NIST Technical Note 1764

High-Temperature Guarded-Hot-Plate and Pipe 

Measurements: 2nd Operators Workshop 

(March 19-20, 2012) Co-sponsored by ASTM 

Committee C16 on Thermal Insulation

Robert Zarr

Thomas Whitaker

Frank Tyler

http://dx.doi.org/10.6028/NIST.TN.1764
NIST Technical Note 1764

High-Temperature Guarded-Hot-Plate and Pipe 

Measurements: 2nd Operators Workshop 

(March 19-20, 2012) Co-sponsored by ASTM 

Committee C16 on Thermal Insulation

Robert Zarr

Engineering Laboratory

Energy and Environment Division

Thomas Whitaker

Industrial Insulation Group

Frank Tyler

Owens Corning

http://dx.doi.org/10.6028/NIST.TN.1764

November 2012

U.S. Department of Commerce 

Rebecca Blank, Acting Secretary

National Institute of Standards and Technology 

Patrick D. Gallagher, Under Secretary of Commerce for Standards and Technology and Director 
Certain commercial entities, equipment, or materials may be identified in this

document in order to describe an experimental procedure or concept adequately.

Such identification is not intended to imply recommendation or endorsement by the

National Institute of Standards and Technology, nor is it intended to imply that the

entities, materials, or equipment are necessarily the best available for the purpose. 

National Institute of Standards and Technology Technical Note 1764

Natl. Inst. Stand. Technol. Tech. Note 1764, 286 pages (November 2012) 

http://dx.doi.org/10.6028/NIST.TN.1764

CODEN: NTNOEF
i

Table of Contents

1. Intronduction.....................................................................................................................................................1

2. Workshop Objective and Goals ......................................................................................................................1

3. Participants...........................................................................................................................................1

4. Agenda ..................................................................................................................................................2

4.1. Session 1............................................................................................................................................2

4.2. Session 2............................................................................................................................................2

4.3. Session 3............................................................................................................................................4

4.4. Session 4............................................................................................................................................4

5. Discussion Summaries...........................................................................................................................5

5.1. Session 1............................................................................................................................................5

5.1.1. Industry needs, ASTM perspective ...............................................................................................5

5.1.2. European perspective ...................................................................................................................5

5.1.3. Summary of NIST research; Overview of NIST SRM & Measurement Services............................6

5.2. Session 2............................................................................................................................................7

5.2.1. Tour of NIST Metrology Laboratories (Advanced Measurement Laboratory Complex)...............7

5.2.2. Laboratoire national de métrologie et d’essais (LNE) GHP – Situation in France.........................7

5.2.3. Tour of NIST GHP Laboratory Facilities.........................................................................................7

5.2.4. Thickness Determination Discussion (Tom Whitaker and Frank Tyler, Moderators)...................7

5.2.5. Sensor Reliability and Accuracy Discussion (Tom Whitaker and Frank Tyler, Moderators).........9

5.2.6. Guard Imbalance Check Discussion (Tom Whitaker and Frank Tyler, Moderators)...................10

5.2.7. Surface(s) Emissivity (Tom Whitaker and Frank Tyler, Moderators)..........................................10

5.3. Session 3..........................................................................................................................................11

5.3.1. Control System Considerations and Steady-State Issues............................................................11

5.3.2. Uncertainty & Reporting.............................................................................................................13

5.4. Session 4..........................................................................................................................................13

5.4.1. NVLAP C177/C518 Proficiency Tests...........................................................................................13

5.4.2. Europe Inter-laboratory comparison..........................................................................................14

5.4.3. High-temperature thermal insulation industry needs................................................................14

5.4.4. Experimental design (DEX) for Pipe Round Robin.......................................................................14

5.4.5. Open Discussion about Workshop (Tom Whitaker and Frank Tyler, Moderators) ....................15

6. Summary and Recommendations.......................................................................................................16

7. Acknowledgments...............................................................................................................................17

Appendix A: Participants ........................................................................................................................................18
ii

Appendix B: 1st Workshop Proceedings.............................................................................................................. 20

Appendix C: 2nd Workshop Proceedings - SESSION 1 Presentations ...............................................................23

Appendix D: 2nd Workshop Proceedings - SESSION 2 Presentations ...............................................................61

Appendix E: 2nd Workshop Proceedings - SESSION 3 Presentations..............................................................174

Appendix F: 2nd Workshop Proceedings - SESSION 4 Presentations..............................................................220
1

1. Introduction

The workshop on high-temperature guarded-hot-plate and pipe measurements was held on March 19-

20, 2012 at the National Institute of Standards and Technology (NIST) in Gaithersburg, Maryland, USA. 

The workshop was co-sponsored by the ASTM International Subcommittee C16:30 on Thermal Measurement and by the National Institute of Standards and Technology. This was the second workshop in a 

series that specifically focused on the needs of operators conducting these types of measurements.

2. Workshop Objective and Goals

The objective of the workshop was to examine and to improve the general understanding of the operation of the guarded-hot-plate and pipe apparatus at elevated temperatures (up to 650 °C).

The ultimate goal of the workshop was to examine and, hopefully, to reduce the present levels of variation in inter-laboratory comparisons of guarded-hot-plate and pipe apparatus measurements at elevated temperatures. To support this effort, five general areas of discussion were identified by the organizers and are presented below:

1) the role of NIST with respect to the development of high-temperature thermal insulation reference materials and/or measurement services for the public;

2) the role of calibration in the metrological traceability for primary input (and some secondary) 

quantities that are required for the determination of steady-state thermal transmission properties;

3) the need for effective and accurate control strategies for the guarded-hot-plate and pipe apparatus;

4) the assessment of measurement uncertainties by using international guidelines such as the 

Guide to Expression of Uncertainty in Measurement (GUM) and,

5) the development and use of design of experiment approach in the planning of future interlaboratory comparisons.

3. Participants

The participants of the workshop included representatives from the following general categories: thermal insulation producers that utilize the equipment, equipment manufacturers, testing laboratories, 

consultants, academics, and government. Exhibit 1 presents a breakdown of the participants. Appendix A is a directory of the participants. There were seven international participants from Canada and 

Europe.

