SPRT Calibration Uncertainties and Internal Quality Control at a ...
©2012 Fluke Corporation SPRT Health 1 Health Monitoring of SPRTs.
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Transcript of ©2012 Fluke Corporation SPRT Health 1 Health Monitoring of SPRTs.
©2012 Fluke Corporation SPRT Health 1
Health Monitoring of SPRTsHealth Monitoring of SPRTs
©2012 Fluke Corporation SPRT Health 2
What is it?
SPRT - Standard Platinum Resistance ThermometerSPRT - Standard Platinum Resistance Thermometer
Your subject Your subject photo herephoto here
©2010 Fluke Corporation Presentation Title 3
• Interpolating instrument for the ITS-90 temperature scale
• 13K to 961.78C - Capsule, Long Stem, HT SPRTs
• Repeatability – 0.5 to 1.0mK
• LT stability (100 hrs) – 0.03 to 1.0 mK possible
• Quartz glass (or metal) sealed sheath
• Specific gas mixture
• 25.5 ohm, 2.5 ohm
SPRTsSPRTs
©2010 Fluke Corporation Presentation Title 4
SPRTs SPRTs
REQUIREMENTS
Stability
Reproducibility
Measurability
DESIGN FEATURES
Strain-free, well-annealed wire
Pure platinum
Protection from contamination
Sealed sheath
Four-lead construction
Good electrical insulation
Standard dimensions
AS A RESULT, SPRTs
are precise
are fragile
have relatively large-sized resistors
have relatively low-valued resistors
Characteristics
©2010 Fluke Corporation Presentation Title 5
The Fluke SPRT design includes the following (to provide the best stability of any commercial SPRT in the industry):
•High quality, well-annealed platinum wire held by an optimum design quartz structure.
•Proprietary gas mixture to provide protection against sensor contamination, at the same time ensuring low oxidation
•High quality quartz tubing with sand blasted exterior to prevent ambient radiation from reaching the sensor
•Lead wires exit through sealed quartz glass (not epoxy)
SPRTs SPRTs
©2012 Fluke Corporation SPRT Health 6
How/why does it drift?
What will damage it?
SPRT - Standard Platinum Resistance ThermometerSPRT - Standard Platinum Resistance Thermometer
Your subject Your subject photo herephoto here
©2010 Fluke Corporation Presentation Title 7
• Drift from Oxidation • Normal and reversible through annealing
• Drift from thermal cycling, vibration, light mechanical shock • Causes strain• Can be reversed if not too bad
• Cold quenching – cooling too fast from above 480C• Sometimes reversible
• Serious mechanical shock• Causes shorting / strain• Not usually reversible
SPRT Drift, DamageSPRT Drift, Damage
©2012 Fluke Corporation SPRT Health 8
What can you do to prevent drift or fix damage?
SPRT - Standard Platinum Resistance ThermometerSPRT - Standard Platinum Resistance Thermometer
Your subject Your subject photo herephoto here
©2010 Fluke Corporation Presentation Title 9
It helps to purchase a stable SPRT to begin with…
The best design yields better long term stability
1. Quartz sheath construction2. Gas mixture
• Too much oxygen promotes too much oxidation of the platinum sensor
• Some oxygen protects the sensor from contamination
3. Sensor and lead wire holding structure• Allow strain-free expansion/contraction of the platinum wire, but still hold the
sensor/wire in place
4. Sheath sealed against air leakage over time• Quartz material melted around the exiting platinum lead wires
• How to solve the problem of mismatch of expansion rates for quartz and platinum?
• Epoxy has been shown not to be a very good long term solution to prevent leakage
SPRT drift preventionSPRT drift prevention
©2010 Fluke Corporation Presentation Title 10
Avoid contamination of the sensor• Furnace should not contain any base metals• Protect SPRT using a platinum sheath• Use graphite or alumina annealing block• Clean the sheath using alcohol before it is exposed to high temperature
SPRT Handling & MaintenanceSPRT Handling & Maintenance
©2010 Fluke Corporation Presentation Title 11
Avoid mechanical shock• Do not leave in baths or furnaces for extended periods of time
• Handle carefully • Train staff
SPRT Handling & MaintenanceSPRT Handling & Maintenance
©2010 Fluke Corporation Presentation Title 12
Avoid cold quenching•Cool slowly (less than 100 degrees/hour) to below 480C
•The SPRT can be taken directly to room temperature when below 480C
SPRT Handling & MaintenanceSPRT Handling & Maintenance
©2010 Fluke Corporation Presentation Title 13
Annealing• At highest useable range for the sensor• Above 450C, preferably above 550C• For many hours (10-100)• In a non-contaminating furnace/block
SPRT Handling & MaintenanceSPRT Handling & Maintenance
©2010 Fluke Corporation Presentation Title 14
Keep a control chart• Record Rtpw regularly• Use to regulate calibration cycle
Check Rtpw when return from calibration
• Drift during shipping• Hand carry where possible
SPRT Handling & MaintenanceSPRT Handling & Maintenance
SPRT SN 1234 CONTROL RTPW CHART
date
RTPW
25.532155
25.532186
25.532215
25.53215
25.53216
25.53217
25.53218
25.53219
25.53220
25.53221
25.53222
25.53223
25.53224
25.53225
MAR0
1_93
APR0
2_93
OCT2
0_93
MAR1
3_94
MAY0
4_94
OCT1
9_94
DEC1
5_94
JAN1
5_95
©2010 Fluke Corporation Presentation Title 15
• Shorting due to coils touching each other cannot be repaired
• Excessive change in resistance from misuse cannot be repaired
SPRT Handling & MaintenanceSPRT Handling & Maintenance
©2010 Fluke Corporation Presentation Title 16
•Recent design improvements have made SPRTs more stable
•Challenges remain in sourcing pure platinum
•Research continues
•Drift is mainly due to handling issues
ConclusionConclusion