Trends in temperature calibration
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Trends in Temperature Calibration. David Southworth VP: Sales and Marketing Isothermal Technology Ltd, UK (Isotech) www.isotech.co.uk. Trends in Temperature Calibration. We see from Industry to Primary Metrology a demand for greater accuracy A demand for more confidence

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Trends in temperature calibration

Trends in Temperature Calibration

David Southworth

VP: Sales and Marketing

Isothermal Technology Ltd, UK (Isotech)

www.isotech.co.uk


Trends in temperature calibration1

Trends in Temperature Calibration

  • We see from Industry to Primary Metrology a demand for greater accuracy

  • A demand for more confidence

  • We have responded with innovative new technology


Introducing isotech

Introducing Isotech

  • David Southworth

    • [email protected]

  • Worked at Isotech since 1984

    • Engineering Background

    • VP Sales and Marketing since 2006


Trends in temperature calibration

UK Company

  • Isotech

    • Established in 1980

    • Premier Supplier of Temperature Equipment

    • Premier UKAS Temperature Calibration Lab

    • Premier Source of Articles and Training


Trends in temperature calibration

NTPL

  • NTPL – Isothermal Technology's Calibration Laboratory


Trends in temperature calibration

NTPL

  • NTPL – Isothermal Technology's Calibration Laboratory

    • Best Measurement Capability, Gallium Fixed Point Cells

      • 0.000,07°C!

    • Within 4uK of NIST Reference Cell – 0.000004°C

    • +/-0.07mK 2 Sigma Uncertainty (NIST only National Lab with smaller uncertainties


National metrology institutes use isotech equipment

National Metrology Institutes use Isotech equipment

  • Primary Standards

    • ITS-90 Fixed Points

    • Standard Thermometers

    • Associated Equipment

Many Nations rely on Isotech for their Primary Temperature Standards


Secondary and industrial

Secondary and Industrial

  • Secondary Calibration Equipment

    • Liquid Baths

    • Fluidized Furnace

    • High Temperature Furnaces

    • Thermometers

    • Instruments

  • Industrial Calibration Equipment

    • Dry Blocks

    • Liquid Baths

    • Probes, Indicators and Software


Introducing isotech1

Introducing Isotech

  • Operated a Calibration Lab Since 1983

  • Achieved Accreditation in 1985

  • We regularly provide training courses


Introducing isotech2

Introducing Isotech

  • Manufacture Calibration Equipment

    • Industrial, Scientific and Primary Laboratories

  • We Use What We Produce

    • Isotech Lab equipped with Isotech products


Introducing isotech3

Introducing Isotech

  • NTPL equipped with Isotech Products

    • Industrial, Scientific and Primary Laboratories

  • UKAS Accreditation

    • Performance Claims Validated with regular audits


Trends in temperature calibration2

Trends in Temperature Calibration

  • Always a demand for greater accuracy

    • NEVER less accuracy – always better


Trends in temperature calibration3

Trends in Temperature Calibration

  • We see a demand to improve the accuracy of calibrating industrial sensors

  • For example Green Buildings

    • Calibrating Thermistors more accurately can save enormous amounts of money and protect the environment


Trends in temperature calibration4

Trends in Temperature Calibration

  • Isotech Response

    • Greater Accuracy with innovative fixed Point Solutions

      • ISOTower

    • Measuring Systems

      • milliK


Introduction

Most calibrations are performed by comparing the unknown characteristics of the thermometer under test to a calibrated reference thermometer

But how are the reference thermometers calibrated?

Introduction


Introduction1

The answer is, in a series of known and fixed temperatures where pure substances (usually metals) melt or freeze

Introduction


Introduction2

Three things are required before a thermometer can be calibrated at a fixed point

A fixed point cell (an ingot of pure metal inside a specially shaped graphite crucible)

An apparatus or furnace to melt and freeze the ingot of metal uniformly

The thermometer must be sufficiently immersed so that the sensing element is at the cell’s temperature

Introduction


Introduction3

Fixed point systems to National Laboratory standards are very expensive and are also inconvenient if the thermometer is short. So shorter and smaller fixed point systems were developed

The shorter, smaller and cheaper fixed points are approximations to those in National Laboratories and they seldom provide sufficient immersion for the thermometer being calibrated

Introduction


Introduction4

To offer the customer small uncertainties the smaller cells are calibrated in large furnaces and the user must make allowance for the stem conductance of his thermometer

This is not very satisfactory

Introduction


A new approach

What if we throw the existing ideas out of the window and start again?

