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Detailed introduction
The full functionality 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 starting and stopping counting, reading, resetting, setting presets, displaying presets, displaying counter contents, and selecting the desired time base. To eliminate unintended operational interference, the computer can be in remote mode with all front panel controls disabled. With the CCNIM option, the computer can read the counter contents, preset values and current display mode. The CCNIM option can directly drive printers with RS-232-C ports.
The MN X 10P option provides maximum flexibility in setting presets. The M and N values provide two-digit precision, while P has the option of decimal. Preset values can be selected from 0.01 to 990,000 seconds, 0.01 to 990,000 minutes, or 1 to 99,000,000 counts. In external (EXT) time base mode, 996 becomes the displayed preset counter. The 996 can be used as a preset timer for the display by changing the position of the circuit board jumpers and using the 0.01-SEC or 0.01-MIN time base.
The front panel provides the counter's positive and negative sensing inputs. The negative input is designed to accept NIM-standard fast negative logic pulses with a fixed threshold of -250 mV over a 50Ω input impedance. The negative input can handle count rates up to 100 MHz. The positive input can accept count rates up to 25 MHz on a 1000 Ω input impedance. To increase the flexibility of the positive input, a precision discriminator is integrated. The discriminator threshold can be adjusted from +100 mV to +9.5 V using the front-panel, 25-turn trimpot. The threshold can be adjusted to suit the amplitude of a specific logic pulse source or used as a precision integrating discriminator on analog pulses. For the latter application, the discriminator's TTL logic output serves as a front-panel test point. This output can be used to trigger the oscilloscope when viewing an analog signal at the oscilloscope's counter input. The oscilloscope trace will show the signal counted by the 996, allowing the threshold to be adjusted accordingly.
All frequently used functions are conveniently accessible via the front panel. Count, stop and reset functions can be manually controlled via three buttons. When counting is enabled on the 996 model, the door LED will illuminate. Use the time base button to select 0.01 second, 0.01 minute or external time base. In external mode, a preset counter counts events at the positive or negative front panel input.
The DISPLAY button switches the display to show the contents of the counter or a preset stop value. To change a preset, you must first select a preset mode using the DISPLAY button. The Preset Select button can then be used to select M, N or P for adjustments. Use the "Preset Advanced" button to change the value of M, N or P. There are LED indicators on the display to indicate whether M, N, or P has been selected, to warn when an overflow occurs in the counter, and to indicate when the computer in remote mode should disable front panel controls.
When using the Model 996 without the plug-in option, a jumper on the circuit board selects automatic recirculation of counting intervals, with a display dwell time of 1 or 10 seconds at the end of each counting interval. The plug-in option disables the dwell/auto-recirculate function when enabled by an external controller.
The counting function of the entire module can be disabled by holding the Gate input below +1.5 V using an external signal source. The door LED will then turn off. If counting mode is activated, an open circuit at the Gate input or greater than +3 V allows the instrument to start counting. The interval output of another ORTEC timer can perform this function to synchronize the Model 996's count with another timer. The interval outputs of all ORTEC timers provide nominal +5 V when counting and less than +0.5 V when counting is disabled.
The interface connector for the plug-in RS-232-C option is located on the rear panel. The counter's overflow output is also located on the rear panel. Counting these overflows on another counter effectively extends the counting capacity of the Model 996.
The Model 996 is powered by ±12 V and +6 V supplies from the standard NIM power box.
