Maximum Performance From Dry-Well Thermometer Calibrators. Mark Finch Product Manager EMEA Fluke Calibration

Transcription

1 Common Problems in Achieving Maximum Performance From Dry-Well Thermometer Calibrators Mark Finch Product Manager EMEA Fluke Calibration

2 Dry-well Thermal Uncertainties Temperature Stability Temperature Uniformity Axial Radial Block Loading Hysteresis of the Control Sensor Immersion Effects (Stem Conduction)

3 Temperature Reference Standard- Direct Mode

4 Temperature Reference Standard- Direct Mode

5 Temperature Stability Temperature Stability Measurement Sigma = ±0.009 C Temperature Deviation, C :00 0:01 0:02 0:03 0:04 0:06 0:07 0:08 0:09 0:11 0:12 0:13 0:14 0:15 0:17 0:18 0:19 0:20 0:22 0:23 0:24 0:25 0:26 0:28 0:29 0:30 0:31 0:33 0:34 0:35 Peak to Peak = C Peak = C / 2 = ±0.013 C Time

6 Temperature Uniformity Axial Uniformity Variation in the temperature along the axial length of the insert (block) within the measurement zone. Radial Uniformity Variation in the temperature between different wells of the insert (block) within the measurement zone. Measurement Zone Space occupied by the sensitive elements of the UUTs measured, both axially and radially. Allow for the range of sensor length.

7 Axial Temperature Uniformity

8 Axial Temperature Uniformity Gradient Measurement Measuring Axial Gradient Deviations Immersion Depth, mm Ref. & Grad. Temps., C Averages check Axial Dif. from Ref., C Reference Gradient Differential 0:00 0:03 0:07 0:11 0:15 0:19 0:22 0:26 0:30 0:34 0:38 0:42 0:46 0:50 0:54 0:58 1:02 1:05 1:09 Time, hr:min

9 Axial Uniformity Gradient Profile Example Dry-well Axial Homogeneity Error at a Specified Temperature Temperature Deviation, C mm Element 20 mm Element Error = C max/2 Error = 0.009C or ±0.016 C mm vs. 40 mm probes, error = C 20 mm vs. 40 mm probes, error = C min. small probe vs. 40 mm, error = ±0.016 C gradient profile Immersion from Bottom

10 Axial Gradient Calibration Optimization Optimizing for Large Axial Gradient, (600 C) Difference in Error between Centered and Bottom UUT Position Profile Error, C Ref. Temp. 20mm UUT Reference Thermometer Center Line 20mm UUT 0.15 C gradient profile C Immersion, mm

11 Radial Temperature Uniformity

12 Radial Temperature Uniformity Measurement Radial Homogeneity Measurement Well Number Reference & Well Temps, C Normalized Temp. Difference, C maximum error :30 17:31 17:32 17:32 17:33 17:34 17:34 17:35 17:36 17:36 17:37 17:38 17:38 17:39 17:40 17:41 17:41 17:42 Time Reference Mover Differential

13 Radial Temperature Uniformity Cyclic Exchange TD = ((P 1 W 1 P 1 W 2 ) + (P 2 W 1 P 2 W 2 )) / 2 TD = Temperature Difference Between Wells P 1, P 2 = Probes 1 and 2 W 1, W 2 = Wells 1 and 2 P 1 W 1 is probe 1 in well 1, etc.

14 Block Thermal Loading Added Heat Loss due to increased numbers or size of thermometers, creates a shift in the temperature gradient in the insert (block) of the dry-well. The Temperature Controller cannot completely compensate for this shift. The result can be a temperature error that is particularly apparent in the Direct Mode.

15 Block Thermal Loading Measurement-Direct Mode Dry-Well Block Loading Effect Probe 2 Probes 3 Probes 4 Probes 3 Probes 2 Probes 1 Probe 0.026ºC error Constant Display Temperature :15 10:23 10:31 10:40 10:48 10:56 11:04 11:12 11:20 11:28 11:36 11:44 11:52 12:00 12:08 12:17 12:25 12:33 12:41 12:49 12:57 13:05 13:13 13:21 13:29 13:37 13:45 13:53 Temp, C Time/event Ref 1 Ref 2

16 Block Thermal Loading Measurement-Indirect Mode Thermal Loading Difference Between Reference Probes ºC Error 13:33 Temp. Difference, e, C 10:15 10:22 10:29 10:37 10:44 10:51 10:58 11:05 11:12 11:19 11:26 11:33 11:40 11:47 11:54 12:01 12:08 12:15 12:22 12:29 12:36 12:43 12:50 12:57 13:04 13:12 13:19 13:26 13:40 13:47 13: Probes 3 Probes 4 Probes 3 Probes 2 Probes Time/Event

17 Control Sensor Hysteresis Control Sensor Hysteresis 700 Actual Tempera ature, C Error Temperature Range Midpoint Error Heating Cooling Average Value Set Point Temperature, C

18 Control Sensor Hysteresis Temperature Range Effect Dry-Well Temperature Hysteresis Over Different Ranges Hysteresis Error, C Hysteresis Set-Point Temperature, C

19 Immersion Effects and Thermometer Stem Conduction Comparison of Immersion Effects of Different Thermometers, 420 C Temperature Devia ation, C mm immersion 125mm immersion 100mm immersion Immersion, cm

20 Uncertainty Budget: Direct Mode Uncertainty Source Probability Distribution Uncertainty, ± C Divisor Contribution, ± C Electronic Measurement Normal NA Ref. Thermometer (SPRT) Normal NA SPRT, long term drift Normal NA Dry-well Accuracy Rectangular Dry-well, long term drift Normal Homogeneity, Axial Rectangular Homogeneity, Radial Rectangular Resolution of indicator Rectangular Temperature Stability Normal Thermal Loading (direct) Rectangular Hysteresis Rectangular Stem Conduction Bias Combined Standard Uncertainty, ± C (k=1) Combined Expanded Uncertainty, ± C (k=2) 0.438

21 Uncertainty Budget-Indirect Mode Uncertainty Source Probability Distribution Uncertainty, ± C Divisor Contribution, ± C Electronic Measurement Normal Ref. Thermometer (SPRT) Normal SPRT, long term drift Normal Dry-well Accuracy Rectangular NA Dry-well, long term drift Normal NA Homogeneity, Axial Rectangular Homogeneity, Axial (SPRT*) Rectangular Homogeneity, Radial Rectangular Homogeneity, Radial (SPRT*) Rectangular Resolution of indicator Rectangular NA Temperature Stability Normal Thermal Loading (indirect) Rectangular Hysteresis Rectangular NA Stem Conduction Bias Combined Standard Uncertainty, ± C (k=1) Combined Expanded Uncertainty, ± C (k=2) 0.247

22 Conclusion Thermal properties inherent in dry-wells contribute to uncertainty of calibration. An estimate of the uncertainty can be made through measurement and analysis. Different modes of use of the dry-well influence the overall uncertainty. Careful testing and analysis can be used to improve accuracy of the calibration for specific cases.

23 Questions