How to create an accurate delay?

[help]

We try to control our 3-D piezostage using PCI-6229. Currently we restricted ourselves to send analog output in only 2-D. We want the increment, say in x-direction, is 0.1V per 10ms.  Using DAQ express indeed speed up the design but it  was done using “wait milliseconds” function(wait 10ms before increase another 0.1V), which is not accurate as the clock is software dependent(interruption from other software in Windows based system). How can I increase the accuracy? Can I use “multiple milliseconds” function or better still, “time” express vi? If we want to use DAQ express and use “hardware time”(external clock) to be the clock, how can it be done? Can someone please help out?

[GDE]

When you say “DAQ express” I assume you mean DAQmx, in LabVIEW 7.0 or later. You could go the route of trying to do precise software timed stuff, but using WinXP you will always run into the problems that you mentioned. Hardware timed, will always be more accurate, but setting up the control may be a bit tricky. To program a hardware timed acquisition you can either do it explicitly with the DAQmx functions, or you can use the DAQ assistant (which is an Express VI). With the DAQ assistant once you drop it down it should be pretty straight forward how to configure it, a window will pop and you will have to fill in what you want. I would also recommend taking a look at some of the shipping examples to get a feel for DAQmx programming without using the DAQ assistant. You can find these examples in LabVIEW by going to: Help Menu >> Find Example. Then from there: Hardware Input and Output >> DAQmx >> Analog Generation. If you look at the examples that are Internally Clocked, those will be the easiest to work with initially. Now I am not too sure how well this will be for stage control, generally this is done either with a motion board or if fine enough control is needed FPGA. But with those examples, it should give you a good starting point to work from.

-GDE

[GDE]

Message Edited by GDE [DE] on 02-10-2006 04:29 PM

[help]

hi, thanks anyway.  i have find a way to solve my problem. Thanks alots

Message Edited by help on 02-26-2006 07:59 AM