How can I output a constant on an analog channel？

[foolooo]

I'm using PCIe-6251 card, and i wanna test the time of response between the input channel and the output. So I just tried to set the analog output channel to output a constant, and then change the value continuously to see the time of delay. I used DAQ assistant to implement this function. I set the sample clock type as inernal, and Generation time as 1 Sample (HW time), and tried to set the rate from 100k Hz to 10M Hz. But the error "DAQmx Wait for Next Sample Clock detected one or more missed sample clocks since the last call to Wait for Next Sample Clock which indicates that your program is not keeping up with the sample clock." appeared all the time. Can anyone tell me about how to set the assistant, or is it able to work as i expected? Thank you.

[Wilfried_71]

Try to post your VI to make us understand your problem.

First remark : you don't have to set up more than 2.8 Mhz for the frequency (limit of the device).

Second remark : try to use a LV example, you must find a start for this kind of simple application.

[Ian Colman]

Hi,

As Wilfried said, it would be good to take a look at your VI so I can get a better understanding of what you are trying to achieve here. Is that possible?

Regards,

Ian Colman
Applications Engineer
National Instruments UK & Ireland


Message Edited by Ian Colman on 01-17-2008 03:14 AM

[foolooo]

Thanks Wilfried and Ian, here is the simple vi file to show my case. Sorry for the stupid question.

P.S. When I chose the Generation mode as Continuous Sample, it showed that the buffer size was too small, even if I changed the Samples to write.

[Ian Colman]

Hi,

Sorry but I am still unsure as to what you want to do exactly. Do you want 2 separate tasks, one for analogue output and one for analogue input? And are you connecting the output to the input physically with a wire? If you let me know exactly what you want to do in as much detail as is necessary I'll be happy to help.

Kind Regards,

Ian

[foolooo]

Sorry for the misunderstood, I just seperated the component out of the original file. For this part, I connected the output to an oscilloscope. If it works, I'll connect the output to the input, and do the rest things.

What I want is to build a loop programme to control the output based on the response. The logic should be like

Output Xn--------> Input Xn--------> Display

   ^                              |

   |                               |

   |                               |

   |                               |

   -------- f(Xn-1)<------- 

Thank you for your patience.

[foolooo]

OK, forget it. I think I've found the reason. Thank you all.

[foolooo]

Here is the file to measure the speed of output and input. When I checked the file generated I found that the 2 loops ran at about 10Hz. How can I enlarge the speed of the data transmission? Thank you all.

[foolooo]

up

[foolooo]

Now I've modified the file, and saw that the bottleneck was the function of "Writing to a file", so is there any possible to improve the speed of recording the data? Thank you.