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Link G4X TCA4+4

CANBus Communications Decoded

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Discussion and questions related to the course CAN Bus Communications Decoded

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Hi there,

I require some confirmation on something please, I got a 8 channel haltech tca for a project which is actually the 4a+4b version not tca 8 so info isnt that easy to find. My bad.

Anyway I made it work with some info from multiple older posts from ADAM @ Link Ecu using

can id 716 for "box a assigned to can tc 1-4" and

id 717 for "box b assigned to can tc 5-8"

Multiplier of 2381 divider of 5850 and offset of -250 which gives me realistic values.

I have Can Tc input#8 as a post turbo charge temp showing 40c in an engine bay with approx 30c ambient temp so I think its right and id generally trust that info from Adam but obviously I cannot test accurately an egt probe to 1000c to confirm the other end of the scale.

My question here is where do the multiplier, divider and offset number come from and how are they calculated? Trial and error ?

I can understand the some of the normal temperature channels transmitting in temperature K and they may be scaled up or down to get the required resolution and when converting from K to C by 0K -273.15 = -273.15C and using the dividers and multipliers to change where the decimal point ends up for example to get the correct number at the destination but these values of the numbers for the multiplier divider and offset in this instance make no sense to me.

I guess what im asking is can someone walk me through the process/math of why these numbers are what they are and why is the offset -250 and not -273 for instance.

Maybe even Adam would be best to answer.


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Either the company making the product that's doing the sending provides you with this info, or you do have to figure it out on your own.

In terms of why there's sometimes a multiplier and a divisor, whole numbers have to be used, but the slope that needs applied isn't always a whole number, and that's how I've ended up using multiplier and divisor.

I believe a method of figuring these items out to scale an item found in a CAN stream is described in the course?

In your particular example if Adam did the calculation then he would have insight on his personal process.

I know it seems odd, but the conversion factor that I got directly from Haltech was Temp(K) = Raw*2381/5850+23.1. I have only changed the offset to -250 in the Link ECU CAN set-up as our ecu expects to receive all temps in °C units.

I did bench test one at 0 & 1250°C with a K type simulator to make sure I didnt mess anything up at the time.

I dont know how it ended up with such an odd scale factor but remember this device is probably more than 15 years old, from a time when CAN was not so common, so it may just broadcast some raw ADC value or maybe it originally had to work around some quirk or resolution issue in the old platinum ecu firmware.

Awesome thanks for the reply.

Not really a good example for going through the process of how to work out the scaling then LOL.

Seems weird they are still using those old values with a new product brought from haltech a few months ago though probably backwards compatibility I suppose.


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