Unsure PXI, Compact RIO ....

[pgaastra]

Hi,

I have a sprayer  application with a large number of analog inputs which needs to be real time.   When I look at the NI site I don't know which path to start down.

I have a brief description of the spec below:

100 photodiodes in groups of 4.  Digitise every photodiode amp voltage every 0.0003 seconds (3600 samples/second)

For each group of 4 photodiodes take six consecutive readings each (24 numbers) do a simple calculation on these numbers as to whether to fire a solenoid valve.   Put this decision in a variable length circular delay buffer with information about when it is to fire. The buffer should be able to be up to 256 readings long. 

The device should have 25 digital outputs for the solenoid valves.

The device should run in real time. i.e. no errors to solenoid firing of greater than .005 seconds.

All the raw data should be able to be stored on harddisk (this is a nice but not essential feature)

Can anyone say ...aha, that's a job for...

[Jordan F]

Hi!

There are a few different paths you could take to solve this problem.  The options are Compact FieldPoint, PXI, CompactRIO or R Series Intelligent Data Acquisition Devices.  The websites for the different options have links to build your own system.  Also, I would recommend the LabVIEW Realtime Module.  This module allows for a more reliable and deterministic performance.

At this time, I can’t recommend any specific cards or modules because there are still a lot of unknowns in your system.  However, you can easily search our website to find which cards would work best. 

http://www.ni.com/dataacquisition/

This website allows you to search different cards and modules by specific properties (Form Factor, Analog input/output channels, Digital I/O channels, etc.).

Some additional things to focus on when searching are:

-Input range of your sensors

-Output current and voltage to control your solenoid valve

-Isolation type

-Delay between the AI read, calculations and valve control

-Environment (Temp, Vibration, etc.)

-Simultaneous sampling

-Portability

We do not usually do this but I would be interested in talking to you more about your options over the phone.  If interested, please give me a call at 1-866-275-6964 and enter in service request number 1265721! 

Jordan Fink

[pgaastra]

Thank you Jordan.

Yes, I did feel pretty hesitant about putting such a question on the forum because I know I'm supposed to do my investigation first.  It's just that I was trying to cut out a couple of hours going down each alley trying to see what would work.  From my point of view the NI web site seems to be organised to tell you what you want to know about a particular product but not about how to go about choosing.  That is probably also because I haven't spent enough time looking.

I hadn't noticed Compat FieldPoint or R Series Intelligent Data Acquisition Devices.  I guess I'm the sort of person who, in spite of all the search capabilities of the web, I still prefer to have a catalogue in my hands. 

I also know we have very knowledgeable NI people down here in Australasia to help, but again, I was scared to ask because I haven't done enough background reading to ask the right questions.