LP201 - Accelerometer Preamp

Low Output Impedance

The output impedance of the LP201 is 150 Ohms which enables long cable runs to be driven without signal loss. Because accelerometers typically operate down to very low frequencies, the power source connected to the LP201 through the XLR must have very low noise and ripple at low frequencies.

The output of the LP201 is provided on a male 3-Pin XLR connector. This connector also supplies power to the LP201 using the LinearX LVP interface. This interface uses a deticated 9VDC supply at about 30mA and can be easily powered directly from the LMS analyzer or by other external power supplies or via battery.

LP201 Selectable Parameters

• Gain: 0dB / 10dB / 20dB
The input gain can be set for 0dB (x1) , 10dB (x3.16), or 20dB(x10). For maximum dynamic range the 0dB setting is commonly used. However if your signal level is relatively low, the +10 or +20 settings can be used to increase the signal to noise ratio with the analyzer input. However using gain will reduce the maximum clipping level. Gain structure through the entire unit is also dependent on the Integrator settings and source spectrum when using the Velocity or Displacement outputs.

• HPF: 0.1Hz / 1.0Hz / 10Hz
The LP201 has several fixed 0.075Hz Highpass filters throughout the circuitry. However the HPF switch enables you to roll-off more of the low frequency response as needed by selecting either 0.1, 1.0, or 10Hz. When accelerometers are integrated to produce Velocity or Displacement, the low frequency gain can become very high. This can result in drift of the output. By using the Highpass filter this can be controlled or reduced as necessary.

• INT: 1 Sec / 100mSec / 10mSec
The time constant of the dual integrators can be selected to optimize the gain structure for various signal spectrums and applications. The smaller the time constant, the higher the gain. The gain increases as frequency decreases. For most loudspeaker applications the 10mSec value is appropriate. If less gain is desired, the 100mSec or 1 Sec values can be used.

• OUT: Acc / Vel / Dis
This switch selects the type of output signal. Either Acceleration, Velocity, or Displacement can be chosen. All output signals maintain positive polarity relative to either input.

LMS-4.6 Accelerometer Setup & Configuration

Beginning in LMS version 4.6, a new setup dialog is provided which enables LMS to be used with the LP201 to easily obtain calibrated data for Acceleration, Velocity, and Displacement (Excursion).

Each accelerometer typically comes with a calibration constant spec which relates the output voltage vs. acceleration. This Acceleration Constant can be entered here in the dialog, along with the other parameter settings of the LP201. The LP201 is simply connected to the LMS Mic Input and is then powered directly by LMS.

The type of data is selected in the Analyzer Parameters dialog for either Acceleration, Velocity, or Excursion. The curves are then drawn in actual units as dictated by the type of data selected.