Exhibit 1. Breakdown of workshop participants by user category

Category Participants

Thermal insulation manufacturer 9

Equipment manufacturer or testing laboratory 7

Consultant 2

Academic 1

Government 8

TOTAL 27
2

4. Agenda

The workshop was organized into four sequential sessions. The technical approach was based on the 1st

Workshop Proceedings (Appendix B), which noted that the plate and pipe methods, although different 

in physical geometry, confront many of the same technical challenges. As a result, this workshop was

organized along common generic issues. Each session included presentations followed by an open discussion period. The discussion minutes were recorded by the Session Secretary, edited by the Workshop Organizers, and described in Section 5. The presentations for Session 1 through Session 4 are represented with permission of their authors in Appendix C through Appendix F, respectively.

4.1. Session 1

Session 1 focused on the current status of high-temperature thermal insulation reference materials in 

North America and Europe. An overview of NIST research activities in this area were given as well as an 

overview of the NIST Standard Reference Data, Standard Reference Material, and Measurement Service 

Program.

4.2. Session 2

Session 2 provided tours of the NIST metrology laboratories for electrical and dimensional measurements

located in the Advanced Metrology Laboratory Complex (AML). (Unfortunately, the temperature metrology laboratories were unavailable due to a schedule conflict with the 9th International Temperature Symposium.) An overview of research activities at the Laboratoire national de métrologie et d’essais (LNE) were 

presented. The presentation was followed by a tour of the NIST guarded-hot-plate facilities which includSession 1 (Day 1)*

Moderator: Bill Healy Secretary: Monyelle Mingo

9:00 Welcome and Introductions Bill Healy

9:15 Workshop Overview Robert Zarr

A. High-temperature Reference Materials and Measurement Services

09:30 Industry needs, ASTM perspective Tom Whitaker

09:50 Europe outlook Erik Rasmussen

Roland Schreiner

10:05 BREAK – 10 min.

10:15 Summary of NIST research Robert Zarr

10:30 Overview of NIST SRM & Measurement Services Robert Watters

11:00 DISCUSSION

12 Noon LUNCH (NIST Cafeteria)

*Building 224, Room B245 unless otherwise stated
3

ed a short presentation on the construction of the 500 mm guarded-hot-plate apparatus and a preview of 

the PID control strategies for the apparatus. Summary discussions were organized afterwards on topics 

identified in the 1st workshop including thickness measurements, sensor reliability and accuracy, guard 

imbalance, and surface emissivity.

Session 2 (Day 1)*

Moderators: Tom Whitaker, Frank Tyler Secretary: Leah Strohsnitter

13:00 Tour of NIST Metrology Laboratories (AML)

 Electrical (Building 218, Room F0013) Rand Elmquist, Richard Steiner, Yi-hua Tang

 Dimensional (Building 219, Room G024) John Stoup

14:30 Laboratoire national de métrologie et d’essais (LNE) GHP Alain Koenen

(Building 224)

15:00 Tour of NIST GHP Facilities (Building 226) Robert Zarr, Bill Healy

(advance demonstration of PID computer model) Bill Thomas

B. Thickness Determination

16:00 DISCUSSION Attendees

Suggested topics:

Plate: use of spacers

Pipe: pin versus circumference methods, bands

Temperature effect (measure or use literature values)

C. Sensor Reliability and Accuracy

16:20 DISCUSSION Attendees

Suggested topics:

Uniformity check: number of sensors, locations

Type of sensor: thermocouple versus platinum resistance thermometer

Thermocouples: sheathed versus non sheathed (grounding issues)

Temperature effect – change with cycling, degradation (how to check)

D. Guard Imbalance Check

16:40 DISCUSSION Attendees

Suggested topics:

Uniformity check: number of sensors, locations

Thermocouples versus thermopile

Imbalance experiment

Gap insulation, emittance, expansion

E. Surface(s) Emissivity

17:00 DISCUSSION Attendees

Suggested topics:

How to measure

Coatings – emittance, durability

17:30 Adjourn Day 1

18:00 Dinner at local restaurant (optional – reservations requested) Return to hotel

*Building 224, Room B245 unless otherwise stated
4

4.3. Session 3

In Session 3, there were three presentations on PID (proportional, integral, derivative) control: 1) how to 

model the apparatus for simulation control strategies, 2) application to the plate method; and 3) application to the pipe method. After the Discussion period, two presentations were given on uncertainty 

analyses with applications on specific examples for the guarded-hot-plate method.

4.4. Session 4

Session 4 presented the results of two inter-laboratory comparisons. The first presentation summarized 

19 years of proficiency testing in North America by NVLAP for Test Method C 177 (guarded-hot-plate 

apparatus) and Test Method C 518 (heat-flow-meter apparatus). The second presentation summarized 

two European inter-laboratory comparisons. After the presentations, the session shifted focus to future 

inter-laboratory needs, specifically for the pipe test method. The first of these two presentations defined needs and goals of the proposed inter-laboratory comparison. The second presentation gave a 

Session 3 (Day 2)*

Moderators: Tom Whitaker, Frank Tyler Secretary: Frank Tyler

F. Control System Considerations and Steady-State Issues

09:00 Simulation of PID control model (plate) Bill Thomas

09:30 Application of PID control model (plate) Robert Zarr

09:55 Industry issues PID control (pipe) Tom Whitaker

10:15 BREAK – 10 min.

10:25 DISCUSSION Attendees

Suggested topics:

PID temperature control versus locking power (temperature drifts)

Level of control at different temperatures (how precise?)

How many data points per run

How to define steady-state

G. Uncertainty & Reporting

11:00 Introduction to GUM Robert Zarr

11:20 Uncertainty Analysis using the GUM and GUM supplement Blaza Toman

11:45 DISCUSSION

Suggested topics:

How to use GUM uncertainty budget to rank sources of uncertainty?

How does uncertainty analysis complement DEX for inter-laboratory study?

Introduction in ASTM C16 test methods

12 Noon LUNCH (NIST Cafeteria)

*Building 224, Room B245 unless otherwise stated
5

statistician’s approach to the design of experiment (DEX) for a general inter-laboratory comparison with 

specific examples to the pipe inter-laboratory comparison under consideration.

