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Fluke – American Fork, UT
• Kurt Zabriskie• 17 Years with Fluke/Hart Scientific
– Western Regional Product Manager - Temperature• [email protected]
AgendaHow to Calibrate an RTD Using a Dry-Block Calibrator
• Quick Dry-block introduction• Dry-block sources of error• Finding solutions for common errors and problems• Calculating uncertainties• How to calibrate probes with odd shapes and sizes• Temperature range concerns• Liquid-in-glass thermometers• RTD calibration example• Dry-block maintenance• Summary
Dry-Block Introduction
Dry-Blocks/Dry-WellsModerate accuracyFixed hole diameterFixed immersion depthDry and cleanPortableFaster temperature changesInternal reference probe
9100SHandheld Dry-well
9190AUltra-CoolField Metrology Well
914X SeriesField Metrology Wells
9103 9140 9141Dry-Block Calibrators
Dry-Block Sources of Errors
• Immersion effects• Stem conduction• Well contact errors• Display accuracy• Stability• Uniformity (radial & axial)• Loading
Dry-Block – Immersion Effects
• Immersion depth of the UUT is critical
• Dry-blocks are generally calibrated by fully inserting a reference probe
Dry-Block – Immersion Effects
• By adding a reference probe, we can be less concerned with the control probe location
• The UUT and Reference can be moved to different depths
• Immersion depth should still be considered
• (15 X Probe Diameter)
• Many Fluke dry-blocks include a reference Input
Dry-Block – Stem Conduction
• May impact the ability to make a good measurement
• The probe sheath acts as heat sink
• Probe diameter matters, length is less critical
• (15 x probe diameter) a good rule to follow
Heat
Dry-Block – Well Contact Errors
• Fit is important
• Loose fitting probes exhibit erratic behavior
• Wells should be 0.005”-0.010” larger than the diameter of the probe for 0.5” diameter probes and smaller.
• Too snug, and the probe may become stuck
Dry-Block – Display Accuracy
• Generally a one year specification on a spec sheet
• Internal control sensors are designed to be robust
• Display accuracy can be one of the largest contributors to the overall uncertainty
Dry-Block – Stability
• Check dry-block specifications
• Units generally come with optimized proportional bands
• Fine tuning the proportional band may help at specific temperatures
Dry-Block – Axial Uniformity
• Axial Uniformity – Variation in the temperature along the axial length of the insert (block) within the measurement zone
• Generally inherent to the dry-block
• The closer the sensing element is to ambient air, the larger the uncertainties
• Higher temperatures present larger errors
• Look for dry-blocks with a calibrated zone for optimal results
Dry-Block – Radial Uniformity
• Radial Uniformity – Variation in the temperature between different wells of the insert (block) within the measurement zone.
• Mostly inherent to the dry-block design
• Heater placement and profiling is critical during engineering of the dry-block
Dry-Block – Loading
• Loading can impact uncertainties.
• Some models have a specification
• Units without specifications can be evaluated in the field
Calculating Uncertainties
• RSS method is generally used to calculate uncertainties when using a reference
23
22
21 )()()( bbbbtotal
222 )()()( uniformitystabilityrefbtotal
222 )02.0()1.0()05.0(113.0 CCCC
Calculating Uncertainties
• GUM compliant example
-38 °C 0 °C 157 °C 232 °C 420 °C 660 °C
Uncertainty Sources: Type mK mK mK mK mK mK
Process Var. (check std) Norm 3.0 3.0 5.0 5.0 5.0 6.0
UUT Precision (noise) Norm 2.8 2.8 2.8 3.3 4.4 5.6
Ref. Precision (noise) Norm 2.8 2.8 2.8 2.8 2.8 5.6
Ref. Calibration Norm 0.2 0.1 0.6 0.5 0.6 1.1
Ref. Drift Rect 1.7 2.0 3.2 3.8 5.1 6.7
Radial Uniformity Rect 10.0 10.0 30.0 30.0 30.0 30.0
Axial Uniformity Rect 6.3 6.3 6.3 6.3 6.3 6.3
Readout (SPRT) Rect 0.2 0.3 0.4 0.5 0.7 0.9
Readout (UUT) Rect 1.3 1.5 2.5 3.1 4.4 6.3
Insulation Leakage Rect 10. 0 10.0 10.0 10.0 10.0 10.0
UUT Repeatability (TPW) Norm 2.8 3.3 5.3 6.3 8.6 11.2
Total (k=2): 20.6 21.0 40.7 41.5 43.9 47.9
Dry-Block – Odd Shaped Probes
• Custom inserts are an option
• Micro-Baths might be a good option to explore
Temperature Range Concerns
• –100 to 1200 ºC• May need to use multiple
units • It’s ok to switch from one
dry-block to the next Model 9190A:–95 to 140 ºC
Model 9143: 33 to 350 ºC
Model 9150:150 to 1200 ºC
Dry-Block – LIG’s
• Liquid and glass thermometers are not recommended for use in a dry-block calibrator
• Mercury thermometers are on their way out due to environmental concerns
Dry-Block – Maintenance
• Keep those wells clean, Scotch-Brite pads and a gun cleaning kit work nicely
• Avoid dropping inserts or other heavy objects into the well
• Avoid the use of thermo grease
• Recalibrate regularly
• Verify stability
RTD Calibration Example
• Three point RTD Calibration• –95 ºC, 0 ºC, 140 ºC• Utilize the 9190A with the “Process
Option” to measure the UUT • Set the 9190A to each of the three
set points, generally starting with the lowest point
• Allow for plenty of soak time at each temperature (15 minutes)
• Record a resistance at each set point• Utilize at tool such as TableWare to
calculate coefficients
When the Super-DAQ is connected to a Fluke Calibration dry-well, fluid bath, or furnace, it can control the temperature source to calibrate up to 40 sensors automatically.
You simply program the setpoint temperatures and their values, select a scan sequence, assign a reference channel, and set the required stability band.
The Super-DAQ monitors the temperature source’s stability through the reference channel, collects the data from the reference probe and the “unit under test” (UUT) once stabilized, and then advances to the next set-point temperature.
After you configure and start the test, you can walk away to work on other things. The Super-DAQ just made your day a whole lot easier!
Automate temperature sensor calibration with the 1586A Super-DAQ
9190A Ultra-Cool Field Metrology Well
1586A Super-DAQ with DAQ-STAQ
Application Note and Video
Application Note: Automating Temperature Sensor Calibration with the 1586A Super-DAQ
Companion Video: Automating Temperature Sensor Calibration with the 1586A Super-DAQ
The application note and video demonstrate the Auto Test function of the 1586A using a 9142 Field Metrology which can be substituted with other Fluke Calibration dry-wells, fluid baths, and furnaces.
Dry-Block – Summary
• Dry-blocks are a great option in many situations
• Highly portable and quick to change temperature
• Sources of error should be considered
• On board references are a great way to combine several instruments into one
• Be sure to contact us any time for help with your specific application
Where Can I Find Out More?• Comparison Calibration Application Notes
– 914X Series Field Metrology Well– 9190A Ultra-Cool Field Metrology Well
• Product information at: www.Transcat.com/Fluke
Limited Time Offer
• Free Temperature Probe with Metrology Well Purchase• Order from Transcat
• Details at: www.transcat.com/Fluke• 800-800-5001
Questions or Comments?Email the moderator, Nicole VanWert:
Transcat: 800-800-5001www.Transcat.com
For related product information, go to:
www.Transcat.com/Fluke