14 A Profibus-based Control System for Nuclear Physics Applications - The 6th World Multi-Conference on Systemics, Cybernetics and Informatics SCI 2002, July 2002

A Profibus-based Control System for Nuclear Physics Applications
O. Mirabella1,3
, V. Bellini2,3
, C. Randieri1,3
, C. Spitale1,3
1) Dept. of Computer Science and Communications, Faculty of Engineering, University of Catania
2) Dept. of Physics, Faculty of Science, University of Catania
3) INFN/LNS Catania
ABSTRACT
In this paper we present the results of implementation of a
remote control system based on ProFiBus technologies used for
the remote control of experimental nuclear physics apparata.
Remote control makes experiment handling more flexible,
eliminating any problems originating from the need for direct
access to the systems being controlled. In the paper we describe
two different applications. The first application of the ProFiBus
is the remote control of a multidetector (made up of a bi-
dimensional array of CsI scintillators) used to detect light
nuclear particles, as protons and/or light ions. In the second
application, we present an implementation of the control of a
vacuum system suitable for a special chamber used for the
development and testing of particle detectors operating in
vacuum conditions.
Keywords: Nuclear physics, Profibus, sensors, vacuum system,
PLC
1. INTRODUCTION
The spread of digital electronics and new networking
technology has strongly modified the techniques and
methodologies used in process control. Particularly today, the
demand for distributed process control involves intelligent
systems, control devices and measurement systems able to
communicate through the network. An important requirement
of these systems is the need for a reduction in connections,
thus simplifying system management and decreasing
maintenance problems. FieldBuses can provide a valid
solution for remote control in industrial production and
measurement and acquisition systems, which are widely
applied in experimental research in nuclear physics.
This field of research requires distributed remote control
apparatus capable of working in very hard operating
environment (strong electromagnetic fields, damage by
radioactive particles, low temperatures etc.) and at the same
time meeting the necessary safety, reliability and simplicity
requirements. The presence of a large number of devices
makes it difficult to perform remote control of the whole
system. Many devices must be controlled locally and this
requires frequent access to the site of the experiments.
Unfortunately, the environment during nuclear experiments is
not safe; so it would be very difficult for a human operator to
reach quickly the experimental equipment in order to tune the
required parameters. For this reason, the use of a FieldBus is a
valid solution since it provides tools for implementing a
remote control system: the ProFiBus (Process FieldBus) is a
communication system widely used in the world of industry
and is highly suitable for this aim.
In this paper we present the results of implementation of a
remote control system based on ProFiBus technologies used
for the remote control of experimental nuclear physics
apparata. Remote control makes experiment handling more
flexible, eliminating any problems originating from the need
for direct access to the systems being controlled. In addition, a
nuclear physics experiment often requires the assembly of
systems of considerable size, thus making frequent access to
the many devices involved onerous and not always possible. In
the paper we describe two different applications.
The first application of the ProFiBus is the remote control of a
multidetector (made up of a bi-dimensional array of CsI
scintillators) used to detect light nuclear particles, as protons
and/or light ions. The mechanical setup has to be moved in
real time, without suspending the beam operation, with very
high precision in three different directions, hence requiring the
remote control of three electrical motors. Through the Profibus
we implemented the remote control of the mechanical setup
with simultaneous on-line monitoring of the every detector’s
position. This application allows us to appreciate the potential
advantages in terms of both reliability and simplicity which
arise from the use of only one bus-based communication
system. Our application shows good performance in terms of
network speed combined with a sophisticated dynamic
interaction between a command console and a remote slave
system.
In the second application, we present an implementation of the
control of a vacuum system suitable for a special chamber
used for the development and testing of particle detectors
operating in vacuum conditions. The overall setup includes
two vacuum pumps, two vacuum sensors and a Programmable
Logic Controller (PLC). The two pumps have to work in
sequence since each of them operates in a specific pressure
range. The PLC monitors the pressure in the chamber and
decides when to switch on each pump. In this application we
show how it is possible to combine the characteristics of
intelligence decentralization, according to the philosophy of
FieldBuses, with supervisor stations, control devices
(regulators, PLC, etc.), actuators and transducers that share the
same communication bus and interact in various ways.
2. REMOTE CONTROL IN NUCLEAR PHYSICS
EXPERIMENTS
As mentioned in the introduction, the apparata used in nuclear
physics experiments is often complex, involving a large
number of measuring devices (sensors) and actuators. The
possibility of handling these devices via remote control has
two advantages: on the one hand it allows operators to
introduce system modifications without the need to remain in
the measuring area, which is often not allowed during
experiments, and on the other it allows a large number of
variables to be monitored in order to keep under control the
progress of the experiment.
The types of information present in the system fall into two
different categories of data. One includes plant supervision
and control data, which is necessary for the system in order to
operate correctly. This information is used to set the operating
conditions that will best meet the specifications defined for the
effective execution of the experiment. Its dynamic is relatively
modest, therefore it can be handled via remote control by
using distributed systems. The other category of information

