ORTEC 570 Service manual

Model 570
Spectroscopy Amplifier
Operating and Service Manual
Printed in U.S.A. ORTEC Part Number 733480 1202
Manual Revision E

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 noother warranties, express or implied, andspecificallyNO WARRANTYOF 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 or purchaseorder, ORTEC’s exclusiveliability and buyer’s exclusive
remedy shall be 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 advanceof 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
usedfor new-productioninstruments. Instruments that are returnedshould bepackedsothat theywillwithstand
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 evidence of external or concealed damage. The
carrier making delivery should be notified immediately of any such damage, since the carrier is normally liable
for 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 assistancecanbeprovidedinmakingdamageclaims andin 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.

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TABLE OF CONTENTS
WARRANTY ..................................................................... i
1 DESCRIPTION .................................................................1
1.1 GENERAL ...................................................................1
1.2 POLE-ZEROCANCELLATION....................................................1
1.3 ACTIVEFILTER...............................................................3
2 SPECIFICATIONS ..............................................................4
2.1 PERFORMANCE ..............................................................4
2.2 CONTROLS ..................................................................4
2.3 INPUT ......................................................................4
2.4 OUTPUTS ...................................................................5
2.5 ELECTRICALANDMECHANICAL.................................................5
3 INSTALLATION ................................................................5
3.1 GENERAL ...................................................................5
3.2 CONNECTIONTOPOWER......................................................5
3.3 CONNECTIONTOPREAMPLIFIER................................................5
3.4 CONNECTIONOFTESTPULSEGENERATOR ......................................6
3.5 SHAPINGCONSIDERATIONS ...................................................6
3.6 LINEAROUTPUTCONNECTIONSANDTERMINATINGCONSIDERATIONS ...............6
3.7 SHORTINGOROVERLOADINGTHEAMPLIFIEROUTPUT ............................7
3.8 BUSYOUTPUTCONNECTION ...................................................7
4 OPERATION ...................................................................7
4.1 INITIAL TESTING AND OBSERVATION
OF PULSE WAVEFORMS ....................................................7
4.3 FRONTPANELCONNECTORS ..................................................8
4.4 REAR PANEL CONNECTORS
.........................................................................8
4.5 STANDARD SETUP PROCEDURE ................................................8
4.6 POLE-ZEROADJUSTMENT .....................................................9
4.7 BLRTHRESHOLDADJUSTMENT................................................11
4.8 OPERATION WITH SEMICONDUCTOR DETECTORS ................................12
4.9 OPERATION IN SPECTROSCOPY SYSTEMS ......................................14
4.10 OTHEREXPERIMENTS.......................................................15
5 MAINTENANCE ...............................................................17
5.1 TESTEQUIPMENTREQUIRED .................................................17
5.2 PULSERTEST* ..............................................................17
5.3 SUGGESTIONSFORTROUBLESHOOTING .......................................19
5.4 FACTORY REPAIR ...........................................................19
5.5 TABULATEDTESTPOINTVOLTAGES ........................................... 19

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ILLUSTRATIONS
Fig. 1.1. Differentiation in Amplifier Without Pole-Zero Cancellation .........................2
Fig.1.2. DifferentiationinaPole-ZeroCanceledAmplifier ................................2
Fig. 1.3. Pulse Shapes for Good Signal-to-Noise Ratios ..................................3
Fig. 4.1. Typical Effects of Shaping-Time Selection on Output Waveforms ...................8
Fig.4.2. TypicalWaveformsIllustratingPole-ZeroAdjustmentEffects.......................9
Fig. 4.3. A Clamp Circuit that can be used to Prevent Overloading the Oscilloscope Input .......10
Fig. 4.4. Pole-Zero Adjustment Using a Square Wave Input to the Preamplifer ...............10
Fig.4.5. BLRThresholdVariableControlSettings .....................................11
Fig. 4.6. System for Measuring Amplifier and Detector Noise Resolution . ...................12
Fig.4.7. NoiseasaFunctionofBiasVoltage .........................................13
Fig.4.8. SystemforMeasuringResolutionwithaPulseHeightAnalyzer ....................13
Fig. 4.9. System for Detector Current and Voltage Measurements .........................13
Fig. 4.10. Silicon Detector Back Current vs Bias Voltage .................................14
Fig. 4.11. System for High-Resolution Alpha-Particle Spectroscopy .........................14
Fig.4.12. SystemforHigh-ResolutionGammaSpectroscopy..............................15
Fig. 4.13. Scintillation-Counter Gamma Spectroscopy System .............................15
Fig. 4.14. High-Resolution X-Ray Energy Analysis System Using a Proportional Counter .........15
Fig. 4.15. Gamma-Ray Charged-Particle Coincidence Experiment ..........................16
Fig.4.16. Gamma-RayPairSpectrometry ............................................16
Fig. 4.17. Gamma-Gamma Coincidence Experiment ....................................17
Fig.5.1. AmplifierBlockDiagram..................................................18
Fig. 6.1. Circuit Used to Measure Nonlinearity ........................................20

