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Switch For Thermocouple Wires

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billhuntersemail(at)gmail
Guest

Posted: Sun Jul 24, 2016 2:39 pm Post subject: Switch For Thermocouple Wires

I do not have sufficient pins left over in my Dynon EMS for my temperature monitoring needs.  

One of the items I do not need to monitor on a regular basis is the turbocharger intercooler outlet temperature (the actual temperature of the air entering the engine inlet) as I just really need to see that on a very hot day.  

Since this airplane is a pusher there is no visual indication of smoke or fire like on a tractor airplane so I would really like to have an internal engine cowling temperature indication using a thermocouple. I envision setting up the Skyview to trigger a red indication and a warning if a fire develops in the engine compartment and the temperature exceeds a preset limit and then I can react faster than waiting for the really bad day to develop.  

Since the engine inlet temperature is a NICE to know item and the engine cowling is a NEED to know... I was thinking about installing two thermocouples one in the inlet and one in the engine compartment and then wire each pair of wires to a DPST switch and then this switch would remain in the position to sence the NEED to knowÂ  information 99 percent of the time and then flicked to the NICE to know position when it is becomes nice to know.  

Other than the usual solid connectors and quality switch requirements is there anything special to consider with thermocouple wires?  

THANKS!!!  

Bill Hunter

ceengland7(at)gmail.com
Guest

Posted: Sun Jul 24, 2016 3:51 pm Post subject: Switch For Thermocouple Wires

On 7/24/2016 5:35 PM, William Hunter wrote:

 	  Quote: 	
		  

 I do not have sufficient pins left over in my Dynon EMS for my 

 temperature monitoring needs.



 One of the items I do not need to monitor on a regular basis is the 

 turbocharger intercooler outlet temperature (the actual temperature of 

 the air entering the engine inlet) as I just really need to see that 

 on a very hot day.



 Since this airplane is a pusher there is no visual indication of smoke 

 or fire like on a tractor airplane so I would really like to have an 

 internal engine cowling temperature indication using a thermocouple. I 

 envision setting up the Skyview to trigger a red indication and a 

 warning if a fire develops in the engine compartment and the 

 temperature exceeds a preset limit and then I can react faster than 

 waiting for the really bad day to develop.



 Since the engine inlet temperature is a NICE to know item and the 

 engine cowling is a NEED to know... I was thinking about installing 

 two thermocouples one in the inlet and one in the engine compartment 

 and then wire each pair of wires to a DPST switch and then this switch 

 would remain in the position to sence the NEED to know  information 99 

 percent of the time and then flicked to the NICE to know position when 

 it is becomes nice to know.



 Other than the usual solid connectors and quality switch requirements 

 is there anything special to consider with thermocouple wires?



 THANKS!!!



 Bill Hunter



To keep accuracy, you need to switch both leads. If you're just 
	


switching between 2 sensors, use a DPDT switch, so that the meter sees 

either both wires from one, or both wires from the other. Reason for 

switching both leads is that any 'junction' (connector, switch 

terminals, etc), particularly when the metal changes, like it would 

going through a switch, causes errors in measurement. If both leads are 

switched in the same space (meaning same temperature), then the errors 

cancel each other.



(Don't forget that your alarm setting in the Dynon may cause false 

alarms if there's a big difference in 'normal' temps between the two 

sensors.)



Charlie

argoldman(at)aol.com
Guest

Posted: Sun Jul 24, 2016 4:41 pm Post subject: Switch For Thermocouple Wires

If you have more probes you can use a rotary switch



Rich



Sent from my iPhone



 	  Quote: 	
		   On Jul 24, 2016, at 6:51 PM, Charlie England <ceengland7(at)gmail.com> wrote:

 

 

 

> On 7/24/2016 5:35 PM, William Hunter wrote:

> 

> I do not have sufficient pins left over in my Dynon EMS for my temperature monitoring needs.

> 

> One of the items I do not need to monitor on a regular basis is the turbocharger intercooler outlet temperature (the actual temperature of the air entering the engine inlet) as I just really need to see that on a very hot day.

> 

> Since this airplane is a pusher there is no visual indication of smoke or fire like on a tractor airplane so I would really like to have an internal engine cowling temperature indication using a thermocouple. I envision setting up the Skyview to trigger a red indication and a warning if a fire develops in the engine compartment and the temperature exceeds a preset limit and then I can react faster than waiting for the really bad day to develop.

> 

> Since the engine inlet temperature is a NICE to know item and the engine cowling is a NEED to know... I was thinking about installing two thermocouples one in the inlet and one in the engine compartment and then wire each pair of wires to a DPST switch and then this switch would remain in the position to sence the NEED to know  information 99 percent of the time and then flicked to the NICE to know position when it is becomes nice to know.

> 

> Other than the usual solid connectors and quality switch requirements is there anything special to consider with thermocouple wires?

> 

> THANKS!!!

> 

> Bill Hunter

 To keep accuracy, you need to switch both leads. If you're just switching between 2 sensors, use a DPDT switch, so that the meter sees either both wires from one, or both wires from the other. Reason for switching both leads is that any 'junction' (connector, switch terminals, etc), particularly when the metal changes, like it would going through a switch, causes errors in measurement. If both leads are switched in the same space (meaning same temperature), then the errors cancel each other.

