BRUEL & KJAER 1621 - Technical Description; Block Diagram; Principle of the Filter Circuit

Region for
Amplifier
BROEL & KJ.LER
Nffirum Denmark
Technical Description
1621.1
Block Diagram
St.p
Tunln!j
Pul~es
Vol log.
from 2 )06
~UIO
...
O Menuol
M--~.
l I
In
put
O---.
Bonowidth
SeLt"c tor
inveri:er
O .... rtoad
Lomp
Int·orotor
Int.grator
Ovtr!ood
~
I II
t I
-
Principle of the Filter circuit
Feedback I
lo
overload
Inlegrotor I Integralor II
>--<1>--------.-.0" V out ..
Feedback il
Region for
Amplifier
Vin
Inverter
The Type 1621 consists of a tunable single pole bullerworth filter with
switchable bandwidths.
The princlple of the filter is as follows:
The Integrators I and II tagether with the first Inverter and feedback I.
works as a tunable oscillator The circuit starts osclllating when the
input Irequency is the same as the tuned-in Irequency Feedback II con-
trals that the amplitude 01 the output is the same as the input amplitude.
When the input Irequency and the filter is tuned to resonanee the ampli-
fication of the integratars will be exactly x 1.
For
an input frequency lower than resonance, the amplilicatlon af Inte-
grator II will be very high due to C2 which through feedback Ideerease
the input to the first Inverter and thus stops the oscillating. Now the eir.
cuits works as a normal amplifier where the amplification is controlled
by Cl and C2.
For an input frequeney higher than resonance the output of Integralor I
decreases due to C 1 which then stops the oscillating and the eireuit
turns over to a normal amplifier condition,
The FREOUENCY RANGE switch seleet a subrange of the overall fre-
quency range between 0,2 Hz and 20kHz. The frequeney is swept
through the subrange by the FREOUENCY TUNING potentiometer
Valid from serial no. 6941 26
9.77
1-1