Using two AI channels at once in ANSI C

Sparkman2 · ‎05-19-2016

Does anyone have an example in ANSI C of collecting data from 2 different transducers at the same time? The examples I have seen are for one AI only. I need to gather the data as two separate streams. The data from AI0 should not be mixed with the data from AI1. Do I start two separate tasks? If so, is there an example available?

jozeywhales · ‎05-20-2016

Are you going to be collecting data on two channels of the same device or are you going to be collecting data from two seperate devices? Also, if you are using one device, are you familiar with channel expansion?

-Joe

Sparkman2 · ‎05-23-2016

I want to use two channels on one device. Using two devices may be a later option. Right now, I can easily access one channel with:

DAQmxErrChk (DAQmxCreateAIVoltageChan(taskHandle,"Dev5/ai0","AnalogInput0",DAQmx_Val_Cfg_Default,-10.0,10.0,DAQmx_Val_Volts,NULL));

As soon as I change this to:

DAQmxErrChk (DAQmxCreateAIVoltageChan(taskHandle,"Dev5/ai0:1","AnalogInput0",DAQmx_Val_Cfg_Default,-10.0,10.0,DAQmx_Val_Volts,NULL));

I get a channel definition error. I need to record the data from two channels at once as part of a regulator pressure response test.

Thanks!

Tim

Norbert_B · ‎05-24-2016

Tim,

you tell us the DAQmxCreateAIVoltageChan is creating an error with that parameters?

Which device are you using as Dev5?

Norbert

Norbert
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Sparkman2 · ‎05-24-2016

USB-6008. All works fine with a single channel, but trying to use two has me stumped. Unfortunately, all of the examples just show using one channel and not multiples or multiple devices.

My frustration level has hit the ceiling!

Norbert_B · ‎05-24-2016

If you run a MAX testpanel, is using that channel string working?

You didn't answer if the create channel is generating the error. I somehow assume that it is more something like e.g. timing which could create an issue.....

Norbert

EDIT: It would be useful if you post a screenshot of the error and some code snippet.

Norbert
----------------------------------------------------------------------------------------------------
CEO: What exactly is stopping us from doing this?
Expert: Geometry
Marketing Manager: Just ignore it.

Sparkman2 · ‎05-24-2016

Yes, the channels are working. It never gets to the point where timing is an issue.

I have used a single channel to gather data and display it on a graph while logging to a TDMS file and that works great. However, trying to expand to a second channel has not worked at all. Just changing the following line make the program choke:
DAQmxErrChk (DAQmxCreateAIVoltageChan(taskHandle,"Dev5/ai0","AnalogInput0",DAQmx_Val_Cfg_Default,-10.0,10.0,DAQmx_Val_Volts,NULL));

to: DAQmxErrChk (DAQmxCreateAIVoltageChan(taskHandle,"Dev5/ai0:1","AnalogInput0",DAQmx_Val_Cfg_Default,-10.0,10.0,DAQmx_Val_Volts,NULL));

I need to know how the program should be structured. I assumed that someone at NI at sometime had actually performed this operation and that the solution would be readily available. If I knew the proper functions to call and the proper syntax, then I would be ready to tackle any timing issues that might arise.

DAQmxCreateTask ("", 0x6DE8C768)