 

 (Don't forget that your alarm setting in the Dynon may cause false alarms if there's a big difference in 'normal' temps between the two sensors.)

 

 Charlie

edpav8r(at)yahoo.com
Guest

Posted: Mon Jul 25, 2016 8:23 am Post subject: Switch For Thermocouple Wires

On Jul 24, 2016, at 3:35 PM, William Hunter <billhuntersemail(at)gmail.com (billhuntersemail(at)gmail.com)> wrote:

 	  Quote: 	
		  

I do not have sufficient pins left over in my Dynon EMS for my temperature monitoring needs.  

[...] 	
Just a few things to add to Charlie's response.

The chromel/alumel wires used with common K-type thermocouples are practically impossible to solder with typical tin/lead, rosin core electronic solder.  They require high temperature silver solder and appropriate flux.  Crimped or screw-down connectors are much easier to use.

A cheap and easy source for additional chromel/alumel extension wire is to buy K-type thermocouples on eBay and cut them up.  They can be had for under a dollar, delivered:

http://preview.tinyurl.com/j88uupr

The ones you see with a threaded metal sensor and spade terminals have fiberglass insulation on the wires and a braided metal outer sheath (suitable for under cowl use).  The ones with a yellow connector have plastic insulation and a fiberglass sheath (smaller diameter, easier to route in the fuselage).

If you have to splice wires for length, you can use any crimped connector to join them, as long as the wires twist around each other to make electrical contact independent of the connector.

The normal color convention for positive/negative connections is reversed for thermocouples: red is negative.  Swapped connections won't damage anything but the instrument will read backwards.

Use chromel/alumel wire from the sensor to the switch *and* from the switch to the instrument.  Don't change to copper wire after the switch.



The following documents might be more than you want to know, but there's a lot of interesting info about understanding and applying thermocouples:

- (Australian) AC 21-99, Aircraft Wiring & Bonding, Sec 2, Chap 16, "Thermocouple Wire Soldering & Installation":

http://preview.tinyurl.com/z5fwrzw



- A Stanford University mechanical engineering professor's advice on thermocouples:

http://preview.tinyurl.com/jl873l4



- An Acromag white paper on temperature measurement with thermocouples:

http://preview.tinyurl.com/hawrxwt

- A Maxim Integrated application note explaining cold junction compensation:

http://preview.tinyurl.com/jm2kku2



Eric

billhuntersemail(at)gmail
Guest

Posted: Tue Jul 26, 2016 4:31 pm Post subject: Switch For Thermocouple Wires

Thanks Charlie,  

 	  Quote: 	
		  Don't forget that your alarm setting in the Dynon may cause false alarms if there's a big difference in 'normal' temps between the two sensors.) 

I am somewhat interested in knowing how hot a fire is... The plan would be to install the Thermocouple on the firewall above the fuel hoses as these are arguably the likely suspects. Then I would have a temperature read out (just numerical value) displayed somewhere on the screen below the engine "guages".  
	


The idea being the display would be white digits until the temperature indication raises above a predetermined values and then turn red.  

Any recommendations on that value should be so as to avoid faulse readings?  

Bill Hunter 

  

On Jul 24, 2016 4:57 PM, "Charlie England" <ceengland7(at)gmail.com (ceengland7(at)gmail.com)> wrote: 	  Quote: 	
		  --> AeroElectric-List message posted by: Charlie England <ceengland7(at)gmail.com (ceengland7(at)gmail.com)>

 

 On 7/24/2016 5:35 PM, William Hunter wrote:

  	  Quote: 	
		   

 I do not have sufficient pins left over in my Dynon EMS for my temperature monitoring needs.

 

 One of the items I do not need to monitor on a regular basis is the turbocharger intercooler outlet temperature (the actual temperature of the air entering the engine inlet) as I just really need to see that on a very hot day.

 

 Since this airplane is a pusher there is no visual indication of smoke or fire like on a tractor airplane so I would really like to have an internal engine cowling temperature indication using a thermocouple. I envision setting up the Skyview to trigger a red indication and a warning if a fire develops in the engine compartment and the temperature exceeds a preset limit and then I can react faster than waiting for the really bad day to develop.

 

 Since the engine inlet temperature is a NICE to know item and the engine cowling is a NEED to know... I was thinking about installing two thermocouples one in the inlet and one in the engine compartment and then wire each pair of wires to a DPST switch and then this switch would remain in the position to sence the NEED to knowÂ  information 99 percent of the time and then flicked to the NICE to know position when it is becomes nice to know.

 

 Other than the usual solid connectors and quality switch requirements is there anything special to consider with thermocouple wires?

 

 THANKS!!!

 

 Bill Hunter

 

 	


 To keep accuracy, you need to switch both leads. If you're just switching between 2 sensors, use a DPDT switch, so that the meter sees either both wires from one, or both wires from the other. Reason for switching both leads is that any 'junction' (connector, switch terminals, etc), particularly when the metal changes, like it would going through a switch, causes errors in measurement. If both leads are switched in the same space (meaning same temperature), then the errors cancel each other.

