Technical Information Manual
Contents
1. o 3 rp ES ul Z o I Revision date Revision 14 06 2004 4 Fig 2 1 Mod N968 Front and back panel NPO Filename 00100 03 N968x MUTx 04 N968_REV4 DOC Number of pages 14 Page 6 CAEN Document type Title Revision date Revision User s Manual MUT Mod N968 Spectroscopy Amplifier 14 06 2004 4 2 4 Front panel controls FINE GAIN COARSE GAIN S F GAIN INPUT SHAPING TIME PZ ADJ DELAY BLR DC 10 turn precision potentiometer with graduated dial for continuously variable direct reading gain factor of x0 5 to x1 5 6 position switch selects feedback resistors for gain factors of 20 50 100 200 500 and 1k Two Jumpers on the printed circuit board select x0 1 attenuation and x2 Amplification see 2 5 SUPERFINE GAIN screwdriver adjustable potentiometer to adjust fine gain adjustment range 2 5 of the FINE GAIN RANGE Locking toggle switch selects either Pos positive or Neg negative input pulse polarity 6 position switch selects time constants for active pulse shaping filter network from 0 5 1 2 3 6 and 10 us Screwdriver adjustable potentiometer to set the pole zero cancellation to compensate input decay times from 40 us to infinity Locking toggle switch allows to set UNIpolar output either to prompt or delayed 2 us 3 position locking toggle switch selects the source of control for the gated baseline restorer discriminator thre2. Shaping determination The proper shaping time constant must be seen as the better compromise in order to match high count rates requirements which lead to small time constant and good signal to noise ratios which lead to big values For scintillation counters the energy resolution depends largely on the detector scintillator and photomultiplier therefore a shaping time constant of about four times the decay time constant of the scintillator is a reasonable value Gas proportional counters usually have a collection time in the 0 5 5 us range so a 2 us time constant could provide a good resolution Instead for surface barrier semiconductors a time constant in the 0 5 2 us range is recommended Equipment facilities In order to provide the User with an equipment suitable for almost any spectroscopy application the Mod N968 includes a Pile up Rejector Live Time Corrector PUR LTC circuitry which allows operation with minimal dependence on system count rate The PUR circuit interrogates incoming pulses for pile up and generates a signal that prevents the ADC from converting the piled up events The LTC circuit then generates a system dead time that extends the collection time to compensate for the events lost due to pileup rejection The result is lower background better resolution and accurate live time information for the best possible analysis results a gated Baseline Restorer BLR which includes a discriminato
3. 7 INPUT OUTPUT CONNECTIONS da 9 2 8 TECHNICAL SPECIFICATION TABLE sccssssssssesessessesencesessensesensensssencsccssenssecasssenacessecssnesecessneneceesecaeseesecaeenens 10 3 FUNCTIONAL DESCRIPTION eseneeneneennnnennennnennnnennnnnnnnnnnnnsss 12 3 1 SHAPING DETERMINATION e 3 6 6c Cate Ete EHE ainia 12 32 EQUIPMENT FACILITIES 2004 Ac rete E e ET RE are edt e e e tie ede 12 3 3 CIRCUIT DESCRIPTION ii N s 13 LIST OF FIGURES FIG 2 1 MOD N968 FRONT AND BACK PANEL msn 6 FIG 2 2 MOD N968 SIDE VIEW WITH JUMPERS LOCATION sens 8 FIG 2 3 UNIPOLAR OUTPUT EQUIVALENT RMS NOISE VS SHAPING TIME TS 11 FIG 2 4 BIPOLAR OUTPUT EQUIVALENT RMS NOISE VS SHAPING TIME TS 11 FIG 3 1 N968 CIRCUIT BLOCK DIAGRAM con iiie eer E EEA EET E R A 13 FIG 32 N968 J O TIMING DIAGRAMA aia 14 LIST OF TABLES TABLE 2 1 POWER REQUIREMENT Svr rerea e ea n e Nee e Denia E e NER ea ea daera e aR 5 TABLE 2 2 MOD N968 TECHNICAL FEATURES cscsccssssscssesssssescscescsssesessesesssesacsesesessesesesecaeseseaaeecseseceeseseseneceeseeesaeess 10 NPO Filename Number of pages Page 00100 03 N968x MUTx 04 N968_REV4 DOC 14 3 CAER Document type Title Revision date Revision User s Manual MUT Mod N968 Spectroscopy Amplifier 14 06 2004 4 1 General description 1 1 Overview The Mod N968 is a spectroscopy amplifier implemented in a single width NIM module It accepts the typical outputs generated from either optical feedback or resis
