DYNAMIC LOAD COMPENSATION

Transcription

1 DYNAMIC LOAD COMPENSATION INCREASING PERFORMANCE OF DRY-BLOCK TEMPERATURE CALIBRATORS Keith Hadley April

2 Learning Objectives Identify inherent sources of measurement errors when using dry-block calibrators Understand technologies employed to address errors Explain Dynamic Load Compensation Technology Advantages Results

3 Dry-Block Temperature Calibrators In the early 1980 s JOFRA developed the first dry-block temperature calibrator The early dry-block calibrators performed as expected and offered a good calibration solution for industrial applications» When compared to a bath the blocks provided Faster heat up and cool down Wider temperature ranges Smaller size equipment for portability No hot or hazardous fluids

4 Dry-Block Temperature Calibrators Components 1. Sensor-under-test 2. Solid metal block 3. Interchangeable insert 4. Internal RTD reference sensor 5. Heating/Cooling elements 6. Cooling fan 4

5 Dry-Block Temperature Calibrators As the technology progressed models with more capabilities and better performance were developed The dry-block was now viewed as a solution for lab applications and not only for industrial use» Other factors came into play Stability Well homogeneity» Axial and radial Loading effect» Basically comparing it to a bath

6 Power Supply Stability Variable power supplies cause variable temperatures When current through the heating elements or Peltier elements fluctuates, temperature fluctuates» Mains Variance Immunity Compensates for power fluctuations Maintains steady energy flow Mains Voltage Temperature without MVI Temperature with MVI

7 Radial Homogeneity The bore-to-bore difference This effect is minimized through» Efficient well design Air flow Element location Reference location» Well control» Efficient insert design and proper materials Consistent heat transfer

8 Axial Homogeneity The top-to-bottom difference This effect is minimized through» Use of well zone control Single zone Passive dual zone Active dual zone» Dynamic Load Compensation DLC

9 Traditional technology Single Zone Control Good accuracy in the bottom No temperature gradient control» Several factors determine gradient Load sensitive Requires proper insulation of SUT IMMERSION DEPTH? Not Loaded Loaded TEMPERATURE Internal Reference

10 Passive Dual Zone Control Proportional technology SUT Main zone for optimum heat dissipation through block Upper zone for compensation of heat losses No need for insulation on SUT Good lower zone homogeneity Calibration of multiple SUT Small vertical gradient Main Zone Upper Zone Fixed energy ratio Set Temperature Internal Reference

11 Active Dual Zone Control Active technology Intelligent energy distribution Temperature change based on loading and dissipation Continuous axial measurement Calibration of short SUT Minimal vertical gradient Main Zone Upper Zone SUT Slave Temperature Difference Set Temperature Master External / Internal Reference

12 Dynamic Load Compensation The next step Dual zone works in the block» Coarse adjust DLC works in the insert» Fine adjust» Measures within the insert and adjusts temperature Main Zone Upper Zone SUT DLC Slave Temperature Difference Set Temperature Master External / Internal Reference

13 What is DLC External Reference SUT Accomplished with Extra sensor in the insert» High accuracy TC» Sensing element at bottom of the insert» Sensing element at 60 mm from the bottom covering the thermo sensitive length (TSL) of nearly all sensors Reads the difference of the two levels» Input to adjust temperature difference to zero DLC

14 DLC Operation Distance from bottom of insert in mm DLC function Off DLC function On TSL Thermo Sensitive Length Axial temperature homogeinity in C DLC Sensor Dynamic Load Compensation sensor

15 DLC Operation 15

16 Scenario Load Compensation RTC-156, S/N : Axial 155 C Load: DLC+Ext. Ref.+3mm SUT. DLC on Load: DLC+Ext. Ref.+3mm SUT + 10mm SUT. DLC off Load: DLC+Ext. Ref.+3mm SUT + 10mm SUT. DLC on Performance loaded nears a straight line with DLC active The maximum deviation is improved by a factor of 6 by activating the DLC Improvement factor = ratio : > 6

17 Scenario Bath Cal Comparison Test setup: SET TRUE SUT1 SUT1 deviation Deviation from bath calibration Bath calibration RTC-156 DLC=off, SUT1 + SUT RTC-156 DLC=on, SUT1 + SUT Uncertainty due to thermal loading is reduced with the DLC active With the DLC active optimum accuracy is achievable Uncertainty reduction factor = ratio : = 3

18 Scenario Uncertainty Budget Calibrator loaded with 10 mm SUT DLC not active 1 Temperature of reference thermometer Uncertainty of reference thermometer (k=2) Normal Resolution of calibrator indicator RMS Hysteresis effect RMS Axial temperature homogeneity RMS Radial temperature homogeneity RMS Loading effect RMS Stability in time RMS k= Geometric sum square root of the sum of the squares k=

19 Scenario Uncertainty Budget Calibrator loaded with 10 mm SUT DLC active 1 Temperature of reference thermometer Uncertainty of reference thermometer (k=2) Normal Resolution of calibrator indicator RMS Hysteresis effect RMS Axial temperature homogeneity RMS Radial temperature homogeneity RMS Loading effect RMS Stability in time RMS k= Geometric sum square root of the sum of the squares k=

20 Scenario Uncertainty Budget Calibrator loaded with 10 mm SUT DLC not active k= Geometric sum square root of the sum of the squares k= Calibrator loaded with 10 mm SUT DLC active k= Geometric sum square root of the sum of the squares k= Active DLC reduces the axial gradient by 85% The calibrator is performing within all specifications even while heavily loaded The total uncertainty is reduced by a factor of 5 with the DLC active Uncertainty reduction factor = ratio : > 5

21 Advantages and Benefits of DLC Calibrate multiple sensors simultaneously Save time and money Calibration of large sensors No insulation or resulting errors Minimal concern over TSL of SUT Confidence Positive indication of DLC Operation active and working Magnitude driving to zero Stability green when zero and stable

22 Questions