How do I determine the number to put into "value to write" for DAQmx Generate Analog Output?

[mistercat]

On the Step Setup for DAQmx Generate Analog Output there is a "Value to Write" field.  I can find no explanation of what it is, how one determines the value to enter, nor what it is writing to.  I am trying to go through the tutorials and this is hanging me up.  

Would someone provide an explanation? 

[Ali M]

 Hello,

Output Tasks:

For generations, the amount of data you write before starting a generation determines the size of the buffer. The first call to a Multiple Samples version of the Write function/VI creates a buffer and determines its size. You also can use the Output Buffer. Config function/VI to create an output buffer. If you use this function/VI, you must use it before writing any data.

The samples per channel attribute/property on the Timing function/VI does not determine the buffer size for output. Instead it is the total number of samples to generate. If n is your buffer size, setting samples per channel to 3×n generates the data in the buffer exactly three times. To generate the data exactly once, set samples per channel to n. NI-DAQmx does not create a buffer when the sample mode on the Timing function/VI is set to hardware-timed single point.

This information can be found in the NI-DAQmx Help buffer size descriptions. Information on other DAQmx functions can also be found here by using the search tab of NI DAQmx Help. To locate the NI-DAQmx Help, navigate to Windows Start>All Programs>National Instruments>NI-DAQ>NI-DAQmx Help

Best regards,

Ali M

Applications Engineer

National Instruments

[wildcatherder]

Note: I am the original poster (mistercat) using a different address.

I'm sorry but your reply means nothing to me.

I was posting specifically to the SignalExpress forum. Nothing in your post applies to my question.  In fact, the phrase "value to write" does not appear in your reply. You seem to think I asked about "samples per channel", which is NOT the case.

Hey, I couldn't find the answer in the provided documentation either.  I was hoping someone had discovered it by trial-and-error. 

[Ali M · Accepted solution]

 Hello,

Value to Write specifies the value to write to channels, lines, or ports selected in Channel Settings. In other words, this value will be the value of your DC output (e.g. if you enter 5, your output will be 5V). To obtain information about the different input fields in SignalExpress, navigate to Help»Context Help. A pane will be included in your work environment which will display information of the field(s) when you place your mouse pointer on them.

For new SignalExpress users:

Generating DC Signals with NI DAQmx Devices: In the DAQmx Generate step, select 1 Sample (On Demand) in the Generation Mode pull-down menu. You can select a programmatic input to generate, or you can remove the checkmark from the Use Programmatic Input checkbox and specify a value to generate in the Value to Write field. The NI-DAQmx Help also provides additional  information about generating data.

Best regards,

Ali M

Applications Engineer

National Instruments

Message Edited by Ali M on 05-25-2010 01:44 PM

[wildcatherder]

Thanks, that answer completely addresses my request.  The context help does work as you say but without your specific statement "your output will be 5 volts", the context help language is not so helpful.   I also learned that the help search will take phrase search requests in quotes, e.g. "Value to write", but, again, finds an extremely terse message.