Welch Allyn GSI 38, Service Manual

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Output Hearing Level Control
Calibrated in dB HL.
Measured in increments of 5 dB
Ranges:
125 Hz -10 to 50 dB HL
500 to 6000 Hz -10 to 90 dB HL
250 and 8000 Hz -10 to 70 dB HL
dB" Extended Range switch, which extends the Maximum HL at all
Additionally a "+1 0
frequencies by IO dB.
Accuracy of all settings of Hearing Level control:
125 to 4000 Hz +/- 3 dB
6000 to 8000 Hz +/- 5 dB
Signal to Noise ratio (in 1/3 Octave): >70 dB or less than -10 dB HL
(for levels less than 60 dB HL)
Tone Switch: This electronic switch turns the stimulus signal on/off with minimal
audible distortion.
Modes: Normal state: Stimulus Off
Activated state: Stimulus On
Rise/Fall Time: 20-50 msec
Measured at the -1 dB and -20 dB points on the signal envelope.
On/Off Ratio: With the tone switch off, the output will be at least -10 dB below
standard reference equivalent threshold with HL setting of 60 dB.
Above 60 dB HL setting: >70 dB
Cross Channel Leakage: At HL settings of 70 dB or greater, the unwanted signal in
the non test earphone shall be at least 70 dB below the tone
in the test earphone.
Stimulus Signals
Continuous signals
Continuous FM
Pulsed