A New Radiation Protection System
Li Juexin

Li Yuxiong*Shao Beibei*Wang Ruopeng*Zhang Shidu

National Synchrotron Radiation Laboratory, University Of Science and Technology of China(Hefei, Anhui 230029, P.R.China)*Engineering Physics Department, Tsinghua University(Beijing 100084, P.R.China)
Abstract
The radiation protection system of the National
Synchrotron Radiation Laboratory (NSRL) has worked forover eight years since the light source began to run. It
guarantees the personal safety for all the operators andexperiment members. Most importantly, its control systemstill has some shortcomings although it works well. Low
speed, less storage area, high power consumption andprogramming difficulty are the main problems. The
synchrotron radiation machine has improved continuously
along with the science development in recent years. So theradiation protection control system is also facing upgrade.
To match the new demands, we have designed anothercontrol system with new ideas, up-to-date technology andthe most suitable equipment. Its characteristics are muchbetter than the old one and it will not be obsolete in severalyears.
A 68HC11 series chip-computer and a Pentium PC areused as the local and main controller respectively in thenew system. It is an all-in-one control system for safety
interlock, area monitoring, environmental monitoring andwarning. Its functions can be expanded easily withincreased demands. It gives safety priority all along, even if
sharing data with central control room.
This paper presents the hardware block diagram,
software structure and function explanation of the newradiation protection control system.
2 Shortcomings of the original system
The original radiation protection control system wasdesigned in the middle 1980′s and is based on a lower
computer technology level. It worked reliably and met ourbasic needs in the past years. The faster the technology
develops, the more shortcomings it exhibits. It can notsatisfy us any more. The main problems are:•Its heart is a special designed computer (DDL) with an
M6809 CPU. It collects area monitoring signals,
recieves interlock states, controls a warning box,
displays varies parameters and data on LCD, etc.
Environmental monitoring is not included. So thewhole radiation protection system is separated intotwo parts.
•The storage area of DDL is not big enough. It hasneither hard disk nor floppy disk drive. So the data in
RAM cannot be saved on disk. The parameter setting
is done in an old way -- by thumb-wheels and keyswitch.
•The software of the original system is programmed in

FLEX Pascal and 6809 assembler language which are
not popular. Only a person who is familiar with 6809
series can program or modify the software kit.
•All the chips in DDL are TTL type and need more
power. Once the power supply is interrupted, it does
not work. The data stored in RAM will be lost and theparameters have to be reset after resuming running.
•The DDL can not communicate with other computer
directly.
What mentioned above cannot be ignored. So the control
system must be updated.
3 Composition of the new system
To keep the advantages of the old system as well as
match information exchange in the computer network, we
selected the local and main controller combination design
to update the control system. The chips with excellent
characteristics and low-power consumption are used in a
local controller. It executes the basic functions. A Pentium
PC is the main controller which carries out the dataprocessing and complete software programming for both
local and main controller. We do not use the PC to control
everything directly for it is not fit for continuous work. It
cannot work on batteries for a long time when the power isinterrupted. But its high-speed, rich application softwareand common interfaces provide a powerful tool to realize
various data processing and graphics output. To avoid
separation, the environmental monitoring system is also
controlled by the new system. This is an importantdifference from the old one. Now the whole radiation
protection system is under unified control.
3.1 Structure of the local controller
The main board is a single-board computer with a68HC11A CPU. It has 128K RAM ( can be expanded to512K when needed) and can store one month of data from16 channels. It drives a color LCD of 100cm2 area.
The environmental and area monitoring input units
receive signals from 16 channels at the same time. Thesignals (current pulses) are transfered to the main board
after conversion to voltage pulses by these units. As an
important effect of the control logic, the interlock statesignals from the linac, storage ring and nuclear physics hall
are input to the main board through interlock input units.
The Warning unit outputs the warning signal to drive thewarning box according to different thresholds.
This local controller can work for one week from amatainence-free battery which is float-charged in normal
conditions.

Interlock System

Main Controller

Printer

Local Controller

Warning Box

Environmental monitoring Detectors

Area Monitoring Detectors

Fig. 1 The diagram of the new system composition.

Input Unit for Linac Interlock

LCD

Input Unit for Storage Ring Interlock

Input Unit for Neuclear Physics hall InterlockMain Borad
Output Unit for Warning Box
Display Select Button

Input Unit for Area Monitoring

Input Unit for Environmental monitoring
Fig.2 The structure of the lower controller.
3.2 Functions of the local controller
The local controller has more functions than the old one.
Its time and parameters can be set or reset by themain controller, and the data in RAM can betransferred to PC as well.
•It collectes signals from detectors and stores them inRAM. The collecting interval can be adjusted from 110 minutes.
•It calculates dose rate for every channel.
•It provides warning signal for warning box according
to the threshold preset.
•The interlock signals are transported from it to PC andthen the relative is displayed on the CRT.
•The LCD displays one of following pictures: interlock
location diagram, dose rate table for all channels, dateand time, etc.
•3.3 Main controller and its functions

A Pentium PC is selected as the main controller of thecontrol system. It communicates with the local controller
by an RS232 port. The control software is a kit running in
the windows environment.
••

Data transfer and storage
The main controller recieves environmental and area
monitoring data from the local controller, and saves
them on disk as a text file which is easy to open indifferent application programs. The file begins withthe corresponding detector calibrating factor andinterval time.
Data display, dose rate curve or diagram display andoutput.
The CRT displays interlock system states and area
monitoring results normally.
The monthly data saved on disk for any channel canbe displayed on the screen or printed.
The dose rate diagram of environmental and area
monitoring can be displayed in different colors (to•••distinguish bremsstrahlung and neutron). The scale isadjusted automatically. The environmental monitoring
result is shown as a curve and the interesting interval
can be expanded.
The real-time diagram showed on the screen can beprinted.
Parameters setting
It adjusts the local controller′s time each time it begins
to work.
The calibrating factor of each detector, time intervaland other parameters for the local controller can be set
by its relative file. This function is protected bypassword to prevent illegal modification.
Calculation
This function includes:
The maxim and minimum dose rate among allchannels at the specified time;
The maxim and minimum gamma dose rate among thecorresponding channels at the specified time;
The maxim and minimum neutron doserate among thecorresponding channels at the specified time;
The accumulated injection time and total operation
time for the synchrotron light source;

The monthly environmental extra dose recorded by every
environmental monitoring station.
These function are seleted by menu.
4 Advantages of the new system••

It controls the entire subsystem at the same time.
The data processing is done in the PC. It can becompleted perfectly due to its rich application
software. Data exchange becomes easier than before.
•Since multi-work mode is applied in the localcontroller′s program, the device works more reliably
than before.
•The program can be developed conveniently. We
program the software for the local controller in C
language in the PC first, then assemble it into 68HC11
assembler language. We can translate it for anothersystem easily when necessary because of the C
language′s universal support. So it is a good solution
for most programmers and technicians.
The new radiation protection control system has been
completed for just several days. It is necessary to check its
characteristics according our needs. We will improve it
continuously.