DJB Instruments Accelerometer Calibration Capability
11 October 2011
DJB Instruments (formerly known as DJ Birchall) has been manufacturing accelerometers, microphones, cables and associated instrumentation in Mildenhall, Suffolk since 1974.
They are a customer focused business offering a bespoke service as well as supplying products from stock. DJB has built a strong reputation for the quality of its products, for providing solutions and resolving customer needs.In 2001 m+p developed an accelerometer calibration capability for DJB which was based around m+p’s original VibPilot controller. The system was used daily for calibration to national standards of new accelerometers, repeat annual calibrations and calibration of accelerometers manufactured by third parties.
The procedure required a sinusoidal frequency sweep performed to a high level of amplitude accuracy using a Reference accelerometer. Measurement of the Reference was made during the sweep whilst also measuring the Unit Under Test (UUT). The ratio of the 2 measurements enabled calculation of the UUT sensitivity at frequencies of interest within the range of the sweep. The variation of sensitivity with frequency was plotted over the entire frequency range.
In 2010 the entire system was upgraded to provide a wider frequency range and a more detailed customer report. The upgraded system uses m+p’s new VibPilot hardware which is 24 bit, providing a signal-to-noise ratio which exceeds 120dB. The frequency range is also extended enabling calibrations to 10kHz. To exploit the controller’s extended frequency range the shaker was upgraded to a Precision Air Bearing Calibration Shaker. The pneumatic suspension configuration of the new shaker had the added advantage of eliminating low frequency suspension resonances in the frequency range of interest.
The User Interface and Calibration Sheet were completely restyled to provide an appearance consistent with DJB Instruments’ latest branding whilst providing more valuable information for the customer.
A major advantage of m+p’s new VibPilot hardware is its compatibility with m+p’s SO Analyser whose applications include time recording, FFT analysis, modal analysis, rotating equipment analysis, octave analysis and measurement of sound pressure, sound power and sound intensity. DJB Instruments’ application was the measurement of an accelerometer’s natural frequency.
The VibPilot has a maximum sampling rate of 102.4kHz providing an alias-free bandwidth of 40kHz, sufficient for all but the tiniest of accelerometers.
In summary, the upgrade gave DJB Instruments the following advantages:
• Wider frequency range
• Higher accuracy: control and measurement
• Resonance free frequency sweep
• More intuitive User Interface
• Enhanced calibration data
• Accelerometer natural frequency
A generic version of the calibration software described above is available to all m+p customers. Please contact us for further information.
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- 18/05/2011 - Digital Acoustic Control Systems for NASA
- 12/05/2011 - M+P revise VibControl with version 2.11 launch
