Model 570Spectroscopy Amplifier

Operating and Service Manual

Printed in U.S.A. ORTEC Part Number 733480 1202Manual Revision E

Advanced Measurement Technology, Inc.

a/k/a/ ORTEC®, a subsidiary of AMETEK®, Inc.

WARRANTYORTEC* warrants that the items will be delivered free from defects in material or workmanship. ORTECmakes no other warranties, express or implied, and specifically NO WARRANTY OF MERCHANTABILITYOR FITNESS FOR A PARTICULAR PURPOSE.

ORTEC’s exclusive liability is limited to repairing or replacing at ORTEC’s option, items found by ORTECto be defective in workmanship or materials within one year from the date of delivery. ORTEC’s liability onany claim of any kind, including negligence, loss, or damages arising out of, connected with, or from theperformance or breach thereof, or from the manufacture, sale, delivery, resale, repair, or use of any item orservices covered by this agreement or purchase order, shall in no case exceed the price allocable to the item orservice furnished or any part thereof that gives rise to the claim. In the event ORTEC fails to manufacture ordeliver items called for in this agreement or purchase order, ORTEC’s exclusive liability and buyer’s exclusiveremedy shall be release of the buyer from the obligation to pay the purchase price. In no event shall ORTECbe liable for special or consequential damages.

Quality ControlBefore being approved for shipment, each ORTEC instrument must pass a stringent set of quality control testsdesigned to expose any flaws in materials or workmanship. Permanent records of these tests are maintainedfor use in warranty repair and as a source of statistical information for design improvements.

Repair ServiceIf it becomes necessary to return this instrument for repair, it is essential that Customer Services be contactedin advance of its return so that a Return Authorization Number can be assigned to the unit. Also, ORTEC mustbe informed, either in writing, by telephone [(865) 482-4411] or by facsimile transmission [(865) 483-2133],of the nature of the fault of the instrument being returned and of the model, serial, and revision ("Rev" on rearpanel) numbers. Failure to do so may cause unnecessary delays in getting the unit repaired. The ORTECstandard procedure requires that instruments returned for repair pass the same quality control tests that areused for new-production instruments. Instruments that are returned should be packed so that they will withstandnormal transit handling and must be shipped PREPAID via Air Parcel Post or United Parcel Service to thedesignated ORTEC repair center. The address label and the package should include the Return AuthorizationNumber 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 TransitShipments should be examined immediately upon receipt for evidence of external or concealed damage. Thecarrier making delivery should be notified immediately of any such damage, since the carrier is normally liablefor damage in shipment. Packing materials, waybills, and other such documentation should be preserved inorder to establish claims. After such notification to the carrier, please notify ORTEC of the circumstances sothat 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 usedherein are the property of their respective owners.

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TABLE OF CONTENTS

WARRANTY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i

1 DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.1 GENERAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2 POLE-ZERO CANCELLATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.3 ACTIVE FILTER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2 SPECIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42.1 PERFORMANCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42.2 CONTROLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42.3 INPUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42.4 OUTPUTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52.5 ELECTRICAL AND MECHANICAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

3 INSTALLATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53.1 GENERAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53.2 CONNECTION TO POWER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53.3 CONNECTION TO PREAMPLIFIER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53.4 CONNECTION OF TEST PULSE GENERATOR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63.5 SHAPING CONSIDERATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63.6 LINEAR OUTPUT CONNECTIONS AND TERMINATING CONSIDERATIONS . . . . . . . . . . . . . . . 63.7 SHORTING OR OVERLOADING THE AMPLIFIER OUTPUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73.8 BUSY OUTPUT CONNECTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

4 OPERATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74.1 INITIAL TESTING AND OBSERVATION

OF PULSE WAVEFORMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74.3 FRONT PANEL CONNECTORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84.4 REAR PANEL CONNECTORS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84.5 STANDARD SETUP PROCEDURE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84.6 POLE-ZERO ADJUSTMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94.7 BLR THRESHOLD ADJUSTMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114.8 OPERATION WITH SEMICONDUCTOR DETECTORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124.9 OPERATION IN SPECTROSCOPY SYSTEMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144.10 OTHER EXPERIMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

5 MAINTENANCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175.1 TEST EQUIPMENT REQUIRED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175.2 PULSER TEST* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175.3 SUGGESTIONS FOR TROUBLESHOOTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195.4 FACTORY REPAIR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195.5 TABULATED TEST POINT VOLTAGES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

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ILLUSTRATIONS

Fig. 1.1. Differentiation in Amplifier Without Pole-Zero Cancellation . . . . . . . . . . . . . . . . . . . . . . . . . 2Fig. 1.2. Differentiation in a Pole-Zero Canceled Amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2Fig. 1.3. Pulse Shapes for Good Signal-to-Noise Ratios . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3Fig. 4.1. Typical Effects of Shaping-Time Selection on Output Waveforms . . . . . . . . . . . . . . . . . . . 8Fig. 4.2. Typical Waveforms Illustrating Pole-Zero Adjustment Effects . . . . . . . . . . . . . . . . . . . . . . . 9Fig. 4.3. A Clamp Circuit that can be used to Prevent Overloading the Oscilloscope Input . . . . . . . 10Fig. 4.4. Pole-Zero Adjustment Using a Square Wave Input to the Preamplifer . . . . . . . . . . . . . . . 10Fig. 4.5. BLR Threshold Variable Control Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11Fig. 4.6. System for Measuring Amplifier and Detector Noise Resolution . . . . . . . . . . . . . . . . . . . . 12Fig. 4.7. Noise as a Function of Bias Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13Fig. 4.8. System for Measuring Resolution with a Pulse Height Analyzer . . . . . . . . . . . . . . . . . . . . 13Fig. 4.9. System for Detector Current and Voltage Measurements . . . . . . . . . . . . . . . . . . . . . . . . . 13Fig. 4.10. Silicon Detector Back Current vs Bias Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14Fig. 4.11. System for High-Resolution Alpha-Particle Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . 14Fig. 4.12. System for High-Resolution Gamma Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15Fig. 4.13. Scintillation-Counter Gamma Spectroscopy System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15Fig. 4.14. High-Resolution X-Ray Energy Analysis System Using a Proportional Counter . . . . . . . . . 15Fig. 4.15. Gamma-Ray Charged-Particle Coincidence Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . 16Fig. 4.16. Gamma-Ray Pair Spectrometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16Fig. 4.17. Gamma-Gamma Coincidence Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17Fig. 5.1. Amplifier Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18Fig. 6.1. Circuit Used to Measure Nonlinearity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

