ORTEC 142IH Service manual

Model 142IH
Preamplifier
Operating and Service Manual
Printed in U.S.A. ORTEC®Part No. 717590 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 or purchaseorder, ORTEC’s exclusiveliabilityandbuyer’s exclusiveremedy 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 berepaired 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 externalor concealeddamage. Thecarrier
making deliveryshouldbenotifiedimmediatelyofanysuchdamage, sincethecarrier is normallyliable 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 assistancecan 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................................................................... 2
2. SPECIFICATIONS ................................................................ 3
2.1. PERFORMANCE ............................................................. 3
2.2. INPUTS .................................................................... 3
2.3. OUTPUTS .................................................................. 3
2.4. CONNECTORS .............................................................. 3
2.5. ELECTRICALANDMECHANICAL................................................ 3
3. INSTALLATION .................................................................. 3
3.1. CONNECTIONTODETECTOR.................................................. 3
3.2. CONNECTIONTOAMPLIFIERS................................................. 4
3.3. INPUTPOWER .............................................................. 4
3.4. TESTPULSE................................................................ 4
3.5. DETECTORBIASINPUT....................................................... 4
4. OPERATION .................................................................... 5
4.1. GENERAL .................................................................. 5
4.2. DETECTORBIAS ............................................................ 6
4.3. ENERGYOUTPUT ........................................................... 6
4.4. TIMINGOUTPUT............................................................. 6
4.5. INPUTPROTECTION ......................................................... 6
5. MAINTENANCE INSTRUCTIONS .................................................... 7
5.1. TESTINGPERFORMANCE..................................................... 7
5.2. FACTORY REPAIR ........................................................... 8

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
NOTICE
This preamplifier has been shipped to you with its
protection circuit connected into the input circuit.
The protection circuit prevents destruction of the
input FET due to large transients that may occur
duringabnormal operatingconditionsandservesas
an impedance matching termination for the input
cable from the detector. The presence of the
protection circuit imposes only a slight resolution
degradation. With the protection circuit installed,
the preamplifier is immune to almost anything the
operator is likely to do that causes transients at
either the detector input or the bias input connector.
The protection circuit does not protect the detector,
but even if the detector breaks down as a result of
overvoltage, the preamplifier will survive the
resulting large transients if the protection circuit is
in. This, of course, would not be true if the
protection circuit were taken out, in which case the
input FET is very susceptible to destruction by
transients at the input connector on the
preamplifier.
If the input protection circuit must be taken out for
any reason, this involves disconnecting one
transistorleadandinstalling a jumper acrossa 51
S
series resistor. The Warranty of the 142IH is void if
the protection circuit is taken out unless all of the
following precautions are taken:
1. COMPLETELY DISCHARGE the bias circuitry
before connecting a lowimpedance, a cable, orany
other capacitive device to the Input connector on
the preamplifier.
2. Discharge the bias circuitry before making any
connections to the Input connector and before
disconnecting the preamplifier from the detector.
3. To discharge the bias circuitry, connect a low
impedance (shorting cap is preferred) for at least
one minute across the Bias connector on the
preamplifier.
The input circuit will be destroyed if the Input
connector isshorted while the bias components are
charged, and the quality of these capacitors is such
that they will retain a charge through a long period
of time. Such a short could result from connecting
a detector, cable, or other capacitive device such
as a voltmeter probe. A short circuit, either short
term or continuous, will cause the applied bias
(stored on C2) to be coupled directly to the input
transistor, causing a catastrophic breakdown.
If a variable bias supply is used, merely turn down
the voltage control to zero and leave it for at least
one minute. This will suffice since the bias circuitry
can discharge itself through the output of the bias
supply.
Sometimes it is necessary to simply disconnect the
bias supply, such as is the case when using
batteriesforbias.Thissituationleavesnodischarge
path, so a path must be provided by placing ashort
circuit or low impedance across the Bias connector
on the rear panel of the preamplifier. DO NOT
SHORT THE INPUT CONNECTOR on the front
panel of the instrument unless the input circuitry
has been completely discharged.

