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4.3.1. Recording the Correction Curve
1 .
Connect the transducer which is measuring the parameter are to be stored and sub-
sequently compensated for. Ensure that the COMPRESSION switch is in the "In" po-
sition.
2
.
Press the two READ IN push keys simultaneously, the left-hand one first.
The pen will move along the top of the chart from its stand-by position and come to rest
at the beginning of the frequency scale. An output level, which corresponds to the nomi-
nal 90 dB sound pressure level indicated on the front panel, is selected automatically
and the 90 dB SPL LED and those in the READ IN push keys should now come on. After
about 1 0 seconds, during which time the output level rises until it corresponds to the se-
lected level, the frequency sweep begins at 100Hz and continues in 256 discrete steps
at 1 ,8% intervals up to 10kHz. At each frequency step the output level is regulated in
0,3 dB steps until it is equal to the nominal value, and the correction required to achieve
this is stored in the memory of the 2116. During this process the pen remains raised
but follows the current frequency along the top of the chart to indicate how far the pro-
cess has progressed
.
When 10kHz is reached, the pen returns to the stand-by position,
the LEDs on both READ -IN pushkeys extinguish, and the pilot lamp in the RETURN
switch lights
.
If the CONTINUE switch on the rear panel is pressed during the READ-IN process, no
valid correction curve will be recorded from that point in the frequency sweep until it is
released again. Subsequent test sweeps will only be valid for those parts of the test
sweep for which the switch was released
.
This facility may be useful where tests are to
be carried out on a test object whose response dynamic range is known to be too large,
or whose normal working frequency range is less than that of the Type 2116. In the lat-
ter case levels may occur, because of resonances, or high cut-off rates at the limits of
the test object's normal frequency range, which lie outside the correction dynamic range
of the 211 6.
If the RETURN pushkey is operated during READ IN, the process is terminated at that fre-
quency and the pen is returned to the stand-by position. Any subsequent test sweeps
will also be terminated at that frequency. These two switches enable the operator to
choose the frequency range over which the test is made. All other switches are inopera-
tive during READ IN
.
4.3.2. Performing the Measurement
1
.
Mount the measurement transducer on the Preamplifier Type 2642 using an adap
-
tor where necessary as described in Section 3. 3 and connect the miniature plug to
the INPUT socket on the rear panel of the instrument
.
2
.
Select the required measurement parameter using the TEST MODE switch, and if
performing a distortion measurement select the required order using the DISTOR-
TION ORDER switch
.
3
.
rf the internal generator is to be used to supply either a regulated test environment
or a constant voltage level, select the required test level using the pushkeys UP and
DOWN until the desired test level is indicated on the row of light emitting diodes.
21
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