DAQmx (Version 9.1) Create Channel for Accelerometer will NOT convert into m/s^2

[Peter_S]

I use DAQmx Create Channel for Accelerometer to get results in the SI unit (m/s^2)

This worked until DAQmx Version 8.9.

Now I tested it with  DAQmxVersion 9.1 and the results are in g (not converted in m/s^2 !)

I use DAQmx Create Channel (AI-Acceleration-Accelerometer).vi  wth the inputs

units=m/s^2

sensitivity units =V/g                      (there is no  sensitivity unit V/(m/s^2) available)

sensitivity = sensitivity Value in V/g

I read the data with

DAQmx Read (Analog 2D DBL NChan NSamp).vi

In DAQmx <= 8.9 the double Numbers are  correct converted to m/s^2

but in  DAQmx 9.1 not (the values are in g and to low by 9.81)

My solution is the following change

units=g

sensitivity units =V/g 

sensitivity = sensitivity Value in V/(m/s^2)

Then the double Numbers are  not converted, but in m/s^2.

And this work in all DAQmx versions.

The problem is:

An older program which use the first settings and tested with DAQmx <=8.9 will get wrong measurement result with DAQmx 9.1 and no error occour!

Peter

[Peter_S]

Here is the code:

the upper, disabled part is the from the last programm version,

wich will result to wrong results (in g but not in m/s^2) in

DAQmx Read (Analog 2D DBL NChan NSamp).vi

That is a real bug in DAQmx 9.1 that the conversion to m/s^2 is ignored!

Message Edited by Peter_S on 04-09-2010 03:04 AM

[TobiD]

Hi Peter,

i can't confirm the bug you're seeing. I have a LV2009SP1 System, DAQmx9.1 and  the Acc.Acq.VI let me choose m/s²:

Maybe you can try a reinstallation of the DAQmx

Regards,

Tobias

[Peter_S]

Hi Tobias,

Yes, I can choose 'm/s²', but the results are in g (to low by factor 9.81!!)

Try a measurement loop and test it with unit = 'm/s²' and compare it with unit = 'g'.

I use Labview 8.6 and a fresh installed DAQmx 9.1 full.

Peter

[Peter_S]

Hi Tobias,

I can reproduce the bug in MAX without programming in Labview:

1. unit=m/s^2 The sensor sensitivity is 10mV/m/s² = 0.1V/g, I use a acceleration exciter  159 Hz, with 10m/s² eff,  14 m/s² peak.

But the result is in g (+/- 1.4 g)

2. unit=g

Peter

PS.

How can I switch the language from MAX to english?

[TobiD · Accepted solution]

Hi Peter,

i'm not in my Office  at the moment and i can't try it out by myself, i forwarded your Request to one of my collegues, i hope he will contact you soon.

Sorry for the delay,

Tobias

The MAX Language Settings depend on the Regional Settings of your Windows OS. See the following page:

http://digital.ni.com/public.nsf/allkb/9893C1767C93D20E86256F49001CDA92

Regards,

Tobias

Message Edited by TobiD on 04-13-2010 09:15 PM

[jtagg]

I've submitted a Corrective Action Request #220294 so that it will be seen by our R&D team.

[Henrik_Volkers]

Good catch Peter

I don't know if it's possible but you should mark your first post as solution for a solution (workaround).

Reminds me to the MARS CLIMATE ORBITER FAILURE

"The MCO MIB has determined that the root cause for the loss of the MCO spacecraft was
the failure to use metric units in the coding of a ground software file ...."

And according to this article ... it will last ..

Message Edited by Henrik Volkers on 04-15-2010 12:41 PM

[AndrewMc]

Hey Peter,

I was not able to reproduce the behavior that you mentioned?  Can you attach an example?

As well, just something to try as a potential workaround (if there is actually an issue): Use a DAQmx Channel Property Node and select Analog Input:Temperature:Units (I realize that you are using Accelerometer- this is not a typo).  Change the property to write (Right-click on property and select "Change All to Write") and create a constant.

Message Edited by AndrewMc on 04-27-2010 12:40 PM

[Peter_S]

Hi Andy,

see the examples in DAQmx - you dont need a program.

The difference is the scaled unit  (in my screenshot 'Skalierte Einheit')

I used the same input signal.

you have to use  Accelerometer - also if it is not a typo -

the result in m/s² are in g !

A simple test is a sine generator with 100 mV at an input , which  represent with the  sensor sensitivity  0.1V/g :

1 g or 9.81 m/s²

Peter

For the test without sensor you have to switch off IEPE Excitation ('Iex Quelle' in the screenshot)

I used a USB 9234.

Message Edited by Peter_S on 04-27-2010 01:01 PM