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1 DESCRIPTION

1.1 GENERAL

The ORTEC 570 Spectroscopy Amplifier is asinglewidth NIM module that features a versatilecombination of switch-selectable pulse-shapingcharacteristics. The amplifier has extremely lownoise, a wide gain range, and excellent overloadresponse for universal application in high-resolutionspectroscopy. It accepts input pulses of eitherpolarity that originate in germanium or siliconsemiconductor detectors, in scintillation counterswith either fast or slow scintillators, in proportionalcounters, in pulsed ionization chambers, in electronmultipliers, etc.

The 570 has an input impedance of approximately1000S and accepts either positive or negative inputpulses with rise times <650 ns and fall times >40:s. Six integrate and differentiate time constantsare switch-selectable to provide optimum shapingfor resolution and count rate. The differentiationnetwork has variable pole-zero cancellation that canbe adjusted to match preamplifiers with decay times>40 :s. The pole-zero cancellation drasticallyreduces the undershoot after the differentiator andgreatly improves overload and count ratecharacteristics. In addition, the amplifier contains anactive filter shaping network that optimizes thesignal-to-noise ratio and minimizes the overallresolving time.

The output is unipolar and is used for spectroscopyin systems where dc coupling can be maintainedfrom the 570 to the analyzer. A BLR (baselinerestorer) circuit is included in the 570 for improvedperformance at all count rates. Baseline correctionis applied during intervals between input pulsesonly, and a front panel switch selects adiscriminator level to identify input pulses. Theunipolar output dc level can be adjusted in therange from -100 mV to +100 mV. This outputpermits the use of the direct-coupled input of theanalyzer with a minimum amount of interfaceproblems.

The 570 can be used for constant-fraction timingwhen operated in conjunction with an ORTEC 551,552, or 553 Timing Single-Channel Analyzer. TheORTEC Timing Single-Channel Analyzers featurea minimum of walk as a function of pulse amplitudeand incorporate a variable delay time on the outputpulse to enable the timing pick-off output to beplaced in time coincidence with other signals.

The 570 has complete provisions, including powerdistribution, for operating any ORTEC solid-statepreamplifier. Normally, the preamplifier pulsesshould have a rise time of 0.25 :s or less toproperly match the amplifier filter network and adecay time greater than 40 :s for proper pole-zerocancellation. The 570 input impedance is 1000S.When long preamplifier cables are used, the cablescan be terminated in series at the preamplifier endor in shunt at the amplifier end with the properresistors. The output impedance is about 0.1S, andthe output can be connected to other equipment bya single cable going to all equipment and shuntterminated at the far end of the cabling. SeeSection 3 for further information.

1.2 POLE-ZERO CANCELLATION

Pole-zero cancellation is a method for eliminatingpulse undershoot after the differentiating network.In an amplifier not using pole-zero cancellation(Fig.1.1), the exponential tail on the preamplifieroutput signal (usually 50 to 500 :s) causes anundershoot whose peak amplitude is roughlydetermined from:

undershoot amplitude differentiation time

= differentiated pulse amplitude preamplifier pulse decay time

For a 1-:s differentiation time and a 50-:s pulsedecay time the maximum undershoot is 2% and thisdecays with a 50-:s time constant. Under overloadconditions this undershoot is often sufficiently largeto saturate the amplifier during a considerableportion of the undershoot, causing excessive deadtime. This effect can be reduced by increasing thepreamplifier pulse decay time (which generallyreduces the counting rate capabilities of thepreamplifier) or compensating for the undershoot bycausing pole-zero cancellation.

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Pole-zero cancellation is accomplished by thenetwork shown in Fig. 1.2. The pole [s + (1/T0)] dueto the preamplifier pulse decay time is canceled bythe zero of the network [s + (k/R2C1)]. In effect, thedc path across the differentiation capacitor adds anattenuated replica of the preamplifier pulse to justcancel the negative undershoot of thedifferentiating network.

Total preamplifier-amplifier pole-zero cancellationrequires that the preamplifier output pulse decaytime be a single exponential decay and matched tothe pole-zero cancellation network. The variablepole-zero cancellation network allows accuratecancellation for all preamplifiers having 40-:s orgreater decay times. Improper matching of thepole-zero network will degrade the overload per-formance and cause excessive pileup distortion atmedium counting rates. Improper matching causeseither an undercompensation (undershoot is noteliminated) or an overcompensation (output afterthe main pulse does not return to the baseline butdecays to the baseline with the preamplifier timeconstant). The pole-zero adjust is accessible on thefront panel of the 570 and can easily be adjusted byobserving the baseline on an oscilloscope with amonoenergetic source or pulser having the samedecay time as the preamplifier under overloadconditions. The adjustment should be made so thatthe pulse returns to the baseline in the minimumtime with no undershoot.

1.3 ACTIVE FILTER

When only FET gate current and drain thermalnoise are considered, the best signal-to-noise ratiooccurs when the two noise contributions are equalfor a given input pulse shape. The Gaussian pulseshape (Fig. 1.3) for this condition requires anamplifier with a single RC differentiate and n equalRC integrates where n approaches infinity. TheLaplace 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 andthe second factor is the n integrates. The 570 activefilter approximates this transfer function.

