Welch Allyn GSI 38, Service Manual

Page: 43 / 96

4 KHz ANSI Standard RTL for 0. dB HL 9.5 dB SPL
Reference HL for Calibration (+)80. dB HL
(+)80.0 dB SPL
(+) or (-) Microphone Correction NA. (+) 1.0 dB SPL
80. dB HL
90.5 dB SPL
The following table contains the ANSI Standard Reference Threshold Levels RTL's at
0 HL for each frequency when using TDH-39P earphones.
Frequency (Hz)
125 250 500 750 1000 1500 2000 3000 4000 6000 8000
ANSI Standard
RTL 45.0 25.5 11.5 7.5 7.0 6.5 9.0 10.0 0.5 15.5 13.0
Measured in dB SPL
Standard Reference Threshold Levels re: for Telephonics TDH-39P earphones
as measured on the National Bureau of Standards 9-A coupler. Reference ANSI S3.6
1989, ISO 389 1975 Standards.
Grason-Stadler has made an effort to minimize calibration time by defaulting the
Reference HL Levels for Calibration to maintain an expected SPL Calibration Level of
between 85 and 95 dB SPL. The Default HL Levels are as follows:
Frequency (Hz) 125 250 500 750 1000 1500 2000 3000 4000 6000 8000
Default HL 40 60 80 80 80 80 80 80 80 80 60
Because the 38 automatically adds the ANSI RTL and reference HL values on the
display (when the Tone Bar, is active) the technician needs only to add or subtract
the appropriate microphone correction to the displayed value when calibrating.
3)
4)
5)
6)
7)
8)
Connect the right ear phone to the Sound Level Meter Artificial Ear.
Press (TONE the display will update from the selected hearing level to
the ANSI Standard RTL value for calibration and the
indicator will
appear).
Adjust the HL knob until the SPL Level measured on the SLM for the selected
frequency and transducer equals the value indicated on the 38 display (+ or
Microphone Correction).
Press Key to store the data in memory.
Repeat for all frequencies, right phone, left phone, ipsi and contra by
selecting the appropriate key on the 38 front panel.
NOTE: Both left phone and right phone must be calibrated.
When finished press the Key to return to the Main Calibration Mode
Menu.