871 Timer and Counter

• 8-decade presettable timer and counter
• 25-MHz positive or negative input count rate
• Crystal-controlled time base
• Auto recycle dwell time control

The ORTEC Model 871 is a nonprinting timer and counter and may be used in any system as a counter and presettable timer, timer and presettable counter, or as two counters. Integrated and hybrid circuitry, combined with an 8-decade light-emitting diode (LED) display, give excellent operational reliability at a very economical cost. A 1-MHz crystal-controlled oscillator, which serves as the standard time base for the unit, provides substantially improved timing accuracy over timers using a line frequency time base. The 8-decade LED display is a highly legible count or time indicator, further enhanced by suppression of the leading zeros, which minimizes the possibility of errors in readout. An LED below the 8-digit display indicates if the reading is for the counter or the timer, and a push-button below the display allows the user to alternate reading the counter or the timer. LED digits are also used to indicate the presets in an M X 10^N format.

The display test is activated by pressing the front-panel Display Test switch, which illuminates all "8s," thereby providing a test for all segments of each display.

The Model 871's two sections accept NIM-standard slow positive logic signals. The counter section also accepts NIM-standard fast negative input logic pulses. The input count rate is guaranteed to 25-MHz with a 40-ns pulse pair resolution. An overflow output pulse is available from each of the counters, which indicates that the 8-decade capacity of either counter has been exceeded.

Preset is accomplished by two front-panel push-buttons labeled INC M and INC N. The displayed information includes two digital characters to indicate the current selection of the values for M and N. Any value from 0 through 9 can be selected for M, and any value from 0 through 7 can be selected for N, thus giving preset capability from 1 through 9 X 10⁷. The Time Base Select push-button allows the operator to choose whether the time base is set for 0.1-s intervals, 1-min intervals, or whether the time base is to be derived from an external source. A decimal point is included in the Time Display to facilitate ease of reading directly in seconds or minutes.

For applications where a number of counts are to be preset and the time required to reach the preset count is of interest, it is possible to furnish pulses at 0.1-s intervals from the internal time base into the nonpresettable portion of the instrument and use the presettable portion as a counter.

Other applications include using the Model 871 as a ratio counter by furnishing pulses from external sources to the presettable portion as well as the nonpresettable counter and setting the preset portion for 100 to get the ratio relationship between the two external sources.

The Dwell control can be rotated to select a delay of <1 s to about 15 s following a preset condition. During the delay period, the contents of the counter can be read. At the end of the dwell interval, the instrument is reset and another counting interval is started immediately.

ORDERING INFORMATION