How to use non-NI hardware with LabView

[HoerMan]

Hello everybody,

first at all sorry for my bad english. I am a new member and just learnt some basics of LabVIEW so please forgive me if i should say something wrong. 

I want to perform some vibration and acoustic measurements. Therefore i've got the DT9837A modules. To analyse them i would like to use LabVIEW 2017. So i downloaded and installed the latest driver. I also installed the LV-Link libary to be able to use the DT with LabVIEW. But here comes the trouble: if i open the DAQ assist to get the data from the analog input i cannot see the DT although it is connected to the Computer (the device manager recognize it). I read that the DAQ only works with NI hardware, is that correct?

I can work with the LV-libary but all i got so far are some voltage data from the analog sensor (ICP accelerometer 352A24, connected to analog input 0) using example "DtAinSingle". Is there any possibility to transform the data that i can measure acceleration? Or is it possible to use my hardware with the DAQ assist?

I appreciate every single help.

Greetings, HoerMan

[Bob_Schor]

If you get voltages from your accelerometer, then there should be a data sheet somewhere that gives the calibration curve for the accelerometer.  Most (many?) are linear in acceleration, and say that there is a Gain ("Volts per "g" of Acceleration") and an Offset (Volts when the Acceleration is 0g, i.e. when the Accelerometer is in free-fall, hard to do in the laboratory).

Some Accelerometers have "accurate" calibrations, others are ±10% (like one that I have).  Here's a quick way to roughly estimate gain and offset for (what I will call) the "vertical" axis, that is, one that points straight up when you place the acceleromater flat on a (horizontal) surface:

1. Measure the voltage when flat, corresponding to an acceleration of +1g (if you let it fall, it would be at 0g and going in the -Z direction, so to keep it stationary on the table, it has to "accelerate" upward at 1g).(sign conventions here are a little arbitrary -- I won't quibble if you want to call this -1g).  Call this Vup.
2. Turn it over so it is "face down" and take another Voltage reading, corresponding to -1g.  Call this Vdown.
3. Given that "Acceleration = Voltage * Gain + Offset", you can quickly work out that Offset = mean (Vup, Vdown) and Gain = mean(Vup - Vdown). 

Bob Schor

[RavensFan · Accepted solution]

DAQmx and the Express VI for that called DAQ Assistant is only for NI hardware.

To use another company's hardware, you'll need to use whatever drivers they provide.

You'll need to read the specs on your sensor to determine how voltage relates to acceleration, and scale your voltage reading accordingly.

[HoerMan]

Thanks for your replies.

The calibration data is: 99.8 mV/g.  But the graph shows a very small amplitude like 0,008 mV, i don't think thats correct. What do you think?

[RavensFan]

What if you shake it,  or drop it?  What does the graph show then?

[Bob_Schor · Accepted solution]

---

@HoerMan wrote:

Thanks for your replies.

The calibration data is: 99.8 mV/g.  But the graph shows a very small amplitude like 0,008 mV, i don't think thats correct. What do you think?

---

I think if you are reading 8 microvolts, then you are not reading the output of your accelerometer.  What happens if you turn it upside down and read again?  That should cause a 2g "swing" -- oops, I'm thinking of a tri-axial accelerometer!  You never mentioned what kind of accelerometer you are using.  Does it have a single axis?  When you took your measurement, was the axis "horizontal", so the correct reading should have been 0 v?

Make six readings -- right-side up, up-side down, right edge down, left edge down, front edge down, back edge down.  Whether it is 1 or 3 axes, you should get a swing of 2 * 99.8mV between two of the readings.  If you don't, you aren't measuring acceleration.  It could be a "hardware problem" (your accelerometer is toast, or your wire isn't connected) or a "software problem" (your LabVIEW code does not work).  Hard to debug from a distance without seeing the code and pictures of the device (please don't send the device and pictures of the code!).

Bob Schor

[HoerMan]

Ok, i think it was milli not micro, the graph shows an amplitude between -4 and 5mV accordingly, translated ~ -0,4 - 0,5 m/s². I have to measure very small vibrations like the one of an electrical toothbrush. Should i expect data of this size? Because i have no reference data i don't know wheter its possible or not.

Its an one axis sensor and it has a shear sensing geometry.

[HoerMan]

Thank you for your support. I was able to find the Problem. Its fixed.

Because it is an IEPE sensor i had to configure the current/voltage source. Now i can see a well-shaped curve.