Proper Use of the
PDT100,PDT110,and PDT120/PDT122 Neutron Pulse Monitoring Modules - 100A,110A,120A
compact neutron monitoring modules designed for high radiation environments
connect directly to neutron counters allowing quickly and easy interconnection
from 1 to over 100 detectors for digital pulse counting measurements. This new
generation of neutron monitoring modules allow new systems to be quickly
configured and existing detector instruments to be easily upgraded. The charge
sensitive amplifiers are designed for Helium-3,boron loaded, fission chamber,
alpha and proton-recoil neutron detector operation. Multiple modules can be
easily interconnected providing a single digital counting channel that will
process pulse rates exceeding 5 MHz. Engineered in a compact ruggedized aluminum
housing that interfaces directly to gas filled detectors, these modules provide
an efficient clean solution in difficult environments.
Series 100A,110A and 120A
modules provide customers with considerable versatility. This application notes
provides users with a basic understanding in the proper using of the 100A ,110A
,120A and 122A instrument.
100A Series Bias Supply
- The 100 series
modules provide an equivalent feature set to the 110A modules but additionally
contains an adjustable high voltage bias supply settable from 0 Volts to 2200
Volts. All modules are configured at the factory for power supply (+Vcc) setting
of either +5 volt operation (default) or +12 volt operation.
High Voltage Bias
Supply: 0 Volt to 2200 Volt Adjustment Span - The
100A produces high voltages and safety precautions should always be administered
when using these instruments. Before applying power, make sure all cables are
properly attached and modules are properly fastened to detectors. Do not apply
power until modules are properly configured in your application ensuring that
the power supply and all cables and detectors are properly connected to earth
The internal bias voltage
(high voltage generator) of each 100A series module channels its HV output to
two connectors, the "HV OUT " SHV connector located on the top of the
module and to the HV PIN ((with suitable filtering applied) located at the
bottom of the module which attaches to the detector. The HV PIN interfaces to
the gas filled detector and is not available to the operator once connected to a
detector. Having the bias supply available at the SHV connector allows customers
to use the 100A as the biasing of the 110A,120A,122A series modules, or other
applications that might additionally require a HV bias supply. For low count
rates, a 100A module can support several 110A modules (4-8).For high count rates
(>50K counts/sec), a 100A module supports three 110A modules.
100A series modules are
available in three basic configurations,100A (standard),100F (Fixed Voltage),
and 100R (Remote control). The 100A is the standard configuration containing an
internal twelve turn variable resistor (trim pot) allowing the user control of
the high voltage bias supply over a range of 0 to 2200 volts by simply changing
the setting on the trim pot. The 100F is nearly equivalent to the 100A,however
the trim pot adjustment span is +/- 100 volts about a preset fixed voltage set
at the factory. The fixed voltage is determined by the user and units can be
shipped with any preset voltage setting between 100-2100 volts. The advantage of
the 100F is improved noise, temperature and mechanical vibration performance.
Since the adjustment range is +/-100 volts, setting the voltage to .1 volt
resolution (i.e..1700.1 Volt!) is easily achievable.
100A and 100F Modules -
Both 100A and 100F
modules provide access to a internal trim pot via a hole labeled "HV ADJ
" located on top of the module. A test point labeled "HV MON "
allows users to monitor the high voltage setting as the trim pot is adjusted.
When adjusting a 100A module, as the trim pot is adjusted from its lowest level
to its highest level (turning the trim pot clockwise using an adjustment tool) a
voltage at the "HV MON " test point is observed that spans from 0 to
2.2 volts resulting in a voltage at the "HV OUT "SHV connector
spanning 0 to 2200 volts. The same approach is used for the 100F although the
voltage adjustment span is greatly limited (+/-100 volts). All 100A units are
shipped from the factory with an "HV OUT " setting of 1700 volts which
corresponds to a voltage of 1.7 volts at the "HV MON " test point.
When monitoring the "HV MON " test point with your DMM meter it is
best to connect the LO (or ground) of your meter to the 100 module ground itself
(via one of the connector cases) rather than at the power supply source ground.
This avoids additional errors resulting from ground current returns. Connecting
the meter LO to one of the connector grounds is best achieved using a alligator
clip since a ground test point is not provided on the module itself.
