X-ray data acquisition dual energy XDAS-V2 1.6mm pitch0 pages

SENS-TECH

X-ray data acquisition dual energy
XDAS-V2 1.6mm pitch
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SENSOR TECHNOLOGIES

description

XDAS-V2 is a modular system of boards for data acquisition in
X-ray linescan and CT systems. It consists of a set of detector
head boards and signal processing boards. Each detector head
board has 128 detector channels. Up to 7 signal processing
boards can be used in a system, each controlling up to 24
detector head boards. Several different detector pitches are
available. This data sheet describes the 1.6mm pitch, dual
energy system. 64 low energy detectors are mounted on the
upper side of the board (closest to X-ray source) and 64 high
energy detectors on the underside. A copper filter can be fitted in
between. The thickness of the filter depends on the X-ray
energy.

2 applications
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security inspection
waste sorting
mineral sorting
fat/lean measurement

3 features
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modular system with up to 24 detector head boards per
single signal processing board
1.6 mm detector pitch
X-ray energy range 30keV to 250keV
low electronic noise
range of scintillator types for single and dual energy
simultaneous data acquisition and read-out
wide dynamic range 3pC to 60pC
16 bit output
100 µs minimum signal integration time

on switch-on, the system is initiated in the last mode used.
The RS485 is compatible with the RS232 serial port on
standard PC's using the interface converter supplied. When
the USB2 interface option is chosen, the communications are
made via this connection.
A system is built up by daisy-chaining detector head boards to
the signal processing board via a 50-way ribbon cable, which
has differential data lines, as shown on the system block
diagram, section 13. Two inputs are provided on the signal
processing board, each of which can be connected to 12
detector head boards giving a total of 24. The system bus
data rate is 2.5 to 20MB/s.

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The signal processing board is connected to the processor via
a Data Control and Interface Module. Two types are
available, providing the following interfaces.

XDAS-V2 system

1. XDAS-DATA3 provides a SCSI output with a cable up
to 50M connecting to:

Current from the photodiodes is integrated by a microcircuit
containing 128 charge sensitive amplifiers. See detector
head block diagram, section 11. Correlated double
sampling is used to minimise common mode noise. The
microcircuit provides a multiplexed serial analogue output to
the signal processing board where data is converted into
14-bit format. Operation is continuous, with one set of data
being read-out whilst the next set is acquired. Dead time is
less than 1µs.
The dynamic range of the system is determined by the
storage capacitors within the ASIC. These can be set to 2pF
or 10pF, providing charge storage of 3pC or 15pC. If this is
insufficient, a multiple sampling facility is provided in the
signal processing board. This enables 2 or 4 samples to be
averaged and the result stored a 16-bit image store. This
provides a maximum dynamic range of 60pC. All 16 bits of
data are output.
The operation of the system is controlled by a gate array
which provides the central intelligence for the signal
processing board and the timing and control signals for
system operation. See signal processing block diagram,
section 12. Control settings are transmitted to the board via
an RS485 interface and stored in non-volatile RAM such that

XDAS-V2 system

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USB2.0 converter box XDAS-USB2
PCI7300 card, via an XDAS-485A-TTL
Frame Grabber, via an XDAS-485A-DFG

2. XDAS-USB2-1 provides a local USB2.0 output, limiting
the distance to the processor to 5 metres.

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data acquisition rate

This is normally determined by the speed of the A/D
converter. The standard is 2.5MHz and this will convert a
single detector head board in 51.2µs. A 10 board system can
be read out in 512µs. The A/D converter normally limits the
integration time that can be used. If faster integration and
read-out is required, further signal processing boards can be
added. For large systems, the speed of the system bus will be
the determining factor but when set for 20MHz a 1.25ms
sample time can be achieved for a system of 24 boards.