GRAS 246AO 1/2” CCP Pressure Standard SysCheck2™ Microphone Set

Introduction

GRAS 246AO with SysCheck2™ is a ½″ high-precision microphone suitable for laboratory work and ideal for production line testing in coupler setups for test of hearing aids, earphones, headphones, and headsets.

GRAS 246AO is a variant of 46AO that contains SysCheck2 functionality that can be accessed with many data acquisition systems, but offers seamless plug-and-play operation with Audio Precision’s APx data acquisition software. 

SysCheck2 and TEDS

Verification with SysCheck2*
SysCheck2 is a GRAS patented technology for verifying measurement chain integrity. This verification tool performs remote health check on microphones, channel gain and cable integrity. The verifications are made on each SysCheck2-enabled microphone connected to a CCP power module with transducer electronic data sheet (TEDS) support and measurement software with one click.. SysCheck2-enabled microphones also provide on-demand environmental data (temperature, barometric pressure and humidity). SysCheck2 functionality is particularly convenient when the microphones are placed where physical verification is a risk (for example, if the microphones are hidden in complex mechanical structures, such as couplers or specialized test boxes on production lines), the locations are difficult or dangerous to reach, or if used in a distributed measurement where there are many microphones spread out over a large area.

SysCheck2 microphones are equipped with an ultra-low power microcontroller located in the microphone preamplifier. This microcontroller is able to produce a reference signal that SysCheck2 compares to a reference measurement to determine the measurement chain status. Changes in microphone or cable capacitance, channel gain or the unexpected use of a filter will result in a measurement deviation and will be reflected in a change in the output from the measurement channel. Once detected, the problem can be examined and then rectified.

The microphone can be set to display visual cues to the health of the measurement chain and can be used for the easy identification of specific microphones. In the evaluation of measurement-chain health, SysCheck2 can detect microphone sensitivity or channel gain changes greater than 0.3 dB. Additionally, the microphone acquires data on local environmental conditons, including temperature, pressure and humidity. This data can help with the tracability of acquired data and help refine testing to reduce the number of erroneous pass-fail results on a production line.

Full SysCheck2 functionality is ready for use out of the box when connected to  APx 500 Measurement Software with GRAS 12BA, 12BB or 12BE power modules and an Audio Precision APx series analyzer or with an Audio Precision APx series analyzer with CCP and TEDS read/write capabiliy.

However, all features are accessible with a suitable CCP-based power module, analyzer and data acquisition system after setup with the GRAS-supplied software developement kit (SDK) or application programming interface (API), depending on your system.

For example, Siemens Simcenter Testlab Signature Acquisition (as of release 2021.1) has integrated SysCheck2 for use with GRAS 246AE microphones with a dedicated remote check procedure, allowing it to smoothly check the validity of a calibration previously performed in the field. After initial calibration of the system, their system enables a remote check to be performed in a dedicated tab. All 246AE SysCheck2 microphones present in the field can be checked with one click, and each microphone’s measured value is stored in that microphone’s TEDS as a reference value.

System verification with TEDS
TEDS is very useful to determine which microphone is connected to which input channel and contains relevant information needed by SysCheck2 and other tools used for measurement setup and verification. However, it is not by itself a check of whether the microphone is within specifications or not.

Design

GRAS 246AO is a high-performance standard microphone set. The set is assembled and sealed with a label in our clean-room environment.

Microphone
The microphone cartridge is the high-quality IEC  61094 WS2P standardized GRAS 40AO 1/2″ Prepolarized Pressure Microphone, designed for long-term reliability in multiple environments.

Preamplifier
The preamplifier is based on the GRAS 26CA ½″ CCP Standard Preamplifier. This preamplifier unites SysCheck2 functionality with our well-known circuit-board substrates. In the industry, these circuit-board substrates are famous for their low self-noise, wide frequency range and excellent slew rate performance.

Compatibility

To perform as specified the GRAS 246AO microphone set requires a constant current input module that can deliver 4 mA and 24 V unloaded CCP voltage supply. If the constant current supply is lower, the capability of driving long cables is reduced and consequently the upper frequency is reduced. If the voltage supply is lower it will influence the upper dynamic range.

The microphone set is terminated with a BNC connector. Ready to use coax cable assemblies of various types and lengths are available in standard as well as customized lengths.

The 246AO is IEEE 1451.4 TEDS v. 1.0 compliant. If your measurement platform is TEDS compatable, you will be able to read and write data such as properties and calibration data.

Service

Should you by mistake damage the diaphragm on a GRAS microphone we will in most cases be able to exchange it at a very reasonable cost and short turn-around time. This not only protects your investment but also meets your quality assurance department since you do not have to worry about new serial numbers etc.

Calibration

When leaving the factory, all GRAS microphones have been calibrated in a controlled laboratory environment using traceable calibration equipment. Depending on the use, measurement environment and internal quality control programs we recommend that the microphone is recalibrated at least once a year.

We offer two kinds of calibration as an optional after-sales service: GRAS Traceable Calibration and GRAS Accredited Calibration.

GRAS Traceable Calibration is a traceable calibration performed by trained personnel under controlled conditions according to established procedures and standards. This is identical to the rigorous calibration that all GRAS microphones are subjected to as an integral part of our quality assurance.

GRAS Accredited Calibration is performed by the GRAS Accredited Calibration Laboratory that has been accredited in accordance with ISO 17025 by DANAK, the Danish Accreditation Fund.

If you want a new microphone set delivered with an accredited calibration in stead of the default factory calibration, specify this when ordering.

For subsequent, needed acoustic verification and checks of your measurement setup, we recommend using a sound source like the GRAS 42AG Sound Calibrator. For sensitivity calibration we recommend using a reference sound source like the GRAS 42AP Intelligent Pistonphone.

Learn more at calibration.

Quality and warranty

GRAS microphone sets are made of components from our proven standard portfolio and are all manufactured of high-quality material and branded parts that were chosen and processed to ensure life-long stability and robustness.

All parts are manufactured and assembled at the factory in Denmark by skilled and dedicated operators in a verified clean-room environment. The microphone diaphragm, body and unique protection grid are made of high-grade stainless steel and make the microphone set resistant to physical damage as well as corrosion caused by aggressive air or gasses.

This, together with the enforced gold-plated microphone terminal guarantees a highly reliable connection. Thanks to the high quality, our warranty against defective materials and workmanship is five years.