 

 (Don't forget that your alarm setting in the Dynon may cause false alarms if there's a big difference in 'normal' temps between the two sensors.)

 

 Charlie

 

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alec(at)alecmyers.com
Guest

Posted: Tue Jul 26, 2016 5:14 pm Post subject: Switch For Thermocouple Wires

No suggestions from me about a good temperature threshold for the fire alarm except that it's just begging for some experimentation 

[quote] On Jul 26, 2016, at 8:29 PM, William Hunter <billhuntersemail(at)gmail.com> wrote:

 Thanks Charlie,

 >Don't forget that your alarm setting in the Dynon may cause false alarms if there's a big difference in 'normal' temps between the two sensors.)

 I am somewhat interested in knowing how hot a fire is... The plan would be to install the Thermocouple on the firewall above the fuel hoses as these are arguably the likely suspects. Then I would have a temperature read out (just numerical value) displayed somewhere on the screen below the engine "guages".

 The idea being the display would be white digits until the temperature indication raises above a predetermined values and then turn red.

 Any recommendations on that value should be so as to avoid faulse readings?

 Bill Hunter 

 On Jul 24, 2016 4:57 PM, "Charlie England" <ceengland7(at)gmail.com> wrote:

> On 7/24/2016 5:35 PM, William Hunter wrote:

> 

> I do not have sufficient pins left over in my Dynon EMS for my temperature monitoring needs.

> 

> One of the items I do not need to monitor on a regular basis is the turbocharger intercooler outlet temperature (the actual temperature of the air entering the engine inlet) as I just really need to see that on a very hot day

billhuntersemail(at)gmail
Guest

Posted: Tue Jul 26, 2016 5:34 pm Post subject: Switch For Thermocouple Wires

I'll light the fuse and let you know  

Bill Hunter 

  

On Jul 26, 2016 6:22 PM, "Alec Myers" <alec(at)alecmyers.com (alec(at)alecmyers.com)> wrote: 	  Quote: 	
		  

No suggestions from me about a good temperature threshold for the fire alarm except that it's just begging for some experimentation 



On Jul 26, 2016, at 8:29 PM, William Hunter <billhuntersemail(at)gmail.com (billhuntersemail(at)gmail.com)> wrote:

 	  Quote: 	
		  

Thanks Charlie,  

 	  Quote: 	
		  Don't forget that your alarm setting in the Dynon may cause false alarms if there's a big difference in 'normal' temps between the two sensors.) 

I am somewhat interested in knowing how hot a fire is... The plan would be to install the Thermocouple on the firewall above the fuel hoses as these are arguably the likely suspects. Then I would have a temperature read out (just numerical value) displayed somewhere on the screen below the engine "guages".  
	


The idea being the display would be white digits until the temperature indication raises above a predetermined values and then turn red.  

Any recommendations on that value should be so as to avoid faulse readings?  

Bill Hunter 

  

On Jul 24, 2016 4:57 PM, "Charlie England" <ceengland7(at)gmail.com (ceengland7(at)gmail.com)> wrote: 	  Quote: 	
		  --> AeroElectric-List message posted by: Charlie England <ceengland7(at)gmail.com (ceengland7(at)gmail.com)>

 

 On 7/24/2016 5:35 PM, William Hunter wrote:

  	  Quote: 	
		   

 I do not have sufficient pins left over in my Dynon EMS for my temperature monitoring needs.

 

 One of the items I do not need to monitor on a regular basis is the turbocharger intercooler outlet temperature (the actual temperature of the air entering the engine inlet) as I just really need to see that on a very hot day.

 

 Since this airplane is a pusher there is no visual indication of smoke or fire like on a tractor airplane so I would really like to have an internal engine cowling temperature indication using a thermocouple. I envision setting up the Skyview to trigger a red indication and a warning if a fire develops in the engine compartment and the temperature exceeds a preset limit and then I can react faster than waiting for the really bad day to develop.

 

 Since the engine inlet temperature is a NICE to know item and the engine cowling is a NEED to know... I was thinking about installing two thermocouples one in the inlet and one in the engine compartment and then wire each pair of wires to a DPST switch and then this switch would remain in the position to sence the NEED to knowÂ  information 99 percent of the time and then flicked to the NICE to know position when it is becomes nice to know.

 

 Other than the usual solid connectors and quality switch requirements is there anything special to consider with thermocouple wires?

 

 THANKS!!!

 

 Bill Hunter

 

 	


 To keep accuracy, you need to switch both leads. If you're just switching between 2 sensors, use a DPDT switch, so that the meter sees either both wires from one, or both wires from the other. Reason for switching both leads is that any 'junction' (connector, switch terminals, etc), particularly when the metal changes, like it would going through a switch, causes errors in measurement. If both leads are switched in the same space (meaning same temperature), then the errors cancel each other.

 

 (Don't forget that your alarm setting in the Dynon may cause false alarms if there's a big difference in 'normal' temps between the two sensors.)

 

 Charlie

 

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ceengland7(at)gmail.com
Guest

Posted: Tue Jul 26, 2016 8:01 pm Post subject: Switch For Thermocouple Wires

Sorry; no idea. What I meant was that measuring different temp ranges (inlet vs cowl), they're likely to have different normal ranges. So, setting up the alarm point in the efis would be different for each source. 

