---------------------------------------------------------- JabiruEngine-List Digest Archive --- Total Messages Posted Sun 08/18/13: 4 ---------------------------------------------------------- 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 _____________________________________ Time: 05:02:09 AM PST US Subject: JabiruEngine-List: Re: Jabiru 3300 CHT Disparity From: "BobP" 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 ________________________________ Message 2 _____________________________________ Time: 01:55:10 PM PST US Subject: JabiruEngine-List: Re: Jabiru 3300 CHT Disparity From: "guccidude" 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 _____________________________________ Time: 02:39:13 PM PST US From: "Robert Haas" Subject: Re: JabiruEngine-List: 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 _____________________________________ Time: 04:27:22 PM PST US Subject: Re: JabiruEngine-List: Re: Jabiru 3300 CHT Disparity From: FLYaDIVE 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 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 > > ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message jabiruengine-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/JabiruEngine-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/jabiruengine-list Browse Digests http://www.matronics.com/digest/jabiruengine-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.