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GAl N CONTROL potentiometer together have an attenuation range
between 0 and 21 dB. The gain of the second amplifier section is fixed at
19 dB. Hence, the overall gain of the input amplifier stage is 40 dB maxi-
mum. The output impedance of this stage is 10
n.
From the input amplifier the signal is fed either to an external filter
(EXT. Fl L TER sockets) or to an internal low pass filter which eliminates
frequencies above 200kHz.
Overload Indicators
An overload of the input amplifier which would introduce distortion into
the signal, may not always be noticed, especially if the output amplifier
itself is not overloaded. Also this overload may be caused by frequencies
which may not be present after filtering or weighting. Therefore, an over-
load indicator is placed at the output of the first amplifier. If the peak
voltage exceeds a certain value (5.0 V) at the output of this amplifier, the
overload lamp will light for at least 0.5 sees, even though the overload
condition may be as short as 200 J.l.Secs.
The input overload indicator and the output overload indicator are con-
nected in parallel to a relay which can be used, for example, to operate a
marker pen on the B & K Level Recorder Type 2305. The output of this
relay is available at the OVERLOAD and FREQUENCY MARKING socket
on the rear panel of the instrument. The screwdriver operated switch at the
side of this socket should be in position "Overload".
Reference Oscillator
A reference oscillator is incorporated in the 2010 for calibration pur-
poses. The oscillator is operated by the push-button "Ref. 50 mV". It pro-
duces an accurate 50 mV sinusoidal voltage at 1000Hz. The amplitude
stability, frequency stability and distortion are better than 2%. A frequency
of 1 kHz was chosen since the weighting networks have no attenuation at
this frequency.
The signal from the input section is either filtered, internally or external-
ly, or carried directly to the output section of the measuring amplifier.
5.2.2. Output Section
A block diagram of the output section is shown is Fig.5.3.
41
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