What if the cell and furnace become one and inseparable?

What if the immersion necessary is calculated and compensated?

Might we end up with a novel but improved solution to fixed point calibration?

A New Approach


New design patents applied for

The key to the new design is a heat siphon in the shape of a Dewar with elongated inner tube

The key feature of the Siphonic Dewar is that it is gradient-free so a cell inside will melt and freeze uniformly

Next the cell fits snugly inside and is sealed in place surrounded by 1 atmosphere of pure argon

New Design (Patents Applied For)


Combining cell and apparatus

The concept was patented and called a Siphonic Cell (S.C.)

Combining Cell and Apparatus


Combining cell and apparatus1

The ideal apparatus to surround a cell is a heat pipe or heat siphon. If the outer wall of a metal clad fixed point cell also becomes the inner wall of the heat siphon then a very simple structure of ideal thermal profile would result

Combining Cell and Apparatus


How does it work

How Does it Work?

  • Two heaters are used, the main heater for the Siphonic Dewar, the second heats the immersion compensator to the same temperature as the cell


Immersion compensator ic

Immersion Compensator IC

  • The depth from metal surface to the bottom of the re-entrant tube is 180mm and this is inadequate for most SPRTs

  • The unit under test therefore needs to go through an isothermal zone above the cell set to the cell’s transition temperature


Immersion compensator ic1

Immersion Compensator IC

  • The Immersion Compensator actively provides the Isothermal Zone


How does it work1

How Does it Work?

  • The control temperature is set above the melt temperature – the cell melts. 0.1°C above yields a 30 hours melt. 0.2°C above 15 hours melt etc

  • Setting the temperature 0.1°C below yields a 30 hour freeze etc


Results

Results

  • A series of melt and freeze plateau graphs follow

Slide: 28


Siphonic sn fixed point cell melt plateau

Siphonic Sn Fixed Point Cell Melt Plateau


Siphonic sn fixed point cell freeze plateau

Siphonic Sn Fixed Point Cell Freeze Plateau


Siphonic zn fixed point cell melt plateau

Siphonic Zn Fixed Point Cell Melt Plateau


Siphonic zn fixed point cell freeze plateau

Siphonic Zn Fixed Point Cell Freeze Plateau


Siphonic al fixed point cell melt plateau

Siphonic Al Fixed Point Cell Melt Plateau


Siphonic al fixed point cell freeze plateau

Siphonic Al Fixed Point Cell Freeze Plateau


German laboratory invested in isotowers

German Laboratory Invested in ISOTowers

  • KK set up a laboratory based on ISOTowers


Isotowers in germany

ISOTowers in Germany

  • Achieved Daaks (formerly DKD accreditation

  • Tin 3mK

  • Zinc 3mK

  • Aluminium 5mK


Trends in temperature calibration5

Trends in Temperature Calibration

  • Always a demand for greater accuracy

    • As well as ISOTowers we have responded with new instrumentation


Trends in temperature calibration6

Trends in Temperature Calibration

  • Isotech Response for Higher Accuracy

    • Measuring Systems

      • milliK


Millik

milliK

  • High Accuracy Precision Thermometer

  • Why called milliK?

    • One thousandth of a ⁰C, 0.001 ⁰C is 1milli Kelvin, mK

    • milliK works to this level


Millik greater accuracy

milliK: Greater Accuracy

  • Resistance thermometers

    • 3mK at 0⁰C

      • 4mK over 1 year

    • Resolution of 0.0001⁰C, 0.1mK

  • Thermocouples

    • 2µV and 4µV over 12 months

      • For Type K – 4µV =0.1 ⁰C


Millik logging

milliK Logging

  • Other instruments can store up to several thousands of data points

  • The milliK has capacity to log time stamped data for up to six months internally, add a low cost USB Memory Drive and store a lifetime of data


Millik usb

milliK USB

  • On the same USB you can plug a Mouse / Keyboard to ease entering probe calibration data, Set Programs etc.