Figure 1.3 illustrates the results of pulse shaping inan amplifier. Of the four pulse shapes shown, thecusp would produce minimum noise but isimpractical to achieve with normal electronic andcircuitry would be difficult to measure with an ADC.The true Gaussian shape deteriorates thesignal-to-noise ratio by only about 12% from that of

the cusp and produces a signal that is easy tomeasure but requires many sections of integration(n 6 00). With two sections of integration thewaveform identified as a Gaussian approximationcan be obtained, and this deteriorates thesignal-to-noise ratio by about 22%. The ORTECactive filter network in the 570 provides a fourth waveform in Fig. 1.3; this waveform hascharacteristics superior to the Gaussianapproximation, yet obtains them with four complex

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poles. By this method the output pulse shape has agood signal-to-noise ratio, is easy to measure, and

yet requires only a practical amount of electroniccircuitry to achieve the desired results.

2 SPECIFICATIONS

2.1 PERFORMANCE

GAIN RANGE Continuously adjustable from X1through X1500.

PULSE SHAPING Gaussian on all ranges withpeaking time equal to and pulse width at 0.1%2 2. τlevel 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, includingcontr ibut ion of ORTEC 551 or 552Constant-Fraction Timing Single-Channel Analyzerusing 50% fraction and 0.5 :s shaping.

COUNT RATE STABILITY The 1.33 MeV gammaray peak from a 60Co source, positioned at 85% ofanalyzer range, typically shifts <0.024%, and itsFWHM broadens <16% when its incoming countrate changes from 0 to 100,000 counts/s using 2 :sshaping and external pileup rejection. The amplifierwill hold the baseline reference up to count rates inexcess of 150,000 counts/s.

OVERLOAD RECOVERY Recovers to within 2%of rated output from X300 overload in 2.5nonoverloaded unipolar pulse widths, usingmaximum gain; same recovery from X1000overload for bipolar pulses.

2.2 CONTROLSGAIN Ten-turn precision potentiometer for continu-ously variable direct-reading gain factor of X0.5 toX1.5.

COARSE GAIN Six-position selector switchselects feedback resistors for gain factors of 20, 50,100, 200, 500, and 1 K.

INPUT ATTENUATOR Jumper on printed circuitboard selects an input attenuation factor of 1 or 10(gain factor of X1 or X0.1).

POS/NEG Locking toggle switch selects inputcircuit for either polarity of input pulses from thepreamplifier.

SHAPING TIME Six-position switch selects timeconstant for active filter network pulse shaping;selections are 0.5, 1, 2, 3, 6, and 10 :s.

PZ ADJ Potentiometer to adjust pole-zerocancellation for decay times from 40 :s to 4.Factory preset at 50 :s to match normalcharacteristics of ORTEC preamplifiers.

BLR Locking toggle switch selects a source for thegated baseline restorer discriminator threshold levelfrom one of three positions.

Auto The BLR threshold is automatically set to anoptimum level as a function of the signal noise levelby an internal circuit. This allows easy setup andvery good performance under most conditions.

PZ Adj The BLR threshold is determined by thethreshold potentiometer. The BLR time constant isgreatly increased to facilitate PZ adjustment. Thisposition may give the lowest noise for conditions of<5000 counts per second and/or longer shapingtimes.

Threshold The BLR threshold is set manually bythe threshold potentiometer. Range is 0 to 300 mVreferred to the positive output signal. The BLR timeconstant is the same as for the Auto switch setting.

DC ADJ Screwdriver potentiometer adjusts theunipolar output baseline dc level; range, +100 mVto -100 mV.

2.3 INPUTINPUT Type BNC front panel connector acceptseither positive or negative pulses with rise times inthe range from 10 to 650 ns and decay times from40 to 2000 :s; Zin ~ 1000S, dc coupled; linearmaximum 1 V (10 V with attenuator jumper set atX0.1); absolute maximum, 20 V.

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2.4 OUTPUTS

UNI Unipolar front panel BNC with Zo <1S. Shortcircuit proof; prompt, full scale linear range 0 to +10V; active filter shaped and dc restored; dc leveladjustable to ±100 mV.

BUSY Rear panel BNC with Zo <10S provides a +5V logic pulse for the duration that the input pulseexceeds the baseline restorer discriminator level.Connect to the ORTEC MCA Busy input for deadtime correction.

PREAMP POWER Rear panel standard ORTECpower connector; Amphenol 17-10090; mates withcaptive and non-captive power cords on allstandard ORTEC preamplifiers.

2.5 ELECTRICAL AND MECHANICAL

POWER REQUIRED (not including any load onthe Preamp Power connector)

+24 V, 80 mA; -24 V, 85 mA; +12 V, 60 mA; -12 V, 30 mA.

FRONT PANEL DIMENSIONS NIM-standardsingle-width module (1.35 by 8.714 in.) perTID-20893 (Rev).

3 INSTALLATION

3.1 GENERAL

The 570 operates on power that must befurnished from a NIM-standard bin and powersupply such as the ORTEC 401/402 Series. Thebin and power supply is designed for relay rackmounting. If the equipment is to be rack mounted,be sure that there is adequate ventilation toprevent any localized heating of the componentsthat are used in the 570. The temperature ofequipment mounted in racks can easily exceedthe maximum limit of 50°C unless precautions aretaken.

3.2 CONNECTION TO POWER

The 570 contains no internal power supply andmust obtain the necessary dc operating power fromthe bin and power supply in which it is installed foroperation. Always turn off power for the powersupply before inserting or removing any modules.After all modules have been installed in the bin andany preamplifiers have also been connected to thePreamp Power connectors on the amplifiers, checkthe dc voltage levels from the power supply to seethat they are not overloaded. The ORTEC 401/402Series Bins and Power Supplies have convenienttest points on the power supply control panel topermit monitoring these dc levels. If any one ormore of the dc levels indicates an overload, someof the modules will need to be moved to another binto achieve operation.

