You can easily accomplish what you want with a pair of simple While loops organized in Producer/Consumer fashion. You'll need to learn some step for this, but I'll try to explain the basic steps.
The Producer Loop consists of using DAQmx to acquire data from your sensor at 200 Hz. Find the NI White Paper "Learn 10 Functions in NI-DAQmx and Handle 80 Percent of your Data Acquisition Applications" (hint -- Web search). Learn how to set up your sensor (plugged into your PC, and tested with a Test Panel using MAX -- you want a Sampling Rate of 200 Hz, a buffer size of 2000 points (or one buffer every 10 seconds), Continuous Sampling (so you don't lose any points). This While Loop, once started, should produce 2000 points every 10 seconds as the output of its Analog Read function (we'll get to what you do with these data in a second). You need a Stop control to stop the Producer Loop whenever you want it to stop.
Now, suppose you could instantaneously transfer those 2000 points to another While Loop that can compute the median of those points and "do something with them". This is your Consumer Loop -- it runs every 10 seconds and plots, saves, or whatever the data you generated. You might, for example, want to do some processing of these data (in addition to taking the median of those 2000 points, which should take a few milliseconds, you might want to do Fourier Transforms, 3-D plotting, who-knows-what, and not worry about mssing some incoming data points).
OK, two independent loops, one producing 2000 data points/10 seconds, the other consuming 2000 data points/10 seconds. How to get the data from Producer to Consumer (and how to stop the Consumer when the Producer stops).
Enter the Stream "Asynchronous Channel Wire" (or the Stream Channel Wire, for short). This is a wonderful feature that made its public appearance with LabVIEW 2016. You right-click on the output of the DAQmx Read (where your 2000-point data appear) and "Create Channel Writer Endpoint", specifying a Stream Channel. 2-4 seconds later, the Channel Writer appears, with the data array going in on the left, and a "pipe" (the design for Channel Wires that can "leap over Structure Edges", such as the output edge of a While Loop to get the data out of the Consumer Loop and into the Producer Loop (which you place to the right of the Producer, so data "flows" from left to right). You now right-click on the Stream Channel inside the Producer Loop and "Create, Channel Reader", specifying a Stream Channel. 2-4 seconds later, there's your connector whose output is the same Array you put into the Producer side, transmitted "instantaneously" (or "Asynchronously") for you to process however you want, without interfering with the Producer.
But how to stop the Consumer? Look closely at the Stream Channel Reader. There is a Boolean input that says "This is the last sample I'm sending" (which is the same Boolean you wire to the Producer's Stop indicator), and a similar Boolean output on the Channel Reader that says "Last Sample" that you can wire to the Consumer's Stop indicator. The Producer (who knows about whether or not more data are coming) tells the Consumer explicitly whether or not more data are coming, and both stop together. Very clear.
Try it. You'll like it.
Bob Schor
