BRUEL & KJAER 2305 - Page 58

The DC voltage output can be fed into a digital voltmeter or other type of
analog-to - digital converter and the digital output so obtained may be stored
on magnetic tape, punched paper tape or IBM punched cards in a standard
digital code, for use in computer programs.
This system, using the B & K Level Recorder and Analog Voltage Read-Out
unit, provides an output which is proportional to the log of the true RMS,
peak, or absolute average value of the signal. Operating thus, as a log
converter, it is capable of slewing rates in excess of 200 dB/sec. Also its
dynamic range can be as great as 75 dB.
It is also possible to obtain an analog voltage output and use the Level
Recorder for writing curves at the same time.
Description.
The Analog Voltage Read-Out consists of thr ee parts :-
1. A linear potentiometer fixed to the shield which fits over the writing
arm of the Lev el Recorder,
2. A contact arrangement for the Rec order's writing system, and
3. A balancing unit with a stabilizer for the voltage supply from the Level
Recorder .
The linear potentiometer has 600 windings over its 50 mm working length
(Level Rec order adjusted to 50 mm writing width) which gives a resolution
of about 2.8 times that of the silver lamellae of the recorder range potentio-
meter.
In order to obtain zero output voltag e with the Level Recorder writing
stylus in its zero position (even though the contact point in the potentiometer
is not in its extreme end position), and correct full scale output voltage
with the Level Recorders writing stylus in its full scale position, a bridge
circuit is employed. This adjustment of the voltage at zero and full scale
(any voltage between 1 and 10 volts) is easily and conveniently carried out
by the use of two high resolution , 10 turn, wire-wound potentiometers.
The power supply is obtained by smoothing and stabilizing the 24 V DC
from the 7- pin socket of the Level Recorder . A socket is provided in the
balancing unit so that the remote control facilities from the Level Recorder
are still avail able. A low pass filter, cut-off frequency 100 Hz (c/s) , is
provided in the output leads which eliminates the contact noise which may
be deve loped at high writing speeds .
Operation.
A. Supply Voltage:
Plug the balancing unit into the 7-pin socket on the Level Recorder.
B. Mounting of Contact and Potentiometer:
I. With the recorder's POTENTIOMETE 'R RANGE dB on "Stand-by",
remove the cover from the writing arm unit on the Level Recorder
Type 2305.
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