NIM Model 321B/321BL Quad Discriminator
Variable Threshold

LRS Model 321B Quad Variable Threshold Discriminator employs an outstanding circuit design to assure stable and reliable operation over a wide range of experimental conditions including variations in temperature, rate, pulse width, amplitude, risetime and supply voltage. It is an extremely versatile instrument, with threshold and other performance characteristics especially chosen for large scale, general purpose use in high energy physics. Compactly packaged, the 321B achieves a low unit cost through volume production techniques and without sacrifice of perform- ance, quality, or flexibility.

Operational Features Include:
* Continuously Variable Threshold from 50 mV to 350 mV on Model 321 B/50 and from 1 00 mV to 800 mV on Model 321 B/100. A low minimum threshold permits proper back termination of phototubes or allows use of small, lower-gain photomultipliers without the necessity for a separate amplifier.
*Threshold Stability is <250 uV/'C, guaranteeing positive, reliable operation over varying experimental conditions.
* Fiddle-free threshold and width controls are screwdriver-adjustable. Recessed behind the front panel, they cannot be changed inadvertently during the course of an experiment.
*Continuously variable output width from 5 ns to .8 us is the widest continuous range offered by any discriminator in its class.
* 100 MHz operation: The double pulse resolution of under 10 ns provides ample speed for most large-scale, general purpose applications.
*High current outputs: Each channel offers one -32 mA output split between two front panel BNC or LEMO connectors (for fanout, terminating, or clipping,) and one -16 mA complementary output.
*Output width is independent of input duration, amplitude, and rate. No need for width cables, etc.
*No multiple pulsing: One - and only one - output pulse is produced regardless of input duration or amplitude.
*Low time slewing permits accurate timing even in experiments experiencing wide distributions of input amplitudes.
*Deadtimeless operation updates the output pulse to reflect the most recent input signal.
*Compact packaging and low power consumption permit up to 24 discriminator channels to be powered from one 72 watt NIM Bin.
* Exhaustive quality control: The threshold of each channel is checked for variation with input width, input risetime, rate, temperature, and supply voltage change to assure optimum performance and long, reliable service life.
* Moderately priced to appeal to today's larger experiments and smaller budgets.

     SPECIFICATIONS

      HIM Model 321B/321BL

  QUAD VARIABLE THRESHOLD DISCRIMINATOR

 INPUT CHARACTERISTICS**

 Signal Input:   Threshold, -100 mV to -800 mV (Model 321 B/1 00); or, - 50 mV to
     - 350 mV (Model 321 B/50); continuously variable (front-panel screw-
     driver adjustment, screwdriver included); 50Ohm protected to +/-50 volt
     transients; direct-coupled; reflections <10% for input pulses 2 ns risetime;
     stability <.25 mV/'C over 20'C to 60'C operating range; offset, 0 +/-2 mV;
     offset temperature coefficient, approximately .01 mV/'C.

 Gate:    Slow gate via rear connector, with rear panel ON-OFF switch; rise and fall
     times, approximately 50 ns; clamp to ground from + 5 inhibits;
     direct-coupled.

 OUTPUT CHARACTERISTICS

 Outputs:    Three, NIM; one positive (quiescently - 16 mA, 0 mA during output),
     two negative (O mA quiescently, - 16 mA during output).

 Duration:    Continuously adjustable via front panel screwdriver control from 5 ns to
     >800 ns. Other ranges, i.e., 15 ns to 8.5 usec, may be obtained as an
     option.

 Temperature Coefficient
 of Output Width:   <.05%/'C.

 Rise and Fall Time:   Less than 2.0 ns, all outputs, 10% to 90%.

 GENERAL

 Maximum Rate:   110 MHz typical, input and output.

 Double Pulse Resolution:  Approximately To /3 + 5.5 ns, where TO is output pulse duration.

 Time Slewing:   <1 ns for input amplitudes 110% of threshold and above.

 Input-Output Delay:   9.0 ns typical.

 Multiple Pulsing:   None, one and only one output pulse of preset duration is produced for
     each input pulse, regardless of input pulse amplitude or duration.

 Packaging:    In conformance with AEC standard for nuclear modules (AEC Report
     TID-20893); RF shielded AEC #2 module, fitting 6/bin; dimensions 2.75
     x 8.75 x 10 inches deep. Completely compatible physically and
     electrically with LRS Power Chassis Model 108P, and with any other AEC
     power bin of any manufacturer.

 Power Requirements:   + 24 volts at 125 mA; - 12 volts at 300 mA; + 12 volts at 160 mA; all
     regulated +/- .1%.

 Total Power Consumption:  8.8 watts.

 **Also available with two high impedance bridged inputs and fixed - 100 mV or - 50 mV threshold;
 respectively referred to as Models 321C/100 and 321C/50. LEMO-type connectors available on special
 order.