Ametek ORTEC 428 Service manual

Model 428
Detector Bias Supply
Operating and Service Manual
Printed in U.S.A. ORTEC®Part No. 733220 062020
Manual Revision D

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 purchase order, ORTEC’s exclusive liability 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 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 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
assistance can be provided in making damage claims and in providing replacement equipment, if necessary.
Copyright © 2020, 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
SAFETYINSTRUCTIONSANDSYMBOLS...................................................iv
SAFETY WARNINGS AND CLEANING INSTRUCTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v
1. DESCRIPTION....................................................................... 1
2. SPECIFICATIONS.................................................................... 1
3. INSTALLATION...................................................................... 2
3.1. GENERAL .................................................................... 2
3.2. CONNECTIONTOPOWER ...................................................... 2
3.3. CONNECTIONSTOTHE428..................................................... 2
4. OPERATINGINSTRUCTIONS .......................................................... 2
4.1. INITIALTESTING .............................................................. 2
4.2. POLARITYSELECTION ......................................................... 2
4.3. BIAS VOLTAGE INDICATOR LIGHT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
4.4. BIASVOLTAGESELECTORS .................................................... 3
4.5. CURRENTMONITORJACKS..................................................... 3
4.6. UNDESIRABLE LEAKAGE CURRENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.7. DETERMINATION OF ACTUAL DETECTOR BIAS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.8. GUARD-RINGVOLTAGESUPPLY................................................. 4
4.9. DETECTOR CONSIDERATIONS AT HIGH BIAS VOLTAGES. . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
5. MAINTENANCE...................................................................... 5
5.1. TESTING PERFORMANCE OF BIAS SUPPLY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
5.2. ADJUSTMENTS ............................................................... 6
5.3. TROUBLESHOOTING SUGGESTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.4. REPAIRS..................................................................... 6

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
This instrument produces voltages that can be
hazardous. Always have power switched off
before connecting or removing cables to or from
the 428 and the units to which its high voltage
outputs are applied. Observe the same
precautions when using the test points for any
purpose.
ORTEC MODEL 428
DETECTOR BIAS SUPPLY
1. DESCRIPTION
The ORTEC 428 Detector Bias Supply provides bias
voltage of either polarity for two semiconductor
detectors. The voltages are selected independently
by 10-turn, direct-reading potentiometers. The
polarity is controlled by a front panel switch. Jacks
are provided on the front panel for external
monitoring of the current in each detector. The
output of the 428 is short-circuit proof and has an
impedance of approximately 1.3 MÙ. The 428 is a
double-width module designed to meet the
recommended standards outlined in DOE Report
TID-20893 (Rev.). It receives the necessary
operating power from the ORTEC 4001/4002 Bin
and Power Supply through the rear module
connector.
WARNING
2. SPECIFICATIONS
PERFORMANCE
NOISE AND RIPPLE <0.0002%
TEMPERATURE STABILITY 0.03%/EC, 0 to
50EC.
LINE STABILITY Directly proportional to dc power
supply stability (<0.02% for 105 to 125 V ac when
using ORTEC 4002A).
CONTROLS
BIAS CONTROLS (A and B) 10-turn direct-reading
potentiometers.
POS/OFF/NEG Front panel switch to control bias
polarity. Off position provides standby condition for
the power supply.
OUTPUTS
OUTPUTS A AND B Two independent circuits,
short-circuit proof, with front panel SHV connector;
range 0 to 1000V; polarity positive or negative (both
outputs same polarity), selectable by front panel
Pos/Off/Neg switch. Output impedance -1.3 MÙ.
CURRENT MONITOR Front panel jacks for
external monitoring of the current in each detector.
ELECTRICAL AND MECHANICAL
POWER REQUIREMENTS +24 V, 205 mA; -24 V,
205 mA.
WEIGHT (Shipping) 7 lb, 4 oz (3.3 kg).
WEIGHT (Net) 4 lb (1.82 kg).
DIMENSIONS NIM-standard double-width module
(2.70 by 8.714 in.) Per TID-20893 (Rev.)
RELATED EQUIPMENT
The 428 is compatible with ORTEC detectors and
ORTEC preamplifiers that have provisions for an
external detector bias voltage.