4. levels saturation and output dynamics reduction The fast differentiator stage allows to acquire the pulse s arrival time through a comparator fast discriminator whose output is used also to form the Count Rate Meter CRM output Another comparator slow discriminator provides the BUSY output operating directly over the UNIpolar output The baseline restorer BLR also operates over the UNIpolar output and its purpose is to keep the baseline constantly at the level set through the DC control in order to decouple the pulse acquisition from the input rate Filename Number of pages Page 00100 03 N968x MUT x 04 N968_REV4 DOC 14 13 CAER Document type Title Revision date Revision User s Manual MUT Mod N968 Spectroscopy Amplifier 14 06 2004 4 N968 INPUT SHAPERS INPUT UNIPOLAR OUTPUT FAST DIFF OUTPUT CRM OUTPUT BUSY OUTPUT INHIBIT OUTPUT LTC OUTPUT MCA RTP OUTPUT NPO The chain is completed by the UNIpolar output stage the delay circuit and the Bipolar forming and output stage The fast and slow discriminators thresholds can be set either manually or automatically in the latter case a circuit provides the threshold value according to the UNIpolar output noise level The gated logic block manages the signals provided by the discriminators the baseline restorer and performs the pile up rejection PUR and live time correction LTC The timing diagram in Fig 3 2 shows the PUR function a
5. T Mod N968 Spectroscopy Amplifier 14 06 2004 4 to pile up Signals whose peak occurs when the INH signal is active must be thus rejected BUSY Rear panel BNC connector with Z lt 10 Q provides a 5 V logic pulse for the duration that the input pulse exceeds the baseline restorer discriminator LTC Rear panel BNC connector provides a positive true TTL logic signal that is used to stop the MCA time counter this allows a precise evaluation of the source actual rate PREAMP POWER Rear panel D type 9 pin female power connector it mates with captive and noncaptive power cords on almost all preamplifiers Contact assignment is shown in Fig 2 1 2 8 Technical specification table Table 2 2 Mod N968 Technical Features Packaging One unit wide NIM unit UNIpolar shape quasi Gaussian peaking time 24 Ts pulse Pulse shape width at 0 196 level equal to 2 9 times the peaking time Bipolar shape approximate derivative time to crossover 3 Ts Integral non linearity t 0 025 O 2 us shaping time Gain lt 50 ppm C DC level UNIpolar output lt 10 uV C Blpolar output lt 30 uV C Bipolar crossover walk lt 3 ns at 2 us Ts for 50 1 dynamic range Temperature instability 0 to 50 C Recovers to within 2 of rated output from X300 overload in 2 5 Overload recovery nonoverloaded pulse widths using a gain of 1000 for UNIpolar Output Same recovery from X1000 overload for Blpolar Typical lt 16 FWHM for a Co 1 33 MeV ga
6. Technical Information M anual Revision n 4 14 June 2004 MOD N 968 SPECTROSCOPY AM PLIFIER MANUAL REV A NPO 00100 03 N 968x M UT x 04 CAEN will repair or replace any product within the guarantee period if the Guarantor declares that the product is defective due to workmanship or materials and has not been caused by mishandling negligence on behalf of the User accident or any abnormal conditions or operations CAEN declines all responsibility for damages or injuries caused by an improper use of the Modules due to negligence on behalf of the User It is strongly recommended to read thoroughly the CAEN User s Manual before any kind of operation CAEN reserves