5. Discussion Summaries

Section 5 summarizes items of interest from the question-and-answer periods, and from the discussions 

that were encouraged by the moderators in each session. The minutes for each session were recorded, 

in outline form, by the Session Secretaries (Section 4) and also by William Healy, NIST. The notes were 

subsequently edited by the Workshop Organizers for review by the workshop attendees. In some cases, 

the names of the meeting attendees have been retained for clarity. Where appropriate, action items 

have been noted.

5.1. Session 1

5.1.1. Industry needs, ASTM perspective

Tom Whitaker voiced concern about initiating student interest in the field of industrial thermal insulation. [This issue was re-iterated in Session 4 with a follow-up question by Robert Zarr to Professor 

Thomas.]

5.1.2. European perspective

Erik Rasmussen and Roland Schreiner discussed expanded glass granulate as a round robin material for 

thermal conductivity to higher temperatures.

• Question 1: Frank Tyler asked if there were any issues with dimensional stability of the glass 

beads. Answer: They are dimensionally stable. The beads are commercially available from a 

company in Germany. The material is inexpensive.

Session 4 (Day 2)*

Moderators: Tom Whitaker, Frank Tyler Secretary: Leah Strohsnitter

H. Inter-laboratory Round Robin Recommendations

13:00 NVLAP C177/C518 Proficiency Tests Jeff Horlick

13:20 Europe Inter-laboratory comparison Helge Hoyer

13:40 BREAK – 10 min.

13:50 High-temperature thermal insulation industry needs Tom Whitaker

14:30 Experimental design (DEX) for Pipe Round Robin Jim Filliben

17:00 Open Discussion about Workshop Tom Whitaker, Frank Tyler

17:15 Concluding Remarks Tom Whitaker, Frank Tyler

17:30 Adjourn Workshop

*Building 224, Room B245 unless otherwise stated
6

• Question 2: What about the temperature differences (delta-T) during the tests? Answer: On the 

guarded-hot-plate (GHP) tests, the delta-T is constant. For the pipe tests, the delta-T is variable.

• Question 3: What about the glass, is there an opacifier? Answer: No opacifier. There is a special 

method to produce an expanded glass. Optical data about the glass are available from FIW.

• Question 4: Is the model given in the presentation part of any standard? Answer: No. The true 

thermal conductivity takes into account conduction, radiation, convection, [etcetera].

• Question 5: Is there a standard for the Nusselt sphere given in the presentation? Answer: No. 

FIW is probably the only one with the sphere test method.

• Question 6: Can the model be standardized? Answer: Could circulate the Ph.D. thesis, but tough 

to understand.

• Comment 1: Five different labs have been part of the testing with glass spheres. They hope to 

have all labs in Europe and some in North America. The five labs have different testing sizes. 

They measured at 50 mm and 100 mm thicknesses. If not capable of measuring at 100 mm, 

measure then at the highest thickness possible. Under 20 mm, an error arises because of glass 

spheres. They have not measured optical effects. The delta-T for the GHP testing was 50 K. Erik 

Rasmussen can get more detailed results of the testing to the [workshop] group, if desired.

5.1.3. Summary of NIST research; Overview of NIST SRM & Measurement Services

Robert Zarr presented specific overview of NIST Guarded Hot Plate (GHP) activities and Robert Watters 

presented a general overview of the NIST SRD (Standard Reference Data), Calibration Services, and 

SRM (Standard Reference Material) programs. Questions and discussion were held to the end of both 

presentations.

• Question 1: Tom Whitaker asked if Europe is working to produce an SRM [using the glass 

spheres]. Response: The current effort is a private initiative.

• Question 2: Erik Rasmussen asked how do you determine the validity period of a reference material? Answer [from Robert Watters]: Some materials we know are inherently stable. Every 

statement on period of validity or expiration date includes the caveat that the SRM is stored and 

used as described in the paragraph on storage and use.. We do, on most occasions, use previous samples in the development of new reference materials. In other words, we may use a current SRM to help develop a new SRM. We do not do work to accelerate degradation. Comment

[from Robert Zarr]: Instrument stability is important as well. To that end, the NIST GHP labs 

check instrument stability by establishing a measurement traceability chain for their primary 

sensors. The NIST GHP labs have begun a rigorous effort to send sensors back to the NIST metrology labs for control and stability checks. The stability check for the test material is more difficult.

• Continued discussion [from attendee]: European reference material typically has a validity period of only 5 years. Fibrous-glass boards should be (much) longer. For example, NIST certificate 

for 1450d has instructions for handing, storage, and use. If one follows these directions for the 

SRM, the certification is valid indefinitely (as stated on the 1450d certificate). Could some NIST 

SRM certificates have a date regarding expiration dates? If so, could these certificates extend 

expiration date?

• Continued discussion: Frank Tyler stated that ASTM Test Method C 518 requires that the SRM (or 

other transfer standard used for calibration purposes) be replaced every 5 years. There has 

been an effort to remove this text from Test Method C 518 but negative votes on the item have 

been found persuasive and the text has remained. The essential point in the negative votes is a 

request for any laboratory to demonstrate, with actual data, that the 5-year limit is either valid 

or invalid. Currently, no one has such data. Action Item: This discussion topic was identified as 

an action item (for the ASTM C 518 task group to collect such data).
7

• Continued discussion: Andrzej Brzezinski asked how to resolve the apparent contradiction given 

in the SRM [1450d] certificate and the 5-year text given in Test Method C 518. Response: It was 

stated that the Test Method C 518 document was probably written assuming that the reference 

materials were not always handled in accordance within their Instructions for use. Comment:

Tim Rasinski noted that, as part of the NVLAP (National Voluntary Laboratory Accreditation Program) accreditation process, the laboratory does not need to discard [the reference material] at 

end of an expiration date. The NVLAP Assessor should not write a nonconformity against expired reference material as long as the lab has some process to show the reference materials 

have not drifted out of tolerance. The requirements of specific test methods will supersede this, 

however. One method to check [stability] could be to have two different units checked in two 

[different] devices.

• Question 3: Andrzej Brzezinski asked if there was a possible timeline for services by NIST. Answer: Robert Zarr responded that, depending on the outcome of the proposed inter-laboratory 

comparisons, the next stage of service from 20 °C to 200 °C is scheduled for the 2012 calendar 

year. The next temperature level would be scheduled afterwards.

