©2012 Fluke Corporation SPRT Health 1 Health Monitoring of SPRTs

©2012 Fluke Corporation SPRT Health 1

Health Monitoring of SPRTsHealth Monitoring of SPRTs


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


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


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


How/why does it drift?

What will damage it?




• 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


What can you do to prevent drift or fix damage?




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


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


Avoid mechanical shock• Do not leave in baths or furnaces for extended periods of time

• Handle carefully • Train staff



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



Annealing• At highest useable range for the sensor• Above 450C, preferably above 550C• For many hours (10-100)• In a non-contaminating furnace/block



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 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


• Shorting due to coils touching each other cannot be repaired

• Excessive change in resistance from misuse cannot be repaired



•Recent design improvements have made SPRTs more stable

•Challenges remain in sourcing pure platinum

•Research continues

•Drift is mainly due to handling issues

ConclusionConclusion

Documents

©2012 Fluke Corporation SPRT Health 1 Health Monitoring of SPRTs