Reading a thermocouple on a PCI-6281 using an SCB 68

[EliG]

Hi All,

I have been looking through the forums for a while trying to solve this problem, but still am at a loss on what is wrong with my setup.

I am trying to read a K type thermocouple using a PCI-6281, a SCB-68 and the DAQMX library in C#.

My Wiring Setup:

1) I have set the switches on my SCB-68 board to enable the on-board differential sensor for use in CJC.

2) I have a K type thermocouple hooked up to AI5 and AI13 (pins 60 and 26) and am reading it as a thermcouple channel in my software.

My Software Setup

1) I used the example code ContAcqThermocoupleSamples_IntClk, and still am getting temperature readings that don't seem to match when reading ai5. (when I change the temp at the thermocouple, I don't see a change in voltage for instance).

2) I used the test panel feature of measurement studio to try out different analog input configurations. I used differential mode when hooked up to AI5 and AI13, and I see a consistent if noisy signal, but still no change in the thermocouple when the temperature is changed. I used RSE mode when hooked up to AI5 and AIGND, and saw similar performance.

When I read AI0 as a voltage channel, i can see temperatures rising and falling from the board sensor as normal, so I know that is working well. Any idea what I coudl be doing wrong? I even hooked up a 10k resistor between AI13 and AIGND per some of the documentation and this did nothing to help.

Thanks for any assistance,

Eli

[TheGeeze]

Hi Eli,

You mentioned you can see the voltage change using test panels in Measurement and Automation Explorer.  Have you tried using a thermocouple task in Measurement and Automation explorer to test out your set up?  To do this right click on your device and select Create Task.  Then select Analog Measurement -> Temperature -> Thermocouple.  If you enter in your information there, you should get an accurate temperature reading.  

Can you try this and let us know how it goes?  This will let us know if the problem is with hardware or with software.

Thanks!

[EliG]

Ryan,

I do not have the ability to create a task in my measurement and automation explorer as far as I can tell, as it just shows me "data neighborhood" with no options when I select create task (see attached screenshot).

As for measuring voltage, I am using the Test Panels function as seen in the same screenshot. I can see voltage hovering around 0 to .002V when I select AI5 in both RSE and differential mode, but when I increase the thermocouple temperature I get no visible change in my voltage feedback. Any ideas on where I have this hooked up wrong? Once I can see a voltage change I figure a temperuare channel will work just fine....but I need to get there first!

-Eli

[TheGeeze]

Another way to create a task is by selecting the devince and then clicking create task.  I can see in your screen shot you certainly have that option.  It is two tabs to the right of the test panels tab.  Are you able to create a task in this manner?

[EliG]

All create task buttons, including the one you mentioned, simply bring up that window as see in the screenshot.

Regardless, I shoudl be able to see the voltage using the test panels, (See screenshot) which seems very noisy and does not change perceptably when I increase the thermocouple temperaure, leading me to believe I have a hardware issue I am not seeing. I verified the thermocouple on an external device, so it is working....so it must be my connection to the SCB-68?

[TheGeeze]

Eli,

First, I am trying to get some hardware set up to test exactly what your set up is.  I ran into some difficulties today so I was unable to get anything working.  I will have access to some different boards tomorrow, so I will try again then.  

Second, I do not like that you cannot create a task.  That will be the easiest way to verify that everything is working once I get things set up.  Can you try repairing your data base and see if that allows you to create a task. Go to Tools -> Reset Configuration Data and run that.  Let me know if that allows you to create a task and I will let you know when I have working hardware on my end.

Thanks!

[EliG]

Thanks Ryan, I reset my configuration data and still cannot create a task. I should mention that I did not purchase any of the extra software packages besides those that came with the PCI-6281 card, does this matter for creating a task? Is there something else I need to install?

Regardless, I can run a temperature task in my C# code, which then uses the CJC of the internal sensor on the SCB-68 just fine. However, I still see a huge amount of noise and my temperature seems to jump from 40 to 80 deg F.....Therefore I was hoping to use the built in software tasks to verify it wasn't something I am doing wrong in my c# code.

[TheGeeze]

Hi Eli, 

I finnally got hardware hooked up and working.  The cjc on the original sbc68 I had was not working properly, I am sorry for the delay.  Since you mentioned your cjc is measuring correctly, I will assume that is fine and is not your issue.

In my set up, I do not have anything special.  I have switch 4 and 5 changed and I am reading from AI2.  I did not need to use anything special to get some rough measurements.

You mentioned that when you just measure the voltage coming in on AI channel 5, you get noise with peaks around 300uV.  From what I can see, your configuration of 100m to -100m is correct.  Have you tried measuring some other voltage with this input terminal?  Have you tried other input terminals?

Also, I am still bothered about you not being able to create a task.  This should be a basic function of Measurement and Automation Explorer.  Do you know what version of the DAQmx drivers you have.  If the above questions do not yield anythign useful and you have some time, I would like you to upgrade to the newest version (9.4).  This can be found by going to ni.com/drivers and searching for daqmx.

Let me know how this goes,

Ryan

[TheGeeze]

note: the new driver install can take an hour, so make sure you have some time before performing the installation!  

[EliG]

Ryan,

I will try to install updated drivers later, but I am more interested in how you have hooked up to AI2 with your thermocouple.

Are you in differential mode or RSE? What do your readings look like when using a test panel like I did? Are you connecting to AIGND in any way?

Also, is it possible I need to install a "full" version of Measurement and Automation explorer? Does the one that came with my card not include basic functionality like creating tasks?

Thanks,

Eli