Meanwhile I'm cheesed off with ATS still because their computer says i have 40' toe in rear wheels and my tracking gauges say I have none. I did hope to make relative adjustments to their read-out but ye olde style tracking gauges cannot lie, ATS have muffed up so i'm back to square one - I can get the rear tracking right but no way of accurately setting to be in line with the front wheels.
one that can read current without having to make contact with the conductor so you can clip on to the cabling, rather than the bare wires either end, or piercing the insulation
there's another way to get accurate front to rear measurements, but it's a bit of a faff....instead of using a 4 x 2 timber, use heavy guage fishing line, and rig up a rectangle around the bus at centre wheel height....basically, you're creating a datum line all around the bus from which to take measurements. Use fixed points for reference (eg end of the stub axles) and set the line distances up so they're identical for either side....at a pinch you could make a accurate rectangular frame (90 degs at each corner) from suitable timber, supported at the right height on axle stands I'd be surprised if a thirty odd year old bus isn't bent
I've found this about the gauge elsewhere. Cylinder Head Temperature Range: 100-700 F. 100-700 F. Use 48" Type J Thermocouples. Input 9.81 mv @ 400f. Do I have a volts drop causing the low readings? It does say to use 48" thermocouple, so having made it 5m longer... Back to the copper extension idea as presumably supplied with @theBusmonkey 's gauge kit?
It crabs just like the ATS readings and my bits of wood suggest, but I've lost faith in the numbers they supplied. I've read (probably you!) about string, sounds like a similar faff arsing about with stuff that keeps coming off TBH but I might give it a go as potentially more accurate. Or I could just drive to another 4 wheel tracking place, pre-armed with numbers from my gauges and from ATS and see what they think it is.
i'd try it....the mv reading as seen by the gauge equates to temp. Thermocouples utilize the voltage difference between two disimilar conductors...the length of the conductors will affect the inherent resistance....makes sense to me...worth ruling it out, if nothing else going off fridge thermocouples and those used on gas boilers etc. they are a fixed length...you'll often see them coiled up for no apparent reason....perhaps the reason is that it has to have a fixed length to excite the gauge/switch/whatever within the gauges working parameters...worth speaking to a tech So...a bit of retro engineering: your bus's cable install is a known length...the actuation for the guage is a known mv....the cyl/heads' operating temp. range is known (each temp will equate with a specific mv...determined by sticking the gauge in water and heating up, while measuring the mv) so it's not impossible to figure out (using resistance tables) what gauge cables you'd need (of a fixed length) to achieve the mv required.... as stated...it's just a hunch
OK...scrap that...here's the gen: "The length of a thermocouple has no effect on its measurement accuracy or its ability to transfer the signal to the instrument. In other words, thermocouples do not experience “voltage drops” or power loss along its length as a high current power line might possess. The reason for this is due to the very low current and voltages associated with temperature measurements...." so there's something else going on
"In practical applications where the thermocouple is a substantial distance from the instrument, electrical noise can be induced and the sensor selected should be shielded and grounded at one end...."
I keep finding diagrams like this one. Have I outwitted myself and skewed the equation by extending with a pair of wires with differing resistances after the cold junction? Or, by extending with thermocouple extension cable have i moved the cold junction 5 metres? Does it matter that I used crimped joiny things, 1 wire in each end? would it make a difference if Itwisted them together and crimped in one end of the connector? There's something stuck under my shift key.
"The J thermocouple is made of an iron wire (+ positive lead colored white) and a copper-nickel (Constantan) alloy wire (- negative lead colored red). It has a sensitivity of approximately 50 microvolts / deg C and an overall temperature range of -210C to 1200C, but is normally limited to narrower ranges. It has a limited range of -40C to 750C due to the Curie point of the iron at 770C. The iron undergoes a molecular change and permanently loses its standard voltage output versus temperature. It does not recover when the iron is cooled." http://www.instrumentationtoolbox.com/2011/05/converting-thermocouple-milivolts-to.html
Yes, at the hot end which they are - soldered together and crimped to the spark plug ring which looks to be a heat sink. Maybe it's in a draught from the cooling.
so your's is the type that uses a ring connector under the spark plug...which is grounded "Although there is electron movement in any single conductor, it is virtually impossible to get a voltage measurement from it. Readers will recall voltage is the difference in electrical potential between two points. Trying to take a voltage reading from a single point on the wire just can’t be done. To get around this limitation, a second wire made from a different metal or alloy attaches to the first wire at the high-temperature point. The connection is called the “hot junction.” Different metals produce different quantities of electron motion when the wires are heated to the same temperature. The imbalance between the number of electrons creates a potential difference (voltage) between the wires. Any other point those wires connect, including terminal blocks and measuring instruments, is called a “cold junction.” One cold junction at the place thermocouples connect to the measuring instrument is unavoidable. This is often called the reference junction. Temperature readings made at the reference junction correct any thermocouple voltage generated there in a process called cold junction compensation. Thermocouple circuits can have more than one cold junction, but that is strongly discouraged and easily avoided. The raw voltage signal that represents temperature is the sum of all the hot and cold junctions. The temperature of the hot junction is determined by subtracting the offsets generated by all of the cold junctions. Thus the output voltage of the thermocouple depends only on the temperature of the hot junction." so shifting the position of the cold/reference junction should'nt make a difference...but it seems to have... it sounds to me that the type of connectors used will influence the raw voltage have you tried mounting the gauge in the engine bay temporarily?
haha, cable not supplied! I put the copper extension in through pure ignorance rather than specialist knowledge.... ...but don't tell anyone, it'll ruin the illusion I've cultivated
I also read tall that text somewhere. Love it when you understand then they throw in this^. WTF does that mean?
your reputation is shot anyway Zed...I wouldn't worry at a pinch...the more cold junctions you have (connector blocks, joins, etc.) the more of an arse it is to recalibrate the reference (temp gauge)
