Mychron

[Robert Horvath]

Has anybody tried this or does anyone know if this will work ?

This is a photo of my homemade A/B temp switch (water temp & exhaust temp) for when you only have one temp. input on your Mychron.

I'm mounting my switch right beside my seat by the engine.

See attachment below:

It consist of a hobby shop A/B switch > Futaba Radio part # FUTSWH13 $9.99

One Aim male connector from Sharkshifter $7.95

Two Aim female connectors from Sharkshifter $7.95

Oconomowoc Bob Horvath

W352N6446 Road J
Oconomowoc Wi 53066 U.S.A.

rhorvath4@wi.rr.com


[img][/img]

[Don Engebretsen]

Bob:

I have done that and it should work fine. As long as your wiring connections are correct and completely isolated you should be good to go. Your A/B switch looks like a superior unit to mine, which would be good.

Of course the only problem you then have is to remember which reading you will be displaying while in the heat of action

Don E

[Chris Reinhardt]

I assume that the need for the splitter is for a twin cyl EGT? One way to know which EGT is which, is to split the water temp with one EGT, so when you switch from one to the other you know the +-140deg is the the water and the +-1000deg is the cylinder you split, the other cylinder remains constant.

CR
_________________
East Coast Super Kart Series
"This is how we roll!"
www.eastcoastsuperkart.webs.com

CR2 Motorsports
"Home of Cobalt Superkarts"
www.CR2MotorSports.webs.com

[Robert Horvath]

Thanks,

Don Engebretsen and Chris Reinhardt

For the helpful replies.

Bob Horvath

[Sam Zavaglia]

You have a problem there.
You are using K-type inputs, thermocouples and connectors however your extensions are using normal copper wire. This is going to give you inaccurate results.
The K-Type works on a difference of resistance in the two different wires.
This is not recommended especially if using H20 where K-Type is not the best accuracy for temps that low.
Google K-Type to find out more, especially about the wire.
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[Robert Horvath]

Sam ,

The answer I got off the Internet is it produces a voltage.

Not a resistance change.

Thermocouple : produces a voltage when heated.

It consists of two dissimilar conductors in the probe not in the cables.

I just tested it over the weekend and I get the same temp. readings either when connected directly or through my switch.

Maybe it worked "OK" because the switch leads are so short ?

Thanks for the info.

Bob Horvath

[Chuck Bunnell]

As long as both legs of each thermocouple see the same changes, i.e. junctions, connectors, switches, conductor material changes, it will work just fine.

[Greg Lindahl]

If you're not looking for ultimate accuracy, and, as long as you are switching both leads, you'll be fine.
For karting-levels of accuracy, short copper extension leads work fine. If you were working with greater than a few feet of extension wire, I would specify extension or thermocouple grade wire.
K-type thermocouples have plenty of range, up and down, for karting applications.
This is a great way to extend the capability of a data collection system and it's not limited to just two thermocouples. You can find selector switches for multiple two-pole inputs if you wish. You'll have to keep track of the data in your memory or keep a notebook handy!

[Sam Zavaglia]

We are talking about small mV (millivolts) of change to make a difference in measurement. Different conductors have different resistance which is directly proportional to the voltage being measured by your unit. (V=IxR - ohms law).

Every time you make a join it changes the desired outcome. You should always limit the amount of junctions with K-Type from the junction (inside the probe) to the meter input. (you have resistance changes from K-Type connector to the copper, to the solder, to the switch contacts, to the solder, to the copper and back to the K-Type connector.

Furthermore, when you put onto a kart you have electrical noise being produced which will also cause a change, that's why the "Yellow" K-Type wire used by AIM has a braided shielding around it's 2 wires it so it's less induced due outside interference. This wires are also made using the correct conducting wires for the + and -


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www.samzavaglia.com

[Robert Horvath]

Chuck Bunnell,Greg Lindahl and Sam Zavaglia

The you gentleman for all the help.

Bob Horvath

[Greg Lindahl]

Sam makes a good point: Inductive coupling can occur if your patch cable is close to a rapidly changing voltage signal, like the sparkplug wire. All thermocouple wires should be kept away from the sparkplug wire.
The yellow cover on the thermocouple wire signifies that the sensor it's meant to be used with is a type K.
Because the foil on the wire is not grounded at one end, it does not provide much help with inductive coupling (twisting the conductors with the correct pitch does).
The circuit from thermocouple to Mychron is series with the thermocouple being a "variable voltage supply" (depending upon temperature sensed).
Resistance in each leg is the same if the leads are the same length (extremely small resistance difference if wires are not exactly the same length).
Voltage measured by the Mychron will be the voltage generated by the thermocouple.

[Chris Reinhardt]

I agree with most everything here but.... try it and see what happens....

Easy enough to test on the bench.... Maybe if you use the K-Type wiring all the way through the switch...

CR
_________________
East Coast Super Kart Series
"This is how we roll!"
www.eastcoastsuperkart.webs.com

CR2 Motorsports
"Home of Cobalt Superkarts"
www.CR2MotorSports.webs.com

[Robert Horvath]

Guys

Thanks to all for the replies and helpful advice.

Oconomowoc Bob

Robert Horvath

W352N6446 Road J
Oconomowoc Wi 53066 U.S.A.


rhorvath4@wi.rr.com