Thermocouples used in big jets.... AS coursework
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From: Europe
Thermocouples used in big jets.... AS coursework
Hi there, I'm just doing my AS level coursework and am using a thermocouple, testing specs, accurace and all the rest of it. I was just wondering if anyone had any interesting uses or thermocouples on modern jet planes. The anti-ice system would be obvious I'd have thought, or in the engines- can anyone spcifically tell me how they work in particular situations and why they are used?
Champ
Champ
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From: UK
Joined: Jan 2008
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From: Dubai
Engine Exhaust Gas probs typically 7-11 probes all round connected in parallel to a junction and then forward with compensated leads. Probs gen alumel chromel junction. Typical fault is EGT under reading or spikes in the EGT trend.
Joined: Oct 2007
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From: UK
old ones used JPT too (Jet pipe Temp)
There is also ITT on some (Inter Turbine Temp) - it just depends where the T/couples are mounted (without meting)
You actually want the temp AT the turbine but it can be inferred from cooler positions.
There is also ITT on some (Inter Turbine Temp) - it just depends where the T/couples are mounted (without meting)
You actually want the temp AT the turbine but it can be inferred from cooler positions.
Joined: Oct 2003
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From: Gweriniaeth Cymru
Apologies for minor thread drift - I've been working on engines for 20 years and am still amazed at how the EGT system for the RR engines and other marques fail in the most unpredictable manner. Does anybody else see this - or am the only unlucky powerplant wallah?
PS - TET - Turbine Entry Temperature
PPS - Remembering that the wires from the T/C have to also be alumel chromel....
Brgd's
N1 Vibes
PS - TET - Turbine Entry Temperature
PPS - Remembering that the wires from the T/C have to also be alumel chromel....
Brgd's
N1 Vibes
Joined: Jan 2001
Posts: 545
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From: Dunstable, Beds UK
N1,
Must say that TGT failures in my experience are not that common.
The RB21 has 17 thermocouples that all route through a ballast resisitor.
Serveral themocouples can be u/s (Open circuit) but not have a dramatic effect on readings.
I have know up to half a dozen u/s with no marked indication problem.
There is usually a few degrees drop in indicated TGT
Of course there is also indicator failure but generally these are obvious faults
Sticking or FSD.
Must say that TGT failures in my experience are not that common.
The RB21 has 17 thermocouples that all route through a ballast resisitor.
Serveral themocouples can be u/s (Open circuit) but not have a dramatic effect on readings.
I have know up to half a dozen u/s with no marked indication problem.
There is usually a few degrees drop in indicated TGT
Of course there is also indicator failure but generally these are obvious faults
Sticking or FSD.
Joined: Dec 2004
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From: Jeddah, Saudi Arabia
RR Allison T56/501 engines have 18 thermocouples (3 per combustion liner). Any 1 thermocouple failing can cause a loss of up 24°C TIT at take off power. Not a lot you say - probably true, but the TD system will then increase fuel flow, i.e. increase TIT, until TIT signal from thermocouples matches input from the coordinator: result turbine overtemp, and eventual burn-out of turbine.
Joined: Oct 2003
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From: Gweriniaeth Cymru
GTT-shirt,
wasn't suggesting RB system is unreliable - in-fact I agree that I've only seen perhaps 1 headscratching defect a year and the local airline has 500 engines on-wing. But, the point I wanted to make was the peculiarity of some of the final fixes. Especially now with causes including FADEC technology, C-duct heatsheld material interference and even one event on a CFM where the Arinc 429 data wire in the pylon actually caused an EGT signal fluctuation.....
Brgd's
N Vibes
wasn't suggesting RB system is unreliable - in-fact I agree that I've only seen perhaps 1 headscratching defect a year and the local airline has 500 engines on-wing. But, the point I wanted to make was the peculiarity of some of the final fixes. Especially now with causes including FADEC technology, C-duct heatsheld material interference and even one event on a CFM where the Arinc 429 data wire in the pylon actually caused an EGT signal fluctuation.....
Brgd's
N Vibes
