Accelerometer Calibration

1. Equipment Description

Introduction:

The purpose of this document is to describe the devices and procedures for accelerometer calibration. Devices include APS Dynamics Model 129 Horizontal Shaker, Model CAL50 Vibration Exciter and TMS 2050E05 Power Amplifier. All important notifications and specifications will be included in the following sections. Calibration procedures are divided into two sections. First section is the wired accelerometer calibration and second section is the MEMS accelerometer calibration.

APS Dynamics Model 129 Horizontal Shaker:

This shaker consists of a Model 113-AB long stroke air bearing electrodynamic force generator attached to a horizontal load mounting table. The shaker imparts transverse base excitation to items mounted on the table. Static and dynamic loads normal to the table surface are transferred through a large area precision air bearing to a rigid guide bar of rectangular cross section. The shaker is used for the low frequency (0 to 200 Hz) accelerometer calibration.

The continuous duty force rating for Model 113-AB is 21 lb (94 N) for frequencies between 0 and 0.1 Hz. The maximum force is 30 lb (133 N) for frequencies between 0.1 and 20 Hz. Frequencies above 20 Hz, the force are degraded from 30 lb. The peak acceleration is 1.6g.

The air bearing system needs clean dry air pressure for proper operation. Operating the shaker without adequate filtered air pressure applied is prohibited. The filtered air can be supplied by using Filter Regulator 5003 and air pressure should keep between 30 to 40 psi or 200 to 280 kPa and a minimum of 1 CFM at 40 psi. There is a Model 502 Low Pressure Switch can be used to protect the air bearing shaker from damage caused by loss of air pressure. When the air pressure is below 30 psi (200 kPa), the switch provides a disconnection from the amplifier and sounds a sonic alarm.

For the load mounting table, load mounting screws bottom-out on air bearing housing should be avoided because it will result in damage to the bearing house. Also, the maximum load for the table should not exceed 50 lb (23kg).

Model CAL50 Vibration Exciter:

This electrodynamic vibration exciter uses the permanent magnet and passing electric current through a wire placed in the magnetic field to generate mechanical motion or force. This force or motion will excite the moving element and generate acceleration or displacement which the calibration needs. The frequencies range of this exciter is 3 to 10000 Hz. The maximum force output is 50 lb and peak acceleration is 50 g.

There is a torque lock system preventing the moving element from rotating when moments are induced and maintaining the moving element alignment. This lock should be engaged whenever tightening or removing transducers at the mounting fixture, or transporting the exciter.

When the exciter is driven for extended periods of time at greater than half of its rated capacity, cooling is required. A cooling package can be used to accomplish this requirement.

TMS 2050E05 Power Amplifier:

This amplifier can be easily operated from the front panel controls. Input and output connections are on the rear panel. Internal over-temperature and over-current protection can protect the amplifier from damage due to high temperature and current. The input power can be 100, 120, 220 and 240 Volts and 48 to 62 Hz.

For lowest distortion, when operating Model 129 Shaker at frequencies below 2 Hz, the amplifier should be switched to Voltage Mode. When operating at higher frequencies and force level of 75% of maximum or less, Current Mode should be used. In general, the Voltage Mode will be used in most conditions.

For Model CAL50, when tests use frequencies greater than 1000 Hz or desired amplitude levels, the amplifier should be switched to Voltage Mode. When tests use force inputs to produce natural response amplitudes at frequencies below 1000 Hz, the amplifier can be operated in Current Mode. But, the amplifier should not be operated in Current Mode if no load is connected to the Output and Return terminals.

2. Equipment Operation Procedures

Equipment Operation Procedures:

APS Dynamics Model 129 Horizontal Shaker:

Power up:

(1)Turn Gain of the amplifier to the detent Reset position.

(2)Change Mode switch of the amplifier to Voltage or Current mode as described in Equipment Description.

(3)Provide the amplifier input signal from the rear panel Input connectors.

(4)Connect Out and Ret in the rear panel of the amplifier to Input of Low Pressure Switch.

(5)Connect Output of Low Pressure Switch to the shaker.

(6)Connect Air Tubing from Air Filter to the shaker and another Air Tubing from the shaker to Low Pressure Switch.

(7)Open Air Filter and adjust the air pressure to 30 to 40 psi.

(8)Check the integrity of Air Tubing attached to the shaker.

(9)Check the utility of Mounting Table of the shaker.

(10)Turn the amplifier power switch to On position (power indicator LED will light).

(11)Slowly turn Gain up to the desired level.

(12)Run the accelerometer calibration following the calibration procedures.

Power down:

(1)Reduce the input signal to zero.

(2)Turn Gain of the amplifier to the detent Reset position.

(3)Allow the fan on the amplifier to cool the amplifier (approximate 1-2 minutes).

