321 Acquisition module technical brief

1. General [block diagram]

The 321 acquisition module contains a high-performance shaping
amplifier and a 120 MHz Wilkinson ADC with software selectable
peak/area input modes (selecting the area input mode has the
same effect like inserting a gated integrator between the amp
and the ADC on conventional systems). It occupies a single
Nukebus slot and consumes less than 6 W of power.
All settings are electronically made. The shaping time constant
is switched by a rotary switch, which is driven by a tiny servo
motor. The only front panel switch is the one for the detector
The module MCU contains various individual (per unit) hardware
error sources which are digitlly compensated by the software
during acquisition (like temperature drift, integral non-linearity,
offset 0 etc).
The module serial number is also available from the MCU EEPROM and
is written by the software to the file, when saving the settings.

2. Controls

All parameters are available to the user from the m321 setup menu.
In most cases, using the load/save settings and the "auto" buttons
will do the job; but if you are an experienced MCA user and you need
access to the lowest level, you will not be denied it.
All 321 module parameters are programmed as separate DPS global
of the "parameter" type; this allows easy access to any of
them from command scripts.

The following parameters can be controlled:
- Preamp power - the preamp power outputs can be switched on/off.
- PZ - automatically adjusted.Manually accessible as well.
- Amplifier gain - from 5 to >5000, in over 4,000,000 steps,
- PUR noise treshold - in 256 steps.The noise level is measured
and known by the computer; in 'auto' mode this treshold is
dynamically held just above the noise floor,
- PUR on/off - when on,pulses detected as piled up are rejected,
- BLR rate - in 256 steps.
- BLR positive treshold,
- BLR negative treshold.The slow signal noise level is also measured
and known by the computer, and in auto mode these tresholds are
adjusted accordingly.
- Integrate time - the time the shaped signal is being integrated
in area mode, in 256 steps. It is shaping time dependent; whenever
the shaping time is switched, the driver software sets the apropriate
integrate time (it takes it from the module's MCU EEPROM). If another
setting is needed for some reason, it must be re-initialized every
time after switching the shaping time.
- ADC conversion factor - the number of channels the spectrum is
acquired into,1024 to 16384.
- Lower level discriminator - 256 steps,
- Upper level discriminator - 256 steps.
- Shaping time constant - 6 positions: 1,2,3,4,6,and 10 microseconds,
- Coincidence detect time window - up to 15 clock periods,
- Coincident operation on/off,
- Coincidence clock source - CCK1 or CCK2 on the Nukebus,
- Coincidence detect line - COI1, COI2 on the Nukebus or external,
- Hold the selected COI line to inhibit any coincidence being

The following read only hardware parameters are available:
- HF noise - the noise level at the input of the 6-th order low
pass filter, 0 to 255 (internal units).
- LF noise - the noise level at the output of the amplifier,
0 to 255 internal units.
- Module board temperature - in degree Celsius, 0.5 deg. resolution,
- Serial number.

Also, all 4 outputs (+/-12 and +/-24) of the preamp power connector
are measured by the MCU in order to switch them off on overload (they
have also hardware current limiting to protect them until the MCU

The following parameters can be accessed like all described above,
but instead of affecting hardware, they have effect over the acquisition
- Linearization on/off. When on, the acquisition task (m321acq) converts
the data from the module FIFOs into an intermediate spectrum, and
periodically ( default 5 times per second) transforms it into the final
(linearized) spectrum. When off, the data from the FIFOs
is processed directly into the final spectrum.
- Linearization period - the time between the transformations of the
intermediate spectrum into the final one (usually set to 0.2 S).
- (DC) offset - works only if linearization is on.


There are the following front connectors:
- Signal in (LEMO) - signal from the detector preamp,
- Unipolar out (LEMO) - the output of the shaping amplifier,
- Preamp power (D-9) - +/- 24V and +/- 12V for the preamp,and
(optionally disconnected) TxD and RxD for a "intelligent
detector" interface.
- Gate (LEMO,optional) - external gating/coincident operation.
The rear connector is a 68-pin Nukebus connector.

3.Technical data
Amplifier section: gain: 5 to 5000,
shaping time constants: 1,2,3,4,6,10 microseconds (other sets on request),
integral nonlinearity: < 0.025% for last 99% of full scale,
noise: <5 microvolts RMS @ 4uS shaping time, gain=500.

ADC & integrator section:
number of channels - 1024 to 16384,
conversion time - N*8.33e-9 [S] (N is the conversion result),
differential nonlinearity - <0.6%.

Power consumption: < 6 Watts.

Phys. dimensions: 118 x 58 x 38 mm

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