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Detailed introduction
A 1 MHz crystal oscillator serves as the standard clock for this device, providing much higher timing accuracy than the timer when using line frequency. The 8-digit decimal LED display is a high-definition count or time display whose functionality is further enhanced by suppressing leading zeros, minimizing the possibility of reading errors. An LED below the 8-digit display is used to indicate whether the reading is for a counter or timer, and a button below the display allows the user to toggle between counter or timer readings. LED numbers are also used to indicate preset values for the M X 10N format.
Display test is activated by pressing the front panel display test switch, which will illuminate all "8s", providing a test for all segments of each display.
Both parts of the Type 871 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 be 25 MHz and the pulse pair resolution is 40 ns. Each counter has an overflow output pulse to indicate that the 8-digit decimal capacity of either counter has been exceeded.
Presets are accomplished by two front panel buttons labeled INC M and INC N. The information displayed includes two numeric characters indicating the current selection of M and N values. You can choose any value between 0 and 9 for M and 0 and 7 for N, giving you a preset capability of 1 to 9 X 107. The time base selection button allows the operator to choose whether to set the time base to 0.1 second intervals or 1 minute intervals, or to select whether to obtain the time base from an external source. The time display includes a decimal point to facilitate direct reading in seconds or minutes.
For applications where multiple counts are to be preset and the time required to reach the preset count is required, pulses can be provided from the internal time base at 0.1 second intervals to the non-presettable portion of the instrument and use the presettable portion as the counter.
Other applications include using the Type 871 as a ratio counter by providing pulses from an external source to the presettable part as well as the non-presettable counter and setting the preset part to 100 to obtain a ratio relationship between the two external sources.
The dwell control can be rotated to select a delay from <1 second to approximately 15 seconds after preset conditions. During the delay, the contents of the counter can be read. At the end of the dwell interval, the instrument resets and immediately begins another counting interval.
