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Detailed introduction
The full functionality of CCNIM™ (Computer Controlled NIM) is available 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, and selecting displayed counters. 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 A and B counts and which counter is being displayed. The CCNIM option can directly drive printers with RS-232-C ports.
The inputs to Counters A and B can be individually selected as positive or negative sensing inputs by changing the input polarity jumpers on the counter printed circuit board (PWB). The negative input mode 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.
Positive input mode can accept count rates up to 25 MHz on 1000Ω input impedance. To increase flexibility in positive input mode, both counters contain precision discriminators. The discriminator threshold can be set 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 integral discriminator on analog pulses. For the latter application, the discriminator's TTL logic output is a test point on the front panel. These outputs can be used to trigger the oscilloscope when viewing analog signals at the oscilloscope's counter input. The oscilloscope trace will show the signal counted by the Model 995, 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 the Model 995 is enabled for counting, the door LED will illuminate. The "Display" button switches the display to display the contents of Counter A or the contents of Counter B. There are LED indicators on the display to indicate whether an overflow has occurred in counter A or B, and when the computer in remote mode should disable the front panel controls.
The counting function of the entire module can be disabled by holding the "enable" 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 Enable input or >+3 V allows the instrument to start counting. The interval output of another ORTEC timer can perform this function to synchronize the Model 995's count with another timer. The interval outputs of all ORTEC timers provide nominal +5 V when counting and <+0.5 V when counting is disabled.
The A and B counter inputs can be independently gated via 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 dedicated rear panel output for signal overflow. Counting these overflows on another counter expands the counting capacity of the Model 995.
The Model 995 is powered by ±12 V and +6 V supplies in a standard NIM chassis. For power boxes that do not include a +6 V power supply, the internal +6 V power supply option is available. This option is field installable and draws power from the 117 V AC power cord in the power box.
