EG&G ORTEC 463 Kullanım ve Servis Kılavuzu - Sayfa 9
Ölçüm Cihazları EG&G ORTEC 463 için çevrimiçi göz atın veya pdf Kullanım ve Servis Kılavuzu indirin. EG&G ORTEC 463 20 sayfaları. Constant fraction discriminator
Sayfayı Yazdır4. OPERATION
After the 463 has been installed and interconnected as
described in Section 3, the only operating functions that
are required are the setting of the Mode switch and an
adjustment of the Disc Level control.
Normally the Mode switch can be set at the switch position
that corresponds to the type of detector being used. Set
the switch at Ge(Li) for signals from a germanium coaxial
detector; set it at Scint/SB if the detector is either a fast
plastic scintillator or a surface barrier type; or set it at Nal
for use with a slower type of scintillator. If the input
signal to the 463 is furnished from a signal source having
a rise time that is longer than 20 nsec, the Ge(Li) switch
position may provide more satisfactory operation than the
Scint/SB position. See Section 7, "Applications," for
further suggestions.
The function of the Disc Level adjustment is to permit
selection of signals of interest and to eliminate response
to smaller signals. The proper setting of this control
depends on the range of signal amplitudes that are
furnished into the input. The range is from -50 mV to -5 V
with the precision 10-turn potentiometer used for precise
setting and excellent resettability.
5. CIRCUIT DESCRIPTION
The signal, in a range of 0 to -10 V, is applied through
Input connector CN1 and routed to a 50f2 T attenuator
consisting of R7, R8, and R9. The output from the T
attenuator has half of the input signal amplitude and is
l imited to approximately -6 V and +0.8 V by diodes
D2 and D3.
The signal from the T attenuator goes to the base of Q2
and to the Shaping Mode switch, 81. Q1 and 02 form a
matched pair to translate the zero baseline and furnish it
and the signal into a fast differential comparator, 101.
When the signal at the base of 02 exceeds the level
selected by the Disc Level control, R11, the output at
pin 8 of 101 switches from its high state of ^^-0.8 V to
its low state of 'V-I.B V. The low state is applied to pin
5 of I04B to enable the And gate for the zero-crossing
signal that wil l come from 102.
The second connection for the output from the T
attenuator is through Shaping Mode switch SI . For each
switch-selected shaping mode the signal is split and routed
through an attenuation network and R19 to the base of
Q3 and through a delay cable DL1 and R21 to the base
of Q4. The switched routing provides a shaping that is
optimum for each mode selection. For Ge(Li) the signal
to Q3 goes through R1 while the signal for Q4 goes
through R2 and DL2A. For Scint/SB, the signal to Q3
passes through R6 while the signal to Q4 passes through
R5. For Nal the signal to Q3 goes through R3 and the
signal to Q4 goes through R4 and DL3.
The shaped signals through the matched pair, Q3 and Q4,
are applied to comparator IC2. When zero-crossing occurs,
the signal at pin 8 of IC2 shifts to the low state and is
applied to the And gate IC4B at pin 4; this is the gate
that has been enabled to accept the signal by the out
put from IC1 . The output from IC2 is also buffered
through IC4A to permit oscilloscope observation at TP1.
Waveforms to show comparative timing of the signals in
this portion of the 463 are shown in Figs. 5.1 and 5.2.
The detection of the zero-crossing point that will be
seen at TP1 is the waveform in Fig. 5.2 identified as
the Zero-Crossing signal from pin 8 of IC2. This signal
is automatically adjusted so that the zero-crossing point
wil l always occur at the proper time. It is accomplished
by making the signal comparison with an adjusted dc
baseline level that is furnished from the internal Walk
Signal Base Q
Signal Base Q.
Signal Base Q
Zero Cross Signal
Pin 1
1C2A
Fig. 5.1. Ideal Pulse Shapes Illustrating the Constant
Fraction Discriminator Operation.