Convert voltage to acceleration and simple test for signal verification

[StathPol]

Hi users,

I am using an accelerometer for vibration measurements capacity of +/- 10,000 g. 

The accelerometer (single ended) is connected with a signal conditioning device to provide excitation/power supply on the accelerometer. The signal conditioning device is then connected with the NI PXIe-6361 module. I have attached the settings used for the power supply and acceleration certificate as well (red marks).

The voltage readings seems to work as they provide signals, but I would like to ask whether the conversion of voltage to acceleration units is correct in the attached vi. As I read from the manuals, the voltage is divided over the sensitivity of the sensor (V/ (mV/g)). On the other hand, each 1 volt corresponds to 1000 g and therefore, +/- 10 V = +/- 10,000g, as per the accelerometer specifications. Moreover, I would like to ask whether a simple test can be carried out to verify the readings (i.e. drop accelerometer or overturn it to read -1g?)

Is there any possibility to advise me what is going wrong with the acceleration setup please?

Many thanks.

Pepis21

[StathPol]

Just a small comment. The nominal zero-g voltage is not zero as it will be the initial offset obtained from the average of the first 1000 points to make it zero. 

Thanks.

[Bob_Schor]

Have you tried using MAX while connected to your accelerometer?  Did you notice that you can create a Custom Scale that will allow you to specify the equation changing Volts into Acceleration (in whatever unit you want, i.e. g's, meter/sec/sec, etc.)?  You could save the Scale in MAX and then use it in your Create Channel function.  You can also specify the Scale using a DAQmx function, Create Scale, that also lets you specify the offset.  So you could start with a Scale that assumes a zero offset, take 1000 readings that are supposed to give you 0 (g's, for example), then "adjust" the Scale to take the offset into account.

As for calibrating your accelerometer, I would not "drop it".  You didn't mention if it is a 1-axis accelerometer or a multi-axis one.  I'm going to assume one axis, and that you are calibrating (or "zeroing") it with the axis horizontal, which should give you 0 g.  Note that turning it upside down should still give you 0 g.  However, turning it 90° so the axis points up or down should give you ±1g.  

Bob Schor

[StathPol]

Hi Bob, 

The accelerometer is 1-axis as shown in the attached image. 

I guess that your recommendation would be to create a custom scale using DAQmx function using MAX scale. I have attempted to do it with the following values usign a table scale. 

Volts (V)   -   Acceleration (g)

-10      -      -10000 

   0      -      0 

+10      -      +10000

It does give an error, scale is wrong??? Even if you create a table, the <in place element structure> does not need to be placed to divide the voltage over the sensitivity of the accelerometer right?

Thanks,

Pepis21  

[StathPol]

I configured the accelerometers by creating a scaling table in MAX. They produce very high g values even with a small touch.