ORTEC 460 Service manual

Model 460
Delay Line Amplifier
Operating and Service Manual
Printed in U.S.A. ORTEC®Part No. 733320 1202
Manual Revision C

Advanced Measurement Technology, Inc.
a/k/a/ ORTEC®, a subsidiary of AMETEK®, Inc.
WARRANTY
ORTEC* warrants that the items will be delivered free from defects in material or workmanship. ORTEC makes
no other warranties, express or implied, and specifically NO WARRANTY OF MERCHANTABILITY OR
FITNESS FOR A PARTICULAR PURPOSE.
ORTEC’s exclusive liability is limited to repairing or replacing at ORTEC’s option, items found by ORTEC to
be defective in workmanship or materials within one year from the date of delivery. ORTEC’s liability on any
claim of any kind, including negligence, loss, or damages arising out of, connected with, or from the performance
or breach thereof, or from the manufacture, sale, delivery, resale, repair, or use of any item or services covered
by this agreement or purchase order, shall in no case exceed the price allocable to the item or service furnished
or any part thereof that gives rise to the claim. In the event ORTEC fails to manufacture or deliver items called
for in this agreement orpurchaseorder, ORTEC’s exclusiveliabilityandbuyer’s exclusive remedy shallbe release
of the buyer from the obligation to pay the purchase price. In no event shall ORTEC be liable for special or
consequential damages. Quality Control
Before being approved for shipment, each ORTEC instrument must pass a stringent set of quality control tests
designed to expose any flaws in materials or workmanship. Permanent records of these tests are maintained for
use in warranty repair and as a source of statistical information for design improvements.
Repair Service
If it becomes necessary to return this instrument for repair, it is essential that Customer Services be contacted in
advance of its return so that a Return Authorization Number can be assigned to the unit. Also, ORTEC must be
informed, either in writing, by telephone [[phone]] or by facsimile transmission[[phone]], of the
nature of the fault of the instrument being returned and of the model, serial, and revision ("Rev" on rear panel)
numbers. Failure to do so may cause unnecessary delays in getting the unit repaired. The ORTEC standard
procedure requires that instruments returned for repair pass the same quality control tests that are used for
new-production instruments. Instruments that are returned should be packed so that they will withstand normal
transit handling and must be shipped PREPAID via Air Parcel Post or United Parcel Service to the designated
ORTEC repair center. The address label and the package should include the Return Authorization Number
assigned. Instruments being returned that are damaged in transit due to inadequate packing will be repaired at the
sender's expense, and it will be the sender's responsibility to make claim with the shipper. Instruments not in
warranty should follow the same procedure and ORTEC will provide a quotation.
Damage in Transit
Shipments should be examined immediately upon receipt for evidenceof external or concealeddamage. Thecarrier
making deliveryshouldbenotifiedimmediately of any suchdamage, sincethecarrier isnormally liablefor damage
in shipment. Packing materials, waybills, and other such documentation should be preserved in order to establish
claims. After such notification to the carrier, please notify ORTEC of the circumstances so that assistance can be
provided in making damage claims and in providing replacement equipment, if necessary.
Copyright © 2002, Advanced Measurement Technology, Inc. All rights reserved.
*ORTEC®is a registered trademark of Advanced Measurement Technology, Inc. All other trademarks used
herein are the property of their respective owners.

