Feedback on NI-Scope fetch terminology

[gregoryng]

I've just been figuring out how to use scope to do high speed acquisition, and it took me a while to discern the difference between certain fetch property nodes.  I think that I finally understand things now, but let me explain what my confusion was.  Here are the nodes that I am confused about, along with their current descriptions in the manual.  (numbers) are referenced below.:

Fetch:Fetch Record Number:
Sets the record to fetch. The record is from a channel you specify⁽¹⁾. The default value is 0. Valid Values: Values greater than or equal to 0
 
Fetch:Fetch Number of Records:
Fetches multiple records. If you want to fetch all records from the record you specify in the Fetch Record Number property to the last record configured, use -1. The default value is -1.
 
Fetch:Fetch Relative To:
Specifies which point⁽²⁾ in the acquired waveform is the first to be fetched. This property specifies what the 'Fetch Offset' is relative to.
 
Fetch:Fetch Offset Sets the offset⁽³⁾ in samples; the samples returned also depend on the Fetch Relative To property. The default value is 0.
 

Here's my comments:

 (1) A channel that I specify?  How, and when? Clearly I don't use this property node to specify which channel, so why mention it here?

(2) I think that the text should say, "Specifies which sample in the acquired waveform is the first to be fetched."  This strengthens
the concept that the fetch offset pointer is an sample-level offset, not a record-level offset. 

(3) IMO, the property node names are not well-differentiated in terms of pointing out that there are two different pointers.  It might be helpful if they were referred to as sample offset" or "record offset," rather than "the offset."  

 Also, I was disappointed that the "Acquiring Data Continuously" topic, and the diagrams within, did not refer to these property nodes by name.  If this had done so, I think I would have figured out things much more quickly. 

Hopefully these suggestions will help someone else figure things out.

[cwolfskill]

Gregory,

Thanks for your feedback on the NI-Scope documentation.  I have submitted a product suggestion to our documentation team with your comments.  With regards to your questions about how to set the channel, you would use the Active Channel property node before Fetch Record Number.  Pass it a string with the name of the channel that you are wishing to change the properties of.  

It sounds like you have pretty much figured everything out, but if you still have outstanding questions about how all these property nodes work, please post them. 

Cheers,

Christina

[耶稣爱我]

能不能 详细 解释下 fetch record number 和 fetch the number of record 啊？如果把fetch the number of records =32 具体 是怎么读取数据的，fetch record number = 32000,在 一个循环中 i*32 和 32000 比，我看了例程 也没明白。。。

 This process takes advantage of the circular buffer created within the board's memory. Once the memory is full, the data will wrap back around to the beginning of the buffer and replace the first samples. Therefore, for this method to work, the fetching process must be fast enough to fetch these samples before the acquisition reaches the end of the buffer in order to pre ... ...

我就是遇到了 这个问题。