3.3 CONNECTION TO PREAMPLIFIER

The preamplifier output signal is connected to the570 through the Input BNC connector on the frontpanel. The input impedance is about 1000S and isdc-coupled to ground; therefore the preamplifieroutput must be either ac-coupled or haveapproximately zero dc voltage under no-signalconditions.

The 570 incorporates pole-zero cancellation inorder to enhance the overload and count ratecharacteristics of the amplifier. This techniquerequires matching the network to the preamplifierdecay-time constant in order to achieve perfectcompensation. The pole-zero adjustment should beset each time the preamplifier or the shaping timeconstant of the amplifier is changed. For details ofthe pole-zero adjustment, see Section 4.6. Analternate method is accomplished easily by using amonoenergetic source and observing the amplifierbaseline with an oscilloscope after each pulse underapproximately X2 overload conditions. Adjustmentshould be made so that the pulse returns to thebaseline in a minimum amount of time with noundershoot.

Preamplifier power at +24 V, -24 V, +12 V, and -12V is available through the Preamp Power connectoron the rear panel. When the preamplifier isconnected, its power requirements are obtainedfrom the same bin and power supply as is used forthe amplifier and this increases the dc loading oneach voltage level over and above the re-quirements for the 570 at the module position in thebin.

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When the 570 is used with a remotely locatedpreamplif ier (i.e., preamplif ier-to-amplif ierconnection through 25 ft or more of coaxial cable),be careful to ensure that the characteristicimpedance of the transmission line from thepreamplifier output to the 570 input is matched.Since the input impedance of the 570 is about1000S, sending-end termination will normally bepreferred; the transmission line should beseries-terminated at the preamplifier output. AllORTEC preamplifiers contain series terminationsthat are either 93S or variable; coaxial cable typeRG-62/U or RG-71/U is recommended.

3.4 CONNECTION OF TEST PULSEGENERATOR

THROUGH A PREAMPLIFIER The satisfactoryconnection of a test pulse generator such as theORTEC 419 Precision Pulse Generator orequivalent depends primarily on two considerations;the preamplifier must be properly connected to the570 as discussed in Section 3.3, and the properinput signal simulation must be applied to thepreamplifier. To ensure proper input signal simu-lation, refer to the instruction manual for theparticular preamplifier being used.

DIRECTLY INTO THE 570 Since the input of the570 has 1000S of input impedance, the test pulsegenerator will normally have to be terminated at theamplifier input with an additional shunt resistor. Inaddition, if the test pulse generator has a dc offset,a large series isolating capacitor is also requiredsince the 570 input is dc coupled. The ORTEC testpulse generators are designed for direct connection.When any one of these units is used, it should beterminated with a 100S terminator at the amplifierinput or be used with at least one of the outputattenuators set at In. (The small error due to thefinite input impedance of the amplifier can normallybe neglected.)

SPECIAL CONSIDERATIONS FOR POLE-ZEROCANCELLATION When a tail pulser is connecteddirectly to the amplifier input, the PZ ADJ should beadjusted if overload tests are to be made (othertests are not affected). See Section 4.6 for thepole-zero adjustment. If a preamplifier is used anda tail pulser is connected to the preamplifier testinput, similar precautions are necessary. In thiscase the effect of the pulser decay must be re-moved; i.e., a step input should be simulated.

3.5 SHAPING CONSIDERATIONS

The shaping time constant on the 570 isswitch-selectable in steps of 0.5, 1, 2, 3, 6, and

10 :s. The choice of the proper shaping timeconstant is generally a compromise betweenoperating at a shorter time constant for accom-modation of high counting rates and operating witha longer time constant for a better signal-to-noiseratio. For scintillation counters, the energyresolution depends largely on the scintillator andphotomultiplier, and therefore a shaping timeconstant of about four times the decay-timeconstant of the scintillator is a reasonable choice(for Nal, a 1-:s shaping time constant is aboutoptimum). For gas proportional counters, thecollection time is normally in the 0.5 to 5 :s rangeand a 2-:s or greater time constant selection willgenerally give optimum resolution. For surfacebarrier semiconductor detectors, a 0.5- to 2-:sresolving time will generally provide optimumresolution. Shaping time for Ge(Li) detectors willvary from 1 to 6 :s, depending on the size,configuration, and collection time of the specificdetector and preamplifier. When a charge-sensitivepreamplifier is used, the optimum shaping timeconstant to minimize the noise of a system can bedetermined by measuring the output noise of thesystem and dividing it by the system gain. Since the570 has almost constant gain for all shaping modes,the optimum shaping can be determined bymeasuring the output noise of the 570 with avoltmeter as each shaping time constant isselected.

3.6 LINEAR OUTPUT CONNECTIONS ANDTERMINATING CONSIDERATIONS

Since the 570 unipolar output is normally used forspectroscopy, the 570 is designed with a greatamount of flexibility in order for the pulse to beinterfaced with an analyzer. A gated baselinerestorer (BLR) circuit is included in this output forimproved performance at all count rates. A switchon the front panel permits the threshold for therestorer gate to be determined automatically,according to the input noise level, or manually, witha screwdriver adjustment. The switch also has acenter PZ ADJ setting that can be used to eliminatethe BLR effect when making pole-zero adjustments.The unipolar output dc level can be adjusted from!0.1 to +0.1 V to set the zero intercept on theanalyzer when direct coupling is used.

Three general methods of termination are used.The simplest of these is shunt termination at thereceiving end of the cable. A second method isseries termination at the sending end. The third is acombination of series and shunt termination, wherethe cable impedance is matched both in series atthe sending end and in shunt at the receiving end.

7

The combination is most effective, but this reducesthe amount of signal strength at the receiving endto 50% of that which is available in the sending in-strument.

To use shunt termination at the receiving end of thecable, connect the output on the 570 front panelthrough 93S cable to the input of the receivinginstrument. Then use a BNC tee connector to attachboth the interconnecting cable and a 100Sterminator at the input connector of the receivinginstrument. Since the input impedance of thereceiving instrument is normally 1000S or more,the effective instrument input impedance with the100S terminator will be of the order of 93S and thiswill match the cable impedance correctly.

