79 231 -LB TIT Probe Question

[DonMuncy]

Take what I say with a grain of salt, as I only know what I have read and heard. 

The TIT is a max temperature to keep you from hurting the turbocharger. No damage to the engine itself. So yes, you don't want to ruin the TC, so being conservative is good. But you aren't worried about your cylinders. For those, the number you need to worry about is CHT.

[gsxrpilot]

I'd agree with @DonMuncy that unlike CHT's, the TIT temp is only to protect the turbo. And there seems to be consensus that even running right at the redline of 1650 is probably fine. And that is very much unlike CHT's.  Certainly going through the red-line of 1650 on your way to LOP and lower temps is fine.

[LANCECASPER]

6 hours ago, DonMuncy said:

Take what I say with a grain of salt, as I only know what I have read and heard. 

The TIT is a max temperature to keep you from hurting the turbocharger. No damage to the engine itself. So yes, you don't want to ruin the TC, so being conservative is good. But you aren't worried about your cylinders. For those, the number you need to worry about is CHT.

I'd also say lower TIT temps are good for another reason. The higher the exhaust temps the harder it is on the exhaust system. On turbo charged airplanes that have been run hard the life of the exhaust system is much less.

[milotron]

5 hours ago, Cardinal767 said:

After all the discussion on how far off the OEM TIT indicator is, I connected(piggy back) my 830 to the OEM TIT probe. The part number on the probe installed is 3199516. Before starting the engine I checked that all CHT/EGT and now the 830's TIT temps all read the same as my aircraft OAT and the 830's independent OAT. All (15) temps were within 2*F of each other. The aircraft TIT of course was off scale too low. After takeoff I monitored both the aircraft TIT and the 830's indication as I climbed from 600 to 8,500 msl. At first, both indications were within 25*F(at 1300*F), with the 830 reading higher of the two, but that was short lived. The higher I climbed, the difference between the two increased, ending with about a 100*F split (830 highest)  . Here is what concerned me, in cruise (2400rpm, 30.0 MP @ 9.5-9.7gph LOP) the aircraft TIT read around 1525*F and the 830 read 1625*F. I tend to take the word of the one closer to the danger zone (and 37 years younger). I went ahead and continued to lean until the 830's TIT dropped below 1600*f to be safe. Being I'm new to LOP, is pushing the 1650*F max TIT normal?

Yes, I know I need to check the calibration of both indicators. Until I do, I just want to be nice to my engine.

Thanks for the help

Bob

My EDM 700 and factory gauge have the same relationship. That poor engine would not last long using the factory CHT and TIT gauges for monitoring!

 

iain

[carusoam]

The 1650°F is an important to be accurate gauge.  When the temp is run exceeding this guideline, the turbo blades suffer erosion issues...

They turn into nubs...

In this really hot chemically active environment, the TIT thermocouple is very much at risk itself.  The Sheath will suffer from some erosion as well.

Have your mechanic pull the TC/sensor to inspect it’s condition.  Comparing two points like OAT and boiling water... should be enough to see if the TC is working properly.

a 100°F error on a TIT reading doesn’t sound very useable.  You won’t be able to tell if the reading is getting worse... setting up your mixture using an unknown or failing system, can get expensive...

Question: Your piggyback 830TC is on the outside of the turbo’s case? The OEM TIT TC is in the exhaust stream internal to the case...  something isn’t right when the outside case reads higher than the inside exhaust stream...

Or do you have an independent EGT TC in the exhaust stream near the turbo inlet?  (This makes more sense for the accuracy of the 830)

The ‘piggyback’ is a name often used for a second ring type CHT TC.  It’s location provides a close, but different temp than the CHT well that it is piggy backing on....

PP thoughts only, not a mechanic...

Best regards,

-a-

[Warren]

My experience from other industries is that turbocharger temperature limits are primarily based on creep properties of the blade materials. The centrifugal forces at high rpm put the blades in tension.  As the temperature increases the yield strength of the material decreases so the blade will start to yield (plastic deformation). In the regime of creep this happens very slowly and is measured over hundreds of hours of testing. I would guess there is lots of margin to run at 1650 for extended periods. The risk is that with increased temperature the creep rate increases. 50 degrees hot could become an issue. As mentioned above this is not an engine issue. Absolute worst case is damage to turbo blades from housing contact.  So be careful to minimize or eliminate time over 1650 but do not be afraid of 1650 if your sensors are accurate. Creep strain rates happen over hundreds of hours at these temperatures. I am a newer pilot but have been running my K model above 1600 consistently. I usually lean to keep it 1620-1630 at 75% power. So far 200 hours of me being pilot with no apparent signs of damage. I realize I should try to check the accuracy of my sensors too. For me it is a JPI-711 which is primary for TIT. 

[milotron]

On 4/27/2018 at 6:59 AM, Warren said:

My experience from other industries is that turbocharger temperature limits are primarily based on creep properties of the blade materials. The centrifugal forces at high rpm put the blades in tension.  As the temperature increases the yield strength of the material decreases so the blade will start to yield (plastic deformation). In the regime of creep this happens very slowly and is measured over hundreds of hours of testing. I would guess there is lots of margin to run at 1650 for extended periods. The risk is that with increased temperature the creep rate increases. 50 degrees hot could become an issue. As mentioned above this is not an engine issue. Absolute worst case is damage to turbo blades from housing contact.  So be careful to minimize or eliminate time over 1650 but do not be afraid of 1650 if your sensors are accurate. Creep strain rates happen over hundreds of hours at these temperatures. I am a newer pilot but have been running my K model above 1600 consistently. I usually lean to keep it 1620-1630 at 75% power. So far 200 hours of me being pilot with no apparent signs of damage. I realize I should try to check the accuracy of my sensors too. For me it is a JPI-711 which is primary for TIT. 

