Upgrading a Small Accelerator Control System
Li JiaQing, Zhang Lin, He MianHong, Lu ChengRong, Sun ChuanChen
Accelerator laboratory , Fudan UniversityShanghai 200433 , China
5.
1 How the question is raised
Fudan is one of the institutions that built and developed asingle stage VDG in China as early as the 1960’s. In 1987,
Fudan imported a 9SDH-2 tandem accelerator withterminal voltage of 3MV from the NEC, USA. It has beenrunning in good condition for ten years, and is playing animportant role in the fields of nuclear physics, ion beam
analysis, ion beam materials modification, archaeology,and medical science.
The accelerator control system consists of four large
instrument panels and includes more than 30 control units.
Experienced technicians are needed in operation and indaily maintenance.
In 1995, we germinated an idea to upgrade the machine
control system with computer aid so as to improve thefeature of machine operation. Running parameters, such as
ion species, beam energies, etc., are input through akeyboard in advance according to the requirements of anexperiment. Operational data of the same type ofexperiment are then picked up from the database, whichkeeps the accelerator running in a normal and steadycondition. What one has to do is to turn the power on, andthe rest will be taken care of by the programmed computer.
2 Minimum control system
At the early stage of upgrading, we selected an “automaticenergy scanning system” as our first goal of the whole longrange plan,
because it related to less adjustment
parameters, and addressed a series of key problems to bedealt with. From the system we can expect to get moreexperiences in hardware and software production anddatabase management for further upgrading to the originalcontrol system later.
The output beam energy E is E=E0+(1+q)eV, where E0 is
the initial ion energy, V is the terminal voltage, and q is thecharge state after stripping. Therefore, there is a linear
dependence of the energy E on the terminal voltage V. We
can change V at equal intervals in order to change E, also
at equal intervals.
The running process of the automatic energy scanningsystem is as follows:
1. Turn on the accelerator manually, adjusting the ion
beam to the target according to the requirements of anexperiment.
2. Input running parameters, such as the initial, final,and interval energies, through a keyboard.
3. Start the automatic energy scanning system. Now thesystem is computer controlled rather than controlled
by hand.
4. Check whether the situation meets the needs of theexperiment.

Send a pulse signal to the digital beam current
integrator and the counting system on the beam line tostart.
6. Specific terminal voltage and beam current arecontrolled and stabilized by computer during theprocess.
7. The automatic energy scanning system automaticallychanges the terminal voltages, in turn, until reaching
the end.
The automatic energy scanning system is reaching ofgreat use in accelerator technique and nuclear physics
experiment. It can precisely and automatically adjust theenergies of accelerated particles, with a tolerance of lessthan 2 keV, which makes it convenient in the measurementof an energy excitation curve.
3 Hardware and software development
The computer control system is composed in MasterSlave architecture. The main part in Master is a personal
computer. It manages the user friendly interface, databasemanagement, communicating with Slave through a serial
port RS232 and monitoring the readout acquired fromSlave, etc. The Slave is a STD bus microcomputer systemused for A/D conversion , D/A output, I/O interface, online monitoring terminal voltage and beam current andcarrying out its PID control, etc. The STD bus is a main
product in industry control field, which adopt the conceptof functional modular. and is convenient to extend I/Ointerface. All of its pins have specific definitions, whichmakes it easy to design an I/O interface.
We designed two modular boards: FDAC-01, FDAC-02,
according to the STD standard. The FDAC-01 is used to do
A/D conversion, D/A conversion, I/O, etc. It is drawn forth
to another INTERFACE through two sockets of D model.
It can be used to measure physical parameters from every
control unit on the accelerator, and also to control theoutput voltage obtained from the computer. FDAC-02 is
used to measure terminal voltage with a precision of 16 bit.
It is also used to send a starting signal to digital current
integrator and to receive a signal sent back from thisintegrator through four I/O channels .
FDAC-01 modular board has four parts: 16 channels A/D,
16 channels D/A, 16 channels IN and OUT. It uses an IC74LS688 and DIP switches to set the board-select address
and is linked with the high 8 bit address bus. (Every board
has a unique address on the STD bus). 3-8 decoder is an
IC-74LS138 which is used as a Chip-Select component.
Chip-Select address is set by a LA4-LA6 in the low 8 bitsof an address bus. MAX306 is a 16-channel CMOS Analog
Multiplexer which is used to select the channel of A/D.
AD574 is used to A/D conversion. Data is output in aparallel mode. A/D channels are directly linked

16A8-A1574LS688
16Chanel A/DAD574

8 Chanels D/AMAX526 X274LS245

8 Chanels
IN74LS245

busControl-Bus
74LS245

8 Chanels
OUT74LS273

4 Channels

B 25 pins D Socket

8 Channels

74LS138

Data-Bus

RD.WR.

