Thermocouple Reading

[rfireton]

All, I'm new to this, getting an old data acquisistion system upgraded.  I've only been through Core 1 training.

I have an issue(s).

I'm using a NI eDAQ-9178 with NI9211 and NI9205.  The NI9205 is taking a simulated flow signal from a frequency conditioner.  I'm using the DAQ Assistant to aquire the signals.  Currently, I'm plotting flow vs temp just to get an understanding of x-y plots.  My issue is this...when I write the temp and flow values to a TDMS file I notice that my thermocouple measurement are as follows (see below).  Not sure what I'm doing wrong, can anyone help, see attached. 

78.52764246
78.52764246
78.52764246
78.45823079
78.45823079
78.45823079
78.45823079
78.5143133
78.5143133
78.5143133
78.44951917
78.44951917
78.44951917
78.44951917
78.45512712
78.45512712
78.45512712

[HeatherBaker]

Hi rfireton,

Can you please elaborate on the issue of the thermocouple data?  This will help ensure we fully address your concerns.

[rfireton]

Not that the data is repeating values in groups of 3 and 4.  Is this a function of the thermocouple or do I have something wrong in my code?

[HeatherBaker]

I would recommend temporarily placing an indicator after the DAQ Assistant to determine what output you are seeing and progressing through the code until you determine the point of issue.  This will help narrow down the source and consequently determine its behavior. 

[John_P1 · Accepted solution]

Hi rfireton,

Is the concern that there are 3-4 duplicate copies of the same data?

The reason for this is that the 9211 is considered a slow-sampled module (14 S/s in this case).  One feature of these modules is that they will let you set a sample rate faster than what is technically possible on the module, but will simply repeat data as necessary.  This feature was a necessity to allow these slow-sampled modules to operate in the same task as faster modules like the 9205.

Indeed, on the older cDAQ chassis (9172), it was required to put all analog input modules in the same task.  On the newer 9178 chassis that you are using this is no longer necessary (but it is still possible).  The 9178 has 3 analog input timing engines, so you can actually run a separate task for your 9211 at a supported rate if you want to avoid receiving duplicate data.

Best Regards,

[rfireton]

Yes, the concern was 3-4 duplicate copies of the same data.  You're answers have explained the issue.  Thank you.