iv

1
1 DESCRIPTION
1.1 GENERAL
The ORTEC 570 Spectroscopy Amplifier is a
singlewidth NIM module that features a versatile
combination of switch-selectable pulse-shaping
characteristics. The amplifier has extremely low
noise, a wide gain range, and excellent overload
responseforuniversalapplicationinhigh-resolution
spectroscopy. It accepts input pulses of either
polarity that originate in germanium or silicon
semiconductor detectors, in scintillation counters
with either fast or slow scintillators, in proportional
counters, inpulsedionizationchambers,inelectron
multipliers, etc.
The 570 has an input impedance of approximately
1000
S andacceptseitherpositiveornegativeinput
pulses with rise times <650 ns and fall times >40
: s. Six integrate and differentiate time constants
are switch-selectable to provide optimum shaping
for resolution and count rate. The differentiation
networkhasvariablepole-zerocancellationthatcan
beadjustedtomatchpreamplifierswithdecaytimes
>40
: s. The pole-zero cancellation drastically
reduces the undershoot after the differentiator and
greatly improves overload and count rate
characteristics.Inaddition,theamplifiercontainsan
active filter shaping network that optimizes the
signal-to-noise ratio and minimizes the overall
resolving time.
The output is unipolar and is used for spectroscopy
in systems where dc coupling can be maintained
from the 570 to the analyzer. A BLR (baseline
restorer) circuit is included in the 570 for improved
performance at all count rates. Baseline correction
is applied during intervals between input pulses
only, and a front panel switch selects a
discriminator level to identify input pulses. The
unipolar output dc level can be adjusted in the
range from -100 mV to +100 mV. This output
permits the use of the direct-coupled input of the
analyzer with a minimum amount of interface
problems.
The 570 can be used for constant-fraction timing
when operated in conjunction with an ORTEC 551,
552, or 553 Timing Single-Channel Analyzer. The
ORTEC Timing Single-Channel Analyzers feature
a minimum of walk as a function of pulse amplitude
and incorporatea variable delay time on the output
pulse to enable the timing pick-off output to be
placed in time coincidence with other signals.
The 570 has complete provisions, including power
distribution, for operating any ORTEC solid-state
preamplifier. Normally, the preamplifier pulses
should have a rise time of 0.25
: s or less to
properly match the amplifier filter network and a
decay time greater than 40
: s for proper pole-zero
cancellation. The 570 input impedance is 1000
S .
Whenlong preamplifier cablesare used, the cables
can be terminated in series at the preamplifier end
or in shunt at the amplifier end with the proper
resistors. The output impedance isabout 0.1
S ,and
the output can be connected to other equipment by
a single cable going to all equipment and shunt
terminated at the far end of the cabling. See
Section 3 for further information.
1.2 POLE-ZERO CANCELLATION
Pole-zero cancellation is a method for eliminating
pulse undershoot after the differentiating network.
In an amplifier not using pole-zero cancellation
(Fig.1.1), the exponential tail on the preamplifier
output signal (usually 50 to 500
: s) causes an
undershoot whose peak amplitude is roughly
determined from:
undershoot amplitude
differentiation time
=differentiated pulse amplitude
preamplifier pulse decay time
For a 1-
: s differentiation time and a 50- : s pulse
decay timethemaximum undershoot is2%andthis
decays witha50-
: 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 effect can be reduced by increasing the
preamplifier pulse decay time (which generally
reduces the counting rate capabilities of the
preamplifier)orcompensatingfortheundershootby
causing pole-zero cancellation.