-------- Original message --------

From: William Hunter  

Date:07/26/2016  7:29 PM  (GMT-06:00) 

To: aeroelectric-list(at)matronics.com 

Subject: Re: AeroElectric-List: Switch For Thermocouple Wires 

Thanks Charlie,  

 	  Quote: 	
		  Don't forget that your alarm setting in the Dynon may cause false alarms if there's a big difference in 'normal' temps between the two sensors.) 

I am somewhat interested in knowing how hot a fire is... The plan would be to install the Thermocouple on the firewall above the fuel hoses as these are arguably the likely suspects. Then I would have a temperature read out (just numerical value) displayed somewhere on the screen below the engine "guages".  

The idea being the display would be white digits until the temperature indication raises above a predetermined values and then turn red.  

Any recommendations on that value should be so as to avoid faulse readings?  

Bill Hunter 

On Jul 24, 2016 4:57 PM, "Charlie England" <ceengland7(at)gmail.com (ceengland7(at)gmail.com)> wrote: 	  Quote: 	
		  --> AeroElectric-List message posted by: Charlie England <ceengland7(at)gmail.com (ceengland7(at)gmail.com)>

 On 7/24/2016 5:35 PM, William Hunter wrote:

  	  Quote: 	

 I do not have sufficient pins left over in my Dynon EMS for my temperature monitoring needs.

 One of the items I do not need to monitor on a regular basis is the turbocharger intercooler outlet temperature (the actual temperature of the air entering the engine inlet) as I just really need to see that on a very hot day.

 Since this airplane is a pusher there is no visual indication of smoke or fire like on a tractor airplane so I would really like to have an internal engine cowling temperature indication using a thermocouple. I envision setting up the Skyview to trigger a red indication and a warning if a fire develops in the engine compartment and the temperature exceeds a preset limit and then I can react faster than waiting for the really bad day to develop.

 Since the engine inlet temperature is a NICE to know item and the engine cowling is a NEED to know... I was thinking about installing two thermocouples one in the inlet and one in the engine compartment and then wire each pair of wires to a DPST switch and then this switch would remain in the position to sence the NEED to know  information 99 percent of the time and then flicked to the NICE to know position when it is becomes nice to know.

 Other than the usual solid connectors and quality switch requirements is there anything special to consider with thermocouple wires?

 THANKS!!!

 Bill Hunter

 To keep accuracy, you need to switch both leads. If you're just switching between 2 sensors, use a DPDT switch, so that the meter sees either both wires from one, or both wires from the other. Reason for switching both leads is that any 'junction' (connector, switch terminals, etc), particularly when the metal changes, like it would going through a switch, causes errors in measurement. If both leads are switched in the same space (meaning same temperature), then the errors cancel each other.

 (Don't forget that your alarm setting in the Dynon may cause false alarms if there's a big difference in 'normal' temps between the two sensors.)

 Charlie

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billhuntersemail(at)gmail
Guest

Posted: Tue Jul 26, 2016 9:10 pm Post subject: Switch For Thermocouple Wires

 	  Quote: 	
		   What I meant was that measuring different temp ranges (inlet vs cowl), they're likely to have different normal ranges. So, setting up the alarm point in the efis would be different for each source.

 
	


Thanksâ€¦the plan would be for the selector switch to live in the COWL TEMP setting 99.3 percent of the time (watching for an engine fire) so the cowl temp predetermined trigger point is really all that I am interested inâ€¦I guess I can just SWAG 500F as the trigger point for the white to red digits in Dynon and after watching the digits during some normal very hot day operations I can see what the usual engine cowl internal temps will be (and the rate of increase) and then adjust accordingly.Â  I wonder if I can teach the nice Dynon girl to say â€œWarningâ€ or â€¦ â€œEngine Fireâ€ or somethingâ€¦a calm British accent would be really cool?!?!?

 

The engine turbo intercooler exhaust is simply a Gee Wizz indication for the remainder 0.7 percent so no real concern for the trigger, colors, or British babe voice.

 

..

 

Cheers!!!

 

BillÂ  Hunter



 

From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Charlie England

Sent: Tuesday, July 26, 2016 8:59 PM

To: aeroelectric-list(at)matronics.com

Subject: Re: Switch For Thermocouple Wires

 

Sorry; no idea. What I meant was that measuring different temp ranges (inlet vs cowl), they're likely to have different normal ranges. So, setting up the alarm point in the efis would be different for each source. 

-------- Original message --------



From: William Hunter 



Date:07/26/2016 7:29 PM (GMT-06:00) 



To: aeroelectric-list(at)matronics.com (aeroelectric-list(at)matronics.com) 



Subject: Re: Switch For Thermocouple Wires 



 



Thanks Charlie, 

 	  Quote: 	
		  Don't forget that your alarm setting in the Dynon may cause false alarms if there's a big difference in 'normal' temps between the two sensors.)

I am somewhat interested in knowing how hot a fire is... The plan would be to install the Thermocouple on the firewall above the fuel hoses as these are arguably the likely suspects. Then I would have a temperature read out (just numerical value) displayed somewhere on the screen below the engine "guages". 
	


The idea being the display would be white digits until the temperature indication raises above a predetermined values and then turn red. 

