Use labview to get sensitivity direction field from 3AXIS accelerometer

[jonathan_juan]

I need to obtain the sensitivity direction from the TEDS channel properties, but I can't find any property that provides this information. Is there a way to retrieve it using LabVIEW?

[santo_13]

Yes, you can read the TEDS content using read TEDS VI from DAQmx.

Using TEDS with NI-DAQmx in LabVIEW - NI

What do you intend to do with that value? if you intend to scale your measurements, if you properly configure DAQmx, it will do it automatically for you.

[jonathan_juan]

I need the sensitivity direction to verify whether the 3‑axis accelerometer (X/Y/Z) is installed correctly. I cannot find any property in the DAQmx channel settings that provides this information. Here is the program I writed.

[santo_13 · Accepted solution]

Please refer below,

Using TEDS with NI-DAQmx in LabVIEW - NI

How Do I Install the TEDS Library into LabVIEW? - NI

Misc read - IEEE 1451.4 TEDS Sensor Templates Overview - NI

[Bob_Schor]

     A decade ago, I was approached by some Biomedical Engineering students who wanted to measure muscle twitches with an inexpensive triaxial accelerometer chip (ADXL335).  We used an NI USB-6009 to record X, Y, and Z accelerations.  We were recording muscle twitches (the accelerometer was taped over the muscle being stimulated).

     Neither my students nor I knew about TEDS -- we approached this the "old-fashioned" way.  First, calibrate the accelerometer (each axis had a gain and bias parameter in V/g, but the values were, as I recall, ±10%).  Then take triaxial readings at, say, 100 Hz, calculate the acceleration magnitude, and report how much it deviated from 1g (the net acceleration due to gravity if the accelerometer were not moving).

     It turned out that these students had never heard of calibrating an instrument.  That was my first "Teaching Moment" for them, helping them come up with an algorithm to do this.  I suspect one could use similar "Brute Force" methods to (quickly and accurately) obtain the parameters for the 6 degrees-of-freedom gain and bias components with simple DAQmx and six triaxial measurements (and a little math).

Bob Schor

[dsb@NI]

To verify whether the 3-axis accelerometer is installed correctly... 

Are you looking to verify the orientation within a few degrees or to verify the accelerometer isn't rotated by 90 or 180 deg around any of the axes? 

If you need to verify within a few deg, I think careful visual inspection is your best tool.

If you need to verify gross orientation, it seems like you need to be able to verify the sensor is sensitive along the expected axis and polarity is positive. I don't think you can read anything from the sensor to know whether it is installed correctly.  Even if find how to read axis from TEDS, that won't tell you if sensor installed upside down. You might be better off verifying by DAQmx physical channel (by measuring response to known stimulus) and assigning the direction in software. Due to geometry of structure,  availability of mounting surfaces,  cable management,  etc. It may not even be possible to mount all accelerometers in the correct orientation where sensor coordinates match global/DUT coordinates. 

[softball]

Hi

dsb@NI gave a nice answer. So I will just add a comment.

The sensitivity direction is merely a 2-bit field used to keep an enumeration of three out of four options ( x, y, z ).

My take on the use of that simple information is that it could be used by a mechanical engineer to quickly figure out how the sensor should be designed in when making a mechanical drawing including the sensor.

Regards

[jonathan_juan]

Thanks for your help. I found the direction from the bitstream data at bit index 100/101.