100R Modules - The
100R provides remote operation, allowing the user to control the high voltage by
applying a precision DC voltage from 0 to 2.2 volts to produce an high voltage
output of 0 to 2200 volts. The 100R is shipped with an permanently attached
cable (for the remote operation) terminated to a BNC. To control the bias supply
voltage, apply a precision DC voltage to the BNC. Be aware that the HV generator
of the 100 series is engineered for low noise and excellent long term stability
operation. When using the 100R,best performance can only be achieved with use of
a low noise and highly stable precision DC voltage. It is best to use a DC
source that provide 50 part per million (50 PPM) stability performance and the
noise performance should be in the 10 PPM region. Generally, power supply
sources will not provide suitable results.
For safety, if the remote
cable is not attached to a source, the 100R is designed to produce a low voltage
(near zero volts) at "HV OUT ".The input resistance of the remote
cable is 10K ohms, high enough that loading of your DC source should not affect
performance. The input resistance of the cable alternatively provides suitable
protection if you happen to connect the remote cable to a voltage greater than
the power supply voltage (+Vcc). The 100R will not be damaged for voltages up to
20 volts applied to the remote cable.
In your application, after
the cables and detector(s) have been properly attached to the 100A series
modules, apply power to the module. Monitor the "HV MON " test point
and adjust either the internal trim pot or the remote DC voltage to obtain the
desired "HV OUT " voltage. Use a 5-1/2 digit voltmeter to obtain good
monitoring information and allow you to simultaneously monitor noise and
Basic Neutron Pulse
Counting - The
100A,110A and 120A series of products provide accurate neutron pulse counting in
a compact user friendly package. A 50nsec digital pulse from the connector labeled
"TTL OUT " is produced each time a bipolar pulse (neutron event)
exceeds the discriminator threshold. The 50nsec adjustable digital pulse
(adjustability available only on the 110A and 120A modules) is achieved via a
variable resistor located beneath a hole labeled "PW " on top of each
module. A light-emitting-diode (LED) emits a flash, providing visual indications
of detected pulses exceeding the discriminator setting. Control of sensitivity
or threshold occurs via a 12 turn trim pot located beneath the hole identified
as "THRES ADJ " on top of the module.
Observation - 100A,110A
and 120A modules contain analog pre-amplification and bipolar amplifier
electronics for pulse generation of detector charge events. The amplifier
produces a 0 to 1 volt bipolar pulse which is feed to the "PULSE MON "
test point. The output impedance of the "PULSE MON " test point is 10K
ohms providing effective monitoring using an oscilloscope and impedance loading
of the test point will not affect the performance of the amplifier. Amplifier
gain is set with the "THRES ADJ " trim pot as identified above.
Using an oscilloscope,
observe the bipolar amplifier pulse at the "PULSE MON " test point. To
simplify the monitoring of the analog pulse, apply the "TTL OUT "
digital pulse to the external trigger of the oscilloscope. Remember that each
time a pulse is detected by the discriminator, the LED flashes. The LED provides
a good troubleshooting aid when monitoring neutron events. With the "TTL
OUT " connected to the external trigger of the oscilloscope, cable the
"TTL OUT " to the input of a counter and begin counting pulses. Using
the 100A module, you can easily increase and decrease the HV supply observing
the change in the gain of the amplifier pulses. Use the HV bias as the amplifier
course gain adjust and use the "THRES ADJ " trim pot as the amplifier
fine gain adjust.
Determining the Proper
HV Setting: Obtaining a Good HV Plateau Curve - Use
a HV plateau to determine the proper HV setting for a Helum-3 neutron counter.
To generate a plateau curve, collect a set of scalar counts ("TTL OUT
" pulses) at fixed time intervals at a series of voltage steps. Plot the
counts versus HV steps producing a plateau curve. The HV region above the knee
of the plateau curve is generally where the detector is operated. Refer to the
voltage setting recommended by the detector manufacturer.
