1. Thermocouple Considerations for fire testing

2. Presentation overview
Introduction to Resonate testing
What is powerplant fire testing?
What do we use thermocouples for and how the standards define which thermocouples can be used
Sources of error and best practice
How we should go forward?

3. Introduction to resonate testing

4. Resonate Testing Ltd- Complimentary environmental testing
Fire and flammability
Vibration
General environmental
General Environmental
Cold and hot – temp cycling, soak and shock
Fire
Oil fuel burner, Gas Bunsen, Crib testing
Vibration
Sine, random , shock
High displacement and velocity

5. Resonate Testing Ltd- Fire Test Facilities
FAA fuel burner tests
Seat Cushions
Cargo Panel
Thermal Acoustical insulation
Powerplant components including fire wall and hoses
FAA (Carlin) Oil Burner
FAA OIL BURNER (NEXGEN) 

6. powerplant fire testing

7. Resonate Testing Ltd- Fire wall testing
Fire wall penetration A firewall is a structure designed to prevent a hazardous quantity of air, fluid, or flame from exiting a fire zone in which a fire has erupted and causing hazard to the aircraft. Firewalls must be fireproof. - Fire proof (exposure of 15 mins) - Fire resistant (exposure of 5 mins) Rig development to give air flows and pressure drops representative of installed environments and to include vibration.

8. Background Fire testing for Powerplant Components
Certification fire testing is used as a means for determining if a component of an aircraft is fire proof or fire resistant to the regulations
Criteria has been established to try to define that all components undergoing such a test are subjected to the same severity of flame from a burner which satisfies set requirements, to ensure that the test is comparative and consistent.
In particular the flame temperature and heat flux produced by the burner have to be calibrated at the given test location both pre and post testing, to qualify the test environment accurately simulates the real world condition.
Approved instrumentation is used to provide calibration data to show the repeatability and consistency of the results achieved.

9. Background Governing standards for powerplant testing
Various test methods, advisories and guides are used to provide criteria used in determining the flame characteristics required to test various components used in aircraft engines, their nacelles and their other supporting structures.
These Include:
FAA Power Plant Engineering Report No. 3A: Standard Fire Test Apparatus and Procedure (For Flexible Hose Assemblies), Revised March 1978
ISO2685: Environmental Test Procedures for Airborne Equipment – Resistance to Fire in Designated Fire Zones, International Standards Organisation
AC : Powerplant Installation and Propulsion System Component Fire Protection Test Methods, Standards and Criteria, Revised 1990
FAA Aircraft Material Fire Test Handbook: Chapter 11 Powerplant Hose Assemblies Test and Chapter 12 Powerplant Fire Penetration Test - used to determine the fire resistance components used in designated fire zones to damage due to flame and vibration for showing compliance with TSO C42, C53A, and C75. April 2000
SAE AIR 1377A: Fire Test Equipment for Flexible Hose and Tube Assemblies, Revised January 1980.
SAE AS 1055: Fire Testing of Flexible Hose, Tube Assemblies, Coils, Fittings and Similar System Components, Revised 1978.

10. Use of thermocouples in Fire testing

11. TC Requirements from the standards

12. TC Requirements from the standards
1/8” outer  24 AWG
1/16” outer  30 AWG
Gauge size 16 18 20 21 22 24 26 28 30
Diameter inches
0.0508
0.0403
0.0320
0.0285
0.0253
0.0201 
0.0159
0.0125
0.010
Diameter mm
1.29
1.02
0.813
0.723
0.643
0.511
0.404
0.320
0.254
AWG to mm
ISO 2685 REQUIREMENT –
AC REQUIREMENT
NB: these wire gauges do not fit in to a 3.0mm sheath under current manufacturing best practice
Wire gauge is more significant than external sheath size for accuracy?

13. Resonate Testing Ltd- Flame calibration instrumentation
7 type K thermocouples
1-inch apart (25mm)
1-inch above centreline
4-inches away from cone
3m external sheath
4-6mm exposed tip
24 AWG (0.5mm) wire

14. sources of error and best practice

15. Sources of error in TC measurements
Thermocouple errors- specification of the TC
Circuitry errors – How we connect the TC to the logger
Instrumentation errors – How we read the TC

16. Sources of error for thermocouples themselves
Thermocouple size:
Wire thickness (gauge)
Bead size
Sheathing outer diameter
Thermocouple Age:
Time in use (hours/days)
Number of cycles (extremely high temp to ambient)
Tip exposed or sheathed?
Type:
K- type thermocouple (is this the correct type for the range?)
Manufactured to a tolerance class and international standard?
Exposed tip or sheathed?
Differences between the temperature measured and ‘real’ temperature of the medium to be measured in a dynamic and turbulent environment?
How do we quantify the impact that each of these factors makes?
Is it 1% or 10% or more?
Which factor is likely to cause the largest error?

