1 Calibration of Thermometry Instruments Nihal Gunasekara Sri Lanka Bangladesh BEST Programme

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

3 Fixed Point Calibration Fixed Point Calibration – ITS-90 Fixed Points Medium – Fixed Point Bath or Furnace Advantage - Very Small Uncertainty Bangladesh BEST Programme

4 Comparison Calibration Comparison – Secondary Standard Medium – Calibration Bath or Dry Well Uncertainty – Larger than Fixed Point Calibration Bangladesh BEST Programme

Calibration Hierarchy 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 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

6 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 Bangladesh BEST Programme

7 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 Bangladesh BEST Programme

8 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 Bangladesh BEST Programme

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

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

11 Stability Conditions Bangladesh BEST Programme Time (min.) t 1 t 2 Temperature (° C ) t 1 - t 2 is the temperature stabilized period at 150 °C

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

13 Performance test results for an oven/incubator (three point) Specification:180 ±1 o C Temp. setting ( o C) Value of the indicator ( o C) Measured mean value ( o C) Exp. Unce. ( o C) k=2 MinMax Near the sensor Upper area Middle area Lower area ±0.3 Uncertainty component=Exp.Unc/2 Bangladesh BEST Programme

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 temperatures Indicated 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

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

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 temperatures Indicated temporal variation : temporal variation computed from indicated temperatures Bangladesh BEST Programme

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 interval Overall variation: difference between the maximum and minimum measured temperatures. Bangladesh BEST Programme

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

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

20 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 Bangladesh BEST Programme

21 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 Bangladesh BEST Programme

22 Selection of Test temperatures- Incubator  Select the temperature settings designed for the incubator 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 T2 T4 T5 T6 T7 Bangladesh BEST Programme

Temperature Specification T± ΔT o C Ex: 100 ± 2.5 o C Bangladesh BEST Programme

Grade of an oven/incubator G = log[100R m /100+D] Where; G: Grade of the oven R m : 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

27 Performance test results Test point:100 ± 2.5 o C (temperature specification) R m, Maximum overall variation=5 o C D= o C G=5 N = 9 Bangladesh BEST Programme

Grade of an oven/incubator Grade (G)Max. permissible overall variation (R m ) °C D = 30D = Bangladesh BEST Programme The above approximate values are provided as examples for guidance only

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

30 T/C Position Maximum ( o C) Minimum ( o C) Difference ( o C) Mid range ( o C) Exp.Unc ( o C), k= ± Indicator value Indicated Enclosure temperature = 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

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 nProgramme

Bangladesh BEST Programme