Thread: K thermocouple cable length

Maybe contact Auber for their advice?

My understanding is that the cable resistance is critical over the supplied length to ensure accurate reading.

Someone like "Drivseafe" with an in depth electrical knowledge hopefully will come along soon if Auber cannot help.

cheers

It is the dissimilar metals that pruduce the temperature sensitive junction. Every junction will produce a voltage proportional to the temperature at the junction. It comes down to what you consider accurate!

Originally Posted by B92 8NW

I have a 6mm VDO thermocouple wired to a VDO pyro via the supplied 5m "compensating cable" (one wire is copper, the other is something else).

I've just bought an Auber exposed tip thermocouple which is suppled with 1.8m of cable. Obviously it advises not to change the length of the cable, but if put a K-type plug on the end and plug it into the VDO compensating loom will it be accurate?

As Drivesafe says, dissimilar metal junctions cause errors in thermocouple circuits. You can extend thermocouple cables (up to >100m in industrial situations in the past) using either the same thermocouple alloy wires or compensating extension cable which has the same thermoelectric properties over a limited temperature span.

Is the VDO cable you're considering the stuff with a redish-brown PVC sheath and red and brown covered wires? If so, it should be an international standard compensating cable for type K.

Are you planning on attaching the Auber probe to your existing VDO analog gauge? If so, I suggest you ensure the total length of cable from the probe to the gauge terminals is a close as possible to that of the original VDO sensor. Analog gauges such as this are low impedence devices and are calibrated not only to the thermoelectric characteristics of the thermocouple but also to allow for the total resistance of the sensor cable. Electronic thermocouple gauges are high impedence devices and are generally unaffected by cable resistance changes.

By the way, I wouldn't use the Auber exposed tip T/C in a pre-turbo (upstream) situation. I'd only ever use a fully sheathed T/C pre-turbo.

Ian

Originally Posted by Leo109

As Drivesafe says, dissimilar metal junctions cause errors in thermocouple circuits. You can extend thermocouple cables (up to >100m in industrial situations in the past) using either the same thermocouple alloy wires or compensating extension cable which has the same thermoelectric properties over a limited temperature span.

Is the VDO cable you're considering the stuff with a redish-brown PVC sheath and red and brown covered wires? If so, it should be an international standard compensating cable for type K.

Are you planning on attaching the Auber probe to your existing VDO analog gauge? If so, I suggest you ensure the total length of cable from the probe to the gauge terminals is a close as possible to that of the original VDO sensor. Analog gauges such as this are low impedence devices and are calibrated not only to the thermoelectric characteristics of the thermocouple but also to allow for the total resistance of the sensor cable. Electronic thermocouple gauges are high impedence devices and are generally unaffected by cable resistance changes.

By the way, I wouldn't use the Auber exposed tip T/C in a pre-turbo (upstream) situation. I'd only ever use a fully sheathed T/C pre-turbo.

Ian

Thanks. To be honest, the proper VDO 6mm probe has a very good response as it is, doesn't keep rising on throttle lift on up hill as some have reported with cheap ones. I think it's probably wise to keep everything VDO then. I might put the Auber one downstream or use it for another project.

As the others have said, length doesn't matter at all, but the proper connectors do.

I use these: Mini K type connectors.

Originally Posted by Leo109

..snip..

By the way, I wouldn't use the Auber exposed tip T/C in a pre-turbo (upstream) situation. I'd only ever use a fully sheathed T/C pre-turbo.

Ian

Is that just due to the possibility of the tip breaking off and going through your turbo?

Steve

Originally Posted by steveG

Is that just due to the possibility of the tip breaking off and going through your turbo?

Steve

Exposed tips aren't to be used generally in pressurised or corrosive environments.