PDT10A and PDT20A compact
neutron monitoring modules designed for high radiation environments connect
directly He-3 detectors. Each instrument contains a precision wide band charge
sensitive pre-amplifier followed by an amplifier, wave shaping and discriminator
circuits. When connected to He-3 detectors, these instruments detect the
presence of charged-sensitive particles. Our focus is to create a compact (1
inch diameter), simple to use, high performance instrument with a variety of
instrument has an analog monitoring test point allowing direct monitoring
of amplified charged events using an oscilloscope. A twelve turn
trim pot is available to finely tune the amplifier sensitivity to the
desired level so you can obtain a good HV plateau for your application.
addition, when a charged event is detected, a TTL OUT pulse is produced.
TTL OUT pulse width is adjustable from 40nSeconds to 500nSeconds.
instrument contains a TTL IN input allowing you to sum outputs from other
modules in a system. This allows quick and easy interconnection from 1 to
over 100 detectors for digital pulse counting measurements.
instrument contains a threshold control trim pot allowing you to control
the discriminator level for your application.
PDT20 is equivalent in performance to the PDT10A but additionally contains
a high performance high voltage generator that can be adjusted over a
range of 0-2200 volts.
PDT20 contains a HV MON test point that allows you to measure and adjust
the high voltage setting.
PDT10 is compact, housed in 1 inch diameter aluminum with a length of 1.5
PDT20 is enclosed in 1 inch diameter aluminum with a length of 3 inches.
PDT10A and PDT20A modules
have been designed for extended temperature and vibration environments. The
products have been tested at temperatures ranging from 0-170 degrees Centigrade
including vibration to 70g from 2Hz to 10kHz.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 10A and 20A modules
provide customers with considerable versatility. This application note provides
users with a basic understanding in the proper using of the 10A and 20A
PDT10A and PDT20A
You can purchase PDT10A and PDT20A modules with a variety
of connector interfaces for He-3 detectors. Modules have the capability to
connect directly to Helium-3 gas filled detectors that us HN, MHV, or SHV type
of connectors. If necessary, you can even cable directly from the PDT10A modules
to the detector using a high voltage cable with the 10A-C.The 10A-C uses a
miniature high voltage connector rated for 5000 volts allowing cable connection
to the detector. PDT can provide the cable with the desired connectors for your
application. Please contact us and we will discuss the cable length, type of
connection on the detector to help simplify your setup. When using the 10A-C it
is important that the cable length is kept as small as possible to minimize both
capacitance and noise. Most PDT modules connect directly to He-3 detectors to
minimize capacitance with the added advantage of providing a more ruggedized
interface to He-3
interface to He-3
interface to He-3
interface to He-3
20A High Voltage
The high voltage generator of the PDT 20A are available in
three configurations, 20A (standard),20F (fixed) or 20R (Remote).Each high
voltage configuration still allows you to select the one of three detector
interface connections, either HN, MHV or SHV. If you desire to order the
standard PDT20A,the proper selection would be PDT20A-HN, if however your
application requires you to interface to a detector that uses an SHV connector
and you want a fixed HV supply at 1400 Volts, then the proper selection would be
PDT20F-SHV @1400 Volts.
HV variable 0-2200 Volts
HV set 100-2100 with +/-100V
HV controlled via external D.C. voltage
The 10A and 20A 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 (adjustable available only on the 10A and
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
and 20A 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 fed 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 20A 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.
