Calibration – Primary Level Primary Laboratories –NPL or NML Comparison Calibration – Secondary Level Secondary Level Laboratories  

Bangladesh BEST

Programme

Slide3

3

Fixed Point Calibration

Fixed Point Calibration – ITS-90 Fixed PointsMedium – Fixed Point Bath or FurnaceAdvantage - Very Small Uncertainty 

Bangladesh BEST

Programme

Slide4

4

Comparison Calibration

Comparison – Secondary StandardMedium – Calibration Bath or Dry WellUncertainty – Larger than Fixed Point Calibration 

Bangladesh BEST

Programme

Slide5

Calibration Hierarchy

ITS 90 Fixed PointsStandard Platinum Resistance Thermometers Upto 1000 °C

Working Standard Platinum Resistance Thermometers

upto 1000 °C

Platinum Resistance Thermometers

Liquid in glass Thermometers

Dial Thermometers

Thermocouples

Thermocouples Type R & S

upto

1500 °C & Thermocouples Type B

upto

1700 °C

Thermocouples

upto

1700

°C

Thermocouples

upto

1000 °C Temperature Baths

Ovens/Incubators

Furnaces

Black Body Radiation Source

Optical Pyrometers

upto

3500 °C

Furnaces

upto

3000 °C

Bangladesh BEST

Programme

Slide6

6

Calibration of Laboratory Equipment

Laboratory Ovens – Mainly used for sterilization of Glassware Normally upto 300 °CLaboratory Incubators -  Mainly used for growing microbial cultures

Normally upto

50 °C

Bangladesh BEST

Programme

Slide7

7

Performance Testing of Ovens/Incubators –Three Point Method

Check the following before commence the testPower supply and its socketTemperature range/ indicator of the oven / incubatorLocation of the built-in temperature sensor of the oven / incubatorVentilation levelsAny other indicators, if available 

Bangladesh BEST

Programme

Slide8

8

Selection of Test Temperatures

Select at least three test points which are approximately equally spaced covering the working rangeIf only one test point is requested select that test pointOven with the range 50 °C to 250 °C select 50 °C, 100 °C, 150 °C, 200 °C and 250 °C Select test point which are not within the ± 15 °C of the requested points by the customerIf the incubator is used for one/two test point/s select that/both test point/s

Bangladesh BEST

Programme

Slide9

9

Placement of Temperature Sensors

Place the temperature sensors in the “upper”, “middle”, “lower” and “near temperature sensor “

Upper

Middle

Lower

Near sensor

Bangladesh BEST

Programme

Slide10

Steady-state Condition

 

Stability “Obtain the readings after stabilized the temperature setting and ensure that the set temperature is stable before commence the record readings” .

Bangladesh BEST

Programme

Slide11

11

Stability Conditions

  Bangladesh BEST

Programme

150

80

100

Time (min.)

t

1

t

2

Temperature

(° C )

t

1

- t

2

is the temperature stabilized period at 150 °C

Slide12

12

Data Recording

Record the maximum / minimum of the built in temperature indicator. Record the temperature from all four test sites at 30 seconds time intervals during the “test interval” (i.e. one hour or three cycles of the controller, which ever is the longer), after stabilization.Record ambient temperature and ambient relative humidity near the oven (i.e. about 1m away from the oven). Repeat the above steps for each of the test temperature settings of the oven.Record all data in a data recording sheet.

Bangladesh BEST

Programme

Slide13

13

Performance test results for an oven/incubator (three point)

Specification:180 ±1oCTemp. setting

(

o

C

)

Value of the indicator

(

o

C)

Measured mean value

(

o

C)

Exp.

Unce

.

(

o

C

)

k=2

Min

Max

Near the sensor

Upper

area

Middle

area

Lower

area

180.0

180.0

179.9

180.1

180.5

180.3

181.1

±0.3

Uncertainty component=

Exp.Unc

/2

Bangladesh BEST

Programme

Slide14

14

Performance Testing of Ovens/Incubators – Multi- Point Method

Definitions :Enclosure temperature: mid-range value of the temperatures obtained from all relevant sites within the enclosure throughout the test interval.Measured enclosure : enclosure temperature computed from the measured temperatures. It is equal to half the sum of the maximum and minimum indicated temperaturesIndicated enclosure temperature : enclosure temperature computed from indicated temperatures. It is equal to half the sum of the maximum and minimum indicated temperatures 

Bangladesh BEST

Programme

Slide15

15

Performance Testing of Ovens/Incubators – Multi- Point Method

Definitions : Spatial variation: difference between the mid-range of all measured temperatures obtained at one site and that at another site for those sites which give the greatest difference. Measured spatial variation: spatial variation computed from measured temperatures Indicated spatial variation: spatial variation computed from indicated temperatures

Bangladesh BEST

Programme

Slide16

16

Performance Testing of Ovens/Incubators – Multi- Point Method

Definitions :Temporal variation: maximum value of the temperature range obtained for each standard site through out the test interval.Measured temporal variation : temporal variation computed from measured temperaturesIndicated temporal variation : temporal variation computed from indicated temperatures

Bangladesh BEST

Programme

Slide17

17

Performance Testing of Ovens/Incubators – Multi- Point Method

Definitions :Maximum measured temperature : the highest measured temperature obtained during the test interval Minimum measured temperature : lowest measured temperature obtained during the test intervalOverall variation: difference between the maximum and minimum measured temperatures.