Digital Pulse Routing:
Digital Summing - 100A,110A,and
120A modules can be daisy-chained by connecting the "TTL OUT " pulses
from one modules to the "TTL IN " inputs of another module. This
connection sums the digital pulses in an OR ’ed fashion allowing several
modules to be daisy-chained, providing a single pulse counting channel. A module
interconnection kit (CKB) provides cables and connectors for daisy-chaining
The "TTL OUT
" Pulse - The
"TTL OUT " uses a 50 ohm source and has been tested with good results
using cable lengths in excess of 100 meters. The pulse width is preset at the
factory to 50nS.However,on the 110A,and 120A modules, the pulse width can be
varied from 40nSec to 500nsec by changing the setting of the trim pot located
beneath the hole labeled "PW ADJ " on the top of the modules.
Analog and Digital Summing - The
120A performs the same functions as a 110A or 100A modules related to neutron
monitoring but is designed to operate with the 122A support module, a charge
collection module.122A modules are easy to setup and operate. Charge events are
collected by the 122 module and routed to the 120A module for amplification via
the connector labeled "DETECTOR PULSE ".Each 120 module can support
input from two to four 122A modules. This interconnection scheme reduces cost,
simplifies cabling, allowing a series of detectors to be operated as a single
120A unit.122A modules have no adjustments, do not require a +Vcc (DC power
supply) input, and provide the lowest cost solution, requiring only "HV IN
" and "DETECTOR PULSE " connections. Note that each 122A module
contains two "DETECTOR PULSE " connectors allowing 122A modules to be
daisy--chained in a analog fashion. Such a scheme allows both analog and digital
pulse summing. The 122A support module channels the analog pulse from the
detector to the 120A via a cable that connects to the "DETECTOR PULSE
".Digital summing can occur simultaneously by summing the "TTL OUT
" to the "TTL IN " between 120A modules as described above in the
Digital Pulse Routing section. Typically, two to three 122A modules would be
used for each 120 module.
Factory Options - Due
to the wide variety of applications,100A,110A,and 120A modules are customized to
a wide variety of needs. Some of the customized applications provided to our
customers are state below. These modules provide enormous versatility, and can
be customized to your application needs.
have requested cable options used to replace the test points. Having a
cable replace the "PULSE MON " and or the "HV MON "
allows users to more simply monitor the analog signal of the neutron event
or the HV voltage by connecting directly to their monitoring equipment.
and 122A modules can be ordered from the factory to interface to gas
filled detectors using HN connectors, SHV, or MHV connectors or direct
modules have been designed for extremely high radiation environments in
excess of 100Mrad.
power customized modules are available for applications requiring
extremely low power. For +5 Volts operation, supply current less than 2mA
are available. For +15 Volt operation, supply current less the 1mA are available.
are designed to be used in unison. The PDT120A is
equivalent to the PDT110A, but includes a dedicated
integrated cable allowing the PDT120A module to interface
directly to the "DETECTOR PULSE"
connector of the PDT122A. Several PDT122A instruments
interface to a single PDT120A module, providing users
with a simple, cost-effective approach for multi-detector
monitoring. The cost of each PDT122A module is about half
the cost of a PDT120A.
A typical and recommended
application uses two PDT122A modules for each PDT120A
module. Each PDT122A module has two connectors labeled DETECTOR
PULSE. The cable from the PDT120A module connects
directly to one of the PDT122A connectors labeled DETECTOR
PULSE. A second PDT122A module connects to
the-remaining DETECTOR PULSE connector. If
desired, additional PDT122A modules can be cascaded for
analog summing. Having two DETECTOR PULSE
connectors on each PDT122A allows cascading of the analog
signals from detector to detector through the PDT122A
modules. As PDT122A modules are added, the input to the
charge sensitivity preamplifier is capacitively loaded.
To increase the sensitivity of the charge-sensitive
amplifier, adjust the "THRES ADJ"
In addition to the two DETECTOR
PULSE connectors, an SHV connector labeled HV IN
provides the input via the module to bias the detector.
