15
Example of System Conversion Gain
Typical Sensitivities for ORTEC preamplifiers are:
Coaxial 150 mV/MeV
GLP 1.7 mV/keV
LO-AX 300 mV/MeV
IGLET 3 mV/keV
SLP 1.7 mV/keV
DSPEC converts the VOLTAGE output signal from a charge-
sensitive preamplifier into a count in a memory location of the
histogram memory. This conversion follows the relationship:
Memory Location = V
in
× K × Total Gain × Total Channels
where:
V
in
is the step-height of the preamplifier signal in volts;
K is a constant equal to (0.855)(total channels)/volt;
Total Gain is the product of the fine and coarse gains;
Total Channels is the total number of channels in the
spectrum.
For example: At 16,384 channels, with the DSPEC set
for a total gain of 2.5, a 200-mV preamplifier signal
(corresponding to a 1.33-MeV gamma ray event in a coaxial
detector) would be stored in:
Channel Location = (0.2)(0.855)(2.5)(16,384)
= 7004.16
or channel 7004, which corresponds to an overall system
conversion gain of 0.19 keV per channel.
5. SPECIFICATIONS
5.1. System Performance
DSPEC is unlike analog systems
consisting of discrete components such
as an amplifier or ADC. Whereas it is
conventional in an analog system to
specify the gain instability of the ADC in
ppm/
C, in DSPEC many of these
conventional functions are emulated in
the digital world by firmware; therefore,
such specifications are DSPEC SYSTEM
specifications. Comparison should be
made ONLY with SYSTEM
specifications in the analog world.
System Gain
0.35 to 100, continuously
computer-adjustable; minimum gain step
is 1/85,000.
Coarse Gain
Computer-selectable as 1,
2, 5, 10, 20, 50, and 100.
Fine Gain
Computer-adjustable from
0.35 to 1.00.
Shaping-Time Constants
Rise and Fall
32 rise and fall times
ranging from 0.8 to 25.6 µs in 0.8-µs
steps; computer-selectable.
Flattop
5 flattop times ranging from
0.8 to 2.4 µs in 0.4-µs steps;
computer selectable.
Cusp Parameter
(adjusts the curvature of the rise and fall time) 6 values that range from
0.5 to <1; computer-selectable.
Memory Segment Size
Computer-selectable as 16384, 8192, 4096, 2048, 1024, or 512
channels full scale.
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