iii
CONTENTS
WARRANTY ....................................................................... ii
SAFETY INSTRUCTIONS AND SYMBOLS ............................................... iv
SAFETY WARNINGS AND CLEANING INSTRUCTIONS ..................................... v
1. DESCRIPTION................................................................... 1
1.1. GENERAL ................................................................ 1
1.2. DUALOUTPUTS ........................................................... 1
1.3. POLE-ZEROCANCELLATION................................................. 1
2. SPECIFICATIONS ................................................................ 2
3. INSTALLATION .................................................................. 3
3.1. GENERAL ................................................................ 3
3.2. CONNECTIONTOPREAMPLIFIER............................................. 3
3.3. CONNECTIONOFTESTPULSEGENERATOR ................................... 4
3.4. CONNECTIONTOPOWER................................................... 4
3.5. SHAPINGCONSIDERATIONS................................................. 4
3.6. SELECTION OF PROMPT OR DELAYED OUTPUT ................................ 5
3.7. OUTPUTCONNECTIONSANDTERMINATINGCONSIDERATIONS ................... 5
4. OPERATING INSTRUCTIONS ....................................................... 5
4.1. INITIAL TESTING AND OBSERVATION OF PULSE WAVEFORMS .................... 5
4.2. FRONTPANELCONTROLS .................................................. 6
4.3. FRONTPANELCONNECTORS(AllTypeBNC) ................................... 6
4.4. REARPANELCONNECTORS................................................. 6
4.5. OPERATION WITH SEMICONDUCTOR DETECTORS .............................. 7
4.6. OPERATION IN NEUTRON-GAMMA DISCRIMINATION SYSTEM WITH STILBENE AND
LIQUIDSCINTILLATORS .................................................... 9
4.7. NEUTRON-GAMMA-RAYDISCRIMINATIONINPROPORTIONALCOUNTERS.......... 12
4.8. OTHEREXPERIMENTS..................................................... 13
4.9. REFERENCES............................................................ 15
5. CIRCUIT DESCRIPTION .......................................................... 16
6. MAINTENANCE................................................................. 18
6.1. TESTEQUIPMENTREQUIRED............................................... 18
6.2. PULSERMODIFICATIONSFOROVERLOADTESTS ............................. 18
6.3. PULSERTEST............................................................ 18
6.4. TROUBLESHOOTING ...................................................... 20
6.5. TABULATEDTESTPOINTVOLTAGESONETCHEDBOARD ....................... 21
6.6. FACTORY REPAIR ........................................................ 21

iv
SAFETY INSTRUCTIONS AND SYMBOLS
This manual contains up to three levels of safety instructions that must be observed in order to avoid
personal injury and/or damage to equipment or other property. These are:
DANGER Indicates a hazard that could result in death or serious bodily harm if the safety instruction
is not observed.
WARNING Indicates a hazard that could result in bodily harm if the safety instruction is not observed.
CAUTION Indicates a hazard that could result in property damage if the safety instruction is not
observed.
Please read all safety instructions carefully and make sure you understand them fully before attempting to
use this product.
In addition, the following symbol may appear on the product:
ATTENTION–Refer to Manual
DANGER–High Voltage
Please read all safety instructions carefully and make sure you understand them fully before attempting to
use this product.

v
DANGER Opening the cover of this instrument is likely to expose dangerous voltages. Disconnect the
instrument from all voltage sources while it is being opened.
WARNING Using this instrument in a manner not specified by the manufacturer may impair the
protection provided by the instrument.
CAUTION To prevent moisture inside of the instrument during external cleaning, use only enough liquid
to dampen the cloth or applicator.
SAFETY WARNINGS AND CLEANING INSTRUCTIONS
Cleaning Instructions
To clean the instrument exterior:
! Unplug the instrument from the ac power supply.
! Remove loose dust on the outside of the instrument with a lint-free cloth.
! Remove remaining dirt with a lint-free cloth dampened in a general-purpose detergent and water
solution. Do not use abrasive cleaners.
! Allow the instrument to dry completely before reconnecting it to the power source.

