974 CCNIM Quad 100Mhz Counter/Timer

• Four 8-decade counters with full computer control and readout (CCNIM™)
• One counter that can function as a presettable timer or counter
• Crystal-controlled time base
• One counter can function as a timer
• 100-MHz negative or 25-MHz positive input count rate
• RS-232-C and IEEE-488 interfaces
• Auto Recycle dwell time control

The ORTEC Model 974 is a four-channel, 100-MHz Counter/Timer in a CCNIM™ (computer-controlled NIM) package. It can be computer-controlled or manually operated. The Model 974 may be used as a three-channel counter with one presettable timer, a four-channel counter (one counter channel presettable), or as a three-channel counter (one counter channel preset-table) with one timer. Any one of the four 100-MHz counter/timer channels can be monitored on the large, 8-decade LED display. In addition to the four 100-MHz channels, the Model 974 incorporates an 8-decade, presettable Event counter that can only be controlled or read through one of the computer interfaces.

Standard computer interfaces built in to the Model 974 include the IEEE-488, RS-232-C, and 20-mA loop. The command format (Table 1) adheres to the Standard NIM Digital Bus,* an easy-to-use language for programming NIM instruments. All front-panel functions (with the exception of Display Test) may be remotely controlled via a computer or dumb-terminal. In addition, several functions not accessible via the front panel are accessible with computer interfaces. The front panel may be locked out by the ENABLE_REMOTE command from a terminal or computer.

The input polarity to each of the four counting channels may be independently set using internal connectors. The maximum count rate for negative signals is 100 MHz; the maximum count rate for positive signals is 25 MHz. Each counting channel can be independently, externally gated through the Gate 1, 2, 3, and 4 inputs. All four counting channels may be simultaneously, externally gated through the Master Gate input.

The architecture of the ORTEC Model 974 Quad 100-MHz Counter/Timer (Fig. 1) is designed for maximum flexibility. Counter channel 1 acts as the gate controller for counter channels 1, 2, 3, and 4. When counting is started, the input gates to counting channels 1, 2, 3, and 4 are opened. When the accumulated counts in counting channel 1 equal the selected preset value (selected and displayed on the front panel), the counting interval is terminated and the input gates to counting channels 1, 2, 3, and 4 are closed. If the Dwell control is turned fully counter-clockwise to the Off position, no new counting cycle will be initiated. If, however, the Dwell control is set for a chosen dwell time, a new counting cycle will be automatically initiated after the end of the chosen dwell time and automatic reset. Since the input to counting channel 1 can be selected as the internal 0.1-second time base, the internal 1-minute time base, or an external source, channel 1 can act as a presettable timer or a presettable counter.

The Event counter, which is accessible only through one of the computer interfaces, is primarily intended as a means of labeling printouts or listings of counting cycles. After the Model 974 receives an ENABLE_EVENT_AUTO command, the Event counter will increment one count at the end of each preset counting interval. The contents of the Event counter, along with the contents of each of the four 100-MHz counting channels, are output during the implementation of a SHOW_COUNTS command. This results in an integer labeling of the counting cycle printout. The Event counter may be used alternately as a counter of external pulses by using the ENABLE_EVENT_EXTERNAL command. The maximum count rate input to the Event counter must be <4 kHz; its capacity is 8 decades. The ENABLE_EVENT_PRE-SET command allows the Event counter to control the total number of counting cycles in a given counting run. After an Event preset value is set via computer interface, the Event counter will allow continuous counter interval recycling until the accumulated value equals the preset value. The complete command file of the Model 974 is shown in Table 1.

Fig. 1.  ORTEC Model 974 Counter/Timer Architecture

ORDERING INFORMATION