Real time DAS

[MogaRaghu]

I am developing a machine control code which has 28 DI, 22 DO, 9 AI and 5 AO. Planning to use two numbers of  PCI6229 or 6229 + 6221. Not a  problem till now as the machine sequence will be with a State Machine running within a 50ms timed loop.

So where is the issue ?

I need to slowly torque a component with a Servo drive (  0.2 Deg angle / sec )  first CW and keep monitoring the resulting pressure ( an AI channel ) and once it matches a set value, capture the current CW angle. Then start the CCW turning and once again when pressure matches a set value,capture the current CCW angle. After this do some more things based on the captured values.

Since I will be polling, I am sure to miss out the precise point of the pressure match. So what card or methodology  must  be adopted to capture the exact match point ?

I am also  browsing the NI site for ideas. But nothin like hearing it from the experts. ( I am on LV 7.1. Have got LV 8.0 upgrade but yet to install it )

Thanks

Raghunathan

[Tom_W_[DE]]

Hi Ragunathan-

It sounds like you may need a way to capture your rotational position with hardware-timed resolution.  An analog level trigger of some sort would be ideal for this application, but in order to offer suggestions I will need to know a bit more about how the rotational information is returned.  Is it an analog level?  A quadrature or rotary encoder?  Please let me know a bit more about the signals in your app and I will be happy to help out.

Thanks-

[MogaRaghu]

Hello,

Thanks for the response. Going by the lack of any replies, I almost came to a conclusion that this requirement is a non-starter with LabVIEW.

Well the angular information will be fed from a quadrature encoder. But quite really I can still decide on this -  the servo drive has a built in encoder output which is the natural choice. But I also can interface a multi turn helipot and get an analog feedback for angle.

The total angle of traverse is just +/- 3 deg or about 6 degrees total.

I do hope that the above inputs will help you help me ?

Raghunathan

[Ryan_V[DE]]

Raghunathan,

It sounds to me like it may be possible to set up an analog input task with an analog start trigger and a buffered position measurement which uses the ai/SampleClock to buffer the position measurements. Does this sound like it would be an option? You will need to acquire at least 2 samples on the analog and counter inputs, though more are certainly possible. You also need to note that the analog trigger must be first in the DAQmx scan list. I have attached an example of such an operation.

The only problem I can forsee is that you may need continusouly running analog input for some other channels. If this is the case, your timing resolution is limited to the rate at which you are acquiring analog data (i.e. 1kS/s will give you +/- 1ms of uncertainty in getting the position at the exact moment your analog voltage crosses the specified level). This is also true with reference triggered operations, as the task is already acquiring data at the specified rate when the reference trigger occurs.

Hope this helps,