Today's Message Index:
----------------------
1. 05:02 AM - Re: Jabiru 3300 CHT Disparity (BobP)
2. 01:55 PM - Re: Jabiru 3300 CHT Disparity (guccidude)
3. 02:39 PM - Re: Re: Jabiru 3300 CHT Disparity (Robert Haas)
4. 04:27 PM - Re: Re: Jabiru 3300 CHT Disparity (FLYaDIVE)
Message 1
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| Subject: | Re: Jabiru 3300 CHT Disparity |
Hi Barry,
I can't see that a plug temperature range will affect the (true) cylinder head
temperature. My understanding is that the terms hotter and colder plugs refer
to the thermal coupling between a plug's centre electrode/ceramic nose, and
the main plug body. The plug temperature range needs to be selected so the plug
nose gets hot enough to burn off oil and carbon that might otherwise kill the
spark, and cool enough not to act as a glow plug resulting in pre-ignition.
All the plug type thermocouples I have seen consist of an aluminium washer that
is squashed between head and cylinder, the washer has a tag extending from it
that "waves in the breeze". The thermocouple junction is crimped into that tag
and so reads the tag temperature rather than the cylinder head temperature,
or even the temperature at the plug/head interface.
--------
BobP
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=406955#406955
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| Subject: | Re: Jabiru 3300 CHT Disparity |
I agree with BobP on the first paragraph. The second paragraph may need a little
explanation. The ring does all that he mentioned but I think it does not read
the "temperature"directly. The ring is the ground. The head temp changes
the resistance value in the ring(ground) and that is what the temp indicator
is displaying. The temp you read off the gauge is a resistance value displayed
as a temp. That is my understanding of temp probes(rings). Dan
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=406988#406988
Message 3
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| Subject: | Re: Jabiru 3300 CHT Disparity |
I concur, But I don't think the heat range is overly affected by the
thermocouple. Bob Haas N380BH N3300BH.
-----Original Message-----
From: guccidude
Sent: Sunday, August 18, 2013 4:52 PM
Subject: JabiruEngine-List: Re: Jabiru 3300 CHT Disparity
I agree with BobP on the first paragraph. The second paragraph may need a
little explanation. The ring does all that he mentioned but I think it does
not read the "temperature"directly. The ring is the ground. The head temp
changes the resistance value in the ring(ground) and that is what the temp
indicator is displaying. The temp you read off the gauge is a resistance
value displayed as a temp. That is my understanding of temp probes(rings).
Dan
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=406988#406988
Message 4
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| Subject: | Re: Jabiru 3300 CHT Disparity |
Dan & Robert H.:
To answer the question correctly you have to tell us what is the Make and
Model of Temperature Gauge. Most gauges use a Thermocouple. It is more
accurate and can handle all sorts of harsh environments. The other option
is a Thermal Resistor not as accurate and environmentally challenged.
In either case GROUND is not used as part of the temperature acquiring
circuit, it is used for noise isolation and and RF isolation. Different
companies have different ideas on how to handle these issues. The three
types of thermocouples are: Open element, Sealed Un-Grounded and Sealed
Grounded. They each have their own advantages and disadvantages.
As for the Ring type thermocouple it is a THERMOCOUPLE not a Thermal
Resistor. The thermal resistor would be destroyed by torquing down the
spark plug. And your idea, you could not count on the contact resistance
being uniform from spark plug to spark plug or from day to day.
Robert - Opinions do not count here, only the facts count. The ring type
thermocouple most definitely does affect the heat range of the spark plug.
It can take the heat range UP two or more range levels. Here is a simple
check you can perform from the comfort of your computer chair:
Ask around of owners of the SAME engine and SAME installation - What their
CHT's are. Also ask which thermocouple they are using... Ring type or
Screwed in type. There is also a bayonet type but not to many owners use
it. You will find Ring thermocouples will always be a Higher Temp.
Hope this information enlightens those gray areas.
Barry
Test Engineer for the past 20 years, developing and doing exactly this type
of testing.
On Sun, Aug 18, 2013 at 4:52 PM, guccidude <dcr@fdltownhomes.com> wrote:
> >
>
> I agree with BobP on the first paragraph. The second paragraph may need a
> little explanation. The ring does all that he mentioned but I think it
> does not read the "temperature"directly. The ring is the ground. The head
> temp changes the resistance value in the ring(ground) and that is what the
> temp indicator is displaying. The temp you read off the gauge is a
> resistance value displayed as a temp. That is my understanding of temp
> probes(rings). Dan
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=406988#406988
>
>
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