Specifications

Guide to Operation
22
In general, pressing the STOP key twice in
succession puts the counters into the reset
condition.
START begins the first COUNT PERIOD of the
programmed scan. If the DWELL time is
programmed, then the scan will continue
automatically. A STOP will pause the scan; the
current COUNT PERIOD is terminated and
ignored. A START while paused will resume the
scan. A STOP while paused resets the scan. If the
DWELL time is EXTERNAL, then a STOP during
the COUNT PERIOD terminates the COUNT
PERIOD and advances the scan. START begins
the next COUNT PERIOD in the scan. A START
during a COUNT PERIOD or programmed
DWELL period is ignored.
A STOP while in a dwell period or pause resets
the scan; all scanned parameters return to their
start values and the counters are reset. In general,
2 consecutive presses of the STOP key will reset
the counters.
The SCAN led is on when a scan is in progress.
The SCAN led is off when the scan is paused or
the counters are reset.
INSTRUMENT STATUS
Six LED's indicate the instrument status. REM is
on when the front panel is locked out, ACT flashes
when there is activity on the computer interfaces,
and ERR flashes when there is a computer
interface error. COUNT is on during each COUNT
PERIOD, OVRN indicates that a counter has
exceeded 10
9
- 1 counts during a COUNT
PERIOD, and RATE flashes whenever a gate
delay or width exceeds the trigger period minus
1 µs. The RATE led also flashes if the trigger rate
exceeds 1 MHz, even if the gates are in the CW
mode.
COUNTER LED'S
The source LED's in the counter sections indicate
what each counter's input is. The counter inputs
are output through the DISC outputs. The SET
LED's indicate which counter, B or T, is the preset
counter. The B SET LED is on when the mode is
A FOR B PRESET, the T SET LED is on
otherwise.
INPUTS
The rising or falling edge of the TRIGGER input
triggers the gate generators. The input impedance
is 10 KΩ and the minimum pulse width is 10 ns.
The trigger level is adjustable from -2V to +2V
with either slope. The minimum pulse amplitude is
0.1 V.
The SIGNAL INPUTS, 1 and 2, are 50 Ω analog
inputs. Photomultiplier or preamplifier outputs are
connected to these inputs. These inputs are linear
between -300 mV to +300 mV and protected to
± 5 Vdc.
EXTERNAL START is a TTL input with the
rising edge active. The minimum pulse width is 20
ns. When the DWELL time is EXTERNAL, the
COUNT PERIOD begins with the rising edge of
START and ends with the preset condition or the
rising edge of STOP. When the DWELL time is
programmed, EXT START begins the scan.
EXTERNAL STOP is a TTL input with the rising
edge active. The minimum pulse width is 20 ns.
When the DWELL time is EXTERNAL, EXT
STOP ends each count period. Reset must be
accomplished via the STOP key or computer
interface. When the DWELL time is programmed,
EXT STOP resets the scan.
OUTPUTS
The DISC outputs are 50 Ω, NIM level, outputs
showing the actual inputs to the three counters.
These outputs are active low (-.7 V) and counting
occurs on the falling edge. The outputs are low
when the signal inputs exceed their threshold
levels with the correct slope.
Cables attached to the DISC outputs should be
kept far from the cables which carry the SIGNAL
inputs. The 0.7 V DISC pulses can be picked up
by the SIGNAL cables and discriminated. This
causes the discriminators to oscillate. This is not a
problem if the threshold is greater than 10 mV. If
smaller thresholds are required, careful
arrangement of the cables is necessary, or the