2
Do not operate this unit without the
protective covers, since lethal voltages are
exposed inside the instrument.
3. INSTALLATION
3.1. GENERAL
The 428 contains an internal power supply that must
be used in conjunction with a Nuclear-Standard Bin
and Power Supply such as the ORTEC 4001/4002.
The 428 is intended for rack mounting; therefore if
vacuum tube equipment is operated in the same
rack, there must be sufficient cooling air circulating
to prevent any localized heating of the all-transistor
circuitry used throughout the module. The
temperature of equipment mounted in racks can
easily exceed the recommended maximum unless
this precaution is taken. The 428 should not be
subjected to temperatures in excess of 120EF
(50EC).
3.2. CONNECTION TO POWER
Turn off power when inserting or removing modules.
The ORTEC 4000 Series is designed so that it is not
possible to overload the Bin Power Supply with a full
complement of modules in the Bin; since, however,
this may not be true when the Bin contains modules
other than those of ORTEC design, the Power
Supply voltages should be checked after the
modules are inserted. The ORTEC 4001/4002 has
test points on the Power Supply control panel to
monitor the dc voltages.
3.3. CONNECTIONS TO THE 428
The ORTEC 428 is compatible with ORTEC
detectors and with preamplifiers that have provisions
to accept bias voltage for the detector. All operating
controls and bias voltage output connectors are
located on the front panel. The output connectors
are the type SHV and are not compatible with
ordinary BNC connectors. A perforated shield
encloses the unit so that high voltages are not
exposed.
WARNING
Tip jacks are provided for monitoring the current in
each detector. See Section 4.5 for information on
appropriate dc meters. Always have power for the
428 turned off before connecting or removing meter
leads. Any meter used as a current monitor is
connected in shunt with 1 MÙon the output circuit
and reduces the output impedance.
4. OPERATING INSTRUCTIONS
4.1. INITIAL TESTING
Refer to Section 5.1 of this manual for information
concerning testing performance.
4.2. POLARITY SELECTION
The Polarity Switch is located on the front panel and
also serves as an On-Off switch for power to the
428. When changing the polarity of the output bias
voltage, stop the switch in the Off position for a few
seconds before switching to the other polarity. This
pause in the Off position is necessary to allow the ac
starting circuit for the dc to dc converter to recharge.
4.3. BIAS VOLTAGE INDICATOR LIGHT
The Bias Voltage indicator light is a neon light
located between the two front panel SHV output
connectors and indicates that the power is turned
on. If the 428 is turned on and the Bias Voltage
indicator light does not illuminate, turn the Polarity
Selection switch to the Off position for approximately
2 sec and then return it to the desired polarity. This
pause in the Off position is necessary to allow the ac
starting circuit for the dc to dc converter to recharge.

3
Fig. 4.1. Semiconductor Detector Bias and Current
Measuring Circuit Using a Floating Meter.
4.4. BIAS VOLTAGE SELECTORS
The desired bias voltage for each output is selected
by its associated 10-turn potentiometer. The voltage
at each output is read directly from its corresponding
dial. The 10-turn potentiometers have a linearity of
±0.25%. The output impedance is approximately 1.3
MÙ, which will normally be negligible compared to
the detector load resistor in the preamplifier. This
resistor typically ranges from 22 to 2000 MÙ. The
voltage at the output connector of the 428 can be
calculated by the formula
Vo= Vdial - ID(1.3 x 106),
where Vo= output voltage, Vdial = voltage indicated
by 10-turn dial, and ID= detector current.
The output impedance of this unit can be decreased
bv methods given in Section 6.2.
4.5. CURRENT MONITOR JACKS
Tip jacks are provided on the front panel as a
convenience for monitoring each detector current.
Typical leakage currents for ordinary room-
temperature surface-barrier detectors range from
0.1 to 1 ìA. Semiconductor detectors cooled to
liquid nitrogen temperature have leakage currents
ranging from 0.1 to 10 nA. This current is measured
by connecting a floating ammeter or voltmeter to the
Current Monitoring jacks as shown in Fig. 4.1.
If an electronic type of meter operated from the
power line is used, the input circuit must be capable
of floating above earth and power line ground so
that the leakage to ground does not load the bias
supply. The low impedance side of the meter must
be connected to the black tip jack rather than to the
white jack; otherwise, the leakage current of the
instrument from the low terminal to power line
ground will be indicated incorrectly as detector
current. If the detector current is measured with an
ammeter,
where 1D= detector current, IM=ammeter current,
and RS= input resistance of ammeter.
If RSis very much less than 1 MÙ, the meter current
can be interpreted as detector current. Since the
smaller RSis connected directly in parallel with 1 MÙ
of the output circuit, Zois reduced.
When a voltmeter is used to measure the detector
current,
where 1D= detector current, VM=measured voltage,
and Rp= input resistance of voltmeter.
If Rpis much greater than 1 MÙ, then
ID= VMx 106ampere.
If a meter that will not float above powerline and
chassis ground is used to measure the detector
current, it should be a microammeter connected as
shown in Fig. 4.2. Do not use the current monitor
jacks unless the meter can be isolated from ground.

