Thermocouple Considerations for fire testing

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?

Introduction to resonate testing

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

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) 

powerplant fire testing

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.

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.

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 20-135: 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.

Use of thermocouples in Fire testing

TC Requirements from the standards

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 – AC20-135 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?

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

sources of error and best practice

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

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?

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

Tolerance class Is this independent of size and/or sheathing? Type K thermocouples compliant with BS EN 60584.1 Pt4 Class 1 375°C to 1000°C ±0.004 . |t| → ± 40°C

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

Difference between temp of junction and the temperature of the medium

Effect of thermocouple size

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

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

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

Additional reference material

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 60068-2-6:2007 Random Vibration Control Power spectral density RTCA DO-160G: SECTION 8.0 IEC 60068-2-64:2008 Shock Testing Classical shock Drop test RTCA DO-160G: SECTION 7.0 IEC 60068-2-27:2008 IEC 60068-2-31:2008 Vibration testing Capabilities Shaker, slip Table and power amplifier

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

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

Resonate at the movies……. Resonate testing ltd ;      https://www.youtube.com/watch?v=rqGaFAFZiLk   Flammability testing ;     https://www.youtube.com/watch?v=ktaKyhzq464   Fire testing ;                     https://www.youtube.com/watch?v=fg-R8zPg1Mw   Vibration testing ;           https://www.youtube.com/watch?v=q1zXWTj_thk