2
ORTEC 142IH PREAMPLIFIER
1. DESCRIPTION
TheORTEC142IHcharge-sensitive Preamplifieris
designed as a minimum-cost general-purpose unit.
It is intended for use in systems where the detector,
rather that the preamplifier, is the major noise
source in the system or in systems where the
ultimatein performance is not required andthe cost
of the system must be minimized. It can be used
with semiconductor detectors, proportional
counters, scintillation counters, ionization
chambers, etc.
A bias circuit is included to accept the operating
voltage required by the detector and to furnish this
bias out to the detector through the signal input
cable. The bias input circuit in the 142IH
Preamplifier includes a 100-M
S load resistor, R4,
and any detector leakage current will have to pass
through this resistance as well as through R1,
1.5 M
S , in series. A considerable voltage drop will
be expected across this 100-M
S resistor for a
detectorwithhighleakage,andresistorR3(shipped
as an accessory) can be installed in parallel with
R4; R3 has a value of only 10 M
S .
An input protection circuit is built into the
preamplifier. It protects the input FET from any
large transient voltages that would otherwise
damage the transistor. This is discussed in the
Notice inside the front cover. The protection circuit
also provides a damping resistance on the input so
that relatively long cable lengths can be used
between the detector and the preamplifier without
disrupting the system stability.
A Test Pulse connector with built-in charge
terminator is provided for use with a pulse
generator such as the ORTEC 419, 448, or 480 to
simulate the signal from the detector. This allows a
check of the system performance while an
experiment is in progress.
The 142IH will accommodate up to ±3000 V for the
detector. The output pulse polarity is the same as
the applied bias polarity. The 142IH Preamplifier
output can be connected to a shaping main
amplifier such as the ORTEC 451, 485, or 572 for
energy spectroscopy or to a timing filter amplifier
such as the ORTEC 474 for time spectroscopy.
Output connectors are provided so that both types
of analysis can be operated simultaneously.
If it is necessary to open the case for any reason,
observe the following instructions carefully to
prevent serious injury to yourself and/or damage to
the instrument.
Observe the steps that are included in the
Notice at the front of the manual to discharge
thehighvoltageandprevent shock; thevoltage
levels that can be used are lethal and the
capacitors are very high quality so they retain a
charge much longer than normally expected.
Do not touch the high-megohm resistors, R4
and R7, with your bare fingers; the presence of
skin oil can reduce the resistance of the
component and alter operating characteristics.
See Section 4 for instructions that involve the
protection circuit.

3
2. SPECIFICATIONS
2.1. PERFORMANCE
NOISEIncreaseswithincreasinginputcapacitance.
Typical performance values, based on silicon
equivalent of
, = 3.6 eV at J = 2µs, are 1.9 keV at
0 pF; these degrade to 4.6 keV at 100 pF and to
35 keV at 1000 pF.
RISETIME Based on a +0.5V signal through either
output into a 93
S circuit and measured from 10%
to 90% of peak amplitude; 20 ns at 0 pF and 50 ns
at 100 pF.
SENSITIVITY Nominal, measured through either
output, 45 mV/MeV Si.
ENERGY RANGE 0 to 100 MeV Si.
ENERGY RATE 3 X 105MeV/s.
DYNAMIC INPUT CAPACITANCE 10,000 pF.
INTEGRAL NONLINEARITY
# 0.05% for 0 to ±7 V
open circuit, or ±3.5 V terminated in 93
S .
TEMPERATUREINSTABILITY
# ±100ppm/°,273
to 323 K (0 to 50°C).
DETECTOR BIAS ISOLATION ±3000 V.
OPEN LOOP GAIN
$ 40,000.
2.2. INPUTS
INPUT Accepts input signal from a detector and
extends operating bias to the detector.
BIAS Acceptsthe biasvoltage forthe detector from
a bias supply.
TEST PULSE Accepts input voltage pulses from a
pulse generator for instrument and system check
and calibration; Rin = 93
S .
