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.
||Count Rate: >10M
count per second
||Pulse Pair Resolution:
+4.75 to +6 Volts
||Operating current: No
counts: 30mA typ; 100Kcounts: 40mA
||Temperature: -55 to
85 Degrees Centigrade
||Warranty: 1 Year
||Maximum Bias Voltage:
+/-1volts/hour, +/-2volts/day, +/-10V/year.
via 0-2.2Volt DC reference or Internally via
||Maximum Bias Current:
||Noise: 50mVrms: 10Hz
||Test Point Monitor: HV
||Monitor Volts: .1%
of output; example, 2000 volts at HV OUT will
register 2 volts at test point
0-2000 volts: .5 seconds. 2000-0 volts: 30
PDT100A modules have three input
connectors: Detector Pin,
"TTL IN," and "+Vcc."
Characteristics at the Detector Pin
at bottom of module and connects directly to HN
Model PDT100A has a nominal threshold referred to
the input of .02pCoulombs. For increased
sensitivity, contact the factory for desired
specifications. For monitoring low level events,
the threshold can be increased five-fold through
a special order from the factory.
||Threshold Control: Control
variability is 20:1 using a 12-turn trimpot
located beneath the hole labeled "THRES
ADJ" on the module top.
25 degree Centigrade, 0 to 50 degrees Centigrade.
||Threshold Supply Voltage
Coefficient: -1%/Volt typically
||Detector Pin Protection: Input
detector pin is protected to 3000 volt spikes if
the total applied energy is less than .6µJoules
(3000 volts discharged by 200pF capacitor)
Characteristics at "TTL IN" Input
||Input Name: "TTL
IN" as indicated on the top decal.
||Connector Type: Micro-coax
female receptacle (miniature snap-on type).
||Signal Characteristics: TTL
TTL signals applied to this input are logically
OR'ed with the signal that is measured at the
detector pin. If no signal is applied (the input
is left open), no summing action occurs.
Connecting +5V to this input will inhibit pulses
from the "TTL OUT" connector.
||Maximum Count rate:
Characteristics at "+Vcc" Input (Power Input)
||Input Name: "+Vcc
" as indicated on the top decal.
||Connector Type: SMB
female receptacle (snap-on type).
||Signal Characteristics: Power
input for the PDT100A accept +5 volts (+4.75 to
6.0 volts) only.
||Supply Current: Typically
150mA for zero count rates, and for count rates
in excess of 100,000 measured by the detector
pin, the supply current is typically 160mA.
"TTL OUT" Connector
||Output Name: "TTL
OUT" as indicated on the top decal.
||Connector Type: SMA
female receptacle (screw-on type).
TTL output matched to 50 ohm characteristic
impedance which has been designed to drive coax
cables of long lengths, in excess of 100 meters.
If driving long cables is not an issue, the
standard TTL out driver can be ordered, which
will reduce the power requirements.
The "TTL OUT" signal either connects
directly to a coincidence counter or can be
connected to the "TTL IN" of another
PDT100A module for cascaded operation.
||Pulse Resolution: Pulse
pair resolution is 500nS.
||Amplifier Count Rate: Maximum
recommended count rate for accurate resolution
should not exceed 1M counts.
Input protected to 3000 volt spikes with total
energy less than .6µJoules. (3000 volts
discharged by 200pF capacitor)
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