Warren, do you still have the factory TIT gauge? How does it read in comparison to your 711?

[Cardinal767]

On ‎4‎/‎26‎/‎2018 at 12:57 AM, carusoam said:

The 1650°F is an important to be accurate gauge.  When the temp is run exceeding this guideline, the turbo blades suffer erosion issues...

They turn into nubs...

In this really hot chemically active environment, the TIT thermocouple is very much at risk itself.  The Sheath will suffer from some erosion as well.

Have your mechanic pull the TC/sensor to inspect it’s condition.  Comparing two points like OAT and boiling water... should be enough to see if the TC is working properly.

a 100°F error on a TIT reading doesn’t sound very useable.  You won’t be able to tell if the reading is getting worse... setting up your mixture using an unknown or failing system, can get expensive...

Question: Your piggyback 830TC is on the outside of the turbo’s case? The OEM TIT TC is in the exhaust stream internal to the case...  something isn’t right when the outside case reads higher than the inside exhaust stream...

Or do you have an independent EGT TC in the exhaust stream near the turbo inlet?  (This makes more sense for the accuracy of the 830)

The ‘piggyback’ is a name often used for a second ring type CHT TC.  It’s location provides a close, but different temp than the CHT well that it is piggy backing on....

PP thoughts only, not a mechanic...

Best regards,

-a-

Let me rephrase. I've connected both TIT gauges to one TIT probe (like JPI said was possible) to see just how far off the two readings are. Until I've verified which reading is closes to accurate, I'll use the higher (830) as the limiting reading. I can not fly with the OEM disconnected to see what the EDM would read solo, and I'm in no hurry to drill a second hole in the exhaust when the EDM can be calibrated. Again, both readings were very close in the 1300*F range. In the 1400's the differences were around 50*F and continued to increase through the 1500's. The OEM indicator topped out around 1530*F with the EDM at 1630*F. I'll do some more testing.

[Warren]

4 hours ago, milotron said:

Warren, do you still have the factory TIT gauge? How does it read in comparison to your 711?

Unfortunately the factory gage was removed with the JPI installation.  I would love to know how they compare after reading all the challenges related above.

[carusoam]

Cardinal,

Interesting how we are stuck using a factory gauge CHT and a piggy back TC when connecting to a JPI 700series...

For something that seems more critical, TIT... JPI says connect one TC to both gauges...?

That just seems to good to be true...

Since TCs Are Reading microvolts, and connecting any two electrical devices has the opportunity to have electrical interference caused by variations in their common grounds...

That is worth looking into.

JPI Customer Service can be a pain to get answers from on tough Questions... but this one isn’t very tough...

you might ask...

1) Why is it OK to connect one TC to two different gauges for TIT...

2) Why is it not OK to connect one TC to two different gauges for CHT...

I think you might have two devices interfering with each other and not getting very reliable data from either...

PP thoughts only, after Seeing how attentive to detail JPI has been for years...

JPI and... bumpy MP fixes, or intercom Interference fixes, or FL gauges, or TIT....  all stuff you read and understand at MS...

Best regards,

-a-

 

[gsxrpilot]

I briefly had my stock gauges installed along with the EDM-900. They never all agreed exactly and I found myself constantly worrying about which gauge was more correct. I knew that I'd be much happier and relaxed if I only had one source of truth for engine parameters. 

It was good to get rid of the stock gauges. I couldn't be happier with the EDM-900.

[Cardinal767]

Being my 830 only has about 300 hours on it, I really don't want to spend another $4,000 for a 900 if the installation manual reads "The EDM-700 TIT cable may be connected in parallel (piggyback) at the TIT probe (preferred), or at the ship's TIT gage. Check the TIT readings between the EDM and the ships TIT gage in flight, then do the following calibration
procedure. (This may be done in flight or on the ground.)' I didn't design the system, but I'm willing to try and make it work

Here's what I plan on doing to test the entire system as it is installed. Top cowling off, TIT probe removed from the exhaust only. The probe lead is about 18 inches long, a industrial heat gun, an exhaust tube I have, and a Type-K thermal coupling probe attached to my capable multi-meter. I'll compare ALL three readings if I can get the temp high enough to get the OEM gauge to read. By adjusting the distance between the heat gun and the tube, I'll be able to regulate the temperature in the tube. Its a start.

Being that impedance was brought up. I was told that the 830 has a very low impedance, so it should not affect the high impedance OEM gauge. FYI, there is a factory cannon plug between the TIT probe and the gauge that can affect the impedance. I solved a flaky OAT gauge readings by disconnecting and reconnecting the two cannon plugs, one in the wing and one  in the cabin at the wing root.    

 

[kortopates]

The JPI TIT sensor reads almost right at 100F higher than the OEM massive TIT probes. I personally put more confidence in the JPI probes indications.

[carusoam]

A typical calibration check for thermocouples includes getting readings at two Known temperatures....

• icewater...
• boiling water...

Unfortunately, I don’t know a 1650°F Standard...

 

Harborfreight does sell some lowcost IR thermometers That May be helpful for the experiment...

Trying to keep your TIT under control without perfect temp indications has got to be pretty annoying...

 

Paul K, do you have or use or recommend a standard for higher temps?

Best regards,

-a-