Programming fieldpoint HW with Labview or VB SW.

[Joe C.]

I am an experienced Labview programmer and a learning VB programmer. I've always used either DAQ devices or some SCXI devices. I am now considering a Fieldpoint system consisting of AI, TC, DI, DO and an ethernet port. How steep is the fieldpoint learning curve?
One specific question... how is data returned? Suppose I want to take 1000 data points from four channels at 500 Hz (assuming correct filtering, etc.) Is data returned as a 4x1000 array or point by point as the device is polled? How about with an ethernet port on the FP rack with it's "event driven" characteristics? Do I get only changes in data and a time stamp? Is the 500 Hz rate accurate? Is it controlled by hardware or software?
Do I run into problems with higher channel counts or multiple FP systems on the same network?

Thanks very much,

Joe

[Aaron_G]

Joe,

The learning curve for FieldPoint is not that steep. FieldPoint programming tends to be simpler than DAQ programming. For example, in LabVIEW, there are dozens of DAQ VI's to offer different functionality, for FieldPoint there are 7 VI's, one of which is infrequently used. A typical FieldPoint App starts with one FP Open.vi, one or more FP Create Tag.vi's (one for each channel or set of channels to be used), one or more FP Read.vi's or FP Write.vi's, and finally a single FP Close.vi. The FP Advise.vi can be used in place of the FP Read.vi but is recommended for more advanced users as it sets up polled communcations and can have some unanticipated side effects if you do not understand how to use it properly.

VB programming is more complicated since National Instruments does not provide a VB interface. Instead, you need to use an OPC Client package (such as National Instruments DataSockets) in VB to talk to the FieldPoint OPC Server.

As for how data is returned, I would recommend that you read KB article #1O3CJ7US at the following link:
http://digital.ni.com/public.nsf/3efedde4322fef19862567740067f3cc/0d418c9097f14e99862567c300666568?OpenDocument
To answer your specific questions in order:
1) Point by point as the device is polled.
2) Depending upon how you set up the application, you may read duplicated data, or only the change in data.
3) You can not specifically set up a 500 Hz acquisition (none of the analog FieldPoint modules sample that fast). Please see the above KB for detailed information on how sampling occurs.
4) Sampling is controlled primarily by hardware for ethernet modules, and by both software and hardware for serial modules.
5) You do not tend to run into problems with high channel counts or multiple banks of FieldPoint (it was designed for large channel count applications).

I would also recommend the following KB articles to increase your understanding of FieldPoint:
http://digital.ni.com/public.nsf/websearch/597c2b4cecef6bb586256831005b913f
http://digital.ni.com/public.nsf/websearch/a2cc1e80eca6661f8625660800617dba
http://digital.ni.com/public.nsf/websearch/7cbf4939b1464d5f86256990004919ac
http://digital.ni.com/public.nsf/websearch/862567530005F09F862568F900666F20
Also, if you want information on using DataSockets in Visual Basic as an OPC Client, I would recommend reading App Note 139.
http://zone.ni.com/devzone/conceptd.nsf/appnotebynumber/87D5C15CAFB2654A86256874005C280C?OpenDocument&node=dz52000_us

Regards,
Aaron

[Jeff (Systems Integrator)]

Your suggested links report design note could not be found.

[JonM]

FieldPoint is remarkably easy to use,
provided you take into account what it can and can't do.

For example you cannot specify a sample rate for the AI modules, the rate of return is determined by the hardware. I would also be very careful using the FP Advise function (it can cause alot of trouble, and is really and honestly doesn't do anything that can't be done with a FP Read).

As for high channel counts, well I have commisioned an ethernet based system with 15 modules (10 AI, 4 RLY, and 1 TC) arranged in 2 banks of 7 and 8, wih an FP1600 controller. I have had no trouble with it, but I know some collegues have had trouble with serial Fieldpoint, although from the sounds of it you are already looking at an ethernet based system.

Putting it bluntly, if you
can master SCXI, Fieldpoint is going to be easy.

Hope that helps,
Jonathan