LabVIEW

cancel
Showing results for 
Search instead for 
Did you mean: 

MAX DAQmx Task acceleration scaling bug

Dear NI

usually I do conversions in my own LabVIEW vis , however today I tried to create an acceleration task in MAX. DAQmx 18.0.0f0  (you can reproduce it with a simulated USB 4432 or so).

After creating the Task I was a little upset, because the sensitivity scaling doesn't support SI units, only something funny like mV/g or V/g ...   but offers the correct scaling units  m/s²

sensitivityfail01b.png

I haven't tested if a conversion to SI units will happen ... will it?

So no valid SI unit's are offered for the sensitivity!  (I think it will scale to g_n but not even the scaling factor is noted, or is it g_local ?? 😉  )

OK, lets do a calibration:

 sensitivityfail05b.png

UUps  WTF   (I haven't supplied correct reading (SIM device) however what scaling is it??)

Spoiler
And you don't write mVolts/?,  it's mV/? ...   let's call it a typo 😉

OK, lets have a look at the value table:

sensitivityfail06b.png

OK 🙂 g seems to be equal to m/s² 😄 😄

and back at the task:

sensitivityfail07.pngsensitivityfail08.png

What will be the output??

 

Finally, let's have a look at the Help link for acceleration:

sensitivityfail02.png

Sorry, german, while I can install LabVIEW in englisch, I can't do it for MAX, DAQmx... would ease a lot

However I assume in all language versions the unit for acceleration is wrong. g is no unit, g_n is a value valid at less than 1% on earth. 

I had customers asking if they should use g_local (they had measured) instead ...

If you want to process acceleration values you have to convert to SI units anyway.

 

So please fix the bug(s) and convert to SI unit.

Even if you change it now, the units will not change after 20. of Mai (start of the new SI) 😉

More help for the use of the SI units :

https://www.nist.gov/pml/special-publication-811

 

 

Greetings from Germany
Henrik

LV since v3.1

“ground” is a convenient fantasy

'˙˙˙˙uıɐƃɐ lɐıp puɐ °06 ǝuoɥd ɹnoʎ uɹnʇ ǝsɐǝld 'ʎɹɐuıƃɐɯı sı pǝlɐıp ǝʌɐɥ noʎ ɹǝqɯnu ǝɥʇ'


Message 1 of 5
(2,263 Views)

It's not a "bug", it's a (careless!) feature.  I think it comes from accelerometer manufacturers -- one of my student teams was building a medical device that incorporated a triaxial accelerometer-on-a-chip, and everything was calibrated in mV/g (or V/g).  In one sense, this made it easy -- we calibrated it by putting it face-up, measuring the voltage, putting it face down, measuring the voltage, then they worked for a half-hour figuring out how to compute "gain" and "offset" (I exaggerate slightly -- it didn't take quite that long).  Note -- the values quoted by the manufacturer said "± 10%", and I had to convince them that calibration was necessary to get meaningful data ...

 

Bob Schor

0 Kudos
Message 2 of 5
(2,231 Views)

Bob, if it's only the support and use of g_n  I would say OK, If they don't know it better ...

and g_local (if you know it) can be used as a primary calibration source 🙂

but the assistant and task generator is buggy by mixing up the units!

AND  at least the SI unit for acceleration should be available. (Should I note that as an idea?)

Sadly enough I often see missinterpretations even from people who should know it.

Spoiler
I do ISO-17025 accreditations for acceleration labs Smiley Tongue , but I'm kind, the labs are allowed to note calibration values also in g_n (because the customers don't know it better)  in addition to the SI unit (m/s²)  if the conversion factor is noted too 😉
ISO 17025 calibration certificates must provide SI units ...  g or g_n isn't a SI unit.
See it like Horsepower ...

 

Greetings from Germany
Henrik

LV since v3.1

“ground” is a convenient fantasy

'˙˙˙˙uıɐƃɐ lɐıp puɐ °06 ǝuoɥd ɹnoʎ uɹnʇ ǝsɐǝld 'ʎɹɐuıƃɐɯı sı pǝlɐıp ǝʌɐɥ noʎ ɹǝqɯnu ǝɥʇ'


Message 3 of 5
(2,226 Views)

I didn't say it was a good (or proper, or admirable) feature ...  You are absolutely right, proper units are important.  And if NI wants to allow acceleration in "g" units, that should be, at best, an option in addition to the proper SI units.

 

Bob Schor

Message 4 of 5
(2,207 Views)

The scary part is, that this task generator/assistant show that inside of NI there is no (or seems to be no) commitment to SI units (or the quality/software rules haven't been checked)...

Just checked it with LV2012... different .. but also buggy.

 

Greetings from Germany
Henrik

LV since v3.1

“ground” is a convenient fantasy

'˙˙˙˙uıɐƃɐ lɐıp puɐ °06 ǝuoɥd ɹnoʎ uɹnʇ ǝsɐǝld 'ʎɹɐuıƃɐɯı sı pǝlɐıp ǝʌɐɥ noʎ ɹǝqɯnu ǝɥʇ'


0 Kudos
Message 5 of 5
(2,199 Views)