Any recommendations on that value should be so as to avoid faulse readings? 

Bill Hunter 

 

On Jul 24, 2016 4:57 PM, "Charlie England" <ceengland7(at)gmail.com (ceengland7(at)gmail.com)> wrote: 	  Quote: 	
		  

--> AeroElectric-List message posted by: Charlie England <ceengland7(at)gmail.com (ceengland7(at)gmail.com)>

On 7/24/2016 5:35 PM, William Hunter wrote: 	  Quote: 	
		  



I do not have sufficient pins left over in my Dynon EMS for my temperature monitoring needs.



One of the items I do not need to monitor on a regular basis is the turbocharger intercooler outlet temperature (the actual temperature of the air entering the engine inlet) as I just really need to see that on a very hot day.



Since this airplane is a pusher there is no visual indication of smoke or fire like on a tractor airplane so I would really like to have an internal engine cowling temperature indication using a thermocouple. I envision setting up the Skyview to trigger a red indication and a warning if a fire develops in the engine compartment and the temperature exceeds a preset limit and then I can react faster than waiting for the really bad day to develop.



Since the engine inlet temperature is a NICE to know item and the engine cowling is a NEED to know... I was thinking about installing two thermocouples one in the inlet and one in the engine compartment and then wire each pair of wires to a DPST switch and then this switch would remain in the position to sence the NEED to know  information 99 percent of the time and then flicked to the NICE to know position when it is becomes nice to know.



Other than the usual solid connectors and quality switch requirements is there anything special to consider with thermocouple wires?



THANKS!!!



Bill Hunter 	




To keep accuracy, you need to switch both leads. If you're just switching between 2 sensors, use a DPDT switch, so that the meter sees either both wires from one, or both wires from the other. Reason for switching both leads is that any 'junction' (connector, switch terminals, etc), particularly when the metal changes, like it would going through a switch, causes errors in measurement. If both leads are switched in the same space (meaning same temperature), then the errors cancel each other.



(Don't forget that your alarm setting in the Dynon may cause false alarms if there's a big difference in 'normal' temps between the two sensors.)



Charlie



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edpav8r(at)yahoo.com
Guest

Posted: Tue Jul 26, 2016 9:32 pm Post subject: Switch For Thermocouple Wires

On Jul 26, 2016, at 5:29 PM, William Hunter <billhuntersemail(at)gmail.com (billhuntersemail(at)gmail.com)> wrote:

 	  Quote: 	
		   

I am somewhat interested in knowing how hot a fire is... 	


For gasoline, ignition temp is 232Â°C and flame temp varies from ~945Â°C to 1,950Â°C depending on conditions.

Eric

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Jul 27, 2016 3:52 am Post subject: Switch For Thermocouple Wires

At 12:31 AM 7/27/2016, you wrote:

  	  Quote: 	
		  On Jul 26, 2016, at 5:29 PM, William Hunter < billhuntersemail(at)gmail.com (billhuntersemail(at)gmail.com)> wrote:

  	  Quote: 	
		  

 I am somewhat interested in knowing how hot a fire is... 	


 For gasoline, ignition temp is 232Â°C and flame temp varies from ~945Â°C to 1,950Â°C depending on conditions.



 Eric 	




   It's been about 30 years since I fiddled with

   fire detection techniques. We looked at them as

   a potential product for Electro-Mech about 1980.



   No software back then . . . all discrete jelly

   beans. There were two techniques that showed

   promise. One involved temperature sensors at

   ram air inlet and cooling outlet ports and

   circuitry that watched for (1) outlet to

   exceed xx degrees along with (2) a rate

   of rise in the differential between the

   two.



   The other technique, and the one most popular

   with our customers involved routing a kind

   of linear thermistor around the engine's

   potential hot spots during a fire. The

   'thermistor' looked for all the world like

   a piece of semi-rigid coax cable. Thin

   metal jacket (stainless I think). Center

   conductor of solid metal. A 'dielectric'

   of thermistor material.



   Looking into the end of the 'coax' one

   would see an infinite number of thermistors

   all tied in parallel.  But should any portion

   of the 'coax' be exposed to flame, the thermistor

   material in that area would present a sharp

   drop in resistance which was detected by

   the electronics.



   We never did pursue the opportunity beyond

   the gee-what-if stage. I went off to work

   the servoed pitch trim controller for the

   Lears . . . Dean did an APU controller for

   Duncan Aviation.



   The long, temperature sensitive 'coax' was

   kinda cool. You could route it as needed in

   the engine space but it was a specialty

   product that was custom-manufactured to

   the design. Breathtaking start-up costs.



   With software one could place one or more

   temperature sensors about the engine spaces

   and write scanning/interpretation routines

   to identify abnormal temperature profiles.



   For an OBAM aviation project, I can see

   a kind of universal fire detection system

   that is first installed in a 'learn' mode

   and flown for xx hours. Once 'normal'

   temperatures are identified and cataloged,

   a 'operate' mode would raise a flag if

   conditions markedly outside the normal

   parameters was detected.



   It's an interesting design study that

   was very low on Electro-Mech's totem pole

   of market opportunities. Under the cowl

   fires just don't figure into a significant

   percentage of bad-days-in-the-cockpit.