vi

1
ORTEC MODEL 460
DELAY LINE AMPLIFIER
1. DESCRIPTION
1.1. GENERAL
The ORTEC 460 Delay Line Amplifier is a nuclear
pulse amplifier that provides delay-line shaping for
all output pulses. It accepts input pulses of either
polarity from the preamplifier and expands their
amplitude by an adjusted gain factor within the
range from 3 through 1000. An integrating time
constant can be selected to shape the rise of the
input pulse as desired. Pole-zero cancellation is
adjustable to match the characteristic of the
preamplifier output.
1.2. DUAL OUTPUTS
Two output pulses are furnished for each input
pulse. One is positive unipolar and is single-delay-
line shaped; it can be furnished as either a prompt
or delayed output pulse. The other is bipolar with
positive polarity leading and is double-delay-line
shaped. Both of these output pulse shapes are
available through front panel connectors with an
output impedance of 1
S and through rear panel
connectors with an output impedance of 93
S .
The main use for the unipolar output pulses is for
energy measurements. For this application the 460
provides high counting rate capabilities, excellent
overload recovery, and dc adjustment of the output
baseline. The unipolar output is preferred for both
single-channel and multichannel analysis because
of its low noise characteristic.
The main use for the bipolar output pulses is for
timing measurements using baseline crossover as
the timing indication. Double-delay-line shaping
provides a precision time at the baseline crossover
point that is independent of the pulse amplitude.
1.3. POLE-ZERO CANCELLATION
Pole-zero cancellation is a method for eliminating
pulse undershoot after the first differentiating
network. The technique employed is described by
referring to the waveforms and equations shown in
Figs. 1.1 and 1.2. In an amplifier not using pole-
zero cancellation, the exponential tail on the
preamplifier output signal (usually 50 to 500
: s)
causes an undershoot whose peak amplitude is
roughly
undershoot amplitude =
differentiated pulse amplitude
differentiation time
preamplifier pulse decay time
For a 1-
: s differentiation on time and a 50- : s
preamplifier pulse decay time, the maximum
undershoot is 2% and decays with a 50-
: s time
constant. Under overload conditions, this
undershoot is often sufficiently large to saturate the
amplifier during a considerable portion of the
undershoot, causing excessive dead time. This
effectcanbereducedbyincreasingthepreamplifier
pulse decay time (which generally reduces the
counting rate capabilities of the preamplifier) or
compensatingfortheundershootbyusingpole-zero
cancellation.
In single-delay-line shaping, differentiation is
accomplished by subtracting a delayed replica of
the signal as shown in Fig. 1.1. The droop in the
input signal during the delay time makes this
subtraction imperfect, and a long under- shoot is
produced. A pole-zero cancellation eliminates this
undershoot by adjusting the amplitude of the
delayed signal as shown in Fig. 1.2.
Total preamplifier-amplifier pole-zero cancellation
requires that the preamplifier output pulse decay
time be a single exponential decay and matched to
the pole-zero-cancellation network. The variable
pole-zero-cancellation network allows accurate
cancellationforall preamplifiershavingdecaytimes
of 25
: s or greater. The network is factory adjusted
to 50
: s, which is compatible with all ORTEC FET
preamplifiers. Impropermatching of thepole-zero-
cancellation network will degrade the overload
performance and cause excessivepileup distortion
at medium counting rates. Improper matching
causes either an under-compensation (undershoot

2
1
Checked in accordance with methods outlined in "IEEE Standards No. 301, USAS N42.2," IEEE Transactions,
Vol NS-16(6) (December 1969).
is not eliminated) or an over-compensation (output
after the main pulse doesnot return to the baseline
and decays to the baseline with the preamplifier
time constant). The pole-zero adjust is accessible
from the front panel of the 460 and can easily be
adjusted by observing the baseline with an
oscilloscope while a monoenergetic source or
pulser having the same decay time as the
preamplifier under overload conditions is being
used. The adjustment should be made so that the
pulse returns to the baseline in the minimum time
with no undershoot.
2. SPECIFICATIONS1
PERFORMANCE
GAIN RANGE 7-position Coarse Gain selection
from 10 through 1000 and single-turn Fine Gain
control from 0.3 through 1; total gain is the product
of Coarse and Fine Gain settings.
SHAPING FILTER Front panel switch permits
selection of integration time constant with
J = 0.04,
0.1, or 0.25
: s (40, 100, or 250 nsec).
INTEGRAL NONLINEARITY
# 0.05%,
NOISE
# 20 : V rms referred to input using 0.25 : s
Integrate and maximum Gain of 1000;
# 25 : V for
Gain = 50;
# 60 : V for Gain = 10.
TEMPERATURE STABILITY
Gain 0.01%/°C, 0 to 50°C.
DC Level
# 0.l mV/°C, 0 to 50°C.
CROSSOVER WALK For constant gain, walk <±l
nsec for 20:1 dynamic range; <±2 nsec for 50:1;
<±2.5 nsec for 100:1. Crossover shifts <±4 nsec for
any adjacent Coarse Gain switch settings.
COUNT RATE STABILITY A pulser peak at 85%
of analyzer range shifts less than 0.2% in the
presence of 0 to 105random counts/sec from a
137Cs source with its peak stored at 75% of analyzer
range.