2.3. OUTPUTS
EANDT (forEnergyand Timing)Twoconnectors
furnish identical signals through two output paths;
either or both outputs can be used as required, and
they are interchangeable; R0= 93
S through each
connector and the output polarity is opposite from
the input pulse polarity (output pulse polarity is the
same as bias polarity).
2.4. CONNECTORS
INPUT and BIAS Type SHV.
TEST PULSE, E, and T Type BNC.
POWER CABLE 10-ft (3 m) captive power cable,
ORTEC 121-C1; longer lengths available from
ORTEC on special order.
2.5. ELECTRICAL AND MECHANICAL
POWER REQUIRED Furnished from NIM bin and
power supply through any ORTEC main amplifier,
or from an ORTEC 114Preamplifier Power Supply;
built-in captive cable is compatible with either
source.
+24 V, 30 mA; -24 V, 10 mA; +12 V, 15 mA;
-12 V, 15 mA.
DIMENSIONS 1.5 x 2.4 x 4.5 in., plus 10-ft cable
(38 x 61 x 114 mm, plus 3 m cable).
3. INSTALLATION
3.1. CONNECTION TO DETECTOR
A direct connection with shielded cable should be
made between the detector and the Input SHV
connector on the preamplifier. The performance of
the 142IH Preamplifier, like that of all similar
instruments, is degraded as the capacity at the
input increases. Therefore it is important that the
length of coaxial cable used between the detector
and the preamplifier be kept at the minimum length
that is necessary. Alsoit ispreferable to use 93
S or
100
S characteristic impedance cable rather than
75
S or 50 S cable because the capacity per foot is
less for the cable with the higher characteristic
impedance. Type RG-62/U cable is recommended;
this has a 93
S impedance and a capacitance of
13.5 pF/ft (40.1 pF/m). An AMP 51426-2 connector
mates with the SHV connector on the 142I
Preamplifier.

4
Once the input cable installation has been made,
the electronic noise performance of the 142IH can
be predicted by calculating the cable capacity from
the above information and adding the capacity
expected from the detector.
3.2. CONNECTION TO AMPLIFIERS
Either or both the E and T outputs of the 142IH can
be connected to an amplifier input for further
processing.Theoutput impedancethrougheitherof
these connectors is 93
S , providing a series
terminationfor93
S cablesothatlongcablelengths
can be driven easily. Although the outputs are
marked E (for Energy) and T (for Timing), the pulse
characteristics are identical and the circuits are
interchangeable.
In an energy spectroscopy system, the preamplifier
output is furnished into a shaping main amplifier. In
a timing spectrometer system, the preamplifier
output isfurnishedinto atimingfilteramplifier. With
the dual output connections on the 142IH, the
signals can be furnished simultaneously to both
types of spectrometer systems. If either the E or T
output connector is not being used, it should simply
be left open-circuited (unterminated).
3.3. INPUT POWER
Power for the 142IH is supplied through the Power
Cable that is captive through the rear panel of the
unit. The normal connection for this power cable is
included on the rear panel of the mating ORTEC
amplifier, furnishing ±12 V and ±24 V from the bin
andpowersupplyinwhichtheamplifierisoperated.
If thisfacility isnot availableor if such a connection
would increase the loading on the bin and power
supply beyond its maximum rated capacity, use an
ORTEC 114 Preamplifier Power Supply to furnish
the operating power requirements through the
captive cable. The ORTEC 114 can furnish power
for two ORTEC preamplifiers simultaneously if
desired.
3.4. TEST PULSE
A voltage test pulse for energy calibration can be
acceptedthrough the TestPulse input connector on
the 142IH without the use of an external charge
terminator. The test input of the preamplifier has an
input impedance of 93
S and its circuitry provides
charge injection to the preamplifier input. The
shape of this pulse should be a fast risetime (less
than 40 ns) followed by a slow exponential decay
back to the baseline (200 to 400 µs). While the test
pulses are being furnished, connect either the
detector (with bias applied) or the equivalent
capacitance (without bias applied) to the Input
connector on the 142IH.