(4)Turn the amplifier power switch to Off position and wait 30-60 seconds for internal power dissipation before disconnecting the amplifier wiring.

(5)Close Air Filter.

Model CAL50 Vibration Exciter:

Power up:

(1)Move Torque Lock Key of the exciter away the exciter Table to release the exciter Table.

(2)Connect Cooling Package to the exciter if the exciter needs to be driven for extended periods of time.

(3)Turn Gain of the amplifier to the detent Reset position.

(4)Change Mode switch of the amplifier to Voltage or Current mode as describe in Equipment Description.

(5)Provide the amplifier input signal from the rear panel Input connectors.

(6)Connect Out and Ret in the rear panel of the amplifier to the exciter.

(7)Turn the amplifier power switch to On position (power indicator LED will light).

(8)Slowly turn Gain up to the desired level.

(9)Run the accelerometer calibration following the calibration procedures.

Power down:

(1)Reduce the input signal to zero.

(2)Turn Gain of the amplifier to the detent Reset position.

(3)Allow the fan on the amplifier to cool the amplifier (approximate 1-2 minutes).

(4)Turn the amplifier power switch to Off position and wait 30-60 seconds for internal power dissipation before disconnecting the amplifier wiring.

(5)Move Torque Lock Key of the exciter toward the exciter Table to lock the exciter Table before remove accelerometers.

3. Calibration Procedures

Wired Accelerometer Calibration Procedures:

(1)Open the Labview program named ICP.

(2)Mount calibrated accelerometers and the reference accelerometer on the shaker.

(3)Select the physical channels used in calibration. The output signal cable of the reference accelerometer should be plugged into the 1st recorded channel on the DAQ device (BNC-2120).

(4)Output signal for controlling shakers is generated at channel DAC0 on Analog Outputs panel. Plug this signal into the 2nd recorded channel on the DAQ device (BNC-2120) and also plug into TMS 2050E05 Power Amplifier.

(5)All accelerometers should use the same gain.

(6)Select the output signal range in Note Panel. (Usually, use +-0.5 voltage)

(7)Enter information in Input Parameters Panel. The output certificate files will be named as Accelerometer model, serial number and test date by default.

(8)Enter calibration parameters in Accelerometer Information Panel.

(9)Start calibration tests by running this Labview program.

(10)In this Labview program, the excitation noise calculation would be included.

MEMS accelerometer calibration procedures:

(1)Open the Labview program named MEMS-A.

(2)Mount the MEMS and the reference accelerometer on the shaker.

(3)Setup the WIDAQ system for the MEMS. (Because of memory limitation of the MEMS, the recorded data of the MEMS for each test should not exceed 21000 points.)

(4)Select the physical channels used in calibration. The output signal cable of the reference accelerometer should be plugged into the 1st recorded channel on the DAQ device (BNC-2120).

(5)Output signal for controlling shakers is generated at channel DAC0 on Analog Outputs panel. Plug this signal into the 2nd recorded channel on the DAQ device (BNC-2120) and also plug into TMS 2050E05 Power Amplifier.

(6)All accelerometers should use the same gain.

(7)Select the output signal range in Note Panel. (Usually, use +-0.5 voltage)

(8)Select the output file folder for Ref Accelerometer data and information.

(9)Enter information in Input Parameters Panel. Note: Enter the number of tests for each frequency. (In order to fit the sampling limit in the MEMS, tests for lower output frequencies should be separated into several parts and recorded in different files. Each part should not exceed 21000 points. For each shaking frequency, the total number of tests should be 10. Enter the file number. (The file number is used to label the sequence of each file which will be selected in Processing Data Program)

(10)Start calibration tests by running MEMS-A and WIDAQ. (Run this Labview program about 1-2 seconds before the WIDAQ system.)

(11)After finishing tests for each output frequencies, repeat procedure 9 and 10 and set the output signal amplitude to 0 for excitation noise calculation.

(12)Do 1G calibration tests by turning MEMS upside down. ( Using sampling frequency = 2000Hz and sampling duration = 10 seconds in WIDAQ and turning MEMS upside down between 3~8 seconds)

(13)After all tests, use Processing Data Program to combine all recorded files and generate calibration certificates.

(14)Open the LabView program named MEMS-B.

(15)Select the type of MEMS. (Single end or Differential)

(16)Enter number of combined files. (Include sensitivity calibration files, excitation noise files and 1G calibration file)

(17)Enter other information in Input Parameters Panel. The output certificate files will be named as Accelerometer model, serial number and test date by default.

(18)Enter accelerometer information in Accelerometer Information Panel.

(19)Start data process by running MEMS-B. Select files following the information in the dialog box. First, select 1G calibration file. Second, select all sensitivity calibration files according to the sequence of the shaking frequencies. Third, select excitation noise calculation files according to the sequence of the shaking frequencies.