 

 

   Bob . . .

ceengland7(at)gmail.com
Guest

Posted: Wed Jul 27, 2016 5:08 am Post subject: Switch For Thermocouple Wires

On Wed, Jul 27, 2016 at 6:49 AM, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:

 	  Quote: 	
		    At 12:31 AM 7/27/2016, you wrote:

  	  Quote: 	
		  On Jul 26, 2016, at 5:29 PM, William Hunter < billhuntersemail(at)gmail.com (billhuntersemail(at)gmail.com)> wrote:

  	  Quote: 	
		  

 I am somewhat interested in knowing how hot a fire is... 	


 For gasoline, ignition temp is 232Ã‚Â°C and flame temp varies from ~945Ã‚Â°C to 1,950Ã‚Â°C depending on conditions.



 Eric 	




 Â  It's been about 30 years since I fiddled with

 Â  fire detection techniques. We looked at them as

 Â  a potential product for Electro-Mech about 1980.



 Â  No software back then . . . all discrete jelly

 Â  beans. There were two techniques that showed

 Â  promise. One involved temperature sensors at

 Â  ram air inlet and cooling outlet ports and

 Â  circuitry that watched for (1) outlet to

 Â  exceed xx degrees along with (2) a rate

 Â  of rise in the differential between the

 Â  two.



 Â  The other technique, and the one most popular

 Â  with our customers involved routing a kind

 Â  of linear thermistor around the engine's

 Â  potential hot spots during a fire. The

 Â  'thermistor' looked for all the world like

 Â  a piece of semi-rigid coax cable. Thin

 Â  metal jacket (stainless I think). Center

 Â  conductor of solid metal. A 'dielectric'

 Â  of thermistor material.



 Â  Looking into the end of the 'coax' one

 Â  would see an infinite number of thermistors

 Â  all tied in parallel.Â  But should any portion

 Â  of the 'coax' be exposed to flame, the thermistor

 Â  material in that area would present a sharp

 Â  drop in resistance which was detected by

 Â  the electronics.



 Â  We never did pursue the opportunity beyond

 Â  the gee-what-if stage. I went off to work

 Â  the servoed pitch trim controller for the

 Â  Lears . . . Dean did an APU controller for

 Â  Duncan Aviation.



 Â  The long, temperature sensitive 'coax' was

 Â  kinda cool. You could route it as needed in

 Â  the engine space but it was a specialty

 Â  product that was custom-manufactured to

 Â  the design. Breathtaking start-up costs.



 Â  With software one could place one or more

 Â  temperature sensors about the engine spaces

 Â  and write scanning/interpretation routines

 Â  to identify abnormal temperature profiles.



 Â  For an OBAM aviation project, I can see

 Â  a kind of universal fire detection system

 Â  that is first installed in a 'learn' mode

 Â  and flown for xx hours. Once 'normal'

 Â  temperatures are identified and cataloged,

 Â  a 'operate' mode would raise a flag if

 Â  conditions markedly outside the normal

 Â  parameters was detected.



 Â  It's an interesting design study that

 Â  was very low on Electro-Mech's totem pole

 Â  of market opportunities. Under the cowl

 Â  fires just don't figure into a significant

 Â  percentage of bad-days-in-the-cockpit.



 

 

 Â  Bob . . .  

	


A number of years ago, there were a few guys playing with optical flame sensors (triggered by the light spectrum of actual flame, instead of heat). Idea was quicker & more discriminating detection of actual fire, vs just high temps. Conversation kinda faded away, so I don't know if they ever got it implemented. IIRC, the detectors were a bit pricey, so given the rather low odds of fire, I never pursued it for myself. William may have more motivation, flying a pusher.

Charlie

sportav8r(at)gmail.com
Guest

Posted: Wed Jul 27, 2016 5:27 am Post subject: Switch For Thermocouple Wires

I'm thinking extreme analog/tinker-toy technology, here, but why not a cotton string across the cowl outlet that holds open a spring-loaded N.O. switch.Â  Fire would presumably burn it through quickly.Â  A cross-check with a cowl air temp indicator would help confirm actual fire vs. "the old string finally rotted-through between annuals." Â 



Since we now fly in the digital age, the obvious modern solution is a belly cam to show the flames licking out of the cowl exit.

-Stormy

On Wed, Jul 27, 2016 at 7:49 AM, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:

 	  Quote: 	
		    At 12:31 AM 7/27/2016, you wrote:

  	  Quote: 	
		  On Jul 26, 2016, at 5:29 PM, William Hunter < billhuntersemail(at)gmail.com (billhuntersemail(at)gmail.com)> wrote:

  	  Quote: 	
		  

 I am somewhat interested in knowing how hot a fire is... 	


 For gasoline, ignition temp is 232Ã‚Â°C and flame temp varies from ~945Ã‚Â°C to 1,950Ã‚Â°C depending on conditions.



 Eric 	




 Â  It's been about 30 years since I fiddled with

 Â  fire detection techniques. We looked at them as

 Â  a potential product for Electro-Mech about 1980.