The Test Pulse input may be used in conjunction
with the output of a pulser such as the ORTEC 419
or 448 to calibrate the preamplifier E output
amplitude in terms of energy for calibration of a
multichannel analyzer. However, due to stray
coupling between the test circuit and other portions
of the preamplifier circuitry, the transient
performance of the preamplifier is best determined
byconnecting theactual detectorsignal throughthe
Input connectorinsteadof usingthepulsegenerator
output signals for this calibration.
A voltage test pulse for transient response in the
142IHcanbeacceptedthroughachargeterminator
and into the Input connector on the 142IH. If
external capacitance is to be included for these
tests, anSHV tee can beinsertedbetweenthe Input
connector and the charge terminator, and this will
then accommodate the test capacitances. Do not
furnish any bias during these tests.
3.5. DETECTOR BIAS INPUT
Operating bias for the detector is supplied to the
Bias connector on the 142IH and, through a filter
and a large bias resistance, to the Input signal
connector.From thereitisfurnishedoutthroughthe
signal input cable to the detector.
Connect a cable from the detector bias supply
(ORTEC428or 459istypical)to theBiasconnector
on the142IH. Type SHV connectorsare used in this
high-voltage circuit and the mating cable shouldbe
furnished with the bias supply module.

5
Fig. 4.1. Simplified Block Diagram of the 142IH Preamplifier.
4. OPERATION
4.1. GENERAL
When the 142IH is installed according to the
appropriate information in Section 3, it operates at
all times when power is applied from the power
source. The power is furnished from either the bin
and power supply through a mating amplifier or
from an ORTEC 114 Preamplifier Power Supply.
Figure 4.1 is a simplified block diagram of the
circuits in the 142IH Preamplifier. The complete
circuit is shown in schematic 142IH-0201-S1,
included at the back of the manual. When the
protection circuit is in, the diode clamp to ground
from a point in the input circuit will protect the input
FET transistor from large transients, which are not
a part of the input pulse information. When the
protection circuit is out, there isnoclamp to ground
and a series input resistor is shorted by a jumper.

6
4.2. DETECTOR BIAS
The amount of bias requiredto operate the detector
is specified in the data furnished with the detector.
The bias that is accepted into the preamplifier
through the SHV Bias connector is furnished
through the load resistance (about 100 M
S ) to the
Input SHV connector of the preamplifier. If the
leakagecurrentthroughthedetectorisappreciable,
a notable voltage drop will occur across the series
load resistance in the preamplifier, andthismust be
added to the detector requirement when the bias
supply level is adjusted.
With the protection circuit in, the input cable can be
removed and reconnected without catastrophic
damage to the preamplifier even with bias applied
to the circuit; but the user must be very cautious to
prevent touching the interior of the connector with
anything other than a good insulator because
potentially lethal highvoltage can bepresent on the
center pin of the Input connector under these
conditions.
With the protection circuit out, the operating bias
level must be reduced gradually to zero before
the detector is either connected to or disconnected
from the Input connector on the 142IH.
4.3. ENERGY OUTPUT
The charge-sensitive loop is essentially an
operational amplifier with a capacitive feedback
through a 1-pF capacitor. The conversion gain is
approximately 45 mV/MeV (Si equivalent). A dc
feedback is applied through a 100-M
S resistor.
The energy signal from the preamplifier is a fast
risetime voltage step with an exponential return to
the baseline with a time constant of 100 µs. The
polarity of signals through the E output is inverted
from the signal polarity at the output of the detector.
When a positive bias polarity is used for the
detector, its output pulses are negative and so the
E output of the preamplifier is positive.
The risetime of the charge-sensitive loop increases
as the external capacity increases. External
capacity is a function of the detector and its cabled
connection to the preamplifier Input.
4.4. TIMING OUTPUT
The T output connector provides an alternate path
for the same output pulses that are furnished
through the E output connector. The intent is to
providebothconnectionsforconveniencewhenthe
142IH Preamplifier is used to drive two systems -
one for energy spectroscopy and the other for
timing spectroscopy.
