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©2012 Fluke Corporation SPRT Health 1 Health Monitoring of SPRTs.

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Presentation on theme: "©2012 Fluke Corporation SPRT Health 1 Health Monitoring of SPRTs."— Presentation transcript:

1 ©2012 Fluke Corporation SPRT Health 1 Health Monitoring of SPRTs

2 ©2012 Fluke Corporation SPRT Health 2 What is it? SPRT - Standard Platinum Resistance Thermometer Your subject photo here

3 ©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 SPRTs

4 ©2010 Fluke Corporation Presentation Title 4 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

5 ©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

6 ©2012 Fluke Corporation SPRT Health 6 How/why does it drift? What will damage it? SPRT - Standard Platinum Resistance Thermometer Your subject photo here

7 ©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, Damage

8 ©2012 Fluke Corporation SPRT Health 8 What can you do to prevent drift or fix damage? SPRT - Standard Platinum Resistance Thermometer Your subject photo here

9 ©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 construction 2.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 prevention

10 ©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 & Maintenance

11 ©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 & Maintenance

12 ©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 & Maintenance

13 ©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 & Maintenance

14 ©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 & Maintenance

15 ©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 & Maintenance

16 ©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 Conclusion

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