Power On Amplifier

Back to: System Noise and Ground Loops

After measuring noise with the auxiliary systems powered on, check for noise related to the amplifier.

1. Put a terminator on the input for the amplifier (where the controller connects).
2. Power on the amplifier and verify that the gain is set to RESET.
3. After 10 seconds, select the Save Data button and name the file “4 – Amp ON Gain Reset.”

4. Power off the amplifier.
5. Terminate the amplifier input with a 50-75ohm terminator.
6. Power on the amplifier and set the gain to 100%.
7. After 10 seconds, click the Save Data button and name the file “5 – Amp ON Gain 100.”

Sources of Noise

Any new noise sources are possibly from EMI picked up by the sensor cable, noise generated by the amplifier’s field supply, or a ground loop passing through the control sensor. To differentiate between EMI and the field supply, remove the accelerometer from the shaker head but keep the accelerometer cable in place. If this action removes the noise, a ground loop is passing through the control sensor.

To correct the ground loop effects:

• Check the ground connections for the amplifier, shaker, and controller.
• Add isolation bases to the control sensor. If this action reduces the noise, a ground loop is the likely source of the noise.
• Short the case of the sensor to the chassis ground screw of the controller. If this action significantly reduces the noise, utilize the front panel jumpers on the VR9500’s front input board. See the lesson on Electromagnetic Interference.

If the above steps do not significantly reduce the noise, it is most likely from an unstable amplifier field supply. Contact the amplifier manufacturer.