Service manual

4
3. INSTALLATION
3.1. GENERAL
The 584 power requirements must be furnished
from a NIM-standard bin and power supply such as
the ORTEC 4001/4002 Series. The bin and power
supply into which the 584 will normally be installed
for operation is designed for rack-mounting. If the
equipment is rack-mounted, there must be
adequate ventilation to prevent any localized
heating in the 584. The temperature of equipment
mounted in racks can easily exceed the maxi mum
limit of 50 C (323 K) unless precautions are taken.
3.2. CONNECTION TO POWER
Turn off the bin power supply before inserting or
removing any modules. To be sure of proper
operation, check the dc voltage levels of the power
supply after all modules have been installed in the
bin. ORTEC bins and power supplies include
convenient monitoring test points on the power
supply control panel.
3.3. INPUT CONNECTION
The 584 Input connector on the front panel accepts
negative input pulses. This input is terminated
internally in 50 . Connect the source of negative
input signals to this connector through a 50
coaxial cable.
3.4. OUTPUT CONNECTIONS
The primary outputs of the 584 are the NIM-
standard fast negative logic signals that are
provided through the front panel BNC connectors
marked Timing Outputs. The circuits driving these
two connectors are independent so that the Timing
Outputs can be used independently. Each negative
NIM output that is used must be terminated in 50 ,
and 50 cable must be used for the interconnec-
tions. Unused outputs need no termination.
The Positive Output on the front panel provides a
NIM-standard slow positive pulse that is initiated
simultaneously with the Timing Outputs on the front
panel. This output can be used with instruments
such as counters or ratemeters which require
positive input signals. The interconnection can be
made with 93 cable, terminated in 100 or more,
in most applications.
3.5 CONSTANT-FRACTION DELAY CABLE
The constant-fraction time derivation circuit is not
complete until an external length of 50 cable has
been connected between the two Delay connectors
on the front panel. The total constant-fraction
shaping delay is equal to the external constant-
fraction shaping delay, t , plus approximately
d(Ext)
0.8 ns.
One important use of the 584 is in fast timing or
counting experiments with scintillators and
photomultiplier tubes (PMTs). ln these applications,
the total constant-fraction shaping delay, t , is
d(Tot)
selected so that the zero crossing of the bipolar
timing signal occurs after the attenuated, undelayed
portion of the constant-fraction signal has reached
its maximum amplitude. Thus the zero crossing
occurs at the same fraction of the input pulse height
regardless of the amplitude of the input signal.
Selection of the constant-fraction shaping delay for
best timing performance with a given scintillator
and PMT is usually accomplished experimentally.
A useful empirical formula for the initial trial
selection of the external shaping delay is
t 1.1 t 0.8 ns,
d(Ext) r
where t is the 10% to 90% rise time of the anode
r
pulses. Walk adjustment can then be accomplished
while observing the delayed CF Mon signal on a
fast oscilloscope which is triggered externally by a
timing output signal from the 584.
An alternate, more accurate method is to make
repeated measurements of the timing spectra of a
timing coincidence system: first, for small (10%)
changes in the initial selection of the external
shaping delay, and second, for small changes in the
Walk adjustment.