2

3
Pole-zero cancellation is accomplished by the
network shown in Fig. 1.2. The pole [s + (1/T0)] due
to the preamplifier pulse decay time is canceled by
the zero of the network [s + (k/R2C1)]. In effect, the
dc path across the differentiation capacitor addsan
attenuated replica of the preamplifier pulse to just
cancel the negative undershoot of the
differentiating network.
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
cancellation for all preamplifiers having 40-
: s or
greater decay times. Improper matching of the
pole-zero network will degrade the overload per-
formance and cause excessive pileup distortion at
medium counting rates. Improper matching causes
either an undercompensation (undershoot is not
eliminated) or an overcompensation (output after
the main pulse does not return to the baseline but
decays to the baseline with the preamplifier time
constant). The pole-zero adjust is accessible on the
front panel of the 570 and can easily be adjusted by
observing the baseline on an oscilloscope with a
monoenergetic source or pulser having the same
decay time as the preamplifier under overload
conditions. The adjustment should be made so that
the pulse returns to the baseline in the minimum
time with no undershoot.
1.3 ACTIVE FILTER
When only FET gate current and drain thermal
noise are considered, the best signal-to-noise ratio
occurs when the two noise contributions are equal
for a given input pulse shape. The Gaussian pulse
shape (Fig. 1.3) for this condition requires an
amplifier with a single RC differentiate and n equal
RC integrates where n approaches infinity. The
Laplace transform of this transfer function is
G (s) = S 1
_________ x __________ (n
! 4 ).
s + (1/RC) [s + (1/RC)]n
where the first factor is the single differentiate and
the secondfactor isthe nintegrates. The 570 active
filter approximates this transfer function.
Figure 1.3 illustratesthe results of pulse shaping in
an amplifier. Of the four pulse shapes shown, the
cusp would produce minimum noise but is
impractical to achieve with normal electronic and
circuitry would be difficult to measure with an ADC.
The true Gaussian shape deteriorates the
signal-to-noise ratio by only about 12% from that of
the cusp and produces a signal that is easy to
measure but requires many sections of integration
(n
6 00). With two sections of integration the
waveform identified as a Gaussian approximation
can be obtained, and this deteriorates the
signal-to-noise ratio by about 22%. The ORTEC
active filter network in the 570 provides a fourth
waveform in Fig. 1.3; this waveform has
characteristics superior to the Gaussian
approximation, yet obtains them with four complex

