EG&G ORTEC 426 Manual de funcionamiento y servicio - Página 8
Navegue en línea o descargue pdf Manual de funcionamiento y servicio para Unidad de control EG&G ORTEC 426. EG&G ORTEC 426 16 páginas. Linear gate
Imprimir páginasignal is regenerated to allow gate width duration to be
independent of the pulse shape of the Enable input.
The minimum recommended width of the Enable Input is
50 nsec measured at 50% amplitude, although narrower
pulses with larger amplitude will trigger the Enable circuitry.
3.4. LOGIC INPUTS TO THE DC INHIBIT INPUT
The same considerations of Section 3.3 apply to input pulses
to the DC Inhibit Input connector. This input provides the
facility to block the passage of signals through the Linear
Gate by the application of a dc voltage either in the basic
form of a battery and switch contact or by the application
of a pulse waveform between dc voltage levels. The input is
dc-coupled and has an impedance of approximately 650J2.
A maximum dc voltage of 20 V is allowed on this input. A
DC Inhibit control is not regenerated internally, but exists
throughout the duration of the inhibiting signal.
3.5. LINEAR OUTPUT SIGNAL CONNECTIONS AND
TERMINATING IMPEDANCE CONSIDERATIONS
The source impedance of the 0- to 10-V standard linear out
puts of most 400 Series modules is approximately 1J2.
Interconnection of l inear signals is thus noncritical, since the
input impedance of circuits to be driven is not important in
determining the actual signal span, e.g., 0-10 V, delivered to
the following circuit. Paralleling several loads on a single out
put is therefore permissible while preserving the 0- to 10-V
signal span. Short lengths of interconnecting coaxial cable
(up to approximately 4 ft) need not be terminated. If,
however, a cable longer than approximately 4 ft is necessary
on a l inear output, it should be terminated in a resistive
load equal to the cable impedance. Since the output imped
ance is not purely resistive and is slightly different for each
individual module, when a certain given length of coaxial
cable is connected and is not terminated in the characteristic
impedance of the cable, oscillations wi l l generally be
observed. These osci llations can be suppressed for any
length of cable by properly terminating the cable either in
series at the sending end or in shunt at the receiving end of
the line. To properly terminate the cable at the receiving
end, it may be necessary to consider the input impedance
of the driven circuit, choosing an additional parallel resistor
to make the combination produce the desired termination
resistance. Series terminating the cable at the sending end
may be preferable in some cases where receiving-end
terminating is not desirable or possible. When series-
terminating at the sending end, full signal span, i.e., amp
litude, is obtained at the receiving end only when it is
essentially unloaded or loaded with an impedance many
times that of the cable. This may be accomplished by insert
ing a series resistor equal to the characteristic impedance of
the cable internally in the module between the actual
amplifier output on the etched board and the output con
nector. Remember that this impedance is in series with the
input impedance of the load being driven, and in the case
where the driven load is 900J2 a decrease in the signal span
of approximately 10% will occur for a 93J2 transmission
line. A more serious loss occurs when the driven load is
93n and the transmission system is 93K2; in this case, a 50%
loss will occur. BNC connectors with internal terminators
are available from a number of connector manufacturers in
nominal values of 50, 100, and 100012. ORTEC stocks in
limited quantity both the 50 and 10012 BNC terminators.
The BNC terminators are quite convenient to use in
conjunction with a BNC tee.
4. OPERATION
4.1. FRONT PANEL CONTROLS
Gate Width A single-turn potentiometer provided to adjust
the gate width to the desired value within the nominal range
of 0.3 to 4 jusec. This control is recess-mounted and as such
is a screwdriver adjustment, but it may be panel-mounted so
that a knob may be added to the potentiometer shaft to
allow finger-thumb adjustment if this seems desirable.
Mode Switch
A 3-position switch used to set the Linear
Gate into one of the following operation modes:
Normal In this mode the Linear Gate normally blocks al l
input signals unless the Enable signal sets the Linear Gate to
pass signals for a selected duration (as set by the Pulse Width
control) after receiving an Enable pulse.
Pulse Inhibit The reciprocal of the Normal mode is available
with the switch in this position, i.e., the Linear Gate passes
all signals except when a pulse isapplied to the Enable input.
The pulse on the Enable input causes the gate to block the
passage of signals through the Linear Gate for a duration set
by the Pulse Width adjustment.
DC Inhibit This mode is identical to the Pulse Inhibit mode
except that the application of an inhibit or block input must
be made on the rear panel BNC connector, and the Linear
Gate wil l remain blocked for the duration that the dc signal
is applied to the DC Inhibit Input connector.
For applications where the Linear Gate is desired to be
switched for Normal, i.e., selectively passing, to a condition
of passing al l signals, the switch should be operated between
Normal and DC Inhibit position and there should be no
connection on the DC Inhibit Input rear panel connector.