For customer convenience, ORTEC stocks theproper terminators and BNC tees, or they can beordered from a variety of commercial sources.

3.7 SHORTING OR OVERLOADING THEAMPLIFIER OUTPUT

The 570 output is dc coupled with an outputimpedance of about 0.1S. If the output is shortedwith a direct short circuit the output stage will limitthe peak current of the output so that the amplifierwill not be harmed. When the amplifier isterminated with 100S, the maximum rate allowedto maintain the linear output is

200 000 cps 10 -------------------- x ---------- .

(:S) V0(V)τ

3.8 BUSY OUTPUT CONNECTION

The signal through the rear panel Busy outputconnector rises from 0 to about +5 V at the onset ofeach linear input pulse. Its width is equal to the timethe input pulse amplitude exceeds the BLRdiscriminator level. It can be used to provide MCAdead time correction, to control the generation ofinput pulses, to observe normal operation with anoscilloscope, or for any of a variety of other ap-plications. Its use is optional and no termination isrequired if the output is not being used.

4 OPERATION

4.1 INITIAL TESTING AND OBSERVATIONOF PULSE WAVEFORMS

Refer to Section 6 for information on testingperformance and observing waveforms at frontpanel test points. Figure 4.1 shows some typicalunipolar output waveforms.

4.2 FRONT PANEL CONTROLS

GAIN A Coarse Gain switch and a Gain 10-turnlocking precision potentiometer select and preciselyadjust the gain factor for the amplification in the570. Switch settings are X20, 50, 100, 200, 500,and 1000. Continuous fine gain range is from X0.5to X1.5, using markings of 500 through 1500 dialdivisions. An internal jumper setting provides oneadditional gain factor selection of either X1.0 orX0.1. Collectively the range of gain can be set atany level from X1.0 through X1500, using all threeof these controls.

POS/NEG A locking toggle switch selects an inputcircuit that accepts either polarity of pulses from thepreamplifier.

PZ ADJ A screwdriver control to set the pole-zerocancellation to match the preamplifier pulse decaycharacteristics. The range is from 40 :s to 00.

DC ADJ A screwdriver control adjusts the dcbaseline level of the unipolar output in the range of-0.1 V to +0.1 V.

SHAPING A 6-position switch selects equalintegrate and differentiate time constants to shapethe input pulses. Settings are 0.5, 1, 2, 3, 6, and 10:s.

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BLR A 3-position locking toggle switch controls theoperation of the internal baseline restorer (BLR)circuit.

The center setting of the switch is effectively Off,and this permits adjustment of the PZ ADJ controlwithout interference from the BLR circuit. The Autosetting of the switch selects a circuit that regulatesthe threshold of the BLR gate according to theoutput noise level. The Threshold setting permitsmanual control of the BLR gate threshold, using thescrewdriver control immediately below the toggleswitch.

4.3 FRONT PANEL CONNECTORS

INPUT Accepts input pulses to be shaped and/oramplified by the 570. Compatible characteristics;positive or negative with rise time from 10 to 650ns; decay time greater than 40 :s for properpole-zero cancellation; input linear amplitude range0 to 10 V, with a maximum limit of ±20 V. Inputimpedance is approximately 1000S.

UNIPOLAR OUTPUT Provides a unipolar positiveoutput with characteristics that are related to inputpeak amplitude, gain, shaping time constants,pole-zero cancellation, and baseline stabilization.The dc baseline level is adjustable for offset to ±0.1V. Output impedance through this connector isabout 0.1S, dc coupled. Linear range 0 to +10 V.

4.4 REAR PANEL CONNECTORS

BUSY Provides a signal that rises to approximately+5 V for the time that the input pulse amplitudeexceeds the BLR discriminator level, which can becontrolled manually or automatically. The outputcan be used to correct for dead time in the ORTECMCA by connecting it to the MCA Busy input.

PREAMP Provides power connections from the binand power supply to the ORTEC preamplifier. Thedc levels include +24 V, -24 V, +12 V, and -12 V.

4.5 STANDARD SETUP PROCEDURE

a. Connect the detector, preamplifier, high voltagepower supply, and amplifier into a basic system andconnect the amplifier output to an oscilloscope.Connect the preamplifier power cable to thePreamp connector on the 570 rear panel. Turn onpower in the bin and power supply and allow theelectronics of the system to warm up and stabilize.

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b. Set the 570 controls initially as follows:

Shaping 2 :sCoarse Gain 50Gain 1.000Internal Jumper X1.0 (factory installedposition)BLR PZ ADJThresh Fully clockwisePos/Neg Match input pulse polarity

c. Use a 60CO calibration source; place it about 25cm from the active face of the detector. Theunipolar output pulse from the 570 should be about8 to 10 V, using a preamplifier with a conversiongain of 170 mV/MeV.

d. Readjust the Gain control so that the higher peakfrom the 60CO source (1.33 MeV) provides anamplifier output at about 9 V.

4.6 POLE-ZERO ADJUSTMENT

The pole-zero adjustment is extremely critical forgood performance at high count rates. Thisadjustment should be checked carefully for the bestpossible results.

USING A GERMANIUM SYSTEM AND 60COa. Adjust the radiation source count rate between 2kHz and 10 kHz.

b. Observe the unipolar output with anoscilloscope. Adjust the PZ ADJ control so that thetrailing edge of the pulses returns to the baselinewithout overshoot or undershoot (see Fig. 4.2).

The oscilloscope used must be dc coupled andmust not contribute distortion in the observedwaveforms. Oscilloscopes such as Tektronix 453,454, 465, and 475 will overload for a 10-V signalwhen the vertical sensitivity is less than 100mV/cm. To prevent overloading the oscillbscope,use the clamp circuit shown in Fig. 4.3.

