EG&G ORTEC 442 Manuel d'utilisation et d'entretien - Page 8
Parcourez en ligne ou téléchargez le pdf Manuel d'utilisation et d'entretien pour {nom_de_la_catégorie} EG&G ORTEC 442. EG&G ORTEC 442 16 pages. Linear gate and stretcher
Imprimer la page4. OPERATION
4.1. SELECTION OF INPUT CIRCUIT
Any of three oircuit connections can be selected with the
slide switch at the top of the front panel: DC Couple,
BLR (Base Line Restorer) Low, or BLR High, The proper
selection wi l l depend on the type of output circuit In the
module from which the l inear input pulses are furnished
to the 442 and on the relative counting rate.
The DC Couple switch position provides an optimum
signal transfer circuit with lOOOO Input impedance If the
pulses are furnished from an amplifier with a dc-coupled
output and a properly adjusted zero basel ine. If the source
does not include baseline restoration, use a capacitive
coupling into the 442 and select either Low or High BLR
In the 442.
For an ac-coupled signal input, select one of the dc-restorer
Input circuits In the 442. There Is no precise dividing l ine,
because of the various shaping time constants which may be
affecting the pulse shape furnished to the 442. For 1-^tsec
pulses the division Is approximately 15,000 counts/sec. If
bipolar pulses are applied to the input the DC-Couple or
BLR Low configurations must be selected. The most
practical method of selecting between High and Low is
observation of the Output, using the circuit that provides
the better results.
4.2. DISCRIMINATOR LEVEL ADJUSTMENT
The Disc Level adjustment is for the purpose of preventing
response to all noise pulses. Therefore, it should be adjusted
high enough in its-i-O.I-to TV range to ensure discrimination
against the maximum noise amplitude that may exist at
the input to the 442 In the system. Since the logic in the
442 prevents response to a new input pulse unti l the
Disc Level has been reset but permits acceptance at that
time unless an output pulse has not been completed, too
high a setting of the Disc Level can permit a small
amount of pileup to occur If the input pulse has a very
long time constant decay. Although this Interference Is
possible. It Is unlikely In most applications. Sti l l , an un
necessarily high adjustment is not recommended.
4.3. OUTPUT DELAY ADJUSTMENT
The adjustment of the Output Delay permits a control
for normalizing timing in the system in which the 442 Is
Included. The delay period is measured from the time that
the internal stretch amplifier senses a peak amplitude in the
accepted linear input pulse and is adjustable through the
range of 0.3 to 3 ^tsec. At the end of the delay period the
output gate Is opened and an output pulse is furnished to
the next Instrument In the system.
4.4. OUTPUT WIDTH ADJUSTMENT
The purpose of this stretch circuit is to provide an output
pulse with a fixed and known width. The range of the
control is 0.5 to 5 usec, and its proper setting wil l be
determined by the Input requirements of subsequent
Instruments In the system. Each output pulse wil l have
the adjusted width, regardless of the wldth(s) of l inear
pulses furnished to the 442 input.
4.5. OUTPUT DC ADJUSTMENT
In normal usage the quiescent level for the output,
through both the front and rear panel connectors, should
be at ground potential. Use the test point for the front panel
Output, and adjust the screwdriver control as necessary
to set the level at ground potential when there are no
output signals. When the DC Input is used on some
analyzers it is necessary that the signal source have a
quiescent dc level other than zero; when the 442 is used In
such applications adjust the output dc level as required.
4.6. GATED OPERATION
No Gate Input pulse is required if the front panel slide
switch is set at Normal. Likewise, if the slide switch Is set
at Gated and the mode selector on the rear panel is set for
Antlcolnc, linear input pulses will be accepted when there
is no signal through the Gate Input connector. Whenever
a signal is furnished through the Gate Input with gated
Antlcolnc effective, al l l inear Input signals are inhibited
throughout the Gate Period. To be effective, the Gate
Period must be adjusted to overlap the period of dis
criminator response to any pulse that Is to be Inhibited
by the Anticoinc signal; if the l inear input triggers the
discriminator before the Gate Input or if the Gate Period
terminates prior to discriminator recovery, there will be
an output, but the amplitude wil l not usually duplicate a
peak Input amplitude.
When the 442 is set for gated coincidence operation, a
l inear Input signal is accepted for stretching If and only If
there Is a time-coincident Gate Input. The Gate Input
signal must occur before the peak amplitude of the l inear
input pulse, and the Gate Period must be long enough to
continue the control beyond the internal detection of the
peak amplitude.
Refer to Section 6.2 for l inear gate pedestal adjustment
procedures.
4.7. OVERALL LOGIC
When an Input pulse arrives at the Linear Input, It Is applied
directly to the discriminator. As Its amplitude rises through