How to plot an XY graph for two analog input channels

[Qifu]

Hi,

I want to measure temperature and strain, and then plot them in one XY graph. Here are my questions. 

1. The sample rate range for the thermocouple is much slower than the one for the strain gauge. Should these two channels be sampled in the same rate? How to do it?

2. The attached is my first tried VI. I used DAQ Assist instead of DAQmx. The sample rates for the two DAQ Assists are set to be the same. Is it the correct way to do it?

3. The XY plot is updated every several seconds (depending on the delay time I set). How to display the plot for the entire time history?

Thanks in advance for the help.

Bei

[Dennis_Knutson]

You have to use a single DAQ Assistant configured to capture both channels. Open one and click on "Add Channels".

[Qifu]

I tried to use one DAQ Assistant and to add the second channel. But there is an error. It is said:

One task cannot contain multiple independent devices. Create one task for each independent device.

We have two DAQs, one for thermocouple, and the other for strain gauge. How to use one DAQ Assistant to create two independent tasks?

Thanks, Bei

[Dennis_Knutson]

Did not realize you are using two different DAQ devices. That sort of information is hidden when you use the DAQ Assistant. In that case, as long as you use the same sample rate, your XY Graph should work just fine when you don't do a reset with each iteration.

[aeastet]

Here is a more efficient way

[Dennis_Knutson]

The reset input of the Express XY Graph still needs to be set to false in order to display all data as was in the op's original post.

[aeastet]

---

@Dennis Knutson wrote:

The reset input of the Express XY Graph still needs to be set to false in order to display all data as was in the op's original post.

---

Just trying to show the more correct way of doing it. I would still do it differently but this was quick and dirty for what he was try to do and I was trying to show concept. I expected that the OP would have to add or change things to make it work for himself.

[tbob]

It has already started.  Postings in LV2010 while I still have LV2009.  I would say time to upgrade, but my company may not let me.  We have to standardize on one version to be compatible with others who work here.  LV2010 is too new to standardize on.  I guess I will have to run both to keep up with the new forum posts.