17. Sources of error in the circuitry
How do these compare to errors due to the TC themselves?
Lead Wires and Terminals:
Where highest accuracy is sought, it is preferable that the thermoelements extend without a break from the measuring junction to a reference junction.
The Reference or Cold Junction and Automatic Cold-Junction Compensation:
Some accuracy may be sacrificed for the convenience of eliminating the ice bath, and some indicating and recording instruments have built-in cold junction compensators.
Rapid variations in temperature at the location of the compensator may lead to errors of several degrees.
Controlled application of heat within a potentiometer in the vicinity of the compensator, as for instance by a thermostatically controlled light bulb, will improve the accuracy of compensation
Then the entire thermocouple circuit between the measuring junctions and the compensator should consist of material with the same thermoelectric properties as the elements constituting the measuring junction.
Ref: SAE AIR46B Type K TC for gas turbines

18. Tolerance class Is this independent of size and/or sheathing?
Type K thermocouples compliant with
BS EN Pt4 Class 1
375°C to 1000°C
± |t| → ± 40°C

19. Exposed tip versus sheathed
Provided the type and age of the thermocouples are the same they essentially read the same value.
The fully sheathed version is slower to respond causing an ‘aliasing’ effect which results in an averaging of the temperature measured
This effect is amplified when the thicker sheathed thermocouple is used - the thicker sheathed thermocouples will often read a lower value as the speed at which they react is much slower in the changing dynamic nature of the flame

20. Difference between temp of junction and the temperature of the medium

21. Effect of thermocouple size

23. Thermocouple age new old
Approximate 40-50°C drop in temperature experienced after several cycles

24. Summary – Thermocouples and temperature calibration
Type K thermocouples are being used at the top end of their range
The actual specified thermocouples are not available and the thermocouple industry has moved away from this definition
Exposed tip thermocouple, while giving fast response time and therefore a more accurate representation of the flame temperature have a finite life and should be replaced often
Thermocouples should be specified to meet international standard for their manufacture to ensure consistency and a minimum accuracy
Age has the biggest impact of the temperature measurement
The thermocouple reading temperature maybe significantly lower than the theoretical gas (flame) temperature in the high temperature environment
A smaller TC indicates a higher TC temperature and provides quicker response time than the bigger TC

25. Summary – Going forward
We would appreciate help from the thermocouple community
To help in specifying the correct thermocouple for this application
To identify the issues which have the biggest impact in the thermocouples not reading the flame temperature accurately

27. Additional reference material

28. Resonate Testing Ltd- Vibration and Shock Testing
Our vibration test laboratory features a high force electrodynamic vibration table capable of a wide range of frequencies, amplitudes and spectrums. In addition to the standards mention we have the capabilities of testing to customer specified requirements and defined vibration profiles.
Swept Sine Vibration Control Resonance Search and Tracked Dwell
Multi Frequency Sine Control
RTCA DO-160: SECTION 8.0 IEC :2007
Random Vibration Control
Power spectral density
RTCA DO-160G: SECTION 8.0 IEC :2008
Shock Testing
Classical shock
Drop test
RTCA DO-160G: SECTION 7.0 IEC :2008
IEC :2008
Vibration testing Capabilities
Shaker, slip Table and power amplifier

29. Resonate Testing Ltd- General Environmental
There are a range of general environmental tests which will be complimentary to the core Vibration and Fire Testing
Current capabilities
Temperature shock
Cold soak
Temp cycling
Icing
Waterproofness IP requirements
Future additions
Altitude
Sand and dust
Salt
Fluid susceptibility

30. Resonate Testing Ltd- Flammability testing
FAA Multi-purpose small scale flammability testing
The facility will also offer small scale testing and measurement of the ignition resistant properties of aircraft materials. This is vertical & horizontal and 45° Material Testing and can be expanded to the requirements of other industries.
To the following specifications:-
FAR Part 25 Appendix F Part I (Vertical, Horizontal, 45° and 60°)
Airbus AITM 2.002, 2.003, 2.004, & 2.005,
Boeing BSS 7230: F-1, F-2, F-3, F-4, F-5, & F-6
Other manufacturer specifications
FAA MULTI-PURPOSE SMALL SCALE FLAMMABILITY

31. Resonate at the movies…….
Resonate testing ltd ;         Flammability testing ;       Fire testing ;                       Vibration testing ;