BRUEL & KJAER 1615 User Manual

2. TECHNICAL DESCRIPTION
The block diagram in Fig.2.1 shows the basic design of the instrument. The
signal is fed via an input amplifier to the filter inputs, which are connected
in parallel. The input amplifier has a high input impedance, and drives the
filters from a low output impedance. The filter outputs are selected by the
50 - position switch. When in the octave mode, the outputs of three
adjacent 1/3 octave filters are connected together (via resistors). The signal
from the filters is fed to two inputs of a buffer amplifier.
A subsidiary range of filters, from 25 Hz to 20 kHz with D, A, B, C and
Linear
filters can also be selected. This is also the only frequency range of
the 1615, which does not possess the low and high frequency filters.
The 50 position switch can be operated by actuating the electromagnetic
drive unit from the remote control socket.
The Filter set can be operated from normal mains supplies or from a 12 V
DC accumulator, for which purpose there is a DC- AC converter.
INPUT AMPLIFIER
The input amplifier provides the low impedance (rv0.8Q) drive required for
the filters. It has an input resistance of 125 KQ in parallel with 55 pF, and a
gain
of 0 dB. Its frequency response is flat from 1.8 Hz- 200kHz within
±0.1 dB.
1/3 OCTAVE FILTERS
The 1/3 octave filters are all 6-pole Butterworth networks and have the
centre frequencies and bandwidths given in Table 1.
The 2 - 200 Hz filters are active circuits consisting of 3 stagger tuned
Wien-bridge amplifiers, with an emitter follower output to reduce the out-
put impedance.
The other 1/3 octave filters are passive networks. Schematic diagrams for
both active and passive 1/3 octave filters are shown in Fig.2.2 and 2.3
5

BRUEL & KJAER 1615 Specifications

General

Brand	BRUEL & KJAER
Model	1615
Category	Measuring Instruments
Language	English