4
Fig. 4.2. Semiconductor Detector Bias and Current
Measuring Circuit Using a Nonfloating Meter.
4.6. UNDESIRABLE LEAKAGE
CURRENTS
Teflon-insulated current monitoring jacks and SHV
connectors are used in an effort to reduce leakage
currents to a minimum in the 428. Insulation
resistance of 1 x 1013 Ùor greater is desirable to
measure a detector leakage current of 1 nA at 1000
V. In order to maintain insulation resistances of this
magnitude, the insulators will have to be cleaned
frequently. Either Freon or methyl alcohol is a good
cleaning agent.
It may not be practical to reduce the leakage in
external cables and connections to a negligible
magnitude. In such cases it may suffice to note the
residual leakage current with all wiring in place
except the detector itself, and then subtract this
residual current from the indicated current to obtain
the actual detector current. If the leakage
phenomenon is essentially a resistance, then its
value may be computed from Ohm's law for use in
determining the residual current at various voltages,
without the necessity of actual measurements.
4.7. DETERMINATION OF ACTUAL
DETECTOR BIAS
In addition to its use as an indicator of physical
condition of the detector, the detector current allows
accurate determination of the actual bias voltage
across the detector, This actual voltage differs from
that indicated by the bias selector dials by the
amount of drop in voltage across the detector load
and filter resistors due to the detector current.
Accurate determination of actual detector voltage is
important, since it is an important parameter in both
the depleted (sensitive) depth of the detector and
the collecting field strength.
To obtain the actual detector voltage, one must
know the sum of all series resistances in the circuit
between voltage source and detector. The
resistance of the internal circuit of the 428 may be
approximated by 1.3 MÙ, unless this has been
reduced by a current monitor (Section 4.5). Detector
load resistors may vary from 10 MÙto 200 MÙin
ordinary applications, and may be several thousand
megohms in special applications involving cooled
detectors. In addition, there is usually a filter resistor
of 1 MÙor more near and in series with the load
resistor. The values of these resistors can usually be
ascertained from the schematic diagram of the
preamplifier used. Once having determined the total
series resistance, the loss of bias in that resistance
can be calculated by Ohm's law.
4.8. GUARD-RING VOLTAGE SUPPLY
When detectors that require a separate bias
connection to a guard ring are used, the 428 will
prove convenient in that the signal electrode bias
can be taken from one bias output connector and
the guard-ring potential taken from the other. In this
way the two potentials can be varied independently
of each other to determine the optimum biasing
condition. The usual optimum is obtained when both
are nearly the same, but a small difference is
sometimes beneficial. In general, that setting which
minimizes the signal electrode current will be near
optimum.

5
4.9. DETECTOR CONSIDERATIONS AT
HIGH BIAS VOLTAGES
Semiconductor radiation detectors that utilize more
than a few hundred volts bias generally require
some care in the application of that bias to reduce
the risk of damaging the detector. It is helpful to
observe the noise output of the main amplifier with
an oscilloscope while the bias voltage is advanced.
Small breakdown phenomena which die out in in
less than a minute can be observed after a bias
increase. For greatest safety, it is advisable to
approach the final operating bias in small
increments, with brief aging periods between
increments.
5. MAINTENANCE
5.1. TESTING PERFORMANCE OF BIAS
SUPPLY
The following paragraphs are intended as aids in the
installation and checkout of the 428. These
instructions include information on the front panel
controls, output voltages, and internal adjustments.
The following or equivalent test equipment is
needed:
Nuclear-Standard Bin and Power Supply, such as
the ORTEC 4001/4002.
Oscilloscope with an input coupling capacitor rated
at more than 500 V.
Voltmeter with input impedance of 100 MÙor
greater on the 1000-V scale.
Before making the performance tests, take the
following preliminary steps:
1. Visually check the module for possible damage
due to shipment.
2. Connect ac power to Nuclear Standard Bin,
ORTEC 4001/4002.
3. Plug module into Bin and check for proper
mechanical alignment.
4. Ensure that the Polarity Selection switch on the
ORTEC 428 is in the Off position.
5. Switch on the ac power and check the dc Power
Supply voltages at the test points on the 401 Power
Supply control panel.
To check the performance of the 428, make the
following tests:
1. Set the bias selector potentiometers to zero.
2. Set the voltmeter to the 1000-V scale and connect
it to output A.
3. Rotate the Polarity Selection switch to Pos.
4. Increase the potentiometer associated with output
A to 1000 and check the output voltage for
approximately 1000 V. The loading effect of the
voltmeter on the circuit should be considered. For
example, a voltmeter with an input impedance of
100 MÙwill produce a 10-ìA current drain on the
output. This output current will produce an 11-V drop
across the series. 1.1-MÙoutput resistance (R15
and R18); therefore the voltmeter should read 989
V. If the output voltage is not in agreement with the
dial reading, see Section 6.2 for calibration
procedure.
5. Reduce the potentiometer back to zero and check
the potentiometer linearity by comparing the output
voltage versus the potentiometer dial reading.
6. Connect the voltmeter to output 8 and repeat
steps 4 and 5.
7. Turn the Polarity-Selection switch to Off for about
2 sec and then to Neg and repeat steps 4, 5, and 6.
8. Set the output voltage to zero and connect output
A to the ac-coupled input of an oscilloscope with a
coaxial cable. Increase the output voltage to 500 V
and check the ripple. It should be less than 1 mV
peak to peak.