 Â  No software back then . . . all discrete jelly

 Â  beans. There were two techniques that showed

 Â  promise. One involved temperature sensors at

 Â  ram air inlet and cooling outlet ports and

 Â  circuitry that watched for (1) outlet to

 Â  exceed xx degrees along with (2) a rate

 Â  of rise in the differential between the

 Â  two.



 Â  The other technique, and the one most popular

 Â  with our customers involved routing a kind

 Â  of linear thermistor around the engine's

 Â  potential hot spots during a fire. The

 Â  'thermistor' looked for all the world like

 Â  a piece of semi-rigid coax cable. Thin

 Â  metal jacket (stainless I think). Center

 Â  conductor of solid metal. A 'dielectric'

 Â  of thermistor material.



 Â  Looking into the end of the 'coax' one

 Â  would see an infinite number of thermistors

 Â  all tied in parallel.Â  But should any portion

 Â  of the 'coax' be exposed to flame, the thermistor

 Â  material in that area would present a sharp

 Â  drop in resistance which was detected by

 Â  the electronics.



 Â  We never did pursue the opportunity beyond

 Â  the gee-what-if stage. I went off to work

 Â  the servoed pitch trim controller for the

 Â  Lears . . . Dean did an APU controller for

 Â  Duncan Aviation.



 Â  The long, temperature sensitive 'coax' was

 Â  kinda cool. You could route it as needed in

 Â  the engine space but it was a specialty

 Â  product that was custom-manufactured to

 Â  the design. Breathtaking start-up costs.



 Â  With software one could place one or more

 Â  temperature sensors about the engine spaces

 Â  and write scanning/interpretation routines

 Â  to identify abnormal temperature profiles.



 Â  For an OBAM aviation project, I can see

 Â  a kind of universal fire detection system

 Â  that is first installed in a 'learn' mode

 Â  and flown for xx hours. Once 'normal'

 Â  temperatures are identified and cataloged,

 Â  a 'operate' mode would raise a flag if

 Â  conditions markedly outside the normal

 Â  parameters was detected.



 Â  It's an interesting design study that

 Â  was very low on Electro-Mech's totem pole

 Â  of market opportunities. Under the cowl

 Â  fires just don't figure into a significant

 Â  percentage of bad-days-in-the-cockpit.



 

 

 Â  Bob . . .

alec(at)alecmyers.com
Guest

Posted: Wed Jul 27, 2016 5:31 am Post subject: Switch For Thermocouple Wires

>> The other technique, and the one most popular

  with our customers involved routing a kind

  of linear thermistor around the engine's

  potential hot spots during a fire. The

  'thermistor' looked for all the world like

  a piece of semi-rigid coax cable. Thin

  metal jacket (stainless I think). Center

  conductor of solid metal. A 'dielectric'

  of thermistor material.



  -There's something that looks a lot like this run in a circle around the wheel wells of various jet transport aircraft I've see, presumably to detect brake/tire fires when the undercarriage is retracted.

enginerdy(at)gmail.com
Guest

Posted: Wed Jul 27, 2016 6:54 am Post subject: Switch For Thermocouple Wires

That’s an interesting idea…



If you’re just looking at an ‘extreme rise’ temperature, you could put a bunch of NTCs* in parallel down a length of wire, and when the impedance drops somewhere, you would get an indication. Electrically it’s pretty similar to the thermistor snake.



Probably a good bit of fab work, but just the cost of some wire, heatshrink, and a handful of NTCs!**



*Negative thermal coefficient thermistors

 	  Quote: 	
		  On Jul 27, 2016, at 6:49 AM, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:

The other technique, and the one most popular  with our customers involved routing a kind  of linear thermistor around the engine's  potential hot spots during a fire.

billhuntersemail(at)gmail
Guest

Posted: Wed Jul 27, 2016 9:34 am Post subject: Switch For Thermocouple Wires

Good information and great ideas (I especially like the string idea)!!!

I think my strategy will be to install a thermocouple at the top of the

firewall on a "L" bracket with the thermocouple sensor end pointing down and

I will cover the wires in Aeroquip fire sleeve from the probe all the way to

the firewall penetration pass through.  



I will then place the cowling temperature digital readout on the Skyview

screen in a location under the CHT readouts.    The digital readout will

just look like "COWL 285F" in white text.  I will monitor the readout for a

few flights and if the temp routinely gets to 300F but no higher I will then

set the Skyview system to change the digits from white to yellow at 400F and

then to red at 500F as a wake up.



If I am ever flying along fat, dumb, and happy and I see the digits rapidly

change from white to yellow to red as the indication shoots up to the 4

digits.and then.the digits begin to display "XXXX" then I guess the day has

become bad and I am still fat.and dumb.but no longer happy.



THANKS AGAIN for your advice!!!

ARGOLDMAN(at)aol.com
Guest

Posted: Wed Jul 27, 2016 1:03 pm Post subject: Switch For Thermocouple Wires

Of course you could always use the technique that Burt Rutan used in the  SS1 engine.. I think that he wrapped a copper (or other low fusing wire around  the engine, ran a small current through it and if there were a breach in the  containment vessel, the wire would burn through and open the circuit.

  

 Alternately use an EGT probe in the area of question.

