Summary of Contents for RoentDek CFD8c
- Page 1 RoentDek Handels GmbH Supersonic Gas Jets Detection Techniques Data Acquisition Systems Multifragment Imaging Systems RoentDek Constant Fraction Discriminators CFD8c, CFD7x, CFD4c, CFD1c and CFD1x (11.0.1701.1)
- Page 2 All rights reserved. Technical changes may be made without prior notice. The figures are not binding. We make no representations or warranties with respect to the accuracy or completeness of the contents of this publication Page 2 of 25 The Constant Fraction Discriminators CFD8c, CFD7x, CFD4c, CFD1c and CFD1x (11.0.1701.1)
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Page 3: Table Of Contents
X PULSE HEIGHT DETERMINATION OPTION ................22 HE B VERSION OF READ OUT OF BIPOLAR INPUT SIGNALS LIST OF FIGURES ................................24 LIST OF EQUATIONS ..............................25 The Constant Fraction Discriminators CFD8c, CFD7x, CFD4c, CFD1c and CFD1x (11.0.1701.1) Page 3 of 25... - Page 4 Page 4 of 25 The Constant Fraction Discriminators CFD8c, CFD7x, CFD4c, CFD1c and CFD1x (11.0.1701.1)
- Page 5 CFD4b and CFD1b Constant Fraction DiscriminatorsCFD8b, (11.0.1701.1) Page 5 of 25...
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Page 6: The Cfd Timing Discriminator Modules
(CFDx) on one of the channels. The CFD8c (see Figure 3.1b) is a standalone unit with 8 independent channels. In the version CFD7x one channel is replaced by a circuit allowing for a pulse height determination on one channel. These units are the recommended versions for operating Hexanode Delay-line detectors. - Page 7 12 V DC (6 W) or max. 0.7 A at 12 V DC (<10 W) for the CFD1x. The CFD4c has the same functions as the CFD8c for 4 channel operation in a 1/12 NIM cassette (W34 mm/L280 mm/H220 mm, weight 1.2 kg) and requires a NIM-bin for operation: The current drawn is max.
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Page 8: 3B.2 Principles Of The Cfd Circuit
“low”. Ideally, the Threshold level is set above electronic noise but low enough to register even the smallest valid input signals. Note that for CFDs the input signal polarity is negative RoentDek Page 8 of 25 The Constant Fraction Discriminators CFD8c, CFD7x, CFD4c, CFD1c and CFD1x (11.0.1701.1) -
Page 9: 3B.3 Adjusting The Cfd Parameter
4.5 ns, i.e. sightly increased by internal delays on the circuit board). Note the M output has a DC offset of about -0.1 V The Constant Fraction Discriminators CFD8c, CFD7x, CFD4c, CFD1c and CFD1x (11.0.1701.1) Page 9 of 25... -
Page 10: 3B.3.1 Threshold Level
If the threshold is set too high, small (but valid) signals are not registered (see Figure 3.8b, left picture), if it is set too low (right picture), the CFD output will also trigger on spurious noise components and produce background counts. Page 10 of 25 The Constant Fraction Discriminators CFD8c, CFD7x, CFD4c, CFD1c and CFD1x (11.0.1701.1) -
Page 11: 3B.3.2 Cfd Delay
CFD delay settings. A non-perfect choice of delay can sometimes be compensated by adjusting the CFD fraction (see below) as long as D/RT is between 0.5 and 1 (see Figure 3.10b). The Constant Fraction Discriminators CFD8c, CFD7x, CFD4c, CFD1c and CFD1x (11.0.1701.1) Page 11 of 25... -
Page 12: 3B.3.3 Cfd Fraction
(< 3 ns FWHM). Furthermore, choosing a very short delay cable (i.e. 0.5 ns) in combination with a high Walk level can force the CFD into the operation mode of a leading edge discriminator. Page 12 of 25 The Constant Fraction Discriminators CFD8c, CFD7x, CFD4c, CFD1c and CFD1x (11.0.1701.1) -
Page 13: 3B.3.4 Walk Level
(left picture) and slightly towards the positive side where the noise triggers begin to vanish (right picture), leading to slightly less intensity in the area right of the arrow. The Constant Fraction Discriminators CFD8c, CFD7x, CFD4c, CFD1c and CFD1x (11.0.1701.1) Page 13 of 25... -
Page 14: 3B.3.5 Output Signal Width
There are three modes of operation: Safe values for “low” are levels between -0.1V and +0.1V, for “high” -0.7V to -1V (on 50 Ohm impedance coax input) Page 14 of 25 The Constant Fraction Discriminators CFD8c, CFD7x, CFD4c, CFD1c and CFD1x (11.0.1701.1) - Page 15 Figure 3.14b: Position of Veto input socket on the CFD8c front panel. For the CFD4c it is found on the rear panel ‘Veto’ mode: The CFD timing outputs are disabled while a NIM level (-0.8 V on 50 Ohm) is present on the Veto input.