USING SQUARE WAVE THROUGH PREAMPLIFIER TEST INPUTA more precise pole-zero adjustment in the 570 canbe obtained by using a square wave signal as theinput to the preamplifier. Many oscilloscopesinclude a calibration output on the front panel andthis is a good source of square wave signals at afrequency of about 1 kHz. The amplifierdifferentiates the signal from the preamplifier sothat it generates output signals of alternatepolarities on the leading and trailing edges of thesquare wave input signal, and these can be

10

compared as shown in Fig. 4.4 to achieve excellentpole-zero cancellation. Use the followingprocedure:

a. Remove all radioactive sources from the vicinityof the detector. Set up the system as for normaloperation, including detector bias.

b. Set the 570 controls as for normal operation; thisincludes gain, shaping, and input polarity.

c. Connect the source of 1-kHz square wavesthrough an attenuator to the Test input of thepreamplifier. Adjust the attenuator so that the570 output amplitude is about 9 V.d. Observe theUnipolar output of the 570 with an oscilloscope,triggered from the 570 Busy output. Adjust the PZADJ control for proper response according to Fig.4.4. Use the clamp circuit or Fig. 4.3 to preventoverloading the oscilloscope input.

Figure 4.4A. shows the amplifier output as a seriesof alternate positive and negative Gaussian pulses.In the other three pictures of this figure, theoscilloscope was triggered to show both positiveand negative pulses simultaneously. These picturesshow more detail to aid in proper adjustment.

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4.7 BLR THRESHOLD ADJUSTMENT

After the amplifier gain and shaping have beenselected and the PZ ADJ control has been set tooperate properly for the particular shaping time,the BLR Thresh control can be used to establishthe correct discriminator threshold for thebaseline restorer circuit. Normally, the toggleswitch can be set at Auto, and the threshold levelwill be set automatically just above the noiselevel. If desired, the switch can be set atThreshold and the manual control just below theswitch can then be used to select the levelmanually as follows:

a. Remove all radioactive sources from the vicinityof the detector. Set up the system as for normaloperation, including detector bias.

b. Set the BLR switch at Threshold and turn thecontrol fully clockwise, for 300 mV.

c. Observe the unipolar output on the 100 mV/cmscale of the oscilloscope, using 5 :s/cm horizontaldeflection. Trigger the oscilloscope with the Busyoutput from the 570.

d. Reduce the control setting until the baselinediscriminator begins to trigger on noise; thiscorresponds to about 200 counts/s from the Busyoutput. Adjust the trigger level according to theinformation in Fig. 4.5.

If a ratemeter or counter-timer is available, it canbe connected to the Busy output and the thresholdlevel can then be adjusted for about 200 counts/s.

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4.8 OPERATION WITH SEMICONDUCTORDETECTORS

CALIBRATION OF TEST PULSER An ORTEC419 Precision Pulse Generator, or equivalent, iseasily calibrated so that the maximum pulse heightdial reading (1000 divisions) is equivalent to10-MeV loss in a silicon radiation detector. Theprocedure is as follows:

a. Connect the detector to be used to thespectrometer system; i.e., preamplifier, mainamplifier, and biased amplifier.

b. Allow excitation from a source of known energy(for example, alpha particles) to fall on thedetector.

c. Adjust the amplifier gain and the bias level of thebiased amplifier to give a suitable output pulse.

d. Set the pulser Pulse Height control at the energyof the alpha particles striking the detector (forexample, set the dial at 547 divisions for a 5.47-MeV alpha particle energy).

e. Turn on the pulser and use its Normalize controland attenuators to set the output due to the pulserfor the same pulse height as the pulse obtained instep c. Lock the Normalize control and do notmove it again until recalibration is required.

The pulser is now calibrated; the Pulse Height dialreads directly in MeV if the number of dial divisionsis divided by 100.

AMPLIFIER NOISE AND RESOLUTIONMEASUREMENTS As shown in Fig. 4.6, apreamplif ier, amplif ier, pulse generator,oscilloscope, and wide-band rms voltmeter such asthe Hewlett-Packard 3400A are required for thismeasurement. Connect a suitable capacitor to theinput to simulate the detector capacitance desired.To obtain the resolution spread due to amplifiernoise:

a. Measure the rms noise voltage (Erms) at theamplifier output.

b. Turn on the 419 Precision Pulse Generator andadjust the pulser output to any convenient readablevoltage, Eo, as determined by the oscilloscope. Thefull width at half maximum (FWHM) resolutionspread due to amplifier noise is then

2.35 Erms Edial

N(FWHM) = ---------------------------------- Eo

where Edial is the pulser dial reading in MeV and2.35 is the factor for rms to FWHM. Foraverage-responding voltmeters such as theHewlett-Packard 400D, the measured noise mustbe multiplied by 1.13 to calculate the rms noise.

The resolution spread will depend on the total inputcapacitance, since the capacitance degrades thesignal-to-noise ratio much faster than the noise.

D E T E C T O R N O I S E - R E S O L U T I O NMEASUREMENTS The measurement justdescribed can be made with a biased detectorinstead of the external capacitor that would be usedto simulate detector capacitance. The resolutionspread will be larger because the detectorcontributes both noise and capacitance to the input.The detector noise-resolution spread can beisolated from the amplifier noise spread if thedetector capacity is known, since

(Ndet)2 + (Namp)

2 = (Ntotal)2,

where Ntotal is the total resolution spread and Namp isthe amplifier resolution spread when the detector isreplaced by its equivalent capacitance.

The detector noise tends to increase with biasvoltage, but the detector capacitance decreases,thus reducing the resolution spread. The overallresolution spread will depend upon which effect isdominant. Figure 4.7 shows curves of typicalnoise-resolution spread versus bias voltage, usingdata from several ORTEC silicon surface barriersemiconductor radiation detectors.

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A M P L I F I E R N O I S E - R E S O L U T I O NMEASUREMENTS USING MCA Probably the mostconvenient method of making resolutionmeasurements is with a pulse height analyzer asshown by the setup illustrated in Fig. 4.8.

