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Are home grown temperature probes feasable?

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rparigoris

Joined: 24 Nov 2009
Posts: 792

Posted: Tue Feb 16, 2010 1:56 am Post subject: Are home grown temperature probes feasable?

Not quite sure if I really want to fly my Europa or just keep finding projects to keep on  adding to build time?Anyway I have a Ilec SC-7 variometer. It comes with a momentary switch to view temperature and comes with one sender. The sender is 3/16" diameter cylinder with a flat and 3/16" long. I forget exactly what the sender is called, but essentially it is a Zener diode. There is 3 legs of the sender but they cut off 1 leg and only use 2 legs. The third leg they cut off is for calibrating. You see since this was for gliders to measure outside air temperature they have a calibration inside unit. I figure could calibrate several senders so they are the same then use a rotary switch to select different locations. Senders are about a buck each. I plan to use a rotary switch with gold contacts. OK so somehow I figure it would be nice to have OAT, temperature under panel by radios to see if my mini fans help, and 3 specific under cowl temperatures. Then I got to thinking it would be nice to monitor airbox temperature on my 914 turbocharged Rotax with intercooler to make sure there are not any sour spots during operation that could be conducive carb ice like high airspeed, fine pitch and very low throttle setting, and even though I plan to start with Evans as a coolant, might as well increase the build time somemore and have ability to monitor coolant temperature. What I propose to make is an airbox probe that would begin life with a slug of hex stock brass, then machineh NPT thread to screw in an aux hole in existing airbox, make a .045" wall blind hole in center bout 1.5" long with a .1875" ID (3/16"). BTW close to dimensions of UMA sender they sell except 1/2" longer. I would insert temperature sender then fill with high temperature JB Weld. I figure that the thin wall tube would not conduct too much heat to the airbox, yet the tip would have sufficient contact area with sender to conduct airbox temperature to it. Similar probe for water temperature. Thoughts on feasability? Or not only is there something that will not work well, but I am going to send a nice chunk of brass and semiconductor through a hot running motor because the coolant sender breached and leaked out all my flamable coolant directing it right onto the hot exhaust, probably precisely towards the beyond red hot turbo housing of the turbo?All comments welcome.Thx.Ron Parigoris   [quote][b]

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rampil

Joined: 04 May 2007
Posts: 870

Posted: Tue Feb 16, 2010 6:38 am Post subject: Re: Are home grown temperature probes feasable?

Hi Ron,



Now come on, we all know you want to keep building 



Dump that Evans coolant for real water!



Yes, you can make all the TC sensors you want with a small spot

welder.  Performance will be highly variable until you can make the

welds perfectly uniform (for the metal-metal interface).

The best choice in your situation is to use ic temp sensors which are

factory calibrated and voltage compensated and run into a factory 

built temp gauge. These sensors put out 0-5 volt so there are no issues

about microvolt voltage drops on dirty rotary switch contacts.

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Ira N224XS

rparigoris

Joined: 24 Nov 2009
Posts: 792

Posted: Tue Feb 16, 2010 8:55 am Post subject: Re: Are home grown temperature probes feasable?

Hi Ira

The sender I want to use is I think the IC you describe,

not make my own thermocouple (have done that though with great success, see

below). JB Weld is a two part epoxy you can get from Aviation Isle at Home

Depot or most Hardware stores.  TG from memory is like 550F and

it is probably as immune to fuel/alcohol as is Redux, just with a much

higher TG. I want to use the JB Weld Epoxy to mount my IC sender to the

tip of my turned brass blind holed hex. JB also makes a product called JB

KWIK and it is called 4 minute epoxy. TG perhaps is 350F going by memory

and strength is down perhaps 15% from JB Weld that has an 8 hour cure

time. It is probably fine for what I need in probe as far as strength and

TG, but it is far more viscous compared to JB Weld. If you warm JB Weld it

gets plenty runny to get it where I want it. JB KWIK has been invaluable

in build thus far.

BTW I have repaired many a thermocouple with using

my Hobart TRT 250 round wave TIG welder! My business is copiers and older

machines used thermocouples that were two dissimilar wires welded together

where the tip was pretty spherical. Anyway they were close to 8" long

and the tips would get brittle and a paper jam could break them. I used to

cut off an inch, jig together and go after with my TIG torch. If a nice

spherical ball happened it was then was good to go again. If the

ball was not nice just redid it till it was nice. I measured against a new

one and if ball was close to what i call nice (using my Mk 1 calibrated

"Eyechrometer")  it was dead on compared to new unit. Used

same technique for other thermocouples, and where I needed longer wire

just bought same material and made a new one in desired length. >

Now come on, we all know you want to keep building  <<You have my

number now don't you!>>  <You>The best choice in your situation is to use ic temp sensors

which are factory calibrated and voltage compensated and run into a

factory built temp gauge. These sensors put out 0-5 volt so there are no

issues about microvolt voltage drops on dirty rotary switch

contacts.< I am pretty certain this is the sender that Ilec uses to

drive their digital readout, it is just a Zener diode. It has 3 wires and

one allows you to calibrate, or in my case match 6 of them. I imagine that

someone selling a sender could precalibrate it for their gauge, but Ilec

cuts off third leg and allows for internal calibration in their

unit. I will buy for a buck each and match calibrations for 6

senders, then calibrate Ilec to the now same values. Using a rotary switch

with gold contacts for such a flea sized amount of electrons flowing

through contacts, I am hopeful it will not cause problems of switching

thermocoulpe wires.

