1
ORTEC MODEL 996
TIMER AND COUNTER
1. DESCRIPTION
1.1. GENERAL
The ORTEC Model 996 Timer and Counter
incorporates a 100-MHz, 8-decade counter and a
blind preset timer. The basic model offers visual
readout via an 8-decade LED display. By plugging
in field-installable options, considerably enhanced
readout and control capability can be added at any
time.
For automated counting applications not requiring
computer interfacing, the standard ORTEC print
loop function is available as a field-installable plug-
in board. In conjunction with an ORTEC Model
777A Printer, this option offers automatic recycling
of the counting and printing of all 8 digits of the
counter'scontents,along withthat of other counters
in the print loop. In place of the 777A, the ORTEC
Model 879 Buffered Interface can be utilized with
the print loop. This solution provides IEEE-488 and
RS-232-C interfaces for all the counters in the print
loop. The Model 879 has the capability,through the
print loop, to start and stop counting, reset, and
read the contents of the counter in the Model 996
along with other counters in the print loop.
The full power of CCNIM™ (Computer Controlled
NIM) is obtainable by adding the IEEE-488 option
or the RS-232-C option. These plug-in boards yield
computer control of all functions normally
selectable from the front panel, including start and
stop count, readout, reset, setting the preset value,
displaying the preset value, displaying the counter
contents, and selecting the desired time base. To
eliminate accidental operator interference, the
computer can disable all front-panel controls in the
remote mode. Computer readout with either of the
two CCNIM™ options includes the contents of the
counter, the preset value, and the current display
mode.The IEEE-488optionalsoreadstheoverflow
status for the counter. Implementationof the IEEE-
488 interface in the Model 996 is compatible with
the NIM/GPIB standard.1The CCNIM options can
directly drive printers having RS-232-C or IEEE-
488 ports.
Excellent flexibility in setting the preset value is
offered by the MN X 10Pselection. The M and N
values provide two-digit precision, while P selects
the decade. Presetscan be chosen in the rangesof
0.01 to 990,000 seconds, 0.01 to 990,000 minutes,
or 1 to 99,000,000 counts. In the external (EXT)
time base mode, the 996 becomes a displayed,
preset counter. The 996 can function as a
displayed, preset timer by changing the position of
a circuit board jumper and using the 0.01-SEC or
0.01-MIN time base.
Both positive and negative sensing inputs to the
counter are available on the front panel. The
negative input is designed to accept standard NIM
fast-negative logic pulses with a fixed threshold of
-250 mV on a 50-
S
input impedance. The negative
input can handle counting ratesupto 100 MHz. The
positive input can accept counting rates up to 25
MHz on a 1000-
S
input impedance. To enhance
the flexibility of the positive input, a precision
discriminator is included. The discriminator
threshold is variable over the range of +100 mV to
+9.5 V using a front-panel, 25-turn trimpot. The
threshold can be adjusted to suit the amplitude of a
specific source of logic pulses or used as a
precision integral discriminator on analog pulses.
For the latter application the TTL logic output of the
discriminator is providedas a test point on the front
panel. This output can be used to trigger an
oscilloscope while viewing the analog signal at the
counter input on the oscilloscope. The oscilloscope
tracewillshowthesignalsthatare beingcountedby
the Model 996, thus permitting a very selective
adjustment of the threshold.
1See: "STANDARD NIM DIGITAL BUS (NIM/GPIS)", DOE/ER-
0173, U.S. NIM committee, August 1983; "IEEE Standard Digital
Interface for Programmable Instrumentation", ANSI/IEEE Std
488-1978, The Institute of Electrical and Electronics Engineers,
345 East 47 Street, New York, NY 10017; and "Codes and
Format Conventions for Use with ANSI/IEEE Std 488-1978",
ANSI/IEEE Std 728-1982, The Institute of Electrical and
Electronics Engineers, 345 East 47 Street, New York, NY 10017.
