Accelerometer (voltage) signals using NI6361 module (PXI)

[StathPol]

Hi guys,

I have posted this question again but I still have problems with the DAQ. I am acquiring a voltage signal using a single axis accelerometer and NI6361 voltage module. I would like to setup the accelerometer to measure a signal range between +/- 5000g.

Accelerometer sensitivity = 0.516 mV/g where

1g = 0.000516 Volts or

1938 g = 1 Volt or

5000 g = 2.58 Volts

- I left the signal conditioning with +/- 10 Volts (Despite the fact that there is another one option to be set to +/- 5 Volts as well) -- Please see attached pdf

- I entered the sensitivity units to g

- I have set labview to measure a signal between +/- 10 Volts from the single ended one-axis accelerometer.

- An oscilloscope was connected with the card and it picked the same peaks with the LabVIEW. -- Please see attached pdf

- By hitting the accelerometer gently, the recorded signal was 400 mV = 0.4 V where it gives an acceleration of 775g.

- The accelerometer was also attached on the bullet for an impact test dropped from a distance of 50 mm. The recorded acceleration was 4000g which is quite high for such a small distance. I was expecting an acceleration of around 200g from even 2 to 4 meters according to some papers as well.

Can you please provide me with any help on how the settings are specified correctly between the accelerometer and coupler? I would highly appreciate whether you could correct me if anything of the above statement is wrong. I have attached a pdf file for your convenience.

Regards,

[Florian.Ludwig]

Hi,

775g seems a lot for "hitting gently". Do you use a heavy tool for that?

Whe I tap my accelerometer with my fingernail I get up to 2g if I'm not too gentle.

Maybe the voltage you read is already scaled in some way?

Best Regards,

Florian

[StathPol]

Hi Florian,

I hit it on the table and it gives a value of 775g which is really weird. I didnt use any scaling in MAX. The card is supported to read pure voltage.

[Florian.Ludwig]

Ok,

hitting it on the table really gently gives me about 80g.

Now by squinting at your pdf for a while I noticed the gain at the coupler is set to 3.87.

Doesn't that mean that the voltage output of the coupler is 3.87 times that of the accelerometer?

If so your 775g would turn to 200g - then we'd be in the same ballpark at least.

[StathPol]

I hit the accelerometer with my fingernail and it produces 38g. 

I have set the range of 10 V to 10000g, the gain became 1.93. Is the gain the attenuation and how does it needs to be taken into account?

Regards, 

StathPOl

[Florian.Ludwig]

I think the gain is the amplification of the signal.

With your accelerometer sensitivity 10V would be reached at 19380g - yielding a gain of 1.

Then the voltage output by the coupler would be the same as the voltage output by the sensor.

Of course it makes sense to have a gain greater than 1 if you don't expect to reach accelerations of such a magnitude - but then you have to factor it in when calculating your accelereation.

[StathPol]

I have tried it again with a gain of 1 but if we don't have high acceleration signals, I agree that the gain will be greater. But even, if we have a gain of 15 for example, we know that g = Voltage / Sensitivity..How the gain calculation is incorporated into calculations?

[StathPol]

I have tried it again with a gain of 1 but if we don't have high acceleration signals, I agree that the gain will be greater. But even, if we have a gain of 15 for example, we know that g = Voltage / Sensitivity..How the gain calculation is incorporated into calculations?

[Florian.Ludwig · Accepted solution]

Since the gain is the scaling factor for the voltage you'll have to devide your results by the gain.

g = Voltage / (Sensitivity*Gain)