5.2. Session 2

5.2.1. Tour of NIST Metrology Laboratories (Advanced Measurement Laboratory Complex)

Rand Elmquest, Richard Steiner, and Yi-hua Tang provided tours of the electrical resistance and voltage 

measurement laboratories located in the Advanced Measurement Laboratory Complex. Afterwards, 

John Stoup provided a tour of a dimensional measurement laboratory for the evaluation of coordinate 

measuring machines.

5.2.2. Laboratoire national de métrologie et d’essais (LNE) GHP – Situation in France

Alain Koenen presented an overview of current GHP activities at LNE.

• Question 1: For the inter-laboratory tests conducted at room temperature, was the variation of 

thickness known? Answer: No, the level of variation in the thermal conductivity data was not 

expected beforehand.

• Comment 1: In conjunction with the low-temperature thermal conductivity data presented, it 

was mentioned that NIST SRM 1450b was characterized to lower temperatures, down to liquid 

nitrogen temperatures (100 K).

5.2.3. Tour of NIST GHP Laboratory Facilities

Robert Zarr and John “Rusty” Hettenhouser presented a short photographic narration of the construction of the NIST 500 mm guarded-hot-plate apparatus. Afterwards, the attendees separated into three 

groups for tours of the NIST 1016 mm guarded-hot-plate facility, the NIST 500 mm guarded-hot-plate 

facility, and also a preview of the PID control model to be presented later in the workshop by Professor 

Thomas.

5.2.4. Thickness Determination Discussion (Tom Whitaker and Frank Tyler, Moderators)

As part of this topic and subsequent discussions on the primary measurements, the moderators began 

the dialogue with an open request for information on how attendees used spacers for their guardedhot-plate apparatus. Subsequent questions addressed thermal expansion issues.

• Question 1: How do you keep your plates spaced? Response: Marinite1 structural insulation machined to 0.001 in.2 (0.03 mm) using drop gauge.

 1 Certain commercial entities, equipment, or materials may be identified in this document in order to describe an 

experimental procedure or concept adequately. Such identification is not intended to imply recommendation or 
8

– Question 1a: Do you change thickness as temperature increases or do you assume constant? 

Response: Assumed to be constant.

– Question 1b: Does test material have different thermal expansion, if so what happens? Response: Usually, the test material is compressible and preconditioned. If you try to correct 

for [test] thickness, you would have to know what the thermal expansion [of the test material] is. If you don’t know, base it [test thickness] on room temp thickness.

– Question 1c: Are you going to change thickness calculation based on movement? Response:

Average data over portion that is stable.

• Question 2: Do other attendees do anything different? In other words, are there any other 

thoughts or methods to be discussed?

– Response: [In Section 7, ASTM C 177 states that, for rigid and high conductance specimens, 

the specimen surfaces should be made flat and parallel.] In actuality, the specimen surfaces 

will never be 100 % parallel. European standards warn against using the average [of thickness measurements] because you need full contact. It is important to use the separation 

between plates. The thermal resistance measurement is between flat surfaces so if they are 

off your measurement is off as well. You will have gaps, need to know that you will have 

good contact. Biggest source of mistakes.

– Comment from Tom Whitaker: For calcium silicate (rigid material), users can’t measure repeatable measurements, [inter-lab results show that we] got different thickness measurements.

• Question 3: Are there other ways that the attendees use to control the thickness of their plates,

other than spacers, and that they consider to be more reliable? Response: For thermal conductivity measurements at 25 °C, the plates are stopped at whatever height you want. Comment 

#1: But if [the test specimen is] compressible, you may modify density. Comment #2: Characterize [the test] material at target density and then decide whether or not to use spacers.

• Question 4: Does everyone neglect to make corrections for [thermal] expansion [for the spacers]? Is it the norm to use room temperature thickness? Response: Most [attendees] agree that 

they use room temperature [thickness]. [The] expansion [effect is limited] up to 1% for temperatures up to 650 °C.

• Question 5: What about for high temperature? Do we make corrections for thermal expansion 

effects? Response: This is a source of error. Comment #1: If you make correction for thickness 

you have to change density. Comment #2: The NIST 500 mm GHP thickness system has capability to measure [in-situ thickness] during the test, but most people do not have this capability.

• Question 6: What about spacers that will experience thermal expansion and therefore change 

[the plate] spacing? Response: The specimen is expanding, not the spacer. Another response: 

What if both expand?

• Question 7: For writing [documentary] standards, what should we do? Response: Have a system 

that you can preload and that you can measure what’s actually going on like NIST’s system. Then 

you can calibrate your system (without specimen or one that you know the expansion of). Or do 

 

endorsement by the National Institute of Standards and Technology, nor is it intended to imply that the entities, 

materials, or equipment are necessarily the best available for the purpose.

2 It is the policy of the National Institute of Standards and Technology to use the International System of Units (SI). 

However, in the North American construction and building materials industries, certain non-SI units are used and 

are reported in this publication (with SI equivalent units) to avoid confusion.
9

calibration with spacing material. Then you must assume the specimen will not expand more 

than spacer.

5.2.5. Sensor Reliability and Accuracy Discussion (Tom Whitaker and Frank Tyler, Moderators)

[Foreword to this Discussion: Dr. Dean Ripple, formerly with the NIST Thermometry Group, provided answers to the temperature questions from the 1st Workshop in Granville, Ohio.]

• Discussion on RTDs (resistive temperature devices) versus type K thermocouples (fine wire in 

metal sheath): One attendee noted that type K thermocouples “drifted.” Another attendee 

suggests [using] type N thermocouples because they don’t drift as much. Robert Zarr states that 

NIST uses type N thermocouples in thermally insulated metal sheaths. As a result of the fabrication process during vacuum brazing, the type N thermocouples were exposed to temperatures 

(near 925 °C) well above operation temperatures.

– Question 1 for NIST: Over the long term can you check the ones [type N thermocouples] that are 

installed? No, they are brazed in [the plates and edge-guard rings]. [However,] if you know how 

stable the PRT is, you should be able to measure drift [of the adjoining thermocouples in the 

plate].

• Question 2 for attendee: What kind of thermocouples do you use? Type K on previous plate systems. In newer plate systems, 100 ohm PRTs – moved away from thermocouples all together. 