Millik innovation

milliK Innovation

  • Colour Display

    • Choice of Strip Chart or Numeric

      • Includes simultaneous view of all three channels


Millik innovation1

milliK Innovation

  • Isolated Inputs

    • High Degree of Galvanic Isolation

      • Sensor Inputs Isolated from current input

      • Avoid Problems with high voltage pick up on TC inputs

    • Safety


Millik innovation2

milliK Innovation

  • Built in 24VDC PSU

    • Isolated

    • Power Transmitters


Millik innovation3

milliK Innovation

  • Connectivity

    • Two Serial Ports

      • For PC connections to PC and Dry Block

      • Easy to program SCPI Style Interface

    • Controls ISOTECH Dry Blocks and Baths


Millik innovation4

milliK Innovation

  • USB Host

    • Memory Stick / Mouse / Keyboard

  • Ethernet

    • Remote control over network


Expandable

Expandable

The millisKanner allows for more channels


Expanding the millik

Expanding the milliK

  • The millisKanner Channel Expander

    • Connect SPRT, PRT, Thermistor or Thermocouple on any channel

  • It is not just a scanner


So what is the milliskanner

So what is the millisKanner?

  • Expands milliK to have more inputs

  • Allows for an SPRT, PRT, Thermistor or Thermocouple on any channel


So what is the milliskanner1

So what is the millisKanner?

  • Flexibility of Inputs

    • No need for lots of expensive modules


So what is the milliskanner2

So what is the millisKanner?

  • Solid State Design

    • No mechanical relays

    • High Reliability

  • Isolated Inputs

    • Galvanic Isolation Between both contacts and PSU and Control Circuitry

    • Benefits – Better Measurements and lower noise


So what is the milliskanner3

So what is the millisKanner?

  • Intelligent Design

    • Automatically adapts to suit sensor type

      • Handles Thermal EMFs for PRT and TCs

  • milliK Automatically Senses new millisKanners

  • All Driven from milliK

  • milliK does the thinking

    • Self configures – no wrong cables


  • So what is the milliskanner4

    So what is the millisKanner?

    • milliK supports maximum of four millisKanners

    • 33 Channels

      • Plus Current Input


    New solution millik

    New Solution: milliK

    • We have a new solution for multiple channel precision measurement

    • Unmatched


    Trends in metrology

    Trends in Metrology

    • NEW SI

    • Interest in redefining the kilogram, the ampere, the kelvin and the mole


    Trends

    Trends

    • Proposed new definition for the Kelvin

    • The Kelvin is currently defined as the fraction 1⁄273.16 of the thermodynamic temperature of the triple point of water (exactly 0.01 °C)


    Trends1

    Trends

    • Rather than have an “artefact” (WTP Cell) goal is to relate the Kelvin terms of the SI unit of energy, the joule by fixing the value of the Boltzmann constant k

      • which is simply the proportionality constant between temperature and thermal energy kT


    Trends2

    Trends

    • A proposed new definition (definition is still being debated)

      • The kelvin is the change of thermodynamic temperature T that results in a change of the thermal energy kT by exactly 1.380 65X X × 10-23 joule, where k is the Boltzmann constant

    • Problem is the Boltzmann Constant is not known to a sufficient level

    • Number of experiments on going to determine the exact numerical value


    Trends3

    Trends

    • For almost all users, the redefinition will pass unnoticed; thermometers calibrated before the change will continue to indicate the correct temperature

    • Water Triple Point Cells will still be used to calibrate SPRTs


    What is a water triple point cell

    What is a Water Triple Point Cell?

    • Most Important Defining Fixed Point

      • All three phases coexisting in thermal equilibrium

        • Solid (Ice)

        • Liquid

        • Vapour

    • Unique

      • only realizable defining fixed point common to the Kelvin Thermodynamic Temperature Scale (KTTS) and the ITS-90

    0.01°C

    (273.16 K )


    Water triple point cells

    Water Triple Point Cells

    • Lots of Different Sizes


    Water triple point cells1

    Water Triple Point Cells

    • A Super Cooled Cell


    Trends in temperature calibration7

    Trends in Temperature Calibration

    • For Primary Standards we see not a new definition but to better understand the fixed points

    • We see a demand to improve ITS-90 Fixed Point Cells and better understand the effects of impurities


    What is an its 90 cell

    What is an ITS-90 Cell?