  

 Rich

  

  In a message dated 7/27/2016 1:23:55 P.M. Pacific Daylight Time,  sportav8r(at)gmail.com writes:

  	  Quote: 	
		     I'm thinking extreme analog/tinker-toy technology, here, but why    not a cotton string across the cowl outlet that holds open a spring-loaded    N.O. switch.  Fire would presumably burn it through quickly.  A    cross-check with a cowl air temp indicator would help confirm actual fire vs.    "the old string finally rotted-through between annuals."      



   Since we now fly in the digital age, the obvious modern solution is a    belly cam to show the flames licking out of the cowl exit.

   



   -Stormy



   

   On Wed, Jul 27, 2016 at 7:49 AM, Robert L. Nuckolls,    III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:

    	  Quote: 	
		       At 12:31 AM 7/27/2016, you wrote:

      	  Quote: 	
		  On Jul 26, 2016, at 5:29 PM, William Hunter        <        billhuntersemail(at)gmail.com (billhuntersemail(at)gmail.com)> wrote:

        	  Quote: 	
		  

I am somewhat interested in knowing how hot          a fire is... 	


For gasoline, ignition temp is 232Â°C        and flame temp varies from ~945Â°C to 1,950Â°C depending on        conditions.



Eric 	




  It's been about 30      years since I fiddled with

  fire detection techniques. We looked at      them as

  a potential product for Electro-Mech about      1980.



  No software back then . . . all discrete jelly

       beans. There were two techniques that showed

  promise. One involved      temperature sensors at

  ram air inlet and cooling outlet ports      and

  circuitry that watched for (1) outlet to

  exceed xx      degrees along with (2) a rate

  of rise in the differential between      the

  two.



  The other technique, and the one most      popular

  with our customers involved routing a kind

  of      linear thermistor around the engine's

  potential hot spots during a      fire. The

  'thermistor' looked for all the world like

  a      piece of semi-rigid coax cable. Thin

  metal jacket (stainless I      think). Center

  conductor of solid metal. A 'dielectric'

       of thermistor material.



  Looking into the end of the 'coax'      one

  would see an infinite number of thermistors

  all tied      in parallel.  But should any portion

  of the 'coax' be exposed      to flame, the thermistor

  material in that area would present a      sharp

  drop in resistance which was detected by

  the      electronics.



  We never did pursue the opportunity      beyond

  the gee-what-if stage. I went off to work

  the      servoed pitch trim controller for the

  Lears . . . Dean did an APU      controller for

  Duncan Aviation.



  The long,      temperature sensitive 'coax' was

  kinda cool. You could route it as      needed in

  the engine space but it was a specialty

       product that was custom-manufactured to

  the design. Breathtaking      start-up costs.



  With software one could place one or      more

  temperature sensors about the engine spaces

  and      write scanning/interpretation routines

  to identify abnormal      temperature profiles.



  For an OBAM aviation project, I can      see

  a kind of universal fire detection system

  that is      first installed in a 'learn' mode

  and flown for xx hours. Once      'normal'

  temperatures are identified and cataloged,

  a      'operate' mode would raise a flag if

  conditions markedly outside      the normal

  parameters was detected.



  It's an      interesting design study that

  was very low on Electro-Mech's totem      pole

  of market opportunities. Under the cowl

  fires just      don't figure into a significant

  percentage of      bad-days-in-the-cockpit.

     

  Bob . . .

edpav8r(at)yahoo.com
Guest

Posted: Wed Jul 27, 2016 1:14 pm Post subject: Switch For Thermocouple Wires

On Jul 27, 2016, at 4:49 AM, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com> wrote:

 	  Quote: 	
		   The other technique, and the one most popular with our customers involved routing a kind of linear thermistor around the engine's potential hot spots during a fire. The 'thermistor' looked for all the world like a piece of semi-rigid coax cable. Thin metal jacket (stainless I think). Center conductor of solid metal. A 'dielectric' of thermistor material.

 

 Looking into the end of the 'coax' one would see an infinite number of thermistors all tied in parallel.  But should any portion of the 'coax' be exposed to flame, the thermistor material in that area would present a sharp drop in resistance which was detected by the electronics.


	


That's the technique that Bombardier uses in their products (at least the ones I flew).  The thermistor loops are installed around the hot section and pylon of each engine, along the anti-ice bleed air ducts, inside the APU enclosure and on the ceiling of the main wheel wells.  Unfortunately I no longer have access to the electronic manuals and my hard copy is in a box somewhere, so I can't post the technical description.



Boeing took a different route; one that, to my mind, seems a bit more fiddly and less robust.  The following is an excerpt from the B-737NG systems manual.  I'm not sure if this system is a relic of the original 1960's design, or a later revision.



 	  Quote: 	
		  >>

Each engine contains two overheat/fire detector loops.  Each loop provides both fire and overheat detection.  When the temperature reaches the Overheat Set Point, the gas in the detector loop expands, closing the Overheat Pressure Switch.  This decreases the resistance of the detector.  The Engine and APU Fire Detection Module uses the decrease in resistance to set the overheat condition.  As temperature increases to the Fire Set Point, the gas continues to expand and closes the Fire Pressure Switch, further decreasing the resistance.  The Engine and APU Fire Detection Module uses the decrease in resistance to set the fire condition.
	


<<<



Eric

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