Making Acceleration Measurements With NI LabVIEW

An IEPE sensor needs an appropriate cable and/or connector to hook into the BNC inputs of the C Series module. Triaxial accelerometers have three outputs, one axis to one acquisition channel, each requiring its own signal conditioning.

The next step is to physically connect the accelerometer to your DSA device. NI DSA devices use BNC or SMB connectors. The center pin of the connector, AI+, provides the DC excitation, when enabled, and the positive input signal connection. The shell of the connector, AI-, provides the excitation return path and the signal ground reference. To minimize ground noise, keep the metal shells of the connectors from touching each other, the DSA device(s), or the chassis/computer.
 

Configuring an Acceleration Task 

You can use MAX to quickly verify the accuracy of your measurement system setup. Using an NI-DAQmx Global Virtual Channel, you can configure an accelerometer measurement without any programming. A virtual channel is a concept of the NI-DAQmx driver architecture used to represent a collection of device property settings that can include a name, a physical channel, input terminal connections, the type of measurement or generation, and scaling information.

Follow these steps to begin:

3. With MAX open, select Data Neighborhood and click Create New.
4. Select NI-DAQmx Global Virtual Channel and click Next.
5. Select Acquire Signals»Analog Input»Acceleration.

6. Select ai0 or whichever physical channel you have connected to your accelerometer. For multiple channels, hold down the Shift key and select all the channels being used. A physical channel is a terminal or pin at which you can measure or generate an analog or digital signal.

 

7. Click Next and enter a name for the global virtual channel or leave the default.
8. Click Finish and you should see the following screen in MAX:

9. On the Settings tab, type in the minimum and maximum acceleration values you expect to read from your accelerometer (-5 g to 5 g by default).
10. Type in the sensitivity value of the sensor. This value is in the units you specify with the sensitivity units input. Refer to sensor documentation to determine this value.
11. Select the source of excitation (Iex Source):
    1. External—Any excitation source other than the built-in excitation source of the device.
    2. Internal—Use the built-in excitation source of the device.
    3. None—Supply no excitation to the virtual channel.
12. Specify the excitation value (Iex Value (A)).
13. Select your terminal configuration. Terminal configuration specifies the grounding mode used for the virtual channel. You can choose Differential or Pseudodifferential depending on your device (see above).
14. Type in the dB Reference value. This is the reference value used when results are computed in decibels. dB Reference is expressed in the selected engineering units.
15. Click the Device tab and choose your Coupling Mode (AC or DC).

Testing the Signal

16. With MAX still open, click back on the NI-DAQmx Global Virtual Channel tab and click on the Run button. You see the acceleration value of your measurement displayed at the top of the screen.