5
and the corresponding dead time during the of all but the 1000
terminators for your
experiment. For each signal accepted through the convenience, as listed below:
start input there must be a conversion, but for each
signal through the stop input there need not be a BNC Tee Connector C-29
conversion. For each start signal that is not followed
by a stop signal within the selected time full range, 50
Terminator C-28
the converter measures a time equal to the total
range, even though no output pulse is generated. 100
Terminator C-27
3.4. LINEAR OUTPUT SIGNAL
CONNECTIONS AND TERMINATING
IMPEDANCE
The source impedance of the standard TAC output
with the 0 to 10V linear range is about 1
through
the connector on the front panel and 93
through
the connector on the rear panel.
For the front panel circuit, the interconnection to
other modules does not usually require any special
considerations, especially if the interconnecting
cable is shorter than 4-ft in length. Paralleling
several loads on a single output will still not reduce
the 0 to 10V signal span significantly unless the
combined load is <100
.
The rear panel TAC output circuit is designed for
use of 93
cable to transfer the signals into a
measuring circuit that has an input impedance of at
least 1000
. With this series impedance-matched
circuit connection, there will usually not be any
interference with the signal. If oscillations should
occur, it will be necessary to provide an additional
shunt termination of 100
in parallel with the input
circuit of the receiving instrument, but this will result
in ~50% loss of signal amplitude.
As with any analog instrument, oscillations may be
observed occasionally when unterminated lengths
of cable are used. Short cable lengths (up to 4ft)
need not be terminated. When longer cable lengths
are required for transfer of a linear signal, the cable
should be terminated in a resistive load equal to the
cable impedance to prevent reflections and
oscillations in the cable. Oscillation suppression can
be effected by either a series termination at the
sending end of the cable or by a shunt termination
at the receiving end. For convenience a BNC tee
can usually accommodate both the cable and a
mating terminator at the input of the receiving
instrument. These units are available commercially,
including BNC terminators with nominal values of
50,100, and 1000
. Ortec stocks a limited quantity
When a shunt termination at the receiving end of
the cable is impractical, consider series termination
at the sending end. For a series termination the
full signal amplitude span is available at the
receiving end only if the input impedance is many
times the characteristic impedance of the cable. For
series termination install the correct resistance
between the actual amplifier output on the etched
circuit board and the output connector. Effectively,
the terminating resistance is in series with the input
impedance of the receiving instrument, and may
result in some loss in signal amplitude. For
example, if the series terminator is 93
and the
driven load is 900
, the available signal span will
be only about 90% of the maximum signal
amplitude for each pulse. The termination of a 93
cable in a 93
load will cause ~50% loss for the
signal.
3.5. CHANGING INPUT POLARITIES
All six input circuits are jumper-selectable to accept
NIM-standard positive or negative pulses. Inputs set
for negative signals will have a built-in 50
terminating impedance, and inputs set for positive
signals will have a nominal 1k
terminating
impedance. Factory settings (listed in Section 2.4)
may be changed or checked by the following
procedure:
1. Turn off NIM bin power switch and remove 567
from NIM bin.
2. Remove the right-side (from front view of
module) cover by removing the four small
fastening screws.
3. Refer to the following table to identify the label
of the desired input jumper to be changed on
the 567.
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