Measure the Controller Noise Floor

Back to: System Noise and Ground Loops

Measuring the controller noise floor is the first step in determining the source of noise in a vibration testing system.

1. Power down the amplifier, blower, hydraulic pumps, and any other auxiliary systems.
2. Disconnect the sensors from the controller.
3. Remove any products or fixtures from the slip table or head expander.
4. Configure the inputs in VibrationVIEW.
   • Select Configuration > Inputs.
   • Set the Ch1 sensitivity to the sensitivity of the control sensor; the appropriate sensitivity will ensure that all recorded values are comparable and at the same relative level.
   • De-select the Accel Power checkbox for the Ch1 input.

Inputs tab in VibrationVIEW.

5. Configure System Check.
   • Select Test > Test Type > System Check.
   • Select the Edit Test button and set the sample rate to 32,768Hz and FFT analysis lines to 32,768. These settings will give a 0.5Hz resolution out to 16kHz.

System Check test settings in VibrationVIEW.

6. The default graphs in System Check should be an acceleration waveform and acceleration spectrum. If the display does not include one or both graphs, add the graph(s).
7. Measure the controller’s base noise floor.
   • Terminate the controller inputs by shorting the input pin to the input shell with a 50-75ohm BNC terminator or jumper.
   • Verify that the amplifier’s power is off and the gain status is RESET.
   • Disconnect the drive cable between the controller and the amplifier.
   • After 10 seconds, select the Save Data button and name the file “1 – Controller Noise Floor.”

This data file will serve as a reference for troubleshooting. It is the lowest amount of noise that will always be visible in the system.

Figure 2.1. Configuration to measure the noise floor.