Question 2a: How many [thermocouples] in the plates in the main heater (say 12 inch plate)? 

Response: For one plate system there are 3 in the main and 2 in the guard. For another plate 

system, there are 9 in the main heater and 8 in the guard. Again, these plate systems use PRTs, 

not thermocouples.

• Same Question (2) for other attendees: What kind of thermocouples do you use?

– Response 2b: Type N, shunted thermocouples. Type K is not stable for long, so they 

switched to type N. Use 5 thermocouples [averaged] for one plate’s temperature.

– Response 2c: Type E for temperatures up to 500 °C; 4 thermocouples on each side of plate 

(2-sided plate). Question from a participant: Why do you use that type? Response: Highest 

output at lowest temperatures. But above 500 °C, you’re ‘pushing it’.

– Response 2d: Type K, periodically push to 700 °C. At this temperature, a type K thermocouple drifts quickly.

• The moderators asked the attendees if there were other comments or questions to be discussed.

– Question 3 for attendees: How long/often do you recalibrate? Response 3a: Some thermocouples cannot be removed, so whole probes are replaced. [In general, one attendee noted 

that the temperature measurement systems are re-built after a certain time period determined by the user.] Response 3b: Some participants have applied external calibrated thermocouples which are used as reference for internal thermocouples calibration. The external 

thermocouples are applied at the same position as the internal mounted thermocouple. 

Question from attendee: How can you be sure your plate is uniform? How can you get external thermocouple on the outside? Response: The external thermocouple is placed in contact with the plate surface (on the outside) at the same location as the plate thermocouple.

– Question 4 from an attendee: Are there any issues with RTD’s breaking by excessive thermal 

expansion? Response: No, they are strong. The sensors are in a metal sheath.
10

• It was suggested that [ASTM] could collect data on what [temperature] sensors were used, how 

thickness measurements were taken, how often and by what means do you calibrate, etc. and 

determine how this affects measurement readings.

5.2.6. Guard Imbalance Check Discussion (Tom Whitaker and Frank Tyler, Moderators)

– Question for attendees: Do you control primarily on thermopile or surface thermocouples on 

plates?

– Response 1: There are several stages; first, control temperature. After [the system is] in 

steady state, switch to gap thermocouples. Main [heater] is controlled by thermocouples 

and the guard is controlled by the thermopiles.

– Response 2: Surface temperatures can give error, gap temperature and edge temperature 

will be different and gap temperature will be somewhere in between. Question from attendee: Is it significant? Response: We control on thermocouples, not thermopiles. It was 

significant enough to warrant concern for change. At 1 degree [unit unspecified], they were 

less than half a percent. Question from attendee: Did you run a guard imbalance test? Response: Yes, but does not have data on hand. Significance may have to do with size and 

thickness.

– Response 3: Other imbalance test: check slope to see difference in imbalance between apparatuses. They have added correction in slope to adjust balance of guard and measuring 

area. Question from attendee: Do you offset it more? Response: Normally it is set to zero, 

but change is usually seen between plus and minus. You see imbalance between guard and 

area, test gives option to make adjustment. Question from attendee: Is test run at different 

temperature? Response: Yes, at different thickness and temperature. Question from attendee: Have you induced a degree change between guard and analyzed the result? Response: 1 degree [unit unspecified] causes about 10%. Half to one degree [unit unspecified] 

imbalance causes significant result. Should look into effects of ratio of metered area to 

plate area.

– Comment: NIST conducts an imbalance check on each “new thickness specimen” received 

from a customer. We purposely do this as part of the uncertainty evaluation. [The gap 

thermopile voltage] never truly runs at zero volts, there is always some offset, usually small 

(on the order of a few tenths of a microvolt). Thus, there is always a small heat flow 

through guard gap. NIST typically combines the uncertainty in this small offset as part of the 

uncertainty analysis. We have discovered that, even though the gap voltage is small, the 

uncertainty can be large, especially as specimens get thicker (i.e., heat flow through the 

specimen is small relative to the heat flow across the guard gap).

5.2.7. Surface(s) Emissivity (Tom Whitaker and Frank Tyler, Moderators)

– Question for attendees: How important is it to get 0.8 (or above) for the plate emissivity?

– Response 1: No, because normally the bulk density of high temperature products is high so 

that radiation through specimen is minimal. For specimens having a low density, it is important to have high emissivity of plate.

– Response 2: High emittance coatings for high temperature testing have been discussed in 

Europe. One laboratory has proposed raising the 0.8 limit to either 0.9 or 0.95. There was, 

however, no clear evidence of benefit, and the value was impossible to maintain in the long

run. The conclusion was that there is no need to go higher than 0.8. Question from an attendee: Should this issue be researched more? Response: Yes, Helge Hoyer noted that he 

has a research report on the subject. It was suggested that the attendees can contact Helge 

Hoyer directly for the report.
11

– Response 3: The NIST GHP laboratory uses a Gier Dunkle1 DB-100 (ASTM E 408) to measure 

the near normal emittance of test samples and to check the plate emittances at room temperature. [Note: The instrument was on display during the GHP tour.] NIST uses a ceramic 

coating for their plate surfaces that measured 0.8 (ASTM E 408). The durability of the plate 

coating was the main issue. Question for NIST: How flat is surface after application? Answer: Very flat, as noted in the presentation, the vendor polishes the coating as part the fabrication process.

5.3. Session 3

5.3.1. Control System Considerations and Steady-State Issues

Bill Thomas, Robert Zarr, and Tom Whitaker presented back-to-back talks on PID control for plate and 

pipe apparatus. Questions and discussion were held to the end of the three presentations.

Professor Thomas described the PID objectives for the simulation model to allow faster tuning than the 

experiment as well as tighter control. For this discussion, the control elements and PID are all for center plate, not for cold sides. The model neglected gradients within plate as far as control surfaces. 

There were 9 knobs to play with; PID for each of 3 sections (main heater plus double guards). The outer guard is set at an offset of 5 μV. The conduction across the gap was modeled as follows:

= ∆

mCp C

T

where m = mass and ΔT = calculated time step.

The heating rate, q was modeled as follows

=

2

el

V

q R

where Rel = electrical resistance (Ω) of a heater element.

