The counting function of the entire module can be
disabled by holding the Enable input below +1.5 V
using an external signal source. This condition
also turns Off the Gate LED. Open circuit or >+3 V
at the Enable input allows the instrument to count,
if the Count mode has been activated. The Interval
output of another ORTEC timer can perform this
function to synchronize the Model 994 counting
with the other timer. The Interval outputs on all
ORTEC timers provide nom5 V when
counting and <+0.5 V when counting is inhibited.
Independent gating of the A and B Counter inputs
can be achieved with the Gate A and Gate B
inputs on the rear panel. The interface connector
for the RS-232-C option is located on the rear
panel. Each counter has a rear-panel output
dedicated to signaling overflows. Counting these
overflows on another counter extends the counting
capacity of the Model 994.
The Model 994 derives its power from the ±12 V
and +6 V supplies in a standard NIM bin with
power supply. For bins that do not contain a +6 V
supply, an In6 V Supply option is available.
This option is field-installable and derives its
power from the 117 V AC lines in the bin.
Specifications
PERFORMANCE
COUNT CAPACITY
8 decades for counts ranging from
0 to 99,999,999 in each of 2 counters.
MAXIMUM COUNTING RATE
100 MHz for negative
inputs, 25 MHz for positive inputs.
TIME BASE
10-MHz clock with minimum preset or
displayed intervals of 0.01 seconds or 0.01 minutes.
Synchronizing error is nominally 100 ns. Also accepts an
external input from the Counter A input (In A) when the
Ext (External) mode is selected.
TIME BASE INACCURACY
±0.0025% over the 0 to
50°C operating temperature range.
PRESET TIME/COUNTS
The module stops counting
when the preset value MN X 10
P
is reached on the blind
preset register. M and N are digits ranging from 0 to 6.
With the 0.01-second time base, preset times from 0.01
to 990,000 seconds can be used. Preset times from 0.01
to 990,000 minutes are available using the 0.01-minute
time base. In the Ext time base mode preset counts in
the range of 1 to 99,000,000 can be used.
POSITIVE INPUT DISCRIMINATOR
Threshold variable
from +100 mV to +9.5 V with a 25-turn trimpot.
PULSE PAIR RESOLUTION
<10 ns for negative inputs;
<40 ns for positive inputs.
INDICATORS
COUNTER DISPLAY
8-digit, 7-segment LED display
with leading zero suppression. When displaying time,
2 digits to the right of a decimal point are included.
OVERFLOW INDICATORS
LED indicators labeled
OVFL A and OVFL B illuminate when the corresponding
A or B Counter exceeds its capacity of 8 decades. The
indicator remains on until a reset is generated.
M, N, AND P INDICATORS
3 LED indicators aid in the
selection of the preset value. When the Preset display
function is activated, the Select push-button selects
which of the 3 LEDs is illuminated. When one of these
LEDs is On, that digit of the preset value can be
incremented using the Advance push-button.
DISPLAY
3 LEDs labeled A, B, and Preset indicate the
information being displayed in the counter display.
Counter A, Counter B, or the Preset value may be
displayed by repeatedly pressing the Display push-
button until the desired LED is illuminated.
TIME BASE
3 LEDs indicate the selected time base
source. By repeatedly pressing the Time Base push-
button, 0.01 Sec, 0.01 Min, or the Ext mode can be
chosen.
GATE
A single LED indicates that the entire instrument
is enabled to count. For the Gate LED to be illuminated,
the module must be placed in the Count mode (either
manually or via the interface option), the Enable input
must be above +3 V, and the preset stop condition must
not have been reached.
REMOTE
A single LED labeled REM indicates that the
Model 994 is under computer control, and all front-panel
controls are disabled. This mode is set by the
ENABLE_REMOTE command.
CONTROLS
DISPLAY
Push-button selects the contents of Counter A
or B, or the Preset value for presentation in the 8-decade
display. Repeatedly pushing the button cycles the
selection through the three choices as indicated by the
A, B, and Preset LEDs.
SELECT
Push-button chooses the M, N, or P digit in the
display of the preset value. Pushing the button advances
the selection through the three choices as indicated by
the illuminated LED. The Select push-button operates
only if the Preset mode has been selected by the Display
push button.
ADVANCE
Push-button increments the preset digit
selected by the Select push-button once each time the
Advance button is depressed. The M and N digit ranges
are both 0 to 9. The P digit range is from 0 to 6. The
Advance push-button operates only if the Preset mode
has been selected by the Display push-button.
TIME BASE
Each push on this button advances the
selection one step through the three time base choices
of 0.01 Sec, 0.01 Min, and Ext to determine the time
base source for the preset register.
STOP
This push-button stops all sections of the
instrument from counting.
RESET
Depressing this button resets both counters to
zero counts and turns Off both overflow indicators. It also
clears any counts accumulated in the blind preset
counter, but does not change the selected preset value.
When power is turned On to the Module, a Reset is
automatically generated.
COUNT
Pushing this button enables the counting
condition for the entire instrument, providing the Enable
input is not held below +1.5 V and the preset value has
not been reached.
THRESH ADJUST (A and B)
Front-panel mounted,
25-turn trimpots to adjust the positive input thresholds for
Counters A and B. The range is from +100 mV to +9.5 V.
Adjacent test points provide the TTL logic signal outputs
from the discriminators to facilitate adjustment using an
oscilloscope.
DWELL
A one-turn potentiometer on the front panel with
an On/Off switch at the fully counterclockwise position.
Adjusts the display dwell time over the nominal range
from 1 to 10 seconds. When the instrument is in the
Recycle mode, dwell time occurs after the preset value
has been reached. Turning the switch Off at the fully
counterclockwise position selects the Single Cycle mode.
If the print loop option is used, the Dwell control is
disabled when the print loop controller is active and
controlling the dwell time.
994
Dual Counter and Timer
2