3
OVERLOADRECOVERYBipolarrecoverstowithin
2% of rated maximum output in less than 5 non-
overloadpulsewidthsfrom X500overload; unipolar
recovers in same time from X100 overload.
TIMEJITTER(50%Amplitude)En/(dv/dt).FWHM
= 29 psec for a Gain = 50 and Eo= 10 V; FWHM =
2.9 psec for a Gain = 50 and Eo= 100 mV.
DELAY LINES 1
: s standard J ; 0.25, 0.5, or 2.0 as
J available. Both delay lines have the same value.
CONTROLS
FINE GAIN Single-turn potentiometer for
continuously variable gain factor of X0.3 to X1.
COARSE GAIN 7-position switch selects gain
factors of X 10, 20, 50, 100, 200, 500, and 1000.
INPUT POLARITY Slide switch, sets input circuit
for either Pos or Neg input polarity.
PZ ADJ Potentiometer to adjust Pole-Zero
cancellation for decay times from 25
: s to 4 ,
INTEG Slide switch selects an integration time
constant of 0.04, 0.1, or 0.25
: s; for 0.04- : s
setting, amplifier rise time is <100 nsec.
DC ADJ Potentiometer to adjust the dc level for
single-delay-line shaped unipolar output pulses.
DELAY IN/OUT Slide switch on rear panel selects
either 1-
: s (In) or prompt (Out) timing for unipolar
output pulses.
INPUT
Accepts either polarity of pulses from preamplifier;
front panel type BNC (UG-1094A/U) connector;
maximum linear input 3.3 V; protected to 20 V; Zin=
1k
S , dc-coupled.
OUTPUTS
UNIPOLARPrompt or delayed withfull-scalelinear
range of 0 to +10 V; single-delay-line shaped;
baseline level adjustable to ±1.0 V; Zo<1
S , dc-
coupled, through front panel BNC (UG-1094A/U)
connector; Zo= 93
S , dc-coupled, through rear
panel BNC (UG-1094/U) connector.
BIPOLAR Prompt output with positive lobe
leading, double-delay-line shaped, with full-scale
linear range of 0 to 10 V; Zo<1
S , dc-coupled,
through front panel BNC (UG-1094A/U) connector;
Zo= 93
S , dc-coupled, through rear panel BNC
(UG-1094/U) connector.
PREAMP Standard ORTEC power connector for
matingpreamplifier; Amphenol type17-10090, rear
panel.
ELECTRICAL AND MECHANICAL
POWER REQUIRED
+24 V, 90 mA; +12 V, 85 mA;
-24 V, 90 mA; -12 V, 75 mA.
WEIGHT (Shipping) 4.25 lb (1.9 kg).
WEIGHT (Net) 2.25 lb (1 kg).
DIMENSIONS Standardsingle-widthmodule(1.35
by 8.714 in.) per TID-20893 (Rev.).
3. INSTALLATION
3.1. GENERAL
The 460 contains no internal power supply but is
used in conjunction with an ORTEC 4001/4002 Bin
and Power Supply and is intended for rack
mounting; therefore if vacuum tube equipment is
operated in the same rack with the 460, there must
be sufficient cooling by circulating air to prevent
localized heating of the all-semiconductor circuitry
used throughout the 460. The temperature of
equipment mounted in racks can easily exceed
120°F (50°C) unless precautions are taken.
3.2. CONNECTION TO PREAMPLIFIER
The preamplifier output signal is connected to the
460 through the BNC connector on the front panel
labeled Input. The input impedance is 1000
S and