Knowing the power supply output, an incremental control algorithm for the simulation as well as for 

the apparatus. A key objective was to avoid overshoot because of the lengthy cool-down time required.

Presentation 2: Robert Zarr described the control strategies for the NIST 1016 mm GHP and for the 500 

mm GHP apparatus. For the 500 mm GHP, the PRT in the center of the meter plate is used as the control sensor for the meter-plate heater. Two formulae for the discrete controller have been tried: the 

positional form and the incremental form. Initial attempts focused on the positional form using proportional and integral (PI) control. The control, however, was unsuccessful due to “integral wind-up,” a 

condition in which the integral term over-accumulates error summation, and then under-accumulates, 

resulting in long-term oscillation. The result is theoretically removable, but NIST, after several months, 

was unsuccessful in removal of the oscillation. At the suggestion of co-worker, the researchers 

switched to the incremental form which has successfully been used in controlling the 1016 mm GHP for 

20 years. For the 500 mm GHP, the scan rate has been set 60 s. The resistance ratio for each SPRT is 

measured using a DC bridge and converted by software to a temperature. The system takes 24 h to 

reach steady-state conditions. Data are collected for the last 4 h.

Presentation 3: Tom Whitaker presented control strategies developed by Industrial Insulation Group for 

the pipe method. Industrial Insulation Group has tried controlling two ways: thermopile versus surface-mounted thermocouples. Once the power is locked, there is some temperature drift but this is of 

no concern (see Discussion). Whitaker noted that the steady-state definitions per ASTM C177 and C335 

need improvement. ISO 8302, he noted, is similar in that regard. Industrial Insulation Group (IIG) is ex-
12

ploring using alternating current (AC) for main heater. New kilowatt-hour technology (shown during 

NIST Electrical lab tour) may enable this and may be better at high temperatures.

Discussion

• Discussion by the attendees focused initially about permanent changes to the material with 

temperature, e.g., hydration/dehydration or decomposition resulting in mechanical movement 

such as shrinkage. Options included: 1) going up “the thermal conductivity/temperature curve,” 

then coming down “the curve;” 2) pre-heating specimen (either in the apparatus or in another 

conditioning chamber), etc. Arguments, pro & con, were advanced by the attendees.

– One viewpoint: Only going up the curve is valid as the material will not “see” temperatures 

beyond its application temperature.

– Counter viewpoint: Processes are designed for temperature excursions at start-up or other 

periods. Therefore, the material will see higher than application temperature.

– Comment 1: Ideally, measurements are conducted both up and down the thermal conductivity/temperature curve. It was noted that some materials exhibit two curves, depending 

on the direction; in essence, signifying that there is no unique thermal conductivity for the 

particular material.

– Comment 2: Only going down the curve may be more representative of field application but 

the process is time intensive due to no active cooling to remove heat from the apparatus.

– Comment 3: In some cases, this discussion is a moot point because the test point order is 

conducted as specified by the customer.

– Comment 4/Open Question: If proceeding up the thermal conductivity/temperature curve, 

how long does one wait at each temperature for the binder, if present, to burn out?

– Comment 5: Robert Zarr requested information on the quality of ASHRAE handbook data for 

industrial insulation materials and whether the data were obtained going up or going down 

with temperature.

– Discussion followed on control technique: In order to minimize shocking the heaters with a 

power surge, IIG will ramp the set point, by software, to next value. IIG uses proportional 

and derivative control (PD) rather than proportional and integral control (PI). Allows [temperature] drift with [power] lock because precision is not a requirement based on overall 

curve. IIG uses Fuji controllers which will do auto-tuning at high temperatures [control] not 

so good at higher temperatures. The controller has ability to respond to software commands. Software can query controller as to the voltage output of the power supply and can 

switch it into constant power.

Control Issues

• New techniques: IIG is now looking at AC for main heater control.

• IIG stated that, for control, the controller requires different PID control constants for different 

temperature regimes.

• Several attendees discussed the requirements for the digital-to-analog (D/A) conversion. Attendees used different D/A converters having the following values: 24 bit, 12 bit, or 10 bit 

(among others). Some attendees noted that 10 bit and 12 bit D/A converters are unsatisfactory 

for precise control due to insufficient resolution capability. It was noted that 16 bit D/A are adequate, commercially available, and are currently inexpensive.

• One attendee noted that, because power is square over [electrical] resistance, if you change the 

control voltage by a factor of 2, the power will change by a factor of 4, which can compound 

control with a “hunting” problem.
13

• One of the issues is when you get to lower outputs because of high thickness insulation, it’s hard 

to control very low power levels.

• Some labs use switchable in-line precision resistors for better control in low/high ranges.

5.3.2. Uncertainty & Reporting

Robert Zarr presented an introductory talk on the GUM and Blaza Toman presented an uncertainty 

analysis based on statistical approach recently approved in GUM supplement.

• Question 1: Bill Healy asked the attendees, with regard to the temperature range, what level of 

uncertainty are the attendees comfortable with at high temperature levels? Response: approximately 5% with some debate.

• Comment 1 and Question 2: Tom Whitaker stated he was somewhat uncomfortable about European EC Certification. He asked how do you go to a lab, get data, and know that you will meet 

that level? Response: Erik Rasmussen answered that the rules are made for consumer protection; not supposed to declare mean, but to declare curve with some kind of uncertainty. In Europe, [we are] aiming for ‘safe values’, not just mean, which reduces liability for the user. Uncertainty in testing is very important to Europeans.

• Comment 2: Tim Rasinski stated that as a NVLAP representative he is asked by participating labs, 

“why do we have to do an uncertainty calculation?” He stated that Germany is putting the uncertainty in the law; Europeans must use GUM and report coverage factor.

• Comment 3: Robert Zarr stated, should we not ask that, during an ASTM inter-laboratory study 

(ILS), each lab report its measurement uncertainty? He noted that this practice is currently required for inter-laboratory key and pilot comparisons among the national metrology laboratories.

• Comment 4: An attendee stated that one cannot attempt the uncertainty analysis to the level of 

commitment from NIST. Rasinski (NVLAP) stated that a laboratory need only have to consider 

primary contributors for the GUM, not necessarily all the sources cited by NIST (Zarr’s presentation).