the right to change partially or entirely the contents of this Manual at any time and without giving any notice CAER Document type Title Revision date Revision User s Manual MUT Mod N968 Spectroscopy Amplifier 14 06 2004 4 TABLE OF CONTENTS 1 GENERAL DESCRIPTION seems 4 1 1 COATI IRAVA I SAY AT NEEE SANASA E REN Re erect terti elect te 4 2 TECHNICAL SPECIFICATIONS sseeneennnennennneennnennnnnnnnnennnnssse 5 2 1 PACKAGING niet tty eR REO E E RE RE Pee re e be e eb RE tg 5 22 POWER REQUIREMENTS la rr er NR UR einen eR A Ti annee lee 5 2 3 FRONT AND BACK PANEL user ie a NUR Saks ER EGRE ERA ER 6 2 4 FRONT PANEL CONTROLS soe b preteen eee YER ge nee a E ni in ete es en Eee re 7 2 5 INTERNALTUMPER Sa UR ti laa 8 2 6 FRONT PANEL DISPLA Sia ET 9 2
7. connector TTL signal 50 Q impedance it is provided by the Multichannel Analyzer MCA to communicate to the amplifier that the ADC lower level threshold is exceeded and the signal has been accepted It is used only in the Live Time Corrector LTC circuit PRS Reset signal on the Rear panel D type 9 pin female connector UNI Front panel BNC connector with Z lt 0 5 Q and rear panel connector with Z 93 Q short circuit maximum duration 10 s Front panel 8 Rear panel full scale linear range of 0 to 10 V active filter shaped DC restored DC level adjustable to 100 mV Front panel UNI output is provided with a test point BI Front panel BNC connector with Z 1 Q and rear panel connector with Z 93 Q short circuit maximum duration 10 s Front panel 8 Rear panel prompt output with positive lobe leading and linear range of 10 V active filter shaped Front panel Bl output is provided with a test point CRM Rear panel BNC connector with Z 10 provides a nominally 5 V 100 ns logic pulse every time the input signal exceeds the baseline restorer fast discriminator threshold INH Rear panel BNC connector with Z 10 Q provides a nominally 5 V logic pulse suitable for the MCA anticoincidence input when the internal pile up rejection logic detects a distortion of the input signal due Filename Number of pages Page N968_REV4 DOC 14 9 CAER Document type Title Revision date Revision User s Manual MU
8. l and is automatically extended by the generation of an Inhibit signal a CRM Count Rate Meter Output which generates a TTL signal every time a valid input pulse arrives Circuit description The input signal provided by the preamplifier is processed in the way described in the Fig 3 1 block diagram BIPOLAR FILTER amp Ey BIPOLAR OUTPUT OUTPUT POLARITY STAGE GAIN STAGES SHAPING STAGE UNIPOLAR OUTPUT STAGE amp DELAY BASE LINE B RESTORI ER gy UNIPOLAR OUTPUT INPUT ATTENUATOR POLE ZERO VISUAL INDICATOR 3 BASELINE BUSY COUNT RATE METER LIVE TIME CORRECTION e RISE TIME PROTECTION MANUAL Y THRESHOLD AUTO THRESHOLD PILE UP DETECTION LOGIC FAST 5 DIFFERENTIATOR INHIBIT Fig 3 1 N968 circuit block diagram The amplifying chain is composed by a preamplifier input stage and the gain stages The coarse fine and super fine gain controls operate over these stages allowing to set the gain level The polarity setting is performed through a stage which is configured either inverting or non inverting The subsequent shaping stage consists of a double 4 pole integrator which forms the pulse semi gaussian profile The chain composed by both the amplifying and the shaping stages is configured as gated amplifier in order to compensate the amplifiers thermical drift and offsets which would lead to high gain