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Page 16: 3B.4.1 Accessing The Jumpers In Cfd1C / Cfd1X
On the front panel only remove the upper middle screw (red circle). Figure 3.18b: Front and rear panel of CFD8c with marked screws You may now remove the rear panel and the top cover. (If you do not have a suitable hex nut driver, you may remove the front panel instead. -
Page 17: 3B.4.3 Accessing The Jumpers In Cfd4C
The Veto jumper block is located next to each channel (see Figure 3.19b). Figure 3.19b: Inside view of the CFD8c with jumper blocks marked by yellow circles (CFD7x similar) Please follow the instructions on how to set the jumpers which are printed on each four-channel board (see Figure 3.16b). -
Page 18: 3B.5 Performance Limitations
If pre-trigger events prevail in spite of best effort-setting of the CFD parameters careful it is best to increase the Threshold level further and/or the CFD delay. Other actions are increasing the Walk level, which may slightly reduce resolution) and/or the CFD fraction. Page 18 of 25 The Constant Fraction Discriminators CFD8c, CFD7x, CFD4c, CFD1c and CFD1x (11.0.1701.1) -
Page 19: 3B.5.3 Cross Talk Problem
(i.e. from x1 and x2 outputs) are not processed on neighbouring channels that share the same internal board. In this sense channels 4 and 5 in case of the CFD8c and channels 3 and 4 in case of the CFD7x do not have to be considered as “neighbours”. - Page 20 CFD1x any time. Please contact version with the option of accordingly coding an external signal’s pulse RoentDek height or a DC level into a delay. Page 20 of 25 The Constant Fraction Discriminators CFD8c, CFD7x, CFD4c, CFD1c and CFD1x (11.0.1701.1)
- Page 21 TDC channel available Note that the CFDx output is turned off while the ramp switch is turned off The Constant Fraction Discriminators CFD8c, CFD7x, CFD4c, CFD1c and CFD1x (11.0.1701.1) Page 21 of 25...
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Page 22: 3B.7 The Bcfd Version Of Read-Out Of Bipolar Input Signals
Figure 3.4b. If an input signal has already the “right” shape it can be routed directly to the walk comparator and additionally to the leading edge comparator (for setting the CFD threshold via the respective potentiometer). Page 22 of 25 The Constant Fraction Discriminators CFD8c, CFD7x, CFD4c, CFD1c and CFD1x (11.0.1701.1) - Page 23 CFD units hosting bCFD boards are recognized by pasted-over CFD fraction potentiometers on the respective RoentDek channels. A CFD7x unit can be modified to host one (standard) CFDx circuit plus up to six bCFD circuits. The Constant Fraction Discriminators CFD8c, CFD7x, CFD4c, CFD1c and CFD1x (11.0.1701.1) Page 23 of 25...
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Page 24: List Of Figures
CFD7 IGURE LEFT AND CLOSE UP OF THE RIGHT SHOWING THE ADDITIONAL INPUT OUTPUT SOCKETS ................20 SWITCH AND CONTROL POTENTIOMETERS FOR THE X CIRCUIT The Constant Fraction Discriminators CFD8c, CFD7x, CFD4c, CFD1c and CFD1x (11.0.1701.1) Page 24 of 25... -
Page 25: List Of Equations
WAS OBTAINED BY 3.25 ) ..22 TEMPORARILY REMOVING THE INPUT TO DURING DATA ACQUISITION SITUATION AS IN IGURE B LEFT List of Equations ................................... 11 QUATION The Constant Fraction Discriminators CFD8c, CFD7x, CFD4c, CFD1c and CFD1x (11.0.1701.1) Page 25 of 25...
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