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billhuntersemail(at)gmail
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 Posted: Wed Aug 02, 2017 6:16 am Post subject: Sharing thermocouple inputs? |
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On a different subject this week but with the same theme of "running out of EMS pins" , the question I have is can thermocouple wires be run through a switch and then routed to the EMS?
I have only one thermocouple input left in my Dynon EMS however I still have two locations that I want to monitor temperature (one on a full-time basis and the other on a once in a great while basis) .
Specifically I have a thermocouple probe mounted in my engine compartment that I want to use as a engine fire sensor and I have programed the EMS to change colors and give an audio warning when the temperature exceeds 400° f.
The second area that I would like to monitor on a once-in-a-while basis is the temperature of my intake air after it has left the intercooler.
I have spliced those two pairs of wires and run one pair to the top two screws of a Honeywell double pole double throw switch and the second pair of wires I ran to the bottom two screws of that switch. The middle two screws of the switch are wired to the EMS pins... the thinking that I can simply position the switch in the direction of the sensor I want to monitor.
The problem is that the EMS indication is the same temperature regardless of where the switch is positioned. In other words I could heat up one probe with my heat gun and regardless of where the switch is positioned I get the same reading on the EMS screen regardless of where I place the switch.
I would have thought that if I heat up the cowling temperature probe and I watch the indication on the screen ride up to 250 degrees Fahrenheit then if I move the switch to the intake temperature probe then the indication would drop back down to ambient temperature however no matter where the switch is placed the indication on the screen will only indicate the temperature of hottest probe... never the coldest.
Is it just unrealistic to be able to expect to Route thermocouple wires through a switch and be able to select the indication?
THANKS AGAIN FOR YOUR ADVICE!!!
Bill Hunter
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ceengland7(at)gmail.com
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| Posted: Wed Aug 02, 2017 8:03 am Post subject: Sharing thermocouple inputs? |
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On Wed, Aug 2, 2017 at 9:15 AM, William Hunter <billhuntersemail(at)gmail.com (billhuntersemail(at)gmail.com)> wrote:
| Quote: |
On a different subject this week but with the same theme of "running out of EMS pins" , the question I have is can thermocouple wires be run through a switch and then routed to the EMS?
I have only one thermocouple input left in my Dynon EMS however I still have two locations that I want to monitor temperature (one on a full-time basis and the other on a once in a great while basis) .
Specifically I have a thermocouple probe mounted in my engine compartment that I want to use as a engine fire sensor and I have programed the EMS to change colors and give an audio warning when the temperature exceeds 400° f.
The second area that I would like to monitor on a once-in-a-while basis is the temperature of my intake air after it has left the intercooler.
I have spliced those two pairs of wires and run one pair to the top two screws of a Honeywell double pole double throw switch and the second pair of wires I ran to the bottom two screws of that switch. The middle two screws of the switch are wired to the EMS pins... the thinking that I can simply position the switch in the direction of the sensor I want to monitor.
The problem is that the EMS indication is the same temperature regardless of where the switch is positioned. In other words I could heat up one probe with my heat gun and regardless of where the switch is positioned I get the same reading on the EMS screen regardless of where I place the switch.
I would have thought that if I heat up the cowling temperature probe and I watch the indication on the screen ride up to 250 degrees Fahrenheit then if I move the switch to the intake temperature probe then the indication would drop back down to ambient temperature however no matter where the switch is placed the indication on the screen will only indicate the temperature of hottest probe... never the coldest.
Is it just unrealistic to be able to expect to Route thermocouple wires through a switch and be able to select the indication?
THANKS AGAIN FOR YOUR ADVICE!!!
Bill Hunter |
Bill,
That's long been a way to monitor 2 (or more) different thermocouples. Conventional wisdom is that as long as you switch *both wires*, there should be minimal error between the two (or more) sensors. The idea is that by switching both leads, the junctions induce equal and opposite errors in the two wires, cancelling the error.
Charlie
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billhuntersemail(at)gmail
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| Posted: Wed Aug 02, 2017 8:40 am Post subject: Sharing thermocouple inputs? |
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!!!IT WORKS!!!
It seems I had on pair mislabeled and polarity connected up backwards. Using alligator clips and jumper wires and a couple of bad words allowed me to figure out my error. Now the correct pair and polarity go to the bottom pair of screws and the other (correct) pair and polarity go to the top pair of screws and out from the middle pair of screws come a couple of wires that get routed to the EMS and now I have thermocouple bliss!!!
..
Cheers!!!
Bill Hunter
From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Charlie England
Sent: Wednesday, August 2, 2017 9:01 AM
To: aeroelectric-list(at)matronics.com
Subject: Re: Sharing thermocouple inputs?
On Wed, Aug 2, 2017 at 9:15 AM, William Hunter <billhuntersemail(at)gmail.com (billhuntersemail(at)gmail.com)> wrote: | Quote: |
On a different subject this week but with the same theme of "running out of EMS pins" , the question I have is can thermocouple wires be run through a switch and then routed to the EMS?
I have only one thermocouple input left in my Dynon EMS however I still have two locations that I want to monitor temperature (one on a full-time basis and the other on a once in a great while basis) .
Specifically I have a thermocouple probe mounted in my engine compartment that I want to use as a engine fire sensor and I have programed the EMS to change colors and give an audio warning when the temperature exceeds 400° f.
The second area that I would like to monitor on a once-in-a-while basis is the temperature of my intake air after it has left the intercooler.
I have spliced those two pairs of wires and run one pair to the top two screws of a Honeywell double pole double throw switch and the second pair of wires I ran to the bottom two screws of that switch. The middle two screws of the switch are wired to the EMS pins... the thinking that I can simply position the switch in the direction of the sensor I want to monitor.
The problem is that the EMS indication is the same temperature regardless of where the switch is positioned. In other words I could heat up one probe with my heat gun and regardless of where the switch is positioned I get the same reading on the EMS screen regardless of where I place the switch.
I would have thought that if I heat up the cowling temperature probe and I watch the indication on the screen ride up to 250 degrees Fahrenheit then if I move the switch to the intake temperature probe then the indication would drop back down to ambient temperature however no matter where the switch is placed the indication on the screen will only indicate the temperature of hottest probe... never the coldest.
Is it just unrealistic to be able to expect to Route thermocouple wires through a switch and be able to select the indication?
THANKS AGAIN FOR YOUR ADVICE!!!
Bill Hunter |
Bill,
That's long been a way to monitor 2 (or more) different thermocouples. Conventional wisdom is that as long as you switch *both wires*, there should be minimal error between the two (or more) sensors. The idea is that by switching both leads, the junctions induce equal and opposite errors in the two wires, cancelling the error.
Charlie
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nuckolls.bob(at)aeroelect
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| Posted: Wed Aug 02, 2017 2:40 pm Post subject: Sharing thermocouple inputs? |
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Thermocouples and their management is covered in some
detail in the 'Connection starting on Page 14-11.
Bob . . .
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billhuntersemail(at)gmail
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| Posted: Wed Aug 02, 2017 6:11 pm Post subject: Sharing thermocouple inputs? |
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Thanks Bob.
I have read, highlighted, studied, re-read and studied your book practically cover to cover.
It is a really great resource.
..
Cheers!!!
Bill Hunter
From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Robert L. Nuckolls, III
Sent: Wednesday, August 2, 2017 3:40 PM
To: aeroelectric-list(at)matronics.com
Subject: RE: Sharing thermocouple inputs?
Thermocouples and their management is covered in some
detail in the 'Connection starting on Page 14-11.
Bob . . .
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