Service Manual
AT235
11
3.2 Equipment requirements
3.2.1 Equipment requirements for impedance calibrations
To ensure proper calibration of audiometric equipment, test instruments must be reliable, stable and their
calibration certified.
The minimum requirements for measuring equipment are:
1) A measuring amplifier with input for condenser microphone or a sound level meter, fulfilling Type 1 of the
IEC 60651 requirements.
2) An acoustics coupler, 6cc and 2cc fulfilling the requirements of IEC 60318-3 and IEC 60318-5.
3) An occluded ear simulator/artificial ear fulfilling the requirements of IEC 60318-4 and IEC 60318-1.
4) A manometer with a range from at least +300 to -600 daPa and an accuracy of ± 5% of reading or ± 5
daPa, whichever is the greatest. Including a syringe (manual pump).
5) CAT55 calibration cavities (0.2/0.5 and 2.0/5.0ml).
6) We recommend the use of an acoustic calibrator for the control of the complete measuring chain.
7) A general purpose frequency counter.
8) A general purpose digital multimeter.
9) A general purpose oscilloscope for the purpose of tracing and monitoring signals.
10) An oscilloscope or peak-peak voltage measurement equipment.
3.2.2 Equipment requirements for audiometer calibrations
1) A Type 1 sound level meter – Octave band filter set (1/3 octave, with range from 125 Hz to 16000 Hz)
must meet Type 1 sound level meter requirements (ANSI S1.4). Sound level meters should be checked
before use by means of a calibrator.
2) A system to measure:
•
Frequency
•
Rise time
•
Fall time
•
Duration
•
Overshoot
•
THD (Total Harmonic Distortion)
3) A Piston phone or sound level meter calibrator.
•
An ear simulator ANSI/ASA S3.7 or IEC 60318-1, Part 1: Electroacoustics - Simulators of human
head and ear Part 1: Ear simulator for the measurement of supra-aural and circumaural earphones.
•
Acoustic Coupler – NBS–9A (6cc) ANSI/ASA S3.7, or IEC 60318-3, Part 3: Electroacoustics –
Simulators of human head and ear – Part 3: Acoustic coupler for the calibration of supra-aural
earphones used in audiometry.
•
IEC 60318-5, Electroacoustics – Simulators of human head and ear – Part 5: 2 cm
³
coupler for the
measurement of hearing aids and earphones coupled to the ear by means of ear inserts.
4) Specification / calibration information for all microphones, filters, SLM, and couplers showing correction
values required for maintaining accuracy.
5) Other couplers and adapters as stated or specified by the manufacturer of the audiometer.
6) Calibration reports/sheets that demonstrate that the audiometer meets the requirements and record the
results of measurement during the calibration.
