Service manual

5
ORTEC modular instruments and multichannel
analyzers.
2.6. ELECTRICAL AND MECHANICAL
POWER REQUIRED +24 V, 55 mA; 24 V, 40
mA; +12 V, 70 mA;
12 V, 75 mA.
WEIGHT
Net 1.5 kg (3.3 lb).
Shipping 3.1 kg (7.0 lb.)
DIMENSIONS Standard single-width NIM module
3.43 × 22.13 cm (1.35 × 8.714 in.) per TID-20893
(Rev).
3. INSTALLATION
3.1. GENERAL
The 575A operates on power that must be furnished
from a NIM-standard bin and power supply such as
the ORTEC 4001A/4002A Series. The bin and
power supply is designed for relay rack mounting.
If the equipment is to be rack mounted, be sure that
there is adequate ventilation to prevent any
localized heating of the components used in the
575A. The temperature of equipment mounted in
racks can easily exceed the maximum limit of 50°C
unless precautions are taken.
3.2. CONNECTION TO POWER
The 575A contains no internal power supply and
must obtain the necessary dc operating power from
the bin and power supply in which it is installed for
operation. Always turn off power for the power
supply before inserting or removing any modules.
After all modules have been installed in the bin and
any preamplifiers have also been connected to the
Preamp Power connectors on the amplifiers, check
the dc voltage levels from the power supply to see
that they are not overloaded. The ORTEC
4001A/4002A Series Bins and Power Supplies have
convenient test points on the power supply control
panel to permit monitoring these dc levels. If any
one or more of the dc levels indicates an overload,
some of the modules will need to be moved to
another bin to achieve operation.
3.3. CONNECTION TO PREAMPLIFIER
The preamplifier output signal is connected to the
575A through the Input BNC connectors on the front
and rear panels. The input impedance is ~1000
and is dc-coupled to ground; therefore, the
preamplifier output must be either ac-coupled or
have approximately zero dc voltage under no-signal
conditions.
The 575A incorporates pole-zero cancellation to
enhance the overload and count rate characteristics
of the amplifier. This technique requires matching
the network to the preamplifier decay-time constant
to achieve perfect compensation. The pole-zero
adjustment should be set each time the preamplifier
or the shaping time constant of the amplifier is
changed. For details of the pole-zero adjustment
see Section 4.5. An alternate method is
accomplished easily by using a monoenergetic
source and observing the amplifier baseline with an
oscilloscope after each pulse under ~×2 overload
conditions. Adjustment should be made so that the
pulse returns to the baseline in a minimum amount
of time with no undershoot.
Preamplifier power at +24 V,
24 V, +12 V, and
12 V is available through the Preamp Power
connector on the rear panel. When the preamplifier
is connected, its power requirements are obtained
from the same bin and power supply as is used for
the amplifier, and this increases the dc loading on
each voltage level over and above the
requirements for the unit at the module position in
the bin.
When the 575A is used with a remotely located
preamplifier (i.e., preamplifier-to-amplifier
connection through 25 ft or more of coaxial cable),
be careful to ensure that the characteristic
impedance of the transmission line from the
preamplifier output to the 575A input is matched.
Because the input impedance of the 575A is
~1000
, sending-end termination will normally be
preferred; the transmission line should be series-
terminated at the preamplifier output. All ORTEC
preamplifiers contain series terminations that are
either 93
or variable; coaxial cable type RG-62/U
or RG-71/U is recommended.