6
5.2. ADJUSTMENTS
If the output voltage does not agree with the dial
reading, it should be recalibrated using the following
procedure:
1. Ensure that the 428 Polarity Selection switch is in
the Off position.
2. Apply power to the 428 through a 401 C-3 or
equivalent extender cable. (The module must be out
of the Bin when this adjustment is made.)
3. Switch on the ac power and check the dc Power
Supply voltages at the test points on the 4002 Power
Supply control panel.
4. Select the 1000-V scale on a voltmeter and
connect it to output A. The input impedance of the
voltmeter should be 100 MÙor greater on this scale.
5. Rotate the Polarity Selection switch to Pos.
6. Increase the potentiometer associated with output
A to 1000 and check the output voltage for
approximately 1000 V. The loading effect of the
voltmeter on the circuit should be considered before
the voltage is adjusted. For example, a voltmeter
with an input impedance of 100 MÙwill produce a
10-ìA current drain on the output. This output
current will produce an 11-V drop across the series
1.1-MÙoutput resistance (R15 and R18); therefore
the voltmeter should read 989 V.
7. If the voltmeter does not read 989 V, calibrate the
output voltage by adjusting resistor R12. Access to
R12 is available through a hole in the top cover of
the module. CAUTION: Use only an insulated
screwdriver to make this adjustment, as lethal
voltages exist inside. This adjustment will calibrate
the unit for both positive and negative polarity.
8. Reduce the potentiometer to zero and check the
output voltage versus the potentiometer dial reading
at several points. Resistors R15 and R 17 provide a
method of measuring the detector current with a
voltmeter. (See Section 4.5 for details.) If these
resistors are shorted the output impedance will be
reduced by 1 MÙ. Resistors R 18 and R 19 limit the
current at the current monitoring jacks and prevent
these voltages from being lethal. The output
impedance will be reduced to 110 K, but the
voltages at the current monitoring jacks will be,
lethal because they are not protected by current
limiters.
5.3. TROUBLESHOOTING SUGGESTIONS
1. Ensure that the proper dc voltage is supplied to
the module.
2. Turn the Polarity Selection switch to the Off
position for approximately 2 sec and ensure that the
output is not shorted.
3. Return the Polarity Selection switch to the desired
polarity.
4. Transistors Q1 and Q2 have been selected for a
Vcbo greater than 140 V. Replacement transistors
should be selected for the same high Vcbo.
5.4. REPAIRS
This instrument can be returned to the ORTEC
factory for service and repair at a nominal cost. Our
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 shipping instructions
and so that the required Return Authorization
Number can be assigned to the unit. Write this
number on the address label and on the package to
ensure prompt attention when it reaches the
ORTEC factory.

7
Pin Function Pin Function
1 +3 V 23 Reserved
2 - 3 V 24 Reserved
3 Spare bus 25 Reserved
4 Reserved bus 26 Spare
5 Coaxial 27 Spare
6 Coaxial *28 +24 V
7 Coaxial *29 - 24 V
8 200 V dc 30 Spare bus
9 Spare 31 Spare
*10 +6 V 32 Spare
*11 - 6 V *33 117 V ac (hot)
12 Reserved bus *34 Power return ground
13 Spare 35 Reset (Scaler)
14 Spare 36 Gate
15 Reserved 37 Reset (Auxiliary)
*16 +12 V 38 Coaxial
*17 - 12 V 39 Coaxial
18 Spare bus 40 Coaxial
19 Reserved bus *41 117 V ac (neutral)
20 Spare *42 High-quality ground
21 Spare G Ground guide pin
22 Reserved
Pins marked (*) are installed and wired in
ORTEC’s 4001A and 4001C Modular System
Bins.
Bin/Module Connector Pin Assignments For
Standard Nuclear Instrument Modules per
DOE/ER-0457T.