Proper HV, Gain and Threshold Setting - Obtaining a Good HV Plateau Curve
Use a HV plateau to determine the proper HV setting
for a Helium-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 also to the high voltage bias setting recommended by the
Both PDT10A and PDT20A
products provide three mechanisms to control the HV Plateau: HV bias setting,
gain setting and threshold seeing. The HV bias control is not available on the
PDT10A series but is controlled indirectly via the PDT20A if the HV bias input
is applied to the PDT20A.Both the 10A and 20A provide gain and threshold setting
capability. The gain setting control is available on the top of the module where
the cables originate. The gain control uses a 12 turn trim pot located beneath
the hole labeled "Gain ADJ ".The threshold setting is on the side
located beneath the decal. The decal does not identify the hole location because
users are not generally encouraged to change the setting. The mention of this
trim pot is available for the more sophisticated user. The threshold trim pot is
a single turn adjustment. The threshold setting is set at the factory to provide
a minimum of .015pC sensitivity. You have the option of either increasing or
decreasing the sensitivity default setting. The gain setting allows the
sensitivity to be varied by about a factor of 20:1.If the minimum threshold
sensitivity is set to .015pC via the threshold adjustment, you can then finely
tune the gain adjustment to a final sensitivity range between .015pC to
.3pC.Combining both the gain and threshold adjustments, the sensitivity can be
controlled over a range of .005pC to 2pC,a very large control
range.NOTE:PDT100/110/120 instruments provide only one sensitivity control
adjustment that is referred to at the "THRES ADJ " control trim pot.
Routing: Digital Summing
10A and 20A modules can be daisy-chained by connecting
the "TTL OUT " pulses from one module 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
The "TTL OUT
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.On both the 10A and 20A modules,
the pulse width can be varied from 40nSec to 500nsec by changing the setting of
the trim pot located on the side of the product just beneath the hole labeled
"PW ADJ ".
Modules for 10A/20A Allow both Analog and Digital Summing
A support module can be purchased to provide analog
summing of the signal from detectors. Charged events are collected by the 12A
support module and routed to the 10A or 20A module for amplification via the
cable labeled "DETECTOR PULSE ".Each 10A or 20A module can support
inputs from two to four support 12A modules. This interconnection scheme reduces
cost, simplifies cabling, allowing a series of detectors to be operated as a
single unit. Support (12A)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
module contains two "DETECTOR PULSE " cabled connectors allowing
modules to be daisy--chained in a analog fashion. Such a scheme allows both
analog and digital pulse summing. Support modules channel the analog pulse from
the detector to the 10A/20A amplifier via a cable that connects to the
"DETECTOR PULSE " connector. Digital summing occurs by connecting the
"TTL OUT " to the "TTL IN " between modules as described
above in the Digital Pulse Routing section. Typically, two to three 12A support
modules would be used for each 10A or 20A module.
20A Series HV
The 20A series modules provide an equivalent feature
set to the 10A modules but additionally contains an adjustable high voltage bias
supply changeable 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.
Voltage Bias Supply:0 Volt to 2200 Volt Adjustment Span
The 20A 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 ground.
The internal bias voltage
(high voltage generator) of each 20A series module channels its HV output to two
connectors, the "HV OUT " SHV cabled 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 20A as the biasing of the 10A series modules, or other applications
that might additionally require a HV bias supply. For low count rates, a 20A
module can support several 10A modules (4-8).For high count rates (>50K
counts/sec), a 20A module supports three 10A modules.
20A series modules are
available in three basic configurations,20A (standard),20F (Fixed Voltage), and
20R (Remote control). Each configuration can be purchased with an HN, SHV or MHV
interface to the He-3 detector. The 20A-HN 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 20F is nearly equivalent to the
20A,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 20F 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.
20A and 20F
Both 20A and 20F modules provide access to a internal
trim pot via a hole labeled "HV ADJ "located on side of the module. A
test point labeled "HV MON " allows you to monitor the high voltage
setting as the trim pot is adjusted. When adjusting a 20A module, as you turn
the trim pot 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 " cabled SHV connector spanning 0 to 2200 volts. The same
approach is used for the 20F,although the voltage adjustment span is greatly
limited (+/-100 volts). All 20A 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 a DMM meter, it is best to connect the LO (or ground) of
the 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.
The 20R 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 20R 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 20R,best performance can
be achieved only with use of a low noise and highly stable precision DC voltage.
It is best to use a DC source that provides 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 20R 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 20R 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 20A 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
stability performance. (After the bias voltage is set to the desired value,
neutron pulse monitoring begins.)
Due to the wide variety of applications,10A and 20A
modules are customized to support many of these needs. Some of the customized
applications provided to our customers are stated 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 20A,modules can be ordered from the factory to interface to gas filled
detectors using HN connectors, SHV or MHV connectors or direct cables.
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
the Data Sheet for the PDT10 and PDT20 Series Modules
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