The basic voltage range of the servo systems is 0 to 5 millivolts for the Y
axis and 0 to 7. 5 millivolts for the X axis for full scale travel. Operation
with greater voltages is obtained by means of a step attenuator inserted be-
tween the input terminals and the balance circuit. Each range step may be
made continuously variable by operation of a transfer switch which inserts
a variable potentiometer and extends that range to about five times its fixed
value. The range position is selected so that the amplitude of the input data
will be within the travel limits of the instrument. Included in the input cir-
cuit is a variable filter which minimizes undesirable noise and ripple dis-
turbances in the input signals.
After passing through the input filter and attenuator, the input signal is ap-
plied to the balance circuit, where it is cancelled by an internally supplied
opposing voltage derived from a reference cell and potentiometer. Under
these conditions there is no signal output from the balance circuit and the
servo system is at rest. When the input signal changes to a new value it is
no longer canceled in the balance circuit and the unbalance voltage, or error
signal, is applied to the chopper where it is converted to a 60-cycle form.
The AC output of the chopper is amplified and applied to the control winding
of a two-phase servo motor. The motor is mechanically coupled to the bal-
ance circuit potentiometer and thus changes the balance voltage until it again
cancels the new value of input signal. If the input data is constantly changing
at rates within the capabilities of the instrument, this rebalancing action is
continuous. Thus the positions of the balance circuit potentiometers and of
the pen and carriage, to which they are coupled, are always directly propor-
tional to the amplitudes of the signals at the respective input terminals.
The use of the X-axis with a variable input voltage or as a sweep circuit is
selectable by a function switch on the rear panel. Operation of the time base
is dependent on the fact that the charging current taken by a condenser will
assume a constant value when the charging voltage is controlled so as to in-
crease at a uniform rate. Existing facilities of the recorder are utilized to
apply a linearly increasing voltage to the X-axis servo amplifier causing the
pen to advance at a uniform rate in total sweeps dependent on the constants
switched into the circuit. These constants are so selected during manufac-
ture that the time required for full scale pen travel equal, in seconds, the .
numerical values of the millivolt steps of the X-axis range selector.
The Model 2s Autograf consists of three major assemblies:
novable aluminum case.
>ase plate assembly, mounting the amplifier chassis (which contains
me chopper, two high gain amplifier channels and a power supply for the
amplifier), the various input plugs (mounted on a side panel), the refer-
ence cells, the primary power control panel, and the vacuum pump.
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ACEC