Operationally, the PDT122A instrument capacitively
collects signals arising from neutron events in the
detector, and channels the signal through the DETECTOR
PULSE connector, through the cable to the
charge-sensitive preamplifier of the PDT120A module. The
PDT120A then processes the signal in a similar fashion to
the PDT110A. PDT122A modules contain only passive parts,
making them ideally suited to high radiation
are designed to be used in unison. The PDT120A is
equivalent to the PDT110A, supporting all of the feature
of the PDT110A, but with one additional feature: a
dedicated cable integral to the PDT120A module allows
direct connection to the "DETECTOR PULSE"
connector of the PDT122A. Several PDT122A instruments can
be interfaced to a single PDT120A module. The
PDT120A/PDT122A combination exits to provide users with a
simple, cost-effective approach for multi-detector
monitoring requirements. The cost of the PDT122A module
is considerably lower than cost of a PDT122A.
of using PDT122 modules
||PDT122A modules use only passive
components so it is ideally suited to high
||PDT122A modules require a power
supply, hence for large systems the power
requirements are reduced.
||PDT122A modules require only a
bias supply HV IN, and cables for routing
the DETECTOR PULSE signal to the PDT120A.
The cable requirements are simple.
A typical and recommended application
uses two PDT122A modules for each PDT120A module. Each
PDT122A module has two connectors labeled DETECTOR PULSE.
The integrated cable from the PDT120A module is connected
to one of the PDT122A connectors labeled DETECTOR PULSE.
The remaining DETECTOR PULSE connector is cabled to a
second PDT122A modules. If desired, additional PDT122A
modules can be cascaded, providing analog summing. Having
two DETECTOR PULSE connectors on each PDT122A allow
cascading of the analog signals from detector to
detector. As PDT122A modules are added, the sensitivity
of the charge-sensitive amplifier of the PDT122A will
likely need to be increased, since adding PDT122A modules
increases the capacitance at the detector head. When
PDT122A modules are ordered, a cable is included for
interconnecting between PDT122A modules. The PDT122A
module contains only passive parts and when connected
directly to a detector, provides an SHV connector to bias
the detector. The PDT122A collects signals arising from
neutron events to channel the signal via the cable to the
charge-sensitive preamplifier of the PDT120A modules.
Preamplifier, Amplifier and Discriminator
During operation, when a neutron event
occurs within the detector, the charge-sensitive
preamplifier captures the signal resulting from the
neutron event. The signal is further amplified,
integrated and differentiated and a TTL pulse produced by
the discriminator is delivered to the output connector
labeled "TTL OUT." PDT120A modules
provide additional versatility to the user by allowing
user control of both the amplifier sensitivity and pulse
width. Generally, the factory setting of the sensitivity
is sufficient to allow good HV plateau curves when 1800
volts is applied to the SHV HV IN input connector
using helium-3 neutron detectors. However, when other
detector types are used, or if the HV bias settings can
not be varied, PDT120A modules provide users the ability
to change the amplifier sensitivity easily, obtaining
good plateau results by simply adjusting a trimpot
labeled "THRES ADJ." The "TTL
OUT" digital pulse is adjusted over a range of
50nS to 500nS by varying the trimpot located beneath the
hole labeled "PW ADJ." Other features
that PDT120 modules provide are digital pulse summing, an
LED that provides visual indication of detected events,
and a test point labeled PULSE MON allowing users
to view the analog pulse at the output of the amplifier.
It is not uncommon that the TTL
OUT signal must drive coaxial cables that are in
excess of hundreds of meters. PDT series modules 100A,
110A and 120A provide either a standard "TTL
OUT" or a 50-ohm line drive to extended cable
Summing: Cascade Operation
Digital pulse summing allows users to
interconnect the digital pulses between PDT120A modules.
The TTL OUT pulse of one PDT120A module is cabled
into the TTL IN input connector of a second
PDT120A module. Each module sums the pulses of the TTL IN
with the pulses obtained from the detector it is
monitoring. If a TTL signal is not applied to the "TTL
IN" input connector, no summing action occurs.
The benefit of summing digital pulse is apparent by
requiring only one signal cable route to the neutron
coincidence counter. The TTL pulse width is factory set
and the user has the option of specifying a range between
the limits of 50nS and 500nS with a default of 50nS. The
amplifier sensitivity can be changed by the user but is
set at the factory to achieve good plateau results at a
bias voltage setting of 1800 volts when using helium-3
||Count Rate: >10M
count per second
||Pulse Pair Resolution:
+5 Volts operation: +4.75 to +6 Volts; For +12
operations: 9 to 18 volts.
counts: 30mA typ; 100Kcounts: 40mA
||Temperature: -55 to
85 Degrees Centigrade
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