Product consultation
Contact
Detailed introduction
Standard computer interfaces built into the Model 974A include RS-232-C and 20-mA loopback. The command format (Table 1) follows standard NIM digital bus rules, an easy-to-use NIM instrument programming language. All front panel functions (except display testing) can be controlled remotely from a computer or dumb terminal. In addition, the computer interface provides access to many functions that are not accessible through the front panel. The front panel can be locked via the ENABLE_REMOTE command from the terminal or computer.
The input polarity of all four counting channels can be set individually using internal connectors. The count rate for negative signals is 100 MHz; the count rate for positive signals is 25 MHz. Each counting channel can be independently gated externally via the gate 1, 2, 3 and 4 inputs. All four counting channels can be gated externally simultaneously via the main gate input.
The architecture of the ORTEC Model 974A Quad 100 MHz Counter/Timer allows for maximum flexibility. Counter channel 1 is used as a gate controller for counter channels 1, 2, 3 and 4. When counting starts, the input gates of counting channels 1, 2, 3 and 4 are opened. When the accumulated count in counting channel 1 equals the selected preset value (selected and displayed on the front panel), the counting interval is terminated and the input gates of counting channels 1, 2, 3 and 4 are closed. If the Dwell control is rotated counterclockwise to the Off position, a new counting cycle will not be started. However, if the dwell control is set to the selected dwell time, a new counting cycle will automatically start after the selected dwell time has expired and auto-reset. Since the input to counting channel 1 can be selected as an internal 0.1 second time base, an internal 1 minute time base, or an external source, channel 1 can be used as a presettable timer or a presettable counter.
Event counters are only accessible through one of the computer interfaces and are primarily used to mark printouts or record counting cycles. After the Model 974A receives the ENABLE_EVENT_AUTO command, the event counter will increment by one count at the end of each preset count interval. The contents of the event counter and the contents of all four 100 MHz counting channels are output during execution of the SHOW_COUNTS command. This will cause the count cycle to be printed out as an integer token. By using the ENABLE_EVENT_ EXTERNAL command, the event counter can again be used as an external pulse counter. The input event counter must have a count rate <4 kHz; its capacity is 8 decimal digits. The ENABLE_EVENT_PRESET command allows the event counter to control the total number of counting cycles in a given counting run. When an event preset value is set through the computer interface, the event counter will allow successive counter interval cycles until the cumulative value equals the preset value.