    • ITS-90 Fixed Points

    A Sealed Fixed Point Cell


    Standard its 90 cells

    Standard ITS-90 Cells


    Its 90 fixed points

    ITS-90 Fixed Points


    Trends in temperature calibration8

    Trends in Temperature Calibration

    • We see a demand to for increased confidence in measurements made with thermometry bridges


    Innovative new bridges microk

    Innovative New Bridges: microK


    Innovative new bridges microk1

    Innovative New Bridges: microK

    • A Thermometry Bridge that can work to 17µK at Wtp (0.000017ºC)

    • As well as SPRTs works with all laboratory standard types

      • PRTs, Thermocouples and Thermistors


    Resistance and voltage

    Resistance AND Voltage

    • microK supports

      • SPRTs and IPRTs

      • Thermistors

      • Thermocouples

        • Only instrument in its class to do this

        • A DVM with comparable performance has a similar cost to the microK alone


    The a to d

    The A to D

    • Uses specially designed analogue to digital converter used in conjunction with a digital signal processor (DSP)

    • Uses a unique adaptation of existing advanced sigma-delta ADC techniques to achieve linearity better than 0.07 ppm.

    • A further major benefit of this ADC technique is its low noise performance,

      • reduced by a factor of 32 over conventional sigma-delta ADC circuits

    • Licensed from NPL


    Zero drift for resistance

    Zero Drift for Resistance

    • The microK uses a “substitution technique” in which the Device-Under-Test and the Reference are successively switched

      • This means that the stability of resistance ratio measurements is immeasurably small

    • Unique – Drift Free in Ratio Measurement


    Three channel

    Three Channel

    • Three Input Channels

      • Best Practise Ready

      • Allows two standards and a device under test to be connected simultaneously

    • Expandable

      • Add up to 90 channels


    Easy to use

    Easy to Use

    • Operated by large touch screen display

      • Intuitive

      • Can add keyboard and mouse


    Easy to use1

    Easy to Use

    • Includes Graphing Facility

      • Auto or Manual Scales

      • Intuitive


    Easy to use2

    Easy to Use

    • Log Data to Internal Memory

    • Or USB Pen Drive


    Solid state reliable

    Solid State - Reliable

    • All Solid Sate

    • Reliable

      • No potentiometers

      • No Dials

      • No Knobs

      • No Relays


    Microk

    microK


    New innovation for thermometry

    New Innovation for Thermometry

    • Isotech microK


    Demand for higher accuracy

    Demand for Higher Accuracy

    • How can you trust a microK?

    • How can you trust an AC Bridge?

    • How can you trust a high accuracy thermometer?


    Ratio measurement

    Ratio Measurement

    • Bridges of this type make ratio measurements


    Trends in temperature calibration increasing bridge confidence

    Trends in Temperature Calibration: Increasing Bridge Confidence

    • One simple method for checking a resistance bridge is to measure a pair of resistors separately, and then measure the two in series

    • Ideally the series measurement should equal the sum of the two individual measurements


    Trends in temperature calibration increasing bridge confidence1

    Trends in Temperature Calibration: Increasing Bridge Confidence

    • Another check is to measure the ratio of two resistances, then swap the resistors and measure the reciprocal ratio (or complement)

    • Ideally the product of the two measurements should equal 1.0 exactly

    • Problem is how to check over the whole range?


    Trends in temperature calibration increasing bridge confidence2

    Trends in Temperature Calibration: Increasing Bridge Confidence

    • The answer is to use the RBC

    • The RBC exploits the same principles as the linearity and complement check

    • It uses a network of four stable four-terminal resistors that can be connected in 35 different series and parallel combinations

    • The combinatorial calibration method is particularly powerful because it is not necessary to know the actual values of the four resistors


    Trends in temperature calibration increasing bridge confidence3

    Trends in Temperature Calibration: Increasing Bridge Confidence

    • Concept developed by Rod White – at the NMI of New Zealand

    • Now an Automatic Version

    • Includes Software to create the report


    Trends in temperature calibration increasing bridge confidence4

    Trends in Temperature Calibration: Increasing Bridge Confidence

    • “A Method for Calibrating Resistance Thermometry Bridges” Rod White evaluated 38 Bridges, small but significant faults were found with 15% of those tested, but “like the walking wounded” they continued to provide a plausible reading.


    Trends in temperature calibration increasing bridge confidence5

    Trends in Temperature Calibration: Increasing Bridge Confidence

    • “A Method for Calibrating Resistance Thermometry Bridges” Rod White evaluated 38 Bridges, small but significant faults were found with 15% of those tested, but “like the walking wounded” they continued to provide a plausible reading.


    New automatic version

    New Automatic Version


    New automatic version1

    New Automatic Version

    • Same Size as a Standard Resistor

      • Can be immersed in oil bath for temperature control

    • Improved Accuracy

    • Fully Automatic

      • Bridge and RBC


    Thank you

    Thank you


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