4
poles. By this method the output pulse shape hasa
good signal-to-noise ratio, is easy to measure, and yet requires only a practical amount of electronic circuitry to achieve the desired results.
2 SPECIFICATIONS
2.1 PERFORMANCE
GAIN RANGE Continuously adjustable from X1
through X1500.
PULSE SHAPING Gaussian on all ranges with
peaking time equal to and pulse width at 0.1%
22. τ
level equal to 2.9 times the peaking time.
INTEGRAL NONLINEARITY <0.05% (0.025%
typical) using 2
: s shaping.
NOISE <8
: V referred to the input (5 : V typical)
using 2
: s shaping and gain $ 100.
TEMPERATURE INSTABILITY
Gain
# 0.0075%/°C, 0 to 50°C.
DC Level <±50
: V/°C, 0 to 50°C.
WALK
# ±3 ns for 50:1 dynamic range, including
contribution of ORTEC 551 or 552
Constant-FractionTimingSingle-ChannelAnalyzer
using 50% fraction and 0.5
: s shaping.
COUNT RATE STABILITY The 1.33 MeV gamma
ray peak from a 60Co source, positioned at 85% of
analyzer range, typically shifts <0.024%, and its
FWHM broadens <16% when its incoming count
rate changes from 0 to 100,000 counts/s using 2
: s
shapingandexternal pileuprejection. Theamplifier
will hold the baseline reference up to count rates in
excess of 150,000 counts/s.
OVERLOAD RECOVERY Recovers to within 2%
of rated output from X300 overload in 2.5
nonoverloaded unipolar pulse widths, using
maximum gain; same recovery from X1000
overload for bipolar pulses.
2.2 CONTROLS
GAIN Ten-turn precision potentiometer for continu-
ously variable direct-reading gain factor of X0.5 to
X1.5.
COARSE GAIN Six-position selector switch
selectsfeedback resistorsfor gain factors of 20, 50,
100, 200, 500, and 1 K.
INPUT ATTENUATOR Jumper on printed circuit
board selects an input attenuation factor of 1 or 10
(gain factor of X1 or X0.1).
POS/NEG Locking toggle switch selects input
circuit for either polarity of input pulses from the
preamplifier.
SHAPING TIME Six-position switch selects time
constant for active filter network pulse shaping;
selections are 0.5, 1, 2, 3, 6, and 10
: s.
PZ ADJ Potentiometer to adjust pole-zero
cancellation for decay times from 40 : s to 4 .
Factory preset at 50
: s to match normal
characteristics of ORTEC preamplifiers.
BLR Locking toggle switch selects a source for the
gatedbaselinerestorerdiscriminatorthresholdlevel
from one of three positions.
Auto The BLR threshold is automatically set to an
optimum level asa functionof the signal noise level
by an internal circuit. This allows easy setup and
very good performance under most conditions.
PZ Adj The BLR threshold is determined by the
threshold potentiometer. The BLR time constant is
greatly increased to facilitate PZ adjustment. This
position may give the lowest noise for conditions of
<5000 counts per second and/or longer shaping
times.
Threshold The BLR threshold is set manually by
the threshold potentiometer. Range is 0 to 300 mV
referred to the positive output signal. The BLR time
constant is the same asfor the Auto switch setting.
DC ADJ Screwdriver potentiometer adjusts the
unipolar output baseline dc level; range, +100 mV
to -100 mV.
2.3 INPUT
INPUT Type BNC front panel connector accepts
either positive or negative pulses with rise times in
the range from 10 to 650 ns and decay times from
40 to 2000
: s; Zin ~ 1000 S , dc coupled; linear
maximum 1 V (10 V with attenuator jumper set at
X0.1); absolute maximum, 20 V.

5
2.4 OUTPUTS
UNI Unipolar front panel BNC with Zo<1 S . Short
circuit proof; prompt, full scale linear range 0 to +10
V; active filter shaped and dc restored; dc level
adjustable to ±100 mV.
BUSY Rear panel BNC with Zo<10
S provides a +5
V logic pulse for the duration that the input pulse
exceeds the baseline restorer discriminator level.
Connect to the ORTEC MCA Busy input for dead
time correction.
PREAMP POWER Rear panel standard ORTEC
power connector; Amphenol 17-10090; mates with
captive and non-captive power cords on all
standard ORTEC preamplifiers.
2.5 ELECTRICAL AND MECHANICAL
POWER REQUIRED (not including any load on
the Preamp Power connector)
+24 V, 80 mA; -24 V, 85 mA;
+12 V, 60 mA; -12 V, 30 mA.
FRONT PANEL DIMENSIONS NIM-standard
single-width module (1.35 by 8.714 in.) per
TID-20893 (Rev).
3 INSTALLATION
3.1 GENERAL
The 570 operates on power that must be
furnished from a NIM-standard bin and power
supply such as the ORTEC 401/402 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
that are used in the 570. 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 570 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 401/402
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 willneed to bemoved to another bin
to achieve operation.
3.3 CONNECTION TO PREAMPLIFIER
The preamplifier output signal is connected to the
570 through the Input BNC connector on the front
panel. The input impedance is about 1000
S 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 570 incorporates pole-zero cancellation in
order to enhance the overload and count rate
characteristics of the amplifier. This technique
requires matching the network to the preamplifier
decay-time constant in order to achieve perfect
compensation.Thepole-zeroadjustmentshouldbe
set each time the preamplifier or the shaping time
constant of the amplifier is changed. For details of
the pole-zero adjustment, see Section 4.6. An
alternate method is accomplished easily byusing a
monoenergetic source and observing the amplifier
baselinewithanoscilloscopeaftereachpulseunder
approximately X2 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 thePreampPowerconnector
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 re-
quirements for the 570 at the module position in the
bin.