9. mma line at 85 of Spectrum broadening full scale for an incoming count rate of 10 to 10 counts s Unipolar Output 2 us shaping Peak position typical shift lt 0 024 for a Co 1 33 MeV gamma line at 85 of full scale measured from 10 to 10 counts s Unipolar Output 2 us shaping T B C 4 uV 6 uV RMS for UNIpolar Bipolar output for 3 us shaping time and coarse gain 100 Equivalent noise 3 5 UV 5 UV RMS for UNIpolar Bipolar output for 3 us shaping time and coarse gain 1000 Fig 2 3 Equivalent RMS Noise Vs Shaping Time Ts NPO Filename Number of pages Page 00100 03 N968x MUTx 04 N968_REV4 DOC 14 10 CAL PR Document type Title Revision date Revision User s Manual MUT Mod N968 Spectroscopy Amplifier 14 06 2004 4 UNIPOLAR OUT Gain 1000 Gain 100 9 8 7 6 5 4 3 2 1 0 gt o E o a o tc c 2 5 Ww Fig 2 3 UNIpolar Output Equivalent RMS Noise Vs Shaping Time Ts BIPOLAR OUT Gain 1000 is Gain 100 Equivalent RMS Noise V ND OO BR O1 o Fig 2 4 BIpolar Output Equivalent RMS Noise Vs Shaping Time Ts NPO Filename Number of pages Page 00100 03 N968x MUTx 04 N968_REV4 DOC 14 1 CAER Document type Title Revision date Revision User s Manual MUT Mod N968 Spectroscopy Amplifier 14 06 2004 4 3 Functional description 3 1 3 2 NPO
10. nd the circuit response to a pulse pile up the second pulse arrives before the circuit recovers from Busy the Fast Differentiator produces another signal that triggers the discriminator to update the Busy output and to provide another CRM pulse In the meantime at the arrival of the second pulse a bistable set by the first pulse produces the Inhibit output The LTC function is also shown in Fig 3 2 after a piled up event detected and then rejected by the MCA with the subsequent production of the RTP signal which communicates that the output has exceeded the MCA internal threshold the LTC signal is produced and kept active until the next RTP While the LTC signal is active the MCA halts its internal time counter thus allowing to obtain a correct input rate value the greater the number of pulses the better the rate value measure in fact the live time measured by the MCA will be obtained by subtracting the MCA dead time and the time the LTC is active from the total time In this way the source actual rate will be equal to the ratio between the number of converted pulses and the live time 3rd event 2nd event distortion due to pileup Fig 3 2 N968 I O timing diagram Filename Number of pages Page 00100 03 N968x MUTx 04 N968_REV4 DOC 14 14
11. r that operates the sensing circuits that normally establish the baseline reference of the Multichannel Analyzer MCA Performance of the spectrometer depends on the precision of the setting of the BLR threshold Such automatic threshold control typically gives as good or better results than those the most experienced operator could achieve manually a Pole Zero PZ Visual Indicator a LED adviser which leads to high precision adjustment of the pole zero cancellation for exact compensation of the decay time of the preamplifier signal Two LEDs indicate either over compensation or under compensation a Bipolar Output which provides a zero crossing pulse suitable for precisely detecting the radiation arrival time In fact the zero crossing of the pulse occurs with a constant delay with respect to the onset of the pulse independently from the amplitude thus allowing to reduce time walk effects an Inhibit Output which provides a pulse when pile up occurs This pulse shall be applied to the MCA s anticoincidence input in order to prevent it from measuring and storing a non valid amplitude Filename Number of pages Page 00100 03 N968x MUTx 04 N968_REV4 DOC 14 12 CAER Document type Title Revision date Revision User s Manual MUT Mod N968 Spectroscopy Amplifier 14 06 2004 4 3 3 NPO a Busy Output which provides a pulse whose width is equal to the time the input pulse exceeds the BLR discriminator leve
