Developing the G.R.A.S. Microphone Calibration System Using NI LabVIEW and National Instruments Hardware
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G.R.A.S. Sound & Vibration designs and manufactures an extensive range of products covering virtually all the front-end equipment needed for the precise, reliable measurement and recording of acoustic signals.
Author(s):
Ed Terrel - GRAS Sound & Vibration
Industry:
ATE/Instrumentation
Products:
Digital I/O Real-Time Devices, LabVIEW, PCI-4461
The Challenge:
Developing a fully automated, traceable microphone calibration system that is reliable enough to be used by in-house production and external calibration labs.
The Solution:
Programming a microphone calibration system using the NI LabVIEW graphical programming environment with automated analog measurements, output to an electrostatic actuator, digital control of a switch box, and RS232 communications to a pistonphone.
"A key reason for selecting National Instruments modular hardware over traditional boxed instrumentation for our application was the ease of integration with LabVIEW, which shortened our overall development time."
G.R.A.S. Sound & Vibration designs and manufactures an extensive range of products covering virtually all the front-end equipment needed for the precise, reliable measurement and recording of acoustic signals. Calibrating microphones is complex, time consuming, and critical to the quality of the measurements. Therefore, when we needed to develop an automated system to calibrate our microphones, we looked for an option that provided a high level of accuracy and measureable results.
Automating Microphone Calibration with Graphical System Design
We selected the NI PCI-4461 dynamic signal acquisition board with two 24-bit analog inputs and two 24-bit analog outputs for the core of the measurement system. With sampling rates of up to 204.8 kS/s, the PCI-4461 board, when coupled to an electrostatic actuator, can determine the frequency response of the microphone from 20 Hz to 90 kHz. A key reason for selecting National Instruments modular hardware over traditional boxed instrumentation for our application was the ease of integration with LabVIEW, which shortened our overall development time.
We use LabVIEW for taking measurements, performing the analog signal processing, and controlling a precision G.R.A.S. pistonphone (Type 42AP) over an RS232 connection for level calibration of the microphone using the insert-voltage technique to determine the open-circuit sensitivity. The system provides additional automation with the NI PCI-6503 digital I/O board controlling a switch box for the various preamplifier signal routing.
We made this system available to external calibration labs and other engineers and scientists who need to calibrate various IEC-standardized measurement microphones. With the measurements and processing fully controlled by the G.R.A.S. Calibration Software SW0002, an application based on LabVIEW, users can be confident their microphone calibrations are accurate and reliable. In addition to the automated calibration procedure, the system also includes data storage management and easy generation of custom-designed calibration certificates.
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