4 Channelsv

306

Chip-Select

D0-D7

Mux
MAX

Address-Bus
STD A0-A3; 74LS245
A7
A4-A6

8 Channels

A 25 pins D Socket

Board-SelectFig.1 FDAC-01 Circuit Diagramwith the objects being controlled. MAX526 is used to D/Aconversion (also in a parallel mode), which has 4 channelsoutput, with 24-PIN , 300 mil plastic DIP, wide SO
packages. It is convenient in hardware development.
FDAC-02 uses MAX195 from MAXIM, which is a 16-bit
self-calibrating, 10 µs sampling ADC and has someproperties: *Three-State Serial-Data Output, * Unipolar
and Bipolar Input Range, *Small 16-Pin DIP and Wide SO
Packages, etc.
We also designed an INTERFACE modular board, on
which were assembled five relays and DaLinDun driving
circuit. We put this board in the control box on accelerator
as a interface between the STD system and the originalcontrol circuit system on accelerator .It is also used totransfer the control mode between the original man-mode
and the computer-mode .When it is in man-mode allcontrol parameters are gotten from the control units on theaccelerator, when computer-mode , the control units on theaccelerator are controlled by the STD machine directly.
The states of relays can be known by 8 LEDs from IN1IN8.
FDAC-01 and MCS51 CPU modular board are linked by
a STD bus. Two 25-Pins D sockets are linked toINTERFACE board. The signal lines can be changed bysome jump-switches on board according to the concreteconditions .
Software on the STD slave machine is written in ASM
assemble language and includes D/A, A/D, I/O ,WatchDog, etc. Timer, interrupt, and communication areused. While numerical value filter, PID control, etc., areused in data processing.
Software on the PC master machine uses Visual Basic 4.0
and Window95. It includes three parts: 1. man-machineinterface 2. on-line monitoring physics parameters from theSTD slave machine 3. database management. It involves
some problems as follows:
1. At first, construct virtual instrument(VI) on PC’s screenwith VB. Beam current, energy, terminal voltage,magnet current and steering voltage must be on-line
controlled and monitored . These can be done by using
a series of visual custom control objects in VB. For
example, “Label” can display data, “Graph” candisplay diagrams, “Slider” can be used as a knob to acontrol instrument.
2. Write event-driven code in VB. Transfer data andcommands between the PC master and STD slave
machine.
3. On-line display of experiment parameters and running
conditions. These data can be saved in a run-timedatabase so that we can resume to a certain stateaccording to the previous data stored in a database.
4 How the work proceeds
The automatic energy scanning system is composed of amaster-slave architecture, which is a distributed control
system. The master is a PC and the slave is an STD bus
microcomputer system. In order to guarantee the hardware
and software can work properly, we also made simulationequipment to simulate the actual running process in theautomatic energy scanning system. We test the hardware
and software with this simulation equipment before we cantest it on the accelerator. We have finished the test workwith FDAC-01 and INTERFACE board and found that thePC master and STD slave communicated properly witheach other. The PC displays various on-line data including
meter readings from the STD slave. Also, it controls theinstruments linked with the STD slave according to acertain control algorithm such as PID, etc. The control
algorithm is to be improved with the expandson of thecontrolling range.

It was the first time that we attempted to upgrade thecontrol system of an imported tandem accelerator.
Subjected to the difficulties, such as lack of experts, limit
financing, and busy beam time to the machine in thelaboratory, the whole process of the upgrading have to go
on step by step from the very beginning. On the premise of
keeping the integrity of the original control system and notinterfering with the experiment work in the laboratory, wedeveloped the needed hardware and software so as to havean easy transfer between the manual mode and thecomputer mode. The design idea that originated one year
ago is being realized. After the design of a minimum
control system, we are planning to expand the control
range step by step to achieve the goal of controlling theaccelerator by computer network.
References[1] MAXIM new releases data book.
[2] VisualBasic4’s Helps Online.