Datalogging: K type Thermal couple setup on NI-9211 module

[jlin9505]

Hi

I've encountered a porblem when datalogging thermal readings using the K type thermal couple wire (Fiberglass-900) with the NI-9211 module. In LabView the recommended setup is to connect the red wire (Ni-Cr) to channel 0 and the yellow wire (Ni-Al) to channel 1 (for the first pair of terminals). However when i did this the thermal response I recieved was the opposite, ie I get a decrease in temperature reading when I really should get an increase.

It wasn't until I switch the wires around that I can get a decent reading from them, so I'm just curious as to what the problem is. ie faulty wire or module? or just a mistake in the LabView illustration.

Any help would be greatly appreciated.

[RavensFan]

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jlin9505 wrote:
Hi

 In LabView the recommended setup is to connect the red wire (Ni-Cr) to channel 0 and the yellow wire (Ni-Al) to channel 1 (for the first pair of terminals).

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Can you post a link to a manual or screenshot as to where you saw this?

For type K thermocouples, the red wire is the negative lead, the yellow wire is the positive lead.  If you have them wired backwards, then you will see and inverse response to temperature.

This link is the manual.  Terminal pinouts are on page 9.

Message Edited by Ravens Fan on 02-24-2008 11:39 PM

[jlin9505]

I see, that would explain everything. By the way here is the LabView connection diagram, I was following the color coding on that. Is that diagram correct? have I miss interpert it?

At any rate, thanks for the help.

[RavensFan]

I would say that picture is wrong, or at least misleading!

I noticed that no matter what T/C type you pick, the colors are always the same.  Red on the + wire, Yellow on the - wire.  Which is either the wrong colors for all other thermocouples, and precisely backwards for a Type K.  The metal designations however seem to be correct for all the T/C types I checked.

Here is a link for a thermocouple color standards.  http://www.omega.com/toc_asp/frameset.html?book=Temperature&file=tc_colorcodes

I hope someone from NI will take a look at this in the DAQ assistant and submit a CAR# for this.

In the meantime, please follow the wiring colors as shown on the link and ignore what the DAQ assistant wiring diagram is telling you.

[J_Thomas]

Hi jlin9505,

The colors used in the DAQ assistant connection diagram are the same regardless of what type of measurement or device you are trying to configure.  This is expected behavior. The colors are the same for a voltage measurement, counter measurement, or in this case a thermocouple measurement.  The use of the red on positive wire and yellow on the negative wire was not intended to represent the actual wire colors for any device or measurement type.

It is unfortunate that the colors R&D choose for the wires happened to be the exact opposite for a Type K thermocouple. We are really sorry for any confusion this may have caused!

In light of this instance, it is a great product suggestion for R&D to match the wire colors to the standardized colors for thermocouples, or at the very least choose colors that wouldn’t create any confusion. A product suggestion has been filed and I would encourage you to do the same.  R&D looks at every product suggestion filed.  You can visit the Product Suggestions Center to make a suggestion.