includes data obtained via measurements carried out during the
experiment itself. The signals are usually obtained at an
aleatory frequency and have a very short duration (generally a
few nanoseconds or less) ; therefore they have to be recorded
in loco by means of dedicated acquisition system and are not
suitable to be transferred via Bus-Based communication
systems.
The experimental setup we will refer to in this paper is a system
designed to study heavy ion reactions, disposed in the “Neutron
Hall”. Shown in Fig.1, the structure is managed by the C.H.I.C.(
Collaboration for Heavy Ion Collisions) research group and is
located at the Laboratori Nazionali del Sud in Catania, property
of the I.N.F.N.(Istituto Nazionale di Fisica Nucleare). The
laboratory comprises a series of airtight chambers, with
observation windows, in which nuclear interferometry
experiments are carried out. A beam of intermediate energy heavy
ions ( 10-50 MeV/A) is deflected in the vacuum and conveyed
towards the reaction chamber by means of magnetic bending (see
the large electromagnets on the left-hand side of the photo). The
beam impinges on nuclear targets and the collision products are
recorded by various detectors (inside the black cylinders visible in
the photo) and the data are acquired and analyzed by human
operators for off-line handling.
Fig.1: The experimental Setup.
After a careful analysis of the relevant information and the
operating modes during the experiment, we decided to confine
our attention to the problem of acquiring and distributing the
monitoring and control data. We observed, in fact, that this is
the part of the experiment that is generally managed in a more
traditional way, often adopting oversimplified solutions.
Although the approach reflects the concern of those
responsible for the experiments to concentrate on
measurement acquisition rather than on handling the
experiment itself, it introduces a whole series of operational
complications that limit the efficiency of the system. This
leads to a waste of operating time, which reduces the
effective data collecting.
More specifically we made the following observations:
• Currently most of the support equipment is activated
manually and located close to the structure;
• During each experiment the presence of radiation that is
harmful for both humans and the electronic
instrumentation requires the experimental cave to be put
• under safety control; any unforeseen intervention due to
faults or other circumstances, requires the beam to be cut
and a certain period of time (from a few minutes up to a
few hours) has to elapse before technicians can safely
enter the cave;
• All connections between the cave and the acquisition
rooms are dedicated point-to-point connections. This
means that there is a large amount of cabling, passing
from the experimental lab to the observation lab through
shielded walls, which therefore represent a potential
radiation leakage point;
On the basis of these considerations, we identified two key
points in the setup where the traditional solution introduced a
number of problems and prolonged measurement times:
• The support system for a multidetector apparatus
comprising 13 CsI light ion detectors, which has to be
moved during the various phases of the experiment in
order to stay at the different best position both in the
calibration and data taking runs.
• The vacuum chamber, which is an essential component of
the research since the beam of particles has to move in
the vacuum, and heavy ion products are degrading their
energy in air. So from the experimental point of view the
vacuum chambers represent an important support system
for the research as they are used for the development and
tuning of the particle detectors.
3. INTRODUCTION OF A FIELDBUS IN THE
EXPERIMENTS.
The FieldBus is a well-established technology for process
control systems [1] . It is widely used in industrial plants but,
in our knowledge, only to a limited extent in experimental
applications like the one being described here. Conceptually, a
FieldBus is based on a very simple idea: replacing current
bundles of cables with a single cable. This simple concept is,
however, a great innovation in process control
communications systems, providing a whole series of
advantages (some direct, others indirect) which are reflected in
the techniques and methodologies used to design the plants
themselves. The main advantages can be summarized as
follows :
1. savings in cabling and installation costs, due to the
replacement of bundles of cables with a single cable.
This also reduces the number of junction boxes,
safety insulation barriers and shunts.
2. easy addition or removal of system devices without
the need for new cables for additional devices. This
is a key point in the management of experiments
which, unlike industrial plants, are continuously
evolving dynamic structures where the addition or
relocation of sensors is a frequent occurrence.
3. a reduction in the number of connections for devices
mounted on mobile parts. This is an undeniable
advantage in apparatus (e.g. the arm of a robot or
mobile supports for measurement systems) which
uses a large number of field devices and for which
bundles of interconnection cables would make
articulations heavier and more rigid. One of the two
applications described here has to cope with this
problem.
4. the need for fewer openings in the walls to pass
cables. When a lab has to be sealed to avoid leakage
of polluting particles, this may be an important
point.
5. a saving in cable weight.
6. a reduction in installation errors. In complex systems
the problem of human errors on field device cabling
should not be underestimated. When hundreds are
being used, a wrong connection (due, for example,
to confusion between two different conductors) may

