回复： Re: 回复： Re: Reading relative position on multiple axis

[xiaofengliu]

Dear David:

I don't want to use 6602 or other DAQ board to acquire the positon information.Every motion board has trigger inputs.Each trigger corresponds an axis.It is said that the postion information at the edge of the trigger can be obtained by buffer high speed caputue.vi.I have done some test and found that I really canobtain the position information of an axis  used the reffered vi.But I can,t obtain the positon information of each axis at the same.The vi is said to be

the same with vector space.But I don't make it.How should I modify the vi to apply in vector space?

[IanC_]

Dear xiaofengliu,

I don't think BHSC will work with a vector space (as you've found!) - you need to configure it separately for each axis.

You can still synchronise capture on multiple axes, though.  Use RTSI lines to route a single trigger signal to your different axes.  This approach has worked for me in the past.

Hope this helps. 

Ian

[xiaofengliu]

Hi Ian C:

If I can,t configure a vector space in buffer high speed capture,I must read the postion information at the rising of the trigger from each axis respectivley.Suppose that I need to obtain the positon information of three axises.Do I need to configure three buffers?Can the three buffer work at the same and not compete?The trigger input of each axis is the same tigger in my experiment.Can the information of each axis obtain at the same when the signal is rising ?without time delay?

[IanC_]

Hi xiafengliu,

Yes, you can configure and use multiple buffers at the same time.  There used to be a bug that prevented this, but NI fixed it in response to this thread (that you referenced in a previous post).  I've only tried doing simultaneous capture with 2 axes in the past, but I'd still expect it to work with 3.

The capture is hardware-timed, so there shouldn't be any noticeable time delay between the axes.  The NI spec quotes it as occurring within 100 ns of the rising edge.

Ian

[xiaofengliu]

Hi,Ian C

Thank you for your kind reply.I will try the latest motion control software and configure multi buffers .But I find no matter there is a trigger signal or not ,I can obtain position coordinates.Is it still a buge?

[IanC_]

Hi xiafengliu,

I'm not sure I understand your question properly - sorry.  Could you try to rephrase it?

If there is no trigger signal, the buffers should be empty.

Ian

[xiaofengliu]

hi Ian C:

I also think that the buffer should be empty if no trigger sigal is input.But I really could read data from the buffer no matter  a trigger sigal is input or not using the buffer high speed capture vi.Have you ever found this problem? 

[IanC_]

Hi xiaofengliu,

No, I've never seen that before.  Is it possible this could be due to electrical noise?  Are you grounding the unused trigger signals or leaving them floating?

Can you post a simple example VI that produces this problem?  What software/firmware versions are you using?

Thanks,

Ian