timing and triggering issues for XY STM control

[lindope]

I am using a NI-PCI-6251 and generating two signals from the ao:0 and ao:1 outputs. One signal should be a single continuous ramp from -10 volts to +10 volts lasting one second. The second signal should be a sawtooth, again starting at -10 ramping to +10 volts, yet repeating 256 times to the single occurance of the first. i.e. 256hz.

The attached VI is my attempt but I don't seem to understand the triggering and/or timing issues. The output I get (which is shown in the attached jpegs) has both signals starting at 0 ramping to +10 then starting over the ramp at -10 back to zero. How can I make them both begin a -10 and end at +10?

My first attempt was using the Sim Arb Sig block and making a spreadsheet of values to define the signal. It worked but was a hastle editing such a large spreadsheet file. Should I go back to that?

Thanks

Christopher

[lindope · Accepted solution]

I set the phase for both of the sawtooth generators to 180. Solved my problem. Thanks for letting me think about this outloud. If anyone has any comments/suggestions on my rookie design feel free to comment. I'm still a little foggy on buffer sizes and sampling rates.

[lindope]

So my next task is to add the tunneling current detection and subsequent Z position control. I am going to sample the voltage between the tip and sample material at a specific rate which I want to begin when this X-Y scan begins. How am I going to trigger those tasks to correspond to this output?

The Z position will be controlled from a second PCI-6251 card, so new channel (and?) task?.  I do have the RSTI cable. Do I link the tasks somehow?