Ron Parigoris

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rampil

Joined: 04 May 2007
Posts: 870

Posted: Tue Feb 16, 2010 9:17 am Post subject: Re: Are home grown temperature probes feasable?

Dont waste your time dinking with zeners!

Nice for an experiment to demonstrate principles but insane for

production use. Especially in your case where you want several, all

needing to be matched!



As I suggested for OAT, use a temp chip like for example:

http://www.analog.com/en/temperature-sensing-and-thermal-management/analog-temperature-sensors/tmp36/products/product.html



It's $0.45 in quantity! why would you even think about zeners. Jim's

spent too much time in the classroom teaching EE techs. Feasible yes,

best choice? not a chance.



PS I have 13 temp probes on my Europa

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Ira N224XS

rparigoris

Joined: 24 Nov 2009
Posts: 792

Posted: Tue Feb 16, 2010 12:11 pm Post subject: Re: Are home grown temperature probes feasable?

Hi Ira

Wayne explained to me the devise I speak of operates or is based on a Zener, I am not exactly sure which one. It is not just an ordinary Zener but a a precision mapped thermal temperature sender and sold as such with accuracy in mapping from one to the other of perhaps 2 or 3 degrees F, and by using the trim feature you can adjust a lot closer than that. I apreciate your advise about not using a Zener. The reason for selecting this specific device is that is what the Mfg of the Ilec SC-7 vario uses to drive their thermal display.

Would you mind listing the 13 locations you have placed sensors and comment if they would be worthy of installing if you were to do it again.

Thx.

Ron Parigoris

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rampil

Joined: 04 May 2007
Posts: 870

Posted: Tue Feb 16, 2010 2:33 pm Post subject: Re: Are home grown temperature probes feasable?

OK Ron,



Actually, it's 15 probes (forgot Oil   and internal BMA avionics temp)



4 CHT on ring probes

2 CHT on Rotax probes

4 EGT t/c

1 OAT

1 Coolant temp

1 Carb heater block

1 Oil temp

1 Blue Mountain avionics overtemp sensor (display starts at 135F)



All except two Rotax probes go to EFIS 2 system for display. All calibrated

by factory and tested by me.



OAT in lower cowl is unreliable read due to radiated engine heat



Ira

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Ira N224XS

mcculleyja(at)starpower.n
Guest

Posted: Tue Feb 16, 2010 7:06 pm Post subject: Are home grown temperature probes feasable?

Ron,



I'm operating a very inexpensive, minimum labor system I put together to 

monitor 18 under-cowl temperatures during some 500 hours of flight 

operation over the past 7 years. The cost was less than about $25 and 

the accuracy is +/- 2 degrees F for temperatures less than 300F. Nothing 

under the cowl aside from CHT and EGT should ever be higher than that!



Contact me directly if you want more detail.



Jim McCulley

mcculleyja(at)starpower.net

===============================================================================



rparigor(at)suffolk.lib.ny.us wrote:

 	  Quote: 	
		   Not quite sure if I really want to fly my Europa or just keep finding 

 projects to keep on  adding to build time?

 Anyway I have a Ilec SC-7 variometer. It comes with a momentary switch 

 to view temperature and comes with one sender. The sender is 3/16" 

 diameter cylinder with a flat and 3/16" long. I forget exactly what the 

 sender is called, but essentially it is a Zener diode. There is 3 legs 

 of the sender but they cut off 1 leg and only use 2 legs. The third leg 

 they cut off is for calibrating. You see since this was for gliders to 

 measure outside air temperature they have a calibration inside unit. I 

 figure could calibrate several senders so they are the same then use a 

 rotary switch to select different locations. Senders are about a buck 

 each. I plan to use a rotary switch with gold contacts. OK so somehow I 

 figure it would be nice to have OAT, temperature under panel by radios 

 to see if my mini fans help, and 3 specific under cowl temperatures. 

 Then I got to thinking it would be nice to monitor airbox temperature on 

 my 914 turbocharged Rotax with intercooler to make sure there are not 

 any sour spots during operation that could be conducive carb ice like 

 high airspeed, fine pitch and very low throttle setting, and even though 

 I plan to start with Evans as a coolant, might as well increase the 

 build time somemore and have ability to monitor coolant temperature. 

 What I propose to make is an airbox probe that would begin life with a 

 slug of hex stock brass, then machineh NPT thread to screw in an aux 

 hole in existing airbox, make a .045" wall blind hole in center bout 

 1.5" long with a .1875" ID (3/16"). BTW close to dimensions of UMA 

 sender they sell except 1/2" longer. I would insert temperature sender 

 then fill with high temperature JB Weld. I figure that the thin wall 

 tube would not conduct too much heat to the airbox, yet the tip would 

 have sufficient contact area with sender to conduct airbox temperature 

 to it. Similar probe for water temperature. Thoughts on feasability? Or 

 not only is there something that will not work well, but I am going to 

 send a nice chunk of brass and semiconductor through a hot running motor 

 because the coolant sender breached and leaked out all my flamable 

 coolant directing it right onto the hot exhaust, probably precisely 

 towards the beyond red hot turbo housing of the turbo?

 All comments welcome.

 Thx.

 Ron Parigoris

===================================================================================

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