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1.1. GENERAL
The ORTEC 419 is a modular precision pulse
generator that simulates the detection of a nuclear
particle reaction in a semiconductor or scintillation
detector. The instrument features excellent stability
as a function of temperature and time, ±0.1%
overall accuracy, and a front-panel NORMALIZE
control so that it can be calibrated to read directly in
terms of equivalent energy deposited in a detector.
The 419 has a rise time control on the front panel to
simulate
the
charge
semiconductor detector. The pulses are generated
with a mercury-wetted relay whose frequency can
be selected by a front-panel switch to be either ac
line frequency or an internal 70-Hz oscillator. The
internal oscillator runs asynchronously from the line
frequency so that an experimenter can measure the
effects of ac hum in his linear system. An internal-
external reference voltage switch in the 419 allows
the experimenter to use either the highly stable
internal reference voltage or a wide-range external
reference voltage that he supplies. The external
reference voltage may be of an arbitrary
waveshape or an arbitrarily high voltage to a limit of
20 V. When used in the external mode, the external
voltage is sampled by the mercury relay and
subsequently applied to the output connector. The
unit has five attenuator toggle switches in a pi-
attenuator arrangement in the attenuated output
line. Maximum attenuation is 2000:1. The direct
output precedes the attenuator switch and provides
a means of oscilloscope triggering. Two terminators
are provided with the unit, a 100-
terminator and a charge terminator. The charge
terminator allows the voltage output pulse of the
419 to be converted to a charge pulse for
subsequent amplification by a charge-sensitive
preamplifier. When not in use, the charge
terminator can be stored in a holder on the rear
panel.
The 419 is a double-width NIM standard module,
per TID-20893 (Rev.). Its operating power is
ORTEC MODEL 419
PRECISION PULSE GENERATOR
1. DESCRIPTION
collection
time
in
voltage
S
1
obtained from an ORTEC 4002A Power Supply
through a 4001A modular Bin. The ORTEC 400
Series is designed so that it is not possible to
overload the Bin Power Supply with a full
complement of modules in the Bin. However, this
may not be the case when the Bin contains
modules other than those of ORTEC design. All
signal levels and impedances are compatible with
other modules in the ORTEC 400 Series.
1.2. BASIC FUNCTION
a
The output pulses provided by the 419 are
characterized by a fast rise time and a slow
exponential decay time. These pulses are
generated by charging a capacitor from a reference
voltage through a mercury relay and discharging
the capacitor through the switching action of the
mercury relay into a fixed resistive load. The use of
mercury-wetted relay contacts provides a very fast
rise time, typically less than 5 ns 10-90% rise time,
with an absolute minimum of contact bounce or
other perturbations of the waveform for the first few
microseconds. The output impedance of the pulse
generator on both the direct and attenuated output
is 100
. The direct output provides a trigger pulse
S
that synchronizes the oscilloscopes or other timing
equipment from a signal which does not vary in
amplitude as the attenuators are switched in and
out. The attenuated output has a series of pi-
attenuators between the mercury-wetted relay
contacts and the output BNC connector. This allows
the signal to be attenuated by a fixed amount,
depending upon the particular switch operated in
the series attenuator. The primary purpose of the
pulse generator is to simulate radiation detection
signals; therefore a rise time control is provided to
simulate the charge collection time in a semi-
conductor detector. Since the pulses are generated
from an electromechanical device (the mercury-
wetted relay), the frequency of the pulse generator
is correspondingly rather slow, approximately 70 Hz
when operated on INT. OSC. and at the frequency
of the ac line for the AC FREQ. position.
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