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

X-ray data acquisition single energy
XDAS-V2 1.6mm pitch
1

SENS-TECH
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 64 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, single energy system.

2 applications
·
security inspection
·
detection of foreign bodies in material produced on a belt
·
thickness measurement
· inspection
log
·
quality control

3

features

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

4

XDAS-V2 system

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.

Current from the photodiodes is integrated by a microcircuit
containing 128 charge sensitive amplifiers, only 64 of which
have detectors fitted in a single energy system. 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 14bit 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 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.

data interface options

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