Isolation Technique Used in HIRFL Control System
Chu Zhensheng, Huang Xinmin
Institute of Modern Physics, Chinese Academy of Sciences
P.O.Box 31, Lanzhou 730000,ChinaAbstrct
HIRFL is a complex system containing a lot of distributed
equipments. Most of them are high power and high precision
devices in the noisy environment. So a high performance ofthe computer control system is required. Especially, as thecontinuous improvement of HIFRL operation performance,
the requirement of control accuracy and reliability become
more and more high. To satisfy the requirement of operation,
isolation technique is one of the most important methods forcontrol system in HIRFL. Its application is discussed in thepaper.
1 The isolated transmission of control and data stream
There are mainly two kinds of isolated transmission forcontrol system in HIRFL. One is pulse transformer isolation.
The another is photoelectric isolated transfer.
1.1 Pulse transformer isolation transmission
The Bit serial transmission is often used. Generally, signals
are transmitted with serial diphasic modulation and received
with diphasic demodulation. The advantage of pulse
transformer isolated transmission is that the transmitting
distance is long, up to 100 meters, the transmitting rate is
fast up from 500Kbits/s to 5M bits/s and the transmission
have the function of parity check. Thus, this mode has hightransmitting reliability and its cost is lower. Usually, it isused in CAMAC interface system.
1.1.1 CAMAC U-port modules(such as KSC-3936 and so on)
These modules are used in CAMAC serial loop to constructmedium to large computer control system. As it has highanti-interference performance in transmission, the operation
is rather reliable. No transmission error of serial loop(usedKSC-3936) has ever happened in control system in HIRFL.
The maximal transmitting rate of CAMAC serial loop is5Mbits/s.
1.1.2 CAMAC module ER16VM
The module has 16 channels with pulse transformer. Everychannel transmits serial isolated data to transmitter- receiver
equipment of the field via LEMO connector and a twistedpair shielding cable. All these are of master-slavecommunication structure. In injection/ejection system ofSSC, there are 16 sets of DC power supplies, 10 sets ofposition regulating equipments and 113 sets of water coolingalarm .The control system have been performed reliable
control and monitor only with 12 channels of the module.
Distance of data communication is more than 100 meters.
The transmission of the data is rather reliable. The maximaltransmitting rate of ER16VM is 500Kbits/s.

1.2 Photoelectronic isolated transmission
At present, photoelectronic isolation technique is broadly
used in data communication of computer automatic control
and monitor system, such as RS-232 current loop
communication board and RS-485 transmitter/receiver withphotoisolator. The photoisolated communication is often
used in multiplex system with bit serial transmission. On theone hand, it can improve the ability of anti-interference withthe result that the reliability of system operation is increased.
On the other hand, it can solve the problem of long distancereliable communication. For multiplex distributed system
without very high speed, the photoelectronic isolation
communication is a simple and cheap solution. As thetendency of complex controlled equipment is characterized
by intelligence, the transmitting mode has been used widely.
Now we have started to develop the intelligent controller in
HIRFL.
In the control system (designed in 1992) of SFC and ECR
source beam line in HIRFL, the multiple-stage isolatedparallel transmitting mode with our designed isolationcontroller has been used (see Fig.1and Fig.2). A few of
CAMAC module and our designed control equipments
accomplish the computer automatic control of decades DC
stabilized current and DC high voltage power supplies. The
control system has achieved reliable results.

2 Isolated transmission of digital signal
As the rational adoption of digital signal isolation can beefficiently realized, the electrical isolation between center
control system and field controlled equipments, becomesvery easy. The isolated transmission of digital signal has
been widely used in the computer automatic monitor andcontrol system at present. It can eliminate the mutualinterference in running process and achieve more efficientand reliable data transmission comparing with HTL
electrical level.
In HIRFL control system, the isolators used are common
photoelectronic couplers with 500-1000V isolated voltage. It
has been proven in practice that the anti-interference ability
and reliability of subsystem which use isolators is better.
In addition, to use the stand-alone relay contacts ofequipments is also an efficient isolation method on theconnection of status signal.
3 Analogous isolated transmission
In HIRFL control system, it is a long-term problem tomeasure the high precision analog signal exactly andreliably. The measurement of analog signal directly affects
the further improvement of HIRFL operation performance