The amplifier noise-resolution spread can bemeasured directly with a pulse height analyzer andthe mercury pulser as follows:

a. Select the energy of interest with an ORTEC 419Precision Pulse Generator. Set the amplifier andbiased amplifier gain and bias level controls so thatthe energy is in a convenient channel of theanalyzer.

b. Calibrate the analyzer in keV per channel, usingthe pulser; full scale on the pulser dial is 10 MeVwhen calibrated as described above.

c. Obtain the amplifier noise-resolution spread bymeasuring the FWHM of the pulser peak in thespectrum.

The detector noise-resolution spread for a givendetector bias can be determined in the samemanner by connecting a detector to thepreamplifier input. The amplifier noise-resolutionspread must be subtracted as described in"Detector Noise-Resolution Measurements." Thedetector noise will vary with detector size and biasconditions and possibly with ambient conditions.

CURRENT-VOLTAGE MEASUREMENTS FOR SiAND Ge DETECTORS The amplifier system is notdirectly involved in semiconductor detectorcurrent-voltage measurements, but the amplifierserves to permit noise monitoring during the setup.The detector noise measurement is a moresensitive method than a current measurement ofdetermining the maximum detector voltage thatshould be used because the noise increases morerapidly than the reverse current at the onset ofdetector breakdown. Make this measurement in theabsence of a source.

Figure 4.9 shows the setup required forcurrent-voltage measurements. An ORTEC 428Bias Supply is used as the voltage source. Biasvoltage should be applied slowly and reducedwhen noise increases rapidly as a function ofapplied bias. Figure 4.10 shows several typicalcurrent voltage curves for ORTEC siliconsurface-barrier detectors.

When it is possible to float the microammeter atthe detector bias voltage, the method of detectorcurrent measurement shown by the dashed lines in

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Fig. 4.9 is preferable. The detector is grounded asin normal operation and the microammeter isconnected to the current monitoring jack on the 428Detector Bias Supply.

4.9 OPERATION IN SPECTROSCOPYSYSTEMS

HIGH-RESOLUTION ALPHA-PARTICLESPECTROSCOPY SYSTEM The block diagram ofa high-resolution spectroscopy system formeasuring natural alpha particle radiation is shownin Fig. 4.11. Since natural alpha radiation occursonly above several MeV, an ORTEC 444 BiasedAmplifier is used to suppress the unused portion ofthe spectrum; the same result can be obtained byusing digital suppression on the MCA in manycases. Alphaparticle resolution is obtained in thefollowing manner:

a. Use appropriate amplifier gain and minimumbiased amplifier gain and bias level. Accumulatethe alpha peak in the MCA.

b. Slowly increase the bias level and biasedamplifier gain until the alpha peak is spread over 5to 10 channels and the minimum-tomaximum-energy range desired corresponds to thefirst and last channels of the MCA.

c. Calibrate the analyzer in keV per channel usingthe pulser and the known energy of the alpha peak(see "Calibration of Test Pulser") or twoknown-energy alpha peaks.

d. Calculate the resolution by measuring thenumber of channels at the FWHM level in the peakand converting this to keV.

HIGH-RESOLUTION GAMMA SPECTROSCOPYSYSTEM A high-resolution gamma spectroscopysystem block diagram is shown in Fig. 4.12.Although a biased amplifier is not shown (ananalyzer with more channels being preferred), itcan be used if the only analyzer available hasfewer channels and only higher energies are ofinterest.

When germanium detectors that are cooled by aliquid nitrogen cryostat are used, it is possible toobtain resolutions from about 1 keV FWHM up(depending on the energy of the incident radiationand the size and quality of the detector).Reasonable care is required to obtain such results.

Some guidelines for obtaining optimum resolutionare:

a. Keep interconnection capacities between the de-tector and preamplifier to an absolute minimum (nolong cables).

b. Keep humidity low near the detector-preamplifierjunction.

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c. Operate the amplifier with the shaping time thatprovides the best signal-to-noise ratio.

d. Operate at the highest allowable detector bias tokeep the input capacity low. S C I N T I L L AT I O N- CO UNT E R G AM M ASPECTROSCOPY SYSTEMS The ORTEC 570can be used in scintillation-counter spectroscopysystems as shown in Fig. 4.13. The amplifiershaping time constants should be selected in theregion of 0.5 to 1 :s for Nal or plastic scintillators.

For scintillators having longer decay times, longertime constants should be selected.

X - R A Y S P E C T R O S C O P Y U S I N GPROPORTIONAL COUNTERS Space chargeeffects in proportional counters, operated at highgas amplification, tend to degrade the resolutioncapabilities drastically at x-ray energies, even atrelatively low counting rates. By using a high-gainlow-noise amplifying system and lower gasamplification, these effects can be reduced and aconsiderable improvement in resolution can beobtained.

The block diagram in Fig. 4.14 shows a system ofthis type. Analysis can be accomplished bysimultaneous acquisition of all data on amultichannel analyzer or counting a region ofinterest in a single-channel analyzer window with acounter and timer or counting ratemeter.

4.10 OTHER EXPERIMENTS

Block diagrams illustrating how the 570 and otherORTEC modules can be used for experimentalsetups for various other applications are shown inFigs. 4.15, 4.16, and 4.17.

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17

5 MAINTENANCE

5.1 TEST EQUIPMENT REQUIRED

The following test equipment should be utilized toadequately test the specifications of the 570Spectroscopy Amplifier:

1. ORTEC 419 Precision Pulse Generator or 448Research Pulser.

2. Tektronix 547 Series Oscilloscope with a type1A1 plug-in or equivalent.

3. Hewlett-Packard 3400A rms Voltmeter.

5.2 PULSER TEST*

FUNCTIONAL CHECKS Set the 570 controls asfollows:

Coarse Gain 1K

Gain 1.5

Input Polarity Positive

Shaping Time Constant 1 :s

BLR PZ ADJ

Variable control Fully CW for 300 mV

a. Connect a positive pulser output to the 570 Inputand adjust the pulser to obtain +10 V at the 570output. This should require an input pulse of 6.6mV, using a 100S terminator at the input.

b. Change the Input polarity switch to Neg and thenback to Pos while monitoring the output for apolarity inversion.

