1
ORTEC MODEL 480
PULSER
1. DESCRIPTION
1.1. GENERAL
The ORTEC 480 is a modular pulse generator
designed to simulate the detection of a nuclear
particle reaction in a solid-s t ate or scintillation
detector. The unit features good stability as a
function of temperature and time, 1% overall
accuracy, and a front panel CaI control which
enables it to be calibrated to read directly in terms of
equivalent energy deposited in a detector. The
pulses are generated with a mercury relay switch
whose frequency is the frequency of the ac line. The
inst rument has an internal stable reference voltage
that is effectively independent of the modular power
supply and ac line voltage changes. The unit has
four attenuator toggle switches for a maximum
attenuation of 1000:1. The direct output precedes
the att enuator switch and provides a means of
stable oscilloscope triggering. Two terminators are
provided with the 480: a charge terminator and a
100
Ù
voltage terminator. The use of a charge
terminator allows the voltage output pulse of the 480
to be converted to a charge pulse for subsequent
amplification by a charge-sensitive preamplifier. A
holder is provided on the rear panel to store the
charge terminator when it is not in use.
This inst rument is designed to meet the
recommended interchangeability standards of US
DOE Report TID-20893 (Rev.). An ORTEC
4001/4002 Series Bin and Power Supply provides all
nec es sary power through the rear module power
c onnector. The ORTEC 400 Series is designed so
that it is not pos s ible to overload the Bin Power
Supply with a full complement of modules in the Bin.
However, this may not be true when the Bin contains
modules of other than ORTEC design. All signal
levels and impedances are compatible with other
modules in the ORTEC 400 Series.
1.2. BASIC FUNCTION
The 480 provides output pulses that are
characterized by a fast rise time and a slow
exponential decay time. These pulses are generated
by charging a capacitor to an int ernal reference
voltage through a mercury relay and then
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 nsec 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
Ù
. The direct output
provides a trigger pulse that allows the stable
synchronization of an oscilloscope or ot her timing
equipment from a signal which does not vary in
amplitude as the attenuators are switched in and
out. The attenuated out put has a series of pi-
attenuators between the mercury-wetted relay
contacts and the output BNC connector. This allows
the attenuation of the signal 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.
Since the pulses are generated from an
electromechanical device (the mercury-wetted
relay), the frequency of the pulse generator is
correspondingly rather slow, i.e., the frequency of
the ac line.
Summary of Contents for ORTEC 480
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