be made and it is not always possible to detect the
error when the system is being tested. If a FieldBus
is used, on the other hand, the various devices are
connected in parallel, on the same bus or on different
buses, and only the configuration of the system and
the application software are responsible for correct
routing of the information flows. It is possible to
implement software modules that will control the
correct setting of the system.
7. a reduction in documentation costs. Although this is
not a major item in the overall costs of a plant, the
documentation phase is one of the most delicate (in
view of subsequent updating of the plant). When
updating (as already mentioned, a nuclear physics
experiment is highly dynamic) involves variations in
the layout of a number of devices, previous schemes
and designs require considerable modification; all
this can be greatly simplified if a FieldBus is used.
FieldBuses also present typical features that have been
optimized for the specific field of application, such as the
following:
8. Unlike other communication networks which only
provide one-to-one communications, a FieldBus also
provides one-to-many (multicast) or one-to-all
(broadcast) connections according to the type of
information being handled. In some applications, in
fact, the data produced by a device may have
different uses as modules of the application process
located in different places
9. but connected via the FieldBus may need to operate
on the same data. The data thus has to be shared
coherently by several users.
10. A FieldBus makes it possible to synchronize
activities carried out by physically distinct devices
connected via the Bus.
11. A FieldBus has to guarantee data quality, by
indicating the presence of transmission errors and
respecting suitable time windows that meet the time
constraints imposed by the process being controlled
in order to provide real-time control.
12. A FieldBus can operate in particularly difficult
climatic, electromagnetic and radiation damage
conditions.
To-day, a large number of different fieldbuses is available on
the market. They use different mechanisms for the
management of the communication medium. Some of them, as
for example Fip [2] use a centralized access control whereas
CAN [3], Profibus [4], P-net [5]use a distributed access
control. Among all, Profibus has gained a large portion of the
market share according to its versatility, engeenering support
and marketing network.
4. THE MOTION CONTROL APPLICATION.
The first application presented here concerns the remote
control of a movement system with three degrees of freedom
for the micrometric positioning of a multidetector includinging
13 CsI light ion detectors. Fig. 2 is a CAD model of the
positioning system: it comprises three linear tracks, arranged
in the three Cartesian directions; two are of the bar type and
are respectively arranged in the horizontal directions x and y,
while movement in the vertical direction z is achieved by
means of a platform supported by four tracks. Each track is
activated by a brushless electric motor with a pulse encoder
and a gear reduction unit; finally, at the end of each track
there are limit switches to detect the maximum stroke.
Fig.2: CAD model of the Positioning System
Fig.3: Architecture of the Control System.
The apparatus is equipped with a dedicated control system. Its
architecture is shown in Fig.3, it comprises a backplane on
which 3 control boards are mounted, each using a specialized
chip (HP HCTL-1100) for the control of brushless or stepping
motors. The backplane interface provides 3 8-bit ports: port A
, which is two-way, is dedicated to the exchange of data from
and to the control chip registers, port B , an input port, is used
to read the limit switch , and finally port C , the output port, is
used to address the chips and generate synchronization signals.
The system is completed by a suitable graphic interface,
shown in Fig.4 which provides the user with some useful
information. The central part of the interface provides a real-
time vision of the status of the moving platform. The position
and values of the three Cartesian axes are visible. The lower
part of the interface provides some commands for the control
of the platform according to three degree of freedom.
Fig.4: Graphic Interface of the Control System