4.5. INPUT PROTECTION
A provision is built into the preamplifier to protect
the input FET from damage when there are high-
voltage transients at its input. These transients can
result from any one or more of many causes
including detector breakdown, moisture
condensation on the Input connector, short circuits
or uncharged capacitance connected across the
input while bias is applied, or disconnection of a
bias voltage without first reducing it gradually to
zero.
The protection circuit is installed in the preamplifier
when the unit is shipped from the factory. Although
it offers protection to the FET, it alsocauses a slight
degradation of the noise performance of the
preamplifier andthisincreasesasdetector capacity
increases.
With the protection circuit in, the emitter lead of
Q11 is attached to the junction between resistor R5
and the FET input. Transistor Q11 is connected as
a diode, with both the base and the collector tied to
ground through R8. This prevents the voltage in the
input circuit from rising beyond the safe limit for the
FET input. To take the protection circuit out, simply
remove the emitter lead of Q11 from its circuit
connection and install a wire jumper across R5.
In order to take full advantage of the risetime
capabilities of the 142IH for timing experiments
(typical risetimes of 20 to 300 ns for input
capacitances from 1 to 500 pF), the total cable
length should be kept as short as possible. Due to
vagaries in the system installation - ground loops,
stray inductances, etc. - and since the maximum
cable length is a factor in the input capacitance of
the preamplifier, it is not possible to give absolute
numbers. In general, it is desirable to keep the
length of the input cable less than two feet so that
the risetime performance with low capacity
detectors will not be degraded significantly.

7
5. MAINTENANCE INSTRUCTIONS
5.1. TESTING PERFORMANCE
As ordinarily used in a counting or spectroscopy
system, the preamplifier is one part of a series
system involving the source of particles to be
analyzed, the detector, the preamplifier, the main
amplifier, and the pulse height analyzer. When the
proper results are not being obtained and tests for
proper performance of the preamplifier and the
other components are indicated, it is important to
realize that rapid and logical testing is possible only
whentheindividual components areseparated from
the system. In proving the performance of the
preamplifier, it should be removed from the system
and be dealt with alone by providing known
electrical signals through the input and testing for
the proper output signals with an oscilloscope as
specified in the following steps:
1. Furnish a voltage pulse to the Test Pulse
connector as outlined in Section 3.4. The polarity of
the test pulse signal should agree with the expected
signal input polarity from a detector.
2. Using a calibrated pulser, the 142IH output,
either E or T, should be inverted from the input and
have a nominal scale factor of 45 mV per 1 MeV
equivalent energy (Si).
3. The noisecontribution of thepreamplifier may be
verified by two basic methods. In either case, the
normal capacity of the detector and associated
cables should be replaced by a capacity of equal
value placed across the Input connector, and no
bias should be applied. This is necessary because
the noise contribution of the preamplifier is
dependentuponinput capacity.Theonlymeaningful
statement of thenoiselevel isone that relates to the
spread caused by the noise in actual spectra. This
can be measured and expressed in terms of the full
width athalf maximum (FWHM) of amonoenergetic
signal afterpassingthroughthepreamplifier andthe
main amplifier in the system.
The noise performance referenced in the
Specifications in Section 2 is stated in these terms,
and verification methods will be described. If
desired, the preamplifier can be tested with no
external capacity on the Input connector, in which
case the noise width should be approximately that
shown for zero external capacity. In any case, the
Input connector and capacitors, when used, should
be completely shielded electrically. A wrapping of
aluminum foil around the Input connector or a
shielding cap attached to the connector will suffice
for testing at zero capacity.
4. The preamplifier must be tested in conjunction
with an associated main amplifier that provides the
required pulse shaping. The typical noise
performancegiveninSection2isobtainedusingan
ORTEC 572 Spectroscopy Amplifier on which 2-µs
timeconstantshavebeenselectedasspecified.For
comparison of these tabulated values, it is
preferable to test the preamplifier under identical
pulse-shaping conditions. It is also important to
ensure that the noise level of the input stage of the
associated main amplifier does not contribute
materially to the total noise. This is usually no
problem provided that the input attenuator, if any,
on the main amplifier is set for minimum
attenuation.