12. shold from Auto The BLR threshold is automatically set to an optimum level as a function of the signal noise by an internal circuit PZ Adj Enables the PZ adjustment the BLR threshold is determined by the Auto function The BLR time constant is also greatly increased to facilitate the PZ adjustment Threshold The BLR threshold is manually set by the threshold potentiometer in the 0 300 mV range Screwdriver adjustable potentiometer to set the Unipolar Output DC level range 100 mV The adjustment must be performed with a low rate input NPO Filename Number of pages Page 00100 03 N968x MUTx 04 N968_REV4 DOC 14 7 CAL Rs Document type Title Revision date Revision User s Manual MUT Mod N968 Spectroscopy Amplifier 14 06 2004 4 2 5 Internal Jumpers Some settings can be performed via internal jumpers location is shown in Fig 2 2 Preamp Gain sw4 allows to set the input preamplifier stage gain either at x1 or x0 1 PRS Polarity sw3 allows to configure the module in order to accept on the PRS input either positive or negative pulses If the preamplifier connected to the N968 does not feature the PRS set the jumper to positive G A Gain sw1 allows to introduce either a x2 or x1 gain factor at the Gated Amplifier stage Th Symmetry sw5 allows to set the BLR negative threshold either symmetric equal to the BLR threshold or asymmetric BLT threshold 300mV PRS POLARITY NEG C POS
13. sw3 ASYMM SYMM C sw5 Fig 2 2 Mod N968 side view with jumpers location NPO Filename Number of pages Page 00100 03 N968x MUTx 04 N968_REV4 DOC 14 8 CAEN Document type Title Revision date Revision User s Manual MUT Mod N968 Spectroscopy Amplifier 14 06 2004 4 2 6 Front panel displays PZ VISUAL INDICATOR PZ Visual Indicator leading to high precision adjustment of the pole zero cancellation for exact compensation of the decay time of the preamplifier signal Left LED signals overcompensation right LED under compensation Setting the BLR switch to the adjust position activates the PZ Visual Indicator Under compensation can be corrected by turning the potentiometer clockwise while over compensation requires the potentiometer to be turned anti clockwise A correct Pole Zero setting is signalled by the two LEDs off or at least blinking low 2 7 Input Output connections INPUTS OUTPUTS NPO 00100 03 N968x MUTx 04 INPUT BNC front and rear panel connectors accept either positive or negative pulses with rise times of 10 to 500 ns and decay times of 40 us to infinity if Preamp Gain 1 Zn 1000 Q DC coupled 500 Q AC coupled if Preamp Gain 0 1 Zn 1000 Q DC coupled AC coupled linear maximum 1V Preamp gain 1 Amplifier gain 10 10 V x01 attenuation selected absolute maximum 10 V Front panel INPUT is provided with a test point RTP Rise Time Protection Rear panel BNC
14. tor feedback preamplifiers connected with nuclear particle detectors A front panel switch allows to select between positive and negative input signals Gain setting can be performed continuously in the 10 1500 range product of Coarse Fine and Superfine Gain Two internal jumpers allow to set a x0 1 attenuation and a further x2 amplification thus extending the gain range to 1 3000 Shaping time Ts values are 0 5 1 2 3 6 10 us The Pole Zero PZ cancellation is performed via a front panel screw trimmer The module features also a Bipolar output to be used for timing purposes An advanced Baseline Restorer BLR circuit with either manual or automatic threshold setting A Pile Up Rejector PUR which allows to reject piled up events NPO Filename Number of pages Page 00100 03 N968x MUTx 04 N968_REV4 DOC 14 4 CAER Document type Title Revision date Revision User s Manual MUT Mod N968 Spectroscopy Amplifier 14 06 2004 4 2 Technical specifications 2 1 Packaging The Model N968 is housed in a single width NIM module 2 2 Power requirements Table 2 1 Power requirements NPO Filename Number of pages Page 00100 03 N968x MUTx 04 N968_REV4 DOC 14 5 CAL Rs Document type Title User s Manual MUT Mod N968 Spectroscopy Amplifier 2 3 Front and back panel SPECTROSCOPY Qe AMPLIFIER D SFG FINE GAIN 0 5 1 5 D COARSE GAIN UNI INPUT BUSY RTP PREAMP OUT
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