5. REMOTE SYSTEM FOR VACUUM GENERATION
The second remote control application presented here is a
research support system for the development and tuning of
particle detectors. A complete scheme of the plant is given in
Fig.5: it comprises a vacuum chamber, a rotating pre-vacuum
pump, a turbo pump to create the vacuum, a pressure gauge,
two pressure transducers for values ranging between 1∗10-3
÷
1∗103
mbar and 1∗10-9
÷ 1∗10-3
mbar , four electrovalves, two
for air return and two to extract air from the chamber ( pre-
vacuum and vacuum).
Fig.5: Scheme of the vacuum system
The remote control must perform the following tasks:
- Monitoring and automatic regulation of the pressure in
the chamber on the basis of a pre-established target;
- The possibility of remote intervention on any of the
activation devices .
Fig. 6 shows the portion of the ProFiBus network dedicated to
control the vacuum system, including the supervisor station
for parametric remote control, a PLC for local control of the
vacuum system and a second slave used to acquire pressure
measurement data.
Fig.6: Profibus Network for the control of Vacuum System.
The task of the PLC is to receive information from the
supervisor station concerning the type of control to be applied
(manual or automatic) and, in the case of automatic control,
the target value for the pressure; on the basis of this
information, the PLC has to carry out the correct time
sequences to activate the pumps and electrovalves in order to
reach the required target pressure in the chamber.
The operations performed by the control system can be
described as follows: an acquisition board converts the analog
pressure measurements into binary data which passes to slave
unit 2; the Applicom supervisor station (Master Unit 1) has the
task of providing the PLC with the current pressure level and
to do so it cyclically scans slave unit 2 (scan period = 100 ms),
transforms the measurements from binary form into floating
point pressure values, executes a filtering algorithm to
eliminate measurement noise, and transmits the value obtained
to the PLC; when automatic control is activated, the PLC uses
the current pressure information obtained by Master Unit 1,
together with the desired target value, to apply its control
algorithm to the actuators and consequently regulate the
pressure inside the chamber.
5.1 Command Interface
Fig. 7 shows the user control panel on the remote terminal for
controlling the vacuum chamber.
Fig.7: Control Interface of the Vacuum System
The central part of the control panel reproduces a scheme of
the plant, together with the operating indicators: any colored in
green indicate that the associated device is active, i.e. a pump
or electro-valve is open; red indicates the remaining states.
The two pressure sensors have two indicators; the one
switched on indicates which of the two devices has currently
Hi
Vacuum
Valve
Return
Valve
Return
Valve
pressure
Display
Turbo
Pre
Vacuum
Valve8
INT Data-Pressure
FP Data-Pressure
Master Unit1
PLC
Slave Unit 2
Control Workstation
Master Unit2
Digital I/O Module

been selected to acquire the pressure measurements. On the
top right-hand side there is a panel with two displays:
the first is a sliding display on a semi-logarithmic scale
showing the trend of the pressure in the chamber; the second
displays the current pressure in mbar.
The Main Panel contains a number of buttons, one for each
control state of the local algorithm. The Diagnostic panel has
two indicators: System Error , which indicates the presence of
malfunctioning of the instrument feeding the pressure
transducers, and Turbo 80% , which informs the user that 80
% of the maximum turbine speed has been reached.
6. CONCLUSIONS
In this paper we presented the results obtained through the use
of the Fieldbus Technology in Nuclear Physics research. In
particular we have studied how to integrate distributed control
systems through the Profibus for two specific applications:
the first application concerns the remote control of a complex
detector (made up of a dimensional array of detectors) used to
detect flows of light ions. This system must be moved in real
time, with very high precision in three different directions,
requiring the control of three electrical motors that move the
detectors. The second application, concerns an implementation
of the control of a vacuum system suitable for a suitable
chamber used for the development and testing of particle
detectors.
The results we obtained encourage us to continue in this
direction. The system can be expanded easily and it is possible
to integrate new devices without any modification in the
communicating system. Moreover, it is also possible to
improve the network speed (the data rate of Profibus can be
increased up to 12 Mbps) and in this way a wider bandwidth is
available, in order to accommodate a larger number of devices.
7. REFERENCES
[1] J.D. Decotignie, P. Pleinevaux: "A survey on industrial
communication networks". Ann. Telecomm. Vol.48 pp.435-
448, 1993.
[2] EN 50170 (1996c). General Purpose Field Communication
System. Vol. 3/3 (FIP),
CENELEC, Brussels.
[3] Controller Area Networks (CAN) - An in-vehicle serial
communication Protocol. SAE JI582, 1992
[4] EN 50170 (1996b). General Purpose Field Communication
System. Vol. 2/3 (PROFIBUS), CENELEC, Brussels.
[5] EN 50170 (1996a). General Purpose Field Communication
System. Vol. 1/3 (P-NET), CENELEC, Brussels.

14 A Profibus-based Control System for Nuclear Physics Applications - The 6th World Multi-Conference on Systemics, Cybernetics and Informatics SCI 2002, July 2002

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14 A Profibus-based Control System for Nuclear Physics Applications - The 6th World Multi-Conference on Systemics, Cybernetics and Informatics SCI 2002, July 2002