5. If a multichannel analyzer is used to measure
the main amplifier output pulses, testing of the
noise performance can be accomplished by merely
using a calibrated test pulse generator with a
charge terminator. With only the charge terminator
connected to the 142IH Input, the spread of the
pulser peak thus analyzed will be due to only the
noise contribution of the preamplifier and the main
amplifier. The analyzer can be calibrated in terms
of keV per channel by observing two different
pulser peaks of known energy, and the FWHM of a
peak can be computed directly from the analyzer
readout.
6. It is also possible to determine the noise
performance of the preamplifier by use of a wide
bandwidth rms ac voltmeter such as the Hewlett-
Packard 3400A, reading the main amplifier output
noise level and correlating it with expected pulse
amplitudes per keV of signal through the input
under the same conditions. Again, a calibrated
pulse generator is required for an accurate
measurement.
In this method the preamplifier and main amplifier
are set up as they would be used normally, but with
a dummy capacitor (or no capacity) in the Input
connector of the 142IH, and with the ac voltmeter
connected to the main amplifier output. The noise
level indicated on the voltmeter, designated Erms, is
then read and noted. Then a test pulse of known
energy, Ein (in keV), is applied to the input and the

8
amplitude of the resulting output pulse, Eout, is
measured in volts with an oscilloscope. The noise
spread can then be calculated from the formula
where Erms is output noise in volts on the 3400A
meter, Ein is the input signal in keV particle energy,
andEout istheoutput signal involtscorrespondingto
the above input. If the gain of the shaping amplifier
is adjusted so that the output pulse height is 2.35 V
for an input of 1 MeV equivalent input charge, then
the rms meter will be calibrated to read directly in
energy (1 mV = 1 keV).
7. The noise performance of the preamplifier, as
measured by these methods, should not differ
significantly from that given in the Specifications in
Section 2.
8. If, during testing of the preamplifier and detector,
the noise performance of the preamplifier has been
verified as outlined in the previous steps or is
otherwise not suspected, a detector may be tested
tosomeextentbyduplicatingthenoiseperformance
tests with the detector connected in place and with
normal operating bias applied. The resulting
combined noise measurement, made by either the
analyzer or voltmeter method, indicates the sum in
quadrature of the separate noise sources of the
amplifier and the detector. In other words, the total
noise is given by
9. Each quantity is expressed in keV FWHM. The
quantity Ndet is known as the “noise width” of the
detector and is included as one of its specified
parameters. By use of the above equation and with
a knowledge of the noise of the preamplifier, the
noise width of the detector can be determined. The
significance of this noise width in evaluating the
detector is subject to interpretation, but generally
the actual resolution of the detector is related
directly to the noise width in itsnormal applications.
Themostusefulpurposefordeterminingthisquality
for the detector is to occasionally monitor the
detector noise width to verify that its characteristics
have not undergone any significant changes during
use.
10. Use an ORTEC 419 Precision Pulse Generator
with a matched charge termination to measure the
risetime of the 142IH through the T or E output
connector. Connect the 419 output through the
charge terminator to the Input of the 142IH and use
an oscilloscope with a fast risetime (1 ns if
possible). Therisetime of the preamplifier can then
be computed by
(Total risetime)2= (Preamplifier risetime)2+
(Pulser risetime)2+ (Oscilloscope risetime)
The risetime of the 419 is typically 3 ns.
5.2. FACTORY REPAIR
This instrument can be returned to ORTEC for
service and repair at a nominal cost. The standard
procedure for repair ensures the same quality
control and checkout that are used for a new
instrument. Always contact Customer Services at
ORTEC [phone], before sending in an
instrument for repair to obtain the necessary
shipping instructions and so that the required
Return Authorization Number can be assigned to
the unit. Write this numberonthe addresslabel and
on the package to ensure prompt attention when it
reaches the factory.