Bangladesh BEST

Programme

Slide18

18

Performance Testing of Ovens/Incubators – Multi- Point Method

Definitions :Test site: location at which a test sensor is positioned for the purpose of temperature measurement during testing of the enclosure.Mid-range value: half the sum of maximum and minimum values of a set of temperatures.Temperature range: difference between the maximum and minimum values of a set of temperatures.

Bangladesh BEST

Programme

Slide19

19

Performance Testing of Ovens/Incubators – Multi- Point Method

Definitions :Test interval: interval of time to which the steady state characteristics. The test interval will commence after stability has been established and shall be of a sufficient period of time to characterize the temporal variation.Apparatus required : A temperature data logger and a set of suitable thermocouples to cover the required temperature range of the incubator.

Bangladesh BEST

Programme

Slide20

20

Performance Testing of Ovens/Incubators – Multi- Point Method

Inspection:Power supply and its socketTemperature range/ indicator of the oven or incubatorLocation of the built-in temperature sensor of the oven or incubator Ventilation levelsAny other indicators, if available

Bangladesh BEST

Programme

Slide21

21

Selection of Test temperatures - Oven

Select at least three test points which are approximately equally spaced covering the working rangeIf only one test point is requested select that test pointOven with the range 50 °C to 250 °C select 50 °C, 100 °C, 150 °C, 200 °C and 250 °C

Select test point which are not within the ± 15 °C of the requested points by the customer

If the incubator is used for one/two test point/s select that/both test point/s

Bangladesh BEST

Programme

Slide22

22

Selection of Test temperatures- Incubator

Select the temperature settings designed for the incubator

Bangladesh BEST

Programme

Slide23

Performance test results for a laboratory oven/incubator (multi point)

Temperature variation

Temperature specificationGrade of an oven/incubatorPerformance test results

Bangladesh BEST Programme

Slide24

Temperature variation inside a chamber

T1

T2

T3

T2

T4

T5

T6

T7

Bangladesh BEST

Programme

Slide25

Temperature Specification

T± ΔT

oC Ex: 100 ±2.5 oC

Bangladesh BEST

Programme

Slide26

Grade of an oven/incubator

G = 8- 6.64log[100R

m/100+D]Where; G: Grade of the oven Rm: Maximum overall variation (Rm=2 ΔT) D : Difference between oven temperature and ambient temperature

N = 3 + 3(G)0.6(V)

0.2 Where; N: Number of standard test sites

V: Volume of the oven

Bangladesh BEST

Programme

Slide27

27

Performance test results

Test point:100 ± 2.5oC (temperature specification)Rm, Maximum overall variation=5oCD= 100-20oC

G=5 N = 9

Bangladesh BEST

Programme

Slide28

Grade of an oven/incubator

Grade (G)

Max. permissible overall variation (Rm ) °C

D = 30

D = 100

4

5.2

8.0

6

2.6

4.0

8

1.3

2.0

9

0.92

1.4

12

0.33

0.5

14

0.16

0.25

Bangladesh BEST

Programme

The above approximate values are provided as examples for guidance only

Slide29

29

Calculation and Derived Quantities

The mid range temperature for the sensor

=

½

(

t

max +

t

min)

Temperature range of the sensor

= (

t

max -

t

min )

Let for specific test temperature :

T

max

is the largest t

max

value obtained from N test sites

T

min

is the smallest t

min

value obtained from N test sites

OVERALL VRIATION = T

max

– T

min

MEASURED ENCLOSURE TEMPERSTURE = ½ (

T

max

+

T

min )

Bangladesh BEST

Programme

Slide30

30

T/C Position

Maximum

(

o

C

)

Minimum

(

o

C

)

Difference

(

o

C

)

Mid range

(

o

C)

Exp.Unc

(

o

C), k=2

1

100.9

100.8

0.1

100.8

±0.3

2

100.5

100.3

0.2

100.4

3

99.9

99.8

0.1

99.8

4

99.0

98.8

0.2

98.9

5

100.2

100.0

0.2

100.1

6

100.5

100.2

0.3

100.4

7

100.2

100.0

0.2

100.1

8

97.9

97.4

0.5

97.6

9

100.8

100.7

0.1

100.6

Indicator value

100.6

100.5

0.1

100.6

Indicated Enclosure temperature = 100.6

o

C

Measured enclosure temperature = 99.2

o

C

Spatial variation = 3.2

o

C

Temporal variation = 0.5

o

C

Overall variation=3.5

o

C Grade = 6

Calibration Results

Bangladesh BEST

Programme

Slide31

ESTIMATION

OF UNCERTAINTY

 Prepare the Uncertainty Budget as per Uncertainty of Measurement GUM JCGM 100 :2008Calculate the CMC value for the scope of accreditation (

not mote than 02 significant figures)

The

reported uncertainty

in your report should

always

be

greater than CMC value

Bangladesh BEST

nProgramme

Slide32

Bangladesh BEST

Programme

Thank you


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