Calibration of Thermometry Instruments

Report
Bangladesh BEST Programme
Calibration of Thermometry Instruments
Nihal Gunasekara
Sri Lanka
1
Bangladesh BEST Programme
Essential Features of Calibration
• Fixed Point Calibration – Primary Level
Primary Laboratories –NPL or NML
• Comparison Calibration – Secondary Level
Secondary Level Laboratories
2
Bangladesh BEST Programme
Fixed Point Calibration
• Fixed Point Calibration – ITS-90 Fixed Points
• Medium – Fixed Point Bath or Furnace
• Advantage - Very Small Uncertainty
3
Bangladesh BEST Programme
Comparison Calibration
• Comparison – Secondary Standard
• Medium – Calibration Bath or Dry Well
• Uncertainty – Larger than Fixed Point Calibration
4
Bangladesh BEST Programme
ITS 90
Fixed Points
Standard Platinum
Resistance
Thermometers Upto
1000 °C
Working Standard Platinum
Resistance Thermometers
upto 1000 °C
Platinum Resistance
Thermometers
Liquid in glass Thermometers
Dial Thermometers
Thermocouples
Calibration Hierarchy
Thermocouples Type R
& S upto 1500 °C &
Thermocouples Type B
upto 1700 °C
Black Body
Radiation
Source
Optical
Pyrometers
upto 3500 °C
Thermocouples upto 1700
°C
Thermocouples upto 1000 °C
Temperature Baths
Ovens/Incubators
Furnaces
Furnaces upto
3000 °C
Bangladesh BEST Programme
Calibration of Laboratory Equipment
• Laboratory Ovens – Mainly used for sterilization of
Glassware
Normally upto 300 °C
• Laboratory Incubators - Mainly used for growing
microbial cultures
Normally upto 50 °C
6
Bangladesh BEST Programme
Performance Testing of Ovens/Incubators –
Three Point Method
•
•
•
•
•
Check the following before commence the test
Power supply and its socket
Temperature range/ indicator of the oven /
incubator
Location of the built-in temperature sensor of the
oven / incubator
Ventilation levels
Any other indicators, if available
7
Bangladesh BEST Programme
Selection of Test Temperatures
• Select at least three test points which are
approximately equally spaced covering the working
range
• If only one test point is requested select that test
point
• Oven 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
8
Bangladesh BEST Programme
Placement of Temperature Sensors
• Place the temperature sensors in the “upper”,
“middle”, “lower” and “near temperature
sensor “
Near sensor
Upper
Middle
Lower
9
Bangladesh BEST Programme
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
Temperature
(° C )
Stability Conditions
150
100
80
t1
t2
Time
(min.)
t1 - t2 is the temperature stabilized period at 150 °C
11
Bangladesh BEST Programme
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.
12
Bangladesh BEST Programme
Performance test results for an oven/incubator (three point)
Specification:180 ±1oC
Temp.
setting
Value of the
indicator
(oC)
(oC)
Measured mean value
Exp.
(oC)
Unce.
(oC)
k=2
Min
180.0
Max
180.0 179.9
Near
the
sensor
Upper
Middle
Lower
area
area
area
180.1
180.5
180.3
181.1
±0.3
Uncertainty component=Exp.Unc/2
13
Bangladesh BEST Programme
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 temperatures
• Indicated enclosure temperature : enclosure temperature
computed from indicated temperatures. It is equal to half the
sum of the maximum and minimum indicated temperatures
14
Bangladesh BEST Programme
Performance Testing of Ovens/Incubators –
Multi- Point Method
Definitions :
• Spatial variation: difference between the midrange 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
15
Bangladesh BEST Programme
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
temperatures
• Indicated temporal variation : temporal
variation computed from indicated temperatures
16
Bangladesh BEST Programme
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
interval
• Overall variation: difference between the
maximum and minimum measured temperatures.
17
Bangladesh BEST Programme
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.
18
Bangladesh BEST Programme
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.
19
Bangladesh BEST Programme
Performance Testing of Ovens/Incubators –
Multi- Point Method
Inspection:
• Power supply and its socket
• Temperature range/ indicator of the oven or
incubator
• Location of the built-in temperature sensor of
the oven or incubator
• Ventilation levels
• Any other indicators, if available
20
Bangladesh BEST Programme
Selection of Test temperatures - Oven
 Select at least three test points which are
approximately equally spaced covering the
working range
 If only one test point is requested select that test
point
 Oven 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
21
Bangladesh BEST Programme
Selection of Test temperatures- Incubator
 Select the temperature settings designed for
the incubator
22
Bangladesh BEST Programme
Performance test results for a laboratory
oven/incubator (multi point)
Temperature variation
Temperature specification
Grade of an oven/incubator
Performance test results
Bangladesh BEST Programme
Temperature variation inside a chamber
T1
T2
T3
T4
T5
T2
T6
T7
Bangladesh BEST Programme
Temperature Specification
T± ΔT oC
Ex: 100 ±2.5 oC
Bangladesh BEST Programme
Grade of an oven/incubator
G = 8- 6.64log[100Rm/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
Performance test results
Test point:100 ± 2.5oC (temperature
specification)
Rm, Maximum overall variation=5oC
D= 100-20oC
G=5
N=9
27
Bangladesh BEST Programme
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
The above approximate values are provided as examples for guidance only
Bangladesh BEST Programme
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 )
29
Bangladesh BEST Programme
Calibration Results
T/C Position
Maximum
Minimum
Difference
Mid range
Exp.Unc
(oC)
(oC)
(oC)
(oC)
(oC), k=2
1
100.9
100.8
0.1
100.8
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
±0.3
Indicated Enclosure temperature = 100.6 oC
Measured enclosure temperature = 99.2 oC
Spatial variation = 3.2 oC
Temporal variation = 0.5 oC
Overall variation=3.5oC
Grade = 6
30
Bangladesh BEST nProgramme
ESTIMATION OF UNCERTAINTY
Prepare the Uncertainty Budget as per Uncertainty of
Measurement GUM JCGM 100 :2008
Calculate 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 Programme

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