The Model 2401B Position Analyzer, signal processing and readout electronics, consists of a rack-mountable controller/analyzer module and a separate four channel preamplifier module (either a high gain or low gain version), all optimized for use with a corresponding 3300 Series position sensitive MCP/RAE sensor head and the desired spatial resolution. The 2401B Position Analyzer provides a number of electronic functions including:

• A rapid ratio calculation to recover the x and y spatial position of each photon.
• Lower and upper-level pulse discriminators, along with fast, look-ahead, pulse-pileup rejection circuits
• Switch-selectable front panel metering for count rate, input level (MCP gain) and system dead-time.
• Front panel edge-gating controls to enable selection of a rectangular, electronic active regions for data acquisition, smaller than the full active area.
• X and Y analog position outputs: approximately 0.5 to 4.5 VDC, linearly proportional to coordinate position of event on sensor, with a quiescent output voltage level of 2.5 volts with no events occurring.
• Analog strobe output and Z-axis blanking output(for XY monitor) activated when valid data is present on analog XY outputs.
• Other inputs/outputs: Veto Gate Input; Sum (diagnostic gain output), Analog Rate (for remote count rate meter) and Busy outputs.

The basic paralyzable dead time of the position analyzer system is 4 microseconds per detected event. For perfectly time-periodic input counts, the 4 µsec dead time translates to a maximum output count rate of 250,000 counts/second. For Poisson-distibuted time-of-arrival statistics encountered in typical applications, this maximum output rate is reduced to approximately 100,000 counts/second, due to the arrival of closely-time-spaced events that are lost from processing. This fixed time period is required for position calculation and preamp/shaper baseline recovery to ensure accurate spatial position calculations of subsequently-occurring event.

In operation, only events exceeding a preset lower threshold discriminator are processed, thus eliminating much of the background noise of other detector approaches, with only one event essentially processed simultaneously. Simultaneous double events and other high-gain events are typically eliminated from processing by an upper-level discriminator and pile-up rejection circuits. Each detected event is processed separately and occupies a fixed amount of signal processing time.

With a pulse-pair resolution of 300 nsec, if a second event is received by the charge-sensitive amplifier within the dead time (in µsec) of a prior event, either one or both of the events are vetoed from further processing to ensure optimum spatial position calculation accuracy. A second event arriving more than 300 nsec but less than 1µsec after a prior event results in both events vetoed from processing; a second event arriving more than 1 µsec but less than the total dead time after a prior event results in the second event vetoed from processing but the first event is processed; events separated by more than the total dead time results in both events processed. If two events arrive within 300 nsec (and combined amplitude does not exceed upper discriminator setting), both events are counted together as a single event with a calculated position between the true positions.

By accumulating single events for a user-determined period of time, spectra and images are developed from the integration of these single events.