• Comment 5: The attendees stated most labs in the U.S. report a precision and bias (PB), based 

upon ASTM method’s P&B section. Rasinski (NVLAP) stated that according to ISO 17025, if the 

equipment is built per prescribed ASTM method, then they can use the PB statement, but the 

reality is, some equipment built per spec is known to be outside the PB so there’s a disconnect.

• Comment 6: Erik Rasmussen stated that this is an excuse (i.e., to use PB). That’s why we’re having this workshop. In Europe, they’re demanding this type of exercise. They may skirt obligation 

in Europe as long as they can prove that they’re ‘working on the subject’.

• Comment 7: Rasinski (NVLAP) stated that if a manufacturer is considering shipping products outside of the U.S., you’re going to have people (i.e., auditors) carefully examining your uncertainties. Rasinski cited a recent case with an auditor in Australia that examined, questioned, and ultimately rejected an uncertainty calculation from a domestic manufacturer.

• Comment 8: Helge Hoyer stated that we need statistics. You will always find a single item that 

will be below a standard, so statistics are needed not only for producers but for consumers.

5.4. Session 4

5.4.1. NVLAP C177/C518 Proficiency Tests

Jeffrey Horlick summarized 19 years of NVLAP proficiency test results for ASTM Test Methods C 177 

and C 518.

• Comment 1: Tim Rasinski announced that NVLAP is currently seeking outside services to help run 

the NVLAP proficiency testing program. This individual person would need to coordinate the attainment of material, preparation of the material, and shipping of material to the laboratory 
14

participants. Mr. Rasinski also stated that NVLAP is also seeking one more individual to conduct 

accreditation assessments of thermal insulation products.

• Comment 2: It is important to note that all of the results presented in the talk by Jeffrey Horlick 

were at room temperature.

• Action Item 1: Robert Zarr recommended that the results of this presentation (which have been 

previously published in the open literature) be forwarded to ASTM Task Group C 177 and Task 

Group C 518 for consideration as new item of business for inclusion as part of the precision and

bias statement of the respective test methods.

• Comment 3: Tom Whitaker noted that over the course of 19 years, we have not made much improvements in the results.

5.4.2. Europe Inter-laboratory comparison

Helge Hoyer presented results from two high-temperature inter-laboratory comparisons conducted in 

Europe by the European Mineral Wool Association.

• Question 1: Was there an attempt to plot thermal conductivity versus bulk density? Answer:

Yes, but the results were not neat.

• Question 2: How much variation for the second material, 38mm? Answer: Four labs used 38 mm 

spacers; two labs 37.8 mm; and one lab 37.99 mm.

• Question 3: What was the range of variation? Answer: Some labs have fixed differences and 

some just use the spacers.

• Question 4: Given small number of labs, were there any statistical tests done? Answer: No.

• Comment 1: Looking at Lab G (on the slides), it’s running low from 100 °C to 500 °C. That is a 1-

in-6 chance of a lab running low. Raising that to the power of 4 will result in variation under 

5 %.

• Question 5: The maximum deviations are all positive, does that mean anything? Answer: No.

• Comment 2: Tests are randomized; the labels A-G do not represent order.

• Question 6: On mineral wool round, was the material preconditioned? Answer: No.

5.4.3. High-temperature thermal insulation industry needs

• Question 1: Where can we improve round robin testing?

– Response 1: Now requiring use of calipers for measurement, give actual measurement. Requiring densities to be presented along with dimension measurements and mass. Asking for 

raw temperature (i.e., thermocouple) data as well as average temperature of the hot and cold 

surfaces.

– Response 2: There is a broad variation in design of equipment and lengths (diameters are the 

same; all are 3 in. pipes). This may have an impact.

– Response 3: The test material has not been selected: difficulties with calcium silicate and with 

mineral wool. Is there a material that works well in a high-temp round robin to be used on a 

pipe apparatus that can be passed from lab to lab, etcetera? With glass piece, you must have 

stronger mechanical support because of weight. Q: How do you get the glass beads around 

the ends? Outside ‘jacket’ is put on (usually plastic). At the last ASTM meeting, a decision was 

made for mineral wool to get the round robin going, objections?

5.4.4. Experimental design (DEX) for Pipe Round Robin

• Comment 1: Comment from Jim Filliben based on the previous discussion:
15

– Observation 1: There is a large k, that is, a large number of factors that can affect the response. (In the previous Discussion [Section 5.3.2], Filliben counted the factors that were discussed and stopped counting when the tally reached 18 [ high enough].)

– Observation 2: n is small, that is the number of tests; and,

– Observation 3: sigma is unknown. Get question nailed down, specification of the problem as 

well.

• Comment 2: We probably need to do a sensitivity analysis before the inter-laboratory comparison. 

A what if? analysis to see what is important. Select a few primary and secondary factors. We do 

not fully understand how sensitive the results are to some of those factors. Prior to jumping into 

inter-laboratory comparison, it might be best to vet some of the issues in a sensitivity analysis.

– Response from attendees: Agreed with that approach.

– Response from Jim Filliben: Most common experiments here [at NIST] are sensitivity studies. 

Filliben typically uses 2-level fractional factorial designs; with 18 factors for this study, (218) is a 

lot of runs. Wants 180 numbers (not sure where he got this number), would run a 2(18-10)= 256 

numbers. Run this fractional factorial experiment, 2 levels. Constructing is relatively easy. 

Good information about main effects, but not necessarily interactions.

• Comment 3: As (mean) temperature increases, there is a curve in temperature [due to radiation 

effects]. Can run four equally spaced points either along the X-axis or Y-axis. For large multifactor 

experiments, look into interactions.

• Comment 4: Previous ASTM round robins (in the United States and North America) have not approached this design. Replication is important for these tests; if we can afford it, replicate everywhere.

• Action Item 2: Importance of sensitivity analysis, always lends valuable data/information about 

system/experiment. Look into doing ‘in-house’ sensitivity analysis. (Action item for next ASTM 

meeting).

5.4.5. Open Discussion about Workshop (Tom Whitaker and Frank Tyler, Moderators)

The following comments and questions were raised in the open discussion.

• Action Item 3: Request for electronic copy of presentations from this workshop to be made 

available.