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c. Vary the DC ADJ control on the front panel whilemonitoring the Unipolar output. Ensure that thebaseline can be adjusted through a range of +0.1 to-0.1 V. Readjust the control for zero.

d. Recheck the output pulse amplitude and adjustif necessary to set it at +10 V with maximum gain.Decrease the Coarse Gain switch stepwise from 1Kto 20 and ensure that the output amplitude changesby the appropriate amount for each step. Returnthe Coarse Gain switch to 1K.

e. Decrease the Gain control from 1.5 to 0.5 andcheck to see that the output amplitude decreasesby a factor of 3. Return the Gain control tomaximum at 1.5.

f. With the Shaping switch set for 1 :s, measurethe time to the peak on the unipolar output pulse;this should be 2.2 :s, for 2.2 . Measure the timeτto baseline crossover of the bipolar output; thisshould be 2.8 :s for 2.8 .τ

g. Change the Shaping switch to 0.5 through 10 :sin turn. At each setting, check to see that the timeto the unipolar peak is 2.2 Return the switch to 1τ:s.

OVERLOAD TESTS Start with maximum gain,= 2 :s, and a +10 V output amplitude. Increaseτ

the pulser output amplitude by X200 and observethat the unipolar output returns to within 200 mV ofthe baseline within 24 :s after the application of asingle pulse from the pulser. It will probably benecessary to vary the PZ ADJ control on the frontpanel in order to cancel the pulser pole andminimize the time required for return to thebaseline.

LINEARITY The integral nonlinearity of the 570can be measured by the technique shown inFig. 5.1. In effect, the negative pulser output issubtracted from the positive amplifier output tocause a null point that can be measured withexcellent sensitivity. The pulser output must bevaried between 0 and 10 V, which usually requiresan external control source for the pulser. Theamplifier gain and the pulser attenuator must beadjusted to measure 0 V at the null point when thepulser output is 10 V. The variation in the null pointas the pulser is reduced gradually from 10 V to 0 Vis a measure of the nonlinearity. Since thesubtraction network also acts as a voltage divider,this variation must be less than (10 V full scale) x(±0.05% maximum nonlinearity) x (1/2 for dividernetwork) =±2.5 V for the maximum null-pointvariation.

OUTPUT LOADING Use the test setup of Fig. 5.1.Adjust the amplifier output to 10 V and observe thenull point when the front panel output is terminatedin 100S. The change should be less than 5 Mv.NOISE Measure the noise at the amplifier Unipolaroutput with maximum amplifier gain and 2 :sshaping time. Using a true-rms voltmeter, the noiseshould be less than 5 :V x 1500 (gain), or 7.5 mV.For an average responding voltmeter, the noisereading would have to be multiplied by 1.13 tocalculate the rms noise. The input must beterminated in 100 S during the noisemeasurements.

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5.3 SUGGESTIONS FORTROUBLESHOOTING

In situations where the 570 is suspected of amalfunction, it is essential to verify suchmalfunction in terms of simple pulse generatorimpulses at the input. The 570 must bedisconnected from its position in any system, androutine diagnostic analysis performed with a testpulse generator and an oscilloscope. It isimperative that testing not be performed with asource and detector until the amplifier performssatisfactorily with the test pulse generator.

The testing instructions in Section 5.2 shouldprovide assistance in locating the region of troubleand repairing the malfunction. The two side platescan be completely removed from the module toenable oscilloscope and voltmeter observations.

5.4 FACTORY REPAIRThis instrument can be returned to the ORTECfactory for service and repair at a nominal cost. Ourstandard procedure for repair ensures the samequality control and checkout that are used for a newinstrument. Always contact Customer Services atORTEC, (865) 482-4411, before sending in aninstrument for repair to obtain shipping instructionsand so that the required Return AuthorizationNumber can be assigned to the unit. This numbershould be marked on the address label and on thepackage to ensure prompt attention when the unitreaches the factory.

5.5 TABULATED TEST POINT VOLTAGES

The voltages given in Table 5.1 are intended toindicate typical dc levels that can be measured onthe printed circuit board. In some cases the circuitwill perform satisfactorily even though, due tocomponent tolerances, there may be some voltagemeasurements that differ slightly from the listedvalues. Therefore the tabulated values should notbe interpreted as absolute voltages but areintended to serve as an aid in troubleshooting.

Note: All voltages measured with no input signal, with the input terminated in 100 S, and all controls set fullyclockwise at maximum.

Location VoltageTP1 ±10 mVTP2 ±30 m VTP3 ±20 mVTP4 ±20 mV TP5 ±30 mVTP6 0 to +3.3 VTP7 ±6 m VQ15E -15 V ±0.8 V Q16E +15 V ±0.8 V IC13 pin 2 +5 V ±0.3 V

Table 5.1. Typical dc Voltages

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BIN/MODULE CONNECTOR PIN ASSIGNMENTSFOR STANDARD NUCLEAR INSTRUMENT

MODULES PER DOE/ER-0457T

Pin Function Pin Function

1 +3 volts 23 Reserved

2 -3 volts 24 Reserved

3 Spare Bus 25 Reserved

4 Reserved Bus 26 Spare

5 Coaxial 27 Spare

6 Coaxial *28 +24 volts

7 Coaxial *29 -24 volts

8 200 volts dc 30 Spare Bus

9 Spare 31 Spare

*10 +6 volts 32 Spare

*11 -6 volts *33 117 volts 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 volts 38 Coaxial

*17 -12 volts 39 Coaxial

18 Spare Bus 40 Coaxial

19 Reserved Bus *41 117 volts ac (Neut.)

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 SystemBins.