EG&G ORTEC 442 Instrukcja obsługi i serwisowania - Strona 5
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Drukuj stronęORTEC 442 LINEAR GATE AND STRETCHER
1. DESCRIPTION
The ORTEC 442 Linear Gate and Stretcher is designed to
increase the duration of short input pulses by stretching
their peak amplitudes for a required minimum pulse
width. This effectively reduces the bandwidth requirements
of analog-to-digital converters in multichannel pulse height
analyzers and improves the resulting l inearity. The linear
gate included in the 442 permits selective control of the
acceptance of input pulses, and is also used to prevent
positive-on-positive pulse pileup.
The 442 accepts l inear signals, during its permissive
gating periods, from any l inear source and reshapes the
input signal as required to provide a suitable waveform
into a circuit that measures the peak amplitude. Any
reshaping of the input pulse must retain the l inear
parameter of the input signal, which is its relative peak
amplitude. The pulse width of the input is unimportant
except from the practical viewpoint of having the peak
amplitude exist long enough to permit accurate response
and measurement.
The input gate can be controlled from an external source,
and operated in either a coincidence or an anticoincidence
mode. The Gate Period generator wi l l be triggered on the
leading edge of a gate input pulse and continue for the
effective period set by the front panel adjustment. The Gate
Period must overlap the linear input pulse peak for coinci
dence mode operation or must overlap the discriminator
response for anticoincidence mode,
A l inear input pulse must exceed the adjusted discriminator
level to initiate a response in the 442. When the discrimina
tor fires, it initiates the stretch action unless the gate
control is in the external coincidence mode and a gate pulse
IS not present. The input gate remains open only until the
peak of the l inear pulse has been detected, and then is
again closed to prevent pileup. An output pulse will be
generated if a peak is detected, and wil l occur at an
adjusted delay following the input peak for an adjusted
width. Both the delay and width adjustments are front
panel controls on the 442. The input gate cannot be
opened again until the output pulse has been completed
and the l inear input pulse has permitted the discriminator
to reset. This internal logic prevents pulse pileup and false
amplitude outputs for the system.
Short-duration linear pulses are associated normally with
biased amplifiers. The 442 can be used in this, or any
other, system to assure an adequate duration of the peak
amplitude where a pulse width might be too short or where
the width variations would otherwise produce a nonlinear
response or measurement. It may be used at any point in
the l inear system after a basic linear amplifier, and its gating
function permits logical placement directly after the linear
amplifier. For best system performance tne 442 should
precede the biased amplifier.
2. SPECIFICATIONS
PERFORMANCE
LINEAR INPUT AMPLITUDE
+0 1 to +10 V, l inear
range; ±12 V maximum.
LINEAR INPUT RISE TIME
100 nsec to 10 /tisec.
LINEAR OUTPUT WIDTH 0.5 to 5/usec.
LINEAR OUTPUT DELAY 0.3 to 3 /ttsec after input pulse
peak.
GAIN Unity ( nominal).
INTEGRAL NONLINEARITY
<0.1% for pulse rise
time >100 nsec and pulse width >400 nsec.
TEMPERATURE INSTABILITY
Gain shift <0.01%/°C,
0 to 50'C.
COUNTING RATE
dc-couplea throughout when DC
Couple input is selected. The centroid of a
pulser
spectrum at 85% of full scale wi ll shift <0.1% when
modulated by 5 x 10" counts/sec of random signals from
'^''Cs source-detector combination \/vith photopeak at
70% of full scale (DC Couple mode and amplifier shaping
time T = 1 /isec). When dc restorer modes are used, count
rate is dependent on shaping amplifier time constants and
pulse undershoot.
CONTROLS
The following controls are on the front panel:
DC COUPLE 3-position slide switch, selects input circuit
desired: BLR High, BLR Low, or DC Couple.
DISC LEVEL
Screwdriver potentiometer; adjusts sen
sitivity level for input discriminator; range +0.1 to +1 V;