DeltaOHM HD2010UC, Руководство пользователя, Страница: 49 / 128

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E
LECTRIC CALIBRATION
The electric calibration, using the partition of charge injected into the microphone preampli-
fier in “charge amplifier” configuration (Capacitive Transducer Calibration), even if it
cannot
completely replace the acoustic calibra-
tion
, provides however a useful means to
keep under control the instrument drifts, mi-
crophone included. The figure on the right
shows the diagram of the CTC technique
consisting in sending an electrical signal to
the preamplifier through a high stability ca-
pacitor, so that the output signal does not de-
pend only on amplification, but also on the
microphone capacity. Many of the micro-
phone malfunctions reflect in a capacity drift
identifiable by means of this calibration tech-
nique. The electric calibration uses as a refer-
ence the result of the last acoustic calibration,
and according to it corrects any possible drift
of the instrument. The electric calibration adjusts the acoustic response of the microphone-sound
level meter chain, both for wideband channels, and for those with a constant percentage bandwidth.
In case of continuous instrument drifts, it is suggested to carry out an acoustic calibration to verify
that there are no other problems both in instrument and microphone.
Operating Procedure
Switch on the sound level meter, if it is the case, press STOP to finish the measurement in progress
and make the following procedure:
1. Press PROG and use the DOWN arrow to select "Electric Calibration".
2. Press SELECT to start the function.
3. The inner signal generator will be turned on and the measured output signal will be com-
pared with the one detected in the last acoustic calibration.
The value that appears on the display (51.3 dBC in the example below), before starting cali-
bration, is the valued measured by the microphone upon pressure of the PROG key, and is
not relate to the calibration in progress.
ELECTRIC CALIBRATION
Last:2003/01/01 10.00
Calibr. level 94.0dB
Leq dBC
51.3
YES
NO
Run calibration
?
4. Press YES to continue and NO to quit.
C
m
C
c
C
f
V
0
Calibration
Signal Source
Transducer
CTC
-A
Charge amplifier
C
b
V
i
V
0
V
i
C
c
C
m
+ C
b
+ C
c
= -
C
b
C
f