• Action Item 4: The last workshop was held in 2007 which was 5 years ago. ASTM C16:30 should 

consider holding more frequent workshops. Question: Are similar workshops [on high temperature plate and pipe methods] held in Europe? Response from Erik Rasmussen: One already that 

has focused on 10 °C, another coming up in September in Belgium. This workshop has been inspiration for further work with high-temperature systems.

• Comment 1: Round robin presentation is similar to the results published by Mark Albers in ASTM 

STP 1426. Tom Whitaker is curious how results in Alber’s paper compare to results presented in 

this workshop. He will e-mail an electronic copy of the paper from ASTM STP 1426.

• Action Item 5: 5-year time interval prescribed in C518, can it be taken out?

• Action Item 6: Temperature sensor variations: This workshop highlighted that, for thermocouples, several different kinds are used among the workshop attendees. Is there a better way? 

Look into platinum resistance.

• Action Item 7: Steady state determination: How to determine what algorithm or criteria is best 

for determining when steady state is reached. How do you define that you’re in control?
16

• Action Item 8: Is it possible to have a guarded hot plate website for posting information and discussion that may occur between other workshop sessions?

• Question for Professor Thomas: As a follow-up to the Session 1 concern, Robert Zarr asked to 

Professor Thomas to comment on how to encourage more students to become involved in this 

area for study and employment. Professor Thomas noted that, quite simply, involve the faculty 

and the students will follow. Research grants are important. Thomas further noted that people 

will only pay attention when something is not working properly. No one pays attention when 

things are running smoothly.

• Comment 2: Good pace and good content during workshop, wide range of topics.

6. Summary and Recommendations

In general, this second workshop on high-temperature guarded-hot-plate and pipe measurements was 

well attended with participants from North America and Europe representing industry, consulting, academia, and government. The main objective of the workshop was to examine and to improve the general understanding of the operation of the guarded-hot-plate and pipe apparatus at elevated temperatures (up to 650°C). To accomplish this objective, the intention of the workshop was to present, and to 

discuss, the reasons and causes of differences between laboratory measurements with the ultimate goal 

to reduce the differences in laboratory comparisons.

To attain these objectives and goals, the workshop was organized into four sessions. Each session covered a particular subject considered important in achieving the overall goal of reducing the differences 

in laboratory comparisons. Session 1 covered the government’s role in providing reference materials to 

the public and Session 2 covered issues of metrological traceability in relation to the calibration of primary measurements for the guarded-hot-plate and pipe apparatus. Session 3 covered instrument control issues and measurement uncertainty. Session 4 presented data from two recent inter-laboratory

comparisons and how to design future inter-laboratory comparisons.

The general conclusion from the attendees was that the workshop was valuable and was also motivating 

with regards to further work with high-temperature systems. It was further noted that the first workshop was held in 2007 (five years ago) and that ASTM C 16:30 should consider holding workshops of this 

type more frequently. It was also requested that the workshop proceedings be made available for electronic publication.

One of the tasks of the Session Moderators was the identification of “action items” for further attention. 

The remaining text in Section 6 summarizes the eight “action items” that were identified by the moderators in the group discussions (Section 5). Recommendations from the workshop organizers are included 

with each action item. The majority of these action items are to be forwarded to the appropriate ASTM 

task group or subcommittee for further discussion.

1) The results of the NVLAP presentation (which have been previously published in the open literature) should be forwarded to ASTM Task Group C 177 and Task Group C 518 for consideration as 

new item of business for inclusion as part of the development of a modified precision and bias 

statement for the respective test methods.

2) The importance of sensitivity analysis always lends valuable data/information about system/experiment. The attendees should look into doing ‘in-house’ sensitivity analysis. (Action 

item for next ASTM meeting).

3) The last workshop was held in 2007 which was 5 years ago. ASTM C16:30 should consider holding more frequent workshops.
17

4) Request for electronic copy of presentations from this workshop to be made available.

5) The 5-year time interval prescribed in C518: can it be taken out?

6) Temperature sensor variations: This workshop highlighted that, for thermocouples, several different kinds are used among the workshop attendees. Is there a better way? Look into platinum 

resistance.

7) Steady state determination: How to determine what algorithm or criteria is best for determining 

when steady state is reached. How do you define that you’re in control?

8) Is it possible to have a guarded hot plate website for posting information and discussion that 

may occur between other workshop sessions?

7. Acknowledgments

The success of the workshop was a direct result of the quality of the speakers and the participants. The 

organizers recognize the contributions from the speakers and the insightful discussions from the participants.
18

Appendix A: Participants

Name Affiliation

Franz Bauer Exova

David Bell Southern Research Institute

Andrzej Brzezinski LaserComp 

Rob Campbell Netzsch Instruments, North America, LLC

Rick Dolin Industrial Insulation Group, LLC

Jim Filliben NIST Statistical Engineering Division

William Healy NIST Energy and Environment Division

Jeff Horlick NIST Standards Coordination Office

Helge Hoyer Rockwool International

Timothy Jonas Knauf Insulation

Alain Koenen Laboratoire national de métrologie et d'essais (LNE)

Niina Lehtinen Paroc Oy Ab R&D

Mark Mantonya Owens Corning

Bhavesh Patel Southern Research Institute

Olivier Pons Y Moll Isover Saint-Gobain CRIR

Tim Rasinski National Voluntary Laboratory Accreditation Program (NVLAP)

Erik Rasmussen Rockwool International

Mitch Rose Netzsch Instruments, North America, LLC

Roland Schreiner FIW München

Stephen Smith SES Consulting Services

Marc Thermitus Consultant

Bill Thomas Virginia Polytechnic Institute and State University (Virginia Tech)

Blaza Toman NIST Statistical Engineering Division

Frank Tyler Owens Corning

Robert Watters NIST Measurement Services Division

Tom Whitaker Industrial Insulation Group, LLC

Robert Zarr NIST Energy and Environment Division
19

Fig. A1 – Attendees at 2nd Operators Workshop

on High-Temperature Guarded-Hot-Plate and Pipe Measurements
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Appendix B: 1st Workshop Proceedings
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Appendix C: 2nd Workshop Proceedings - SESSION 1 Presentations
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