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4.2.1. Direct Acoustic Calibration using Calibrator or Pistonphone
The protection grid must be in place over the microphone diaphragm. Either a Sound Le-
vel Calibrator Type 4230
,
which produces a 94 ±0,25 dB (Re 20
X
1
o-
6
Pa) pure tone
at 1000Hz, or a Pistonphone Type 4220 can be used. When using the Pistonphone the
calibration level will vary slightly with ambient atmospheric pressure from its nominal
124 dB value
.
The 211 6 must be calibrated taking account of this factor
,
which can be
found from the barometer and chart delivered with the Pistonphone.
The instrument is calibrated as follows
:
1.
Insert the microphone into the cavity of the Calibrator (or Pistonphone), using the
plastic adaptor DB 0311 in the case of a half inch Microphone, and press gently
onto the seating ring so that a good flush fit is obtained.
2.
Switch on the Calibrator (or Pistonphone)
,
place a chart on the chart bed of the
211 6, and press the CALIBRATE pushkey on the right-hand side of the operating
panel.
The LED in the CALIBRATE pushkey should light and the pen should move down the
left-hand margin of the chart to the marked calibration position, 94 dB when using
the Sound Level Calibration or 124 dB (Nominal) when using the Pistonphone
.
3.
Using a small screwdriver
,
adjust the potentiometer to the right of the CALIBRATE
switch so that the pen lies exactly on the calibration mark
.
4
.
Press RETURN and the CALIBRATE again to check that the adjustment is correct.
This ensures that the calibration level is always approached from the same direction
and also avoids errors which could arise if the pen arm is moved without passing
through the standby position, e.g
.
when changing pens.
The instrument is now calibrated and ready for use.
4.2.2. Direct Vibration Calibration using Accelerometer Calibrator Type 4291
Fig.
4. 2
.
The Type
4291
Accelerometer Cal1brator
17
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