4
is dc-coupled to ground; therefore the output of the
preamplifier must be either ac-coupled or have
approximately zero dc voltage under no-signal
conditions.
The 460 incorporates Pole-zero cancellation in
order to enhance theoverload characteristics of the
amplifier. This technique requires matching the
network to the preamplifier decay time constant in
order to achieve perfect compensation. The
network is variable and factory adjusted to 50 µs to
approximatelymatchallORTECFETpreamplifiers.
If other preamplifiers or more careful matching is
desired, the adjustment is accessible from the front
panel. Adjustment is easily accomplished by using
a monoenergetic source and observing the
amplifier baseline with an oscilloscope after each
pulseunderoverloadconditions.Adjustmentshould
be made so that the pulse returns to the baseline in
a minimum of time with no undershoot.
Preamplifier power of +24 V, +12 V, -24 V and -12
V is available on the preamplifier power connector.
When using the 460 with a remotely located
preamplifier (i.e., preamplifier-to-amplifier
connection through 25 ft or more of coaxial cable),
care must be taken to ensure that the characteristic
impedance of the transmission line from the
preamplifier output to the 460 input is matched.
Since the input impedance of the 460 is 1000
S ,
sending end termination will normally be preferred;
i.e., the transmission line should be series-
terminated at the output of the preamplifier. All
ORTEC preamplifiers contain series terminations
that are either 93
S or variable; coaxial cable type
RG-62/U or RG-71/U is recommended.
3.3. CONNECTION OF TEST PULSE
GENERATOR
Connection to the 460 Through a Preamplifier
The satisfactory connection of a test pulse
generator such as the ORTEC 419 or equivalent
depends primarily on two considerations: the
preamplifier must be properly connected to the 460
as discussed in Section 3.2, and the proper input
signal simulation must be applied to the
preamplifier. To ensure proper input signal
simulation, refer to the instruction manual for the
particular preamplifier being used.
Direct Connection to the 460 Since the input of
the 460 has 1000
S input impedance, the test pulse
generator will normallyhavetobeterminated at the
amplifier input with an additional shunt resistor. If
the test pulse generator hasadcoffset greater than
1 V, a large series isolating capacitor is also
required since the input of the 460 is dc-coupled.
ORTEC Test Pulse Generators are designed for
direct connection. When any of these units are
used, they should be terminated with a 100
S
terminator at the amplifier input or be used with at
least one of the output attenuators set at In. (The
small error due to the finite input impedance of the
amplifier can normally be neglected.)
Special Considerations for Pole-Zero
Cancellation The pole-zero-cancellation network
in the 460 is factory-adjusted for a 50-
: s decay
time to match ORTEC FET preamplifiers. When
a tail pulser is connected directly to the amplifier
input, the PZ Adj should be adjusted if overload
tests are to be made (other tests are not affected).
See Section 6.2 for the details.
If a preamplifier is used and a tail pulser is
connected to the preamplifier test pulse input,
similar precautions arenecessary. In thiscase the
effect of the pulser decay must be removed, i.e., a
step input should be simulated. Details for this
modification are also given in Section 6.2.
3.4. CONNECTION TO POWER
Turn off the Bin Power Supply when inserting or
removing modules. The ORTEC NIM modules are
designed so that it is not possible to overload the
Bin Power Supply with a full complement of
modulesintheBin. Since,however, thismaynotbe
true when the Bin contains modules other than
those of ORTEC design, check the Power Supply
after inserting the modules. The4001/4002 has test
points on the Power Supply control panel for
monitoring the dc voltages.
3.5. SHAPING CONSIDERATIONS
The rise time of the output pulses from the 460 will
be a function of the rise time furnished from the
preamplifier and of the setting of the front panel
Integ switch. When the switch is set at 0.04
: s, the
rise time for a step input from the preamplifier will
be less than 100 nsec. The 0.1- and 0.25-
: s switch
settings will provide proportionately longer rise
times. Check the input specifications for the
instrument into which the 460 output pulses will be