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I have been tasked with (semi) automating flow velocity data collection using a pitot tube in a minaturized wind tunnel. The pitot is mounted on a two axis stepper motor system which is controlled by an arduino and manually moved with a GCode sender on a computer. The actual flow line is connected to an Ashcroft DPT with a 0.1 IWC and 4-20mA output. Since we don't have a variable current datalogger, we record the voltage over a connected resistor with a hydra fluke (variable voltage) data bucket and their proprietary software, which exports data to .csv files.

The only part of this system that cannot be changed is the pitot tube itself - everything else can be modified.

I am going to make the stepper motor system 3-axis then I would like to create a program that allows me to do the following:

  1. Position the pitot tube at a fixed location on any 2 axis and span the third at a fixed interval
  2. At each point on the span, pause movement and dynamically record ~25 data points
  3. (Optionally) also record capacitive current in another wire
  4. Save all data for a given run in a .csv file local to a computer
  5. If at any point the material on the plate being studied 'burns', it shorts a 20kV circuit. The power supply has a good overload shutoff system, but I would like this to also stop the automatic program

Currently, I am looking at using either an Arduino or NI MyRio for this system. Since there is no good way I have found to interface with the Hydra system other than their software, I would like to remove it from the system if possible. Preferably, I could measure current directly from the DPT (would probably also be voltage over connected resistor).

So to the question, I would prefer to use the arduino but I am not sure if it is possible to get high resolution data. The NI seems like a pain all things considered, but I am wondering if there is anyone who has input on this project before I dig deep in and find out there isn't a plausible way to do it with the selected device. Are there any reasons to choose on over the other or hardware/procedural suggestions which may improve the system.

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  • $\begingroup$ Could you define high resolution data( sampling frequency and/or bits)? Because the Arduino and myrio will be significantly different. $\endgroup$
    – NMech
    Dec 21, 2021 at 5:25

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Sounds like you want a 4-20mA Data Logger, which is a common category of product with many interface options and price ranges. As long as you're willing to do the scripting to sync it with whatever you're using to control your stepper, you should be able to find something that works.

Regarding National Instruments products -- trying to stay out of product-review territory here -- but together with LabView, NI equipment is widely used in labs, so that makes it at least okay, often very nice, for almost any data acquisition project. If your project might last beyond your personal involvement, the fact that it's easy to find others to work on it, is a key selling point.

The disadvantage of NI/Labview is cost, a heavyweight software environment, and a programming notation sold on the basis of "it's not programming". In reality it is programming, only the notation is unconventional (perhaps hieroglyphic, not meant as a put-down). Which has its advantages when starting out, but it tends to discourage complexity down the road, or even punish it. Something to keep in mind in case you are envisioning more sophisticated automation or soft integration for your project in the future. However as a caution, if you roll your own, you may be stuck maintaining it.

Regarding point 5 -- if what you mean is that your system can become shorted to a 20kV circuit... it should be obvious, but it calls for extreme caution. This could become the biggest factor in system design. Get an experienced EE to review any circuitry you are hooking up. If you want to go into more detail on overvoltage protection and/or electrical isolation, you might get a response at https://electronics.stackexchange.com/

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