ORTEC 994 User guide

994

Dual Counter and Timer

•Two 8-decade counters and a timer with the
configuration flexibility to serve a variety of
measurement needs

•RS-232-C option provides CCNIM capability
with full computer control and readout

•Can directly drive printers having RS-232-C
ports

•An 8-decade LED display provides
instantaneous readout of the entire counter
capacity, even in dimly lighted rooms

•All commonly used controls are easily
accessible on the front panel

•100-MHz counting rate capability

•Preset time or counts set with the precision
of a two-digit and decade selection

•All options are field-installable

The ORTEC Model 994 Dual Counter and Timer
incorporates two eight-decade counters and a
blind preset timer. Considerable functional
flexibility is designed into the instrument,
allowing it to be configured for a variety of

easurement tasks. Typically, it can be used as

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two counters recording separate events under
the control of the preset blind timer. When
continuous readout of the time is needed,

ounter A can be diverted to count the time

C
while Counter B records external events. This
provides the function of a counter and a
displayed preset timer. In some applications, the
time taken to count a preset number of events
must be measured. For this application, Counter
A, coupled with the preset blind counter, can be
used as a preset counter while Counter B
records the time in 0.01-second intervals. In
measurements where it is important to correct
for the dead time of the detector and its
associated electronics, the Gate A input can be
switched to also gate the time clock On and Off
with a 100-ns time resolution. A positive logic
signal that defines the system live time is
connected to the Gate A input. This configuration
provides a live-time clock (Counter A) and a
counter (B).

Excellent flexibility in setting the preset value is
offered by the MN X 10
values provide two-digit precision, while P
selects the decade. Presets can be chosen in
the ranges of 0.01 to 990,000 seconds, 0.01 to
990,000 minutes, or 1 to 99,000,000 counts.

The basic Model 994 includes an 8-decade LED
display that offers instantaneous visual readout
of the full contents of Counter A or B, even in a
dimly lighted room. By adding field-installable
options, considerably enhanced readout and
control capabilities can be incorporated.

The full power of CCNIM (Computer-Controlled
NIM) can be obtained by adding the RS-232-C
option. This plug-in board allows computer
control of all functions normally selectable from
the front panel, including start and stop count,
readout, reset, setting the preset value, selecting
the displayed counter, and selecting the desired
time base. To eliminate accidental operator
interference, the computer can disable all front­panel controls in the Remote mode. Computer
readout with the CCNIM option includes A and B
counts, the preset value, and which counter is
being displayed. The CCNIM option can directly
drive printers having RS-232-C ports.

The inputs to Counters A and B are individually
selectable as either positive or negative sensing
inputs by changing the Input Polarity Jumpers on
the counter printed wiring board (PWB). The

P

selection. The M and N

negative input mode is designed to accept NIM­standard, fast-negative logic pulses with a fixed
threshold of –250 mV on a 50- input
impedance. The negative inputs can handle
counting rates up to 100 MHz. The positive input

ode can accept counting rates up to 25 MHz

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on a 1000- input impedance. To enhance the
flexibility of the positive input mode, precision
discriminators are included on both counters.

he discriminator thresholds are variable over

T
the range from +100 mV to +9.5 V using front­panel, 25-turn trimpots. The thresholds can be
adjusted to suit the amplitude of a specific
source of logic pulses or used as precision
integral discriminators on analog pulses. For the
latter application, the TTL logic outputs of the
discriminators are provided as test points on the
front panel. These outputs can be used to trigger
an oscilloscope while viewing the analog signal
at the counter input on the oscilloscope. The
oscilloscope trace will show the signals that are
being counted by the Model 994, thus permitting
a very selective adjustment of the threshold.

All the commonly used functions are
conveniently accessible on the front panel.
Manual control of the Count, Stop, and Reset
functions is via three push-buttons. The Gate
LED is illuminated when the Model 994 is
enabled to count. Selection of the 0.01 second,

0.01 minute, or external time base is made by
the Time Base push-button. In the external
mode, the preset counter counts the events at
the counter A input. The Display push-button
switches the display to show the contents of
Counter A, the preset stop value, or the contents
of Counter B. To change the preset value, the
Preset mode must first be selected with the
Display push-button. Subsequently, the Preset
Select push-button is used to choose M, N, or P
for adjustment. Changing the value of M, N, or P
is accomplished with the Preset Advance push­button. The display contains LED flags to
indicate whether M, N, or P has been selected,
to warn when overflows have occurred in
Counter A or Counter B, and to advise when the
front-panel controls are disabled by the computer
in the Remote mode. When the Model 994 is
used in the automatic recycle mode, the Dwell
knob adjusts the dwell time of the display from 1
to 10 seconds.

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

994

Dual Counter and Timer

timer can perform this function to synchronize
the Model 994 counting with the other timer. The
Interval outputs on all ORTEC timers provide
nominally +5 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 Internal +6 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
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.

P

is reached on the

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 push­button until the desired LED is illuminated.

TIME BASE 3 LEDs indicate the selected time base
source. By repeatedly pressing the Time Base push­button, 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 front­panel 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 push­button 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.

INPUT POLARITY JUMPERS Two jumpers located
on the printed wiring board (PWB) separately select
the desired input polarities for inputs In A and In B. P =
positive, N = negative.

A COUNTER/TIMER JUMPER Two-position jumper
located on the PWB. In the Counter position, Counter
A always counts and displays the events connected to
In A. When set to the Timer position, Counter A counts
and displays the time if either the 0.01-Sec or the

0.01-Min time base is selected. If the Ext time base is
selected, Counter A will count and display the events
from In A.

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