BRUEL & KJAER 2672, Руководство пользователя

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Chapter 4 — Using Type 2672
Selection of Input
Sound Quality Conditioning Amplifier Type 2672
User Manual
BE 1461 –11
4
−
3
4.3 Selection of Input
When you are using a Head and Torso Simulator (HATS) to record binaural sound,
the input to use depends on whether you are using Type 4100 or Type 4100 D:
●
Type 4100 uses Microphones Type 4190 with Preamplifiers Type 2669 L – select
Pol. Voltage 200 and connect the preamplifiers to the Preamp. input.
●
Type 4100 D uses Microphones Type 4189 with DeltaTron
®
Preamplifiers Type
2671 – connect the preamplifiers to the Dir./CCLD input. No polarization volt-
age is required and, as the polarization voltage is not applied to this input, the
setting of Pol. Voltage is irrelevant.
4.4 Charge-injection Calibration
4.4.1 Brüel & Kjær’s Patented Charge-injection Calibration Technique
The charge-injection calibration (CIC) technique is a method for remotely verifying
the condition of the entire measurement set-up including the microphone. This
is a great improvement over the traditional insert-voltage calibration method which
virtually ignores the state of the microphone. The CIC technique is very sensitive to
any change in the microphone and preamplifier input capacitance which is a relia-
ble indicator of the condition of the microphone and preamplifier.
The technique works through a small, built-in, accurately defined capacitance Cc
(typically 0.2 pF) with a very high leakage resistance (greater than 50000 G
Ω
) into
the circuit of the preamplifier, see Fig.4.1, upper diagram. C
i
and R
i
represent the
preamplifier’s high input impedance and A its gain (
≈
1).
Fig.4.1 Upper diagram: Charge-injection calibration method. Lower diagram: Insert-voltage calibra-
tion method
940528e
C
m
C
c
C
i
R
i
Housing + cable
A
C
m
C
i
R
i
V
0
V
0
V
i
Calibration
Signal Source
Microphone
Typical Values : C
m
= 15 – 20 pF C
i
= 0.3 pF C
c
= 0.2 pF A
≈
1
V
i
V
0
V
i
C
c
C
m
+ C
i
+ C
c
= A
( )
V
0
V
i
C
m
C
m
+ C
i
= A
( )
A
Insert-
voltage
CIC