HBK 4231, User Manual

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How the Calibrator Works
16 Sound Calibrator Type 4231
User Manual
• an adjustment for the sound pressure level
• an amplifier with adjustable gain
3.8.2 SPL Reference
The SPL reference is a voltage that the calibrator uses for two critical
applications: for comparison with the feed-back and as the
polarization for the reference microphone. Using the same voltage
source for these applications makes the calibrator insensitive to
variation in this voltage.
3.8.3 Variable Amplitude Sine Generator
The variable amplitude sine generator produces a 1 kHz sine wave
which drives the loudspeaker (see Fig.3.4). The output from feedback
circuit is used to control the signal produced by the variable amplitude
sine generator.
3.8.4 Frequency Reference
This is a quartz-controlled oscillator used to maintain the stability of
the frequency of the sine wave produced by the variable amplitude sine
generator.
3.8.5 Control Circuit
The control circuit switches the calibrator on or off when you press the
button. It also adjusts the gain in the feedback circuit when the
button is pressed.
The control circuit checks to make sure that the sound pressure level
generated by the calibrator is within the accepted range. If the sound
pressure level is outside the accepted range (for example, if a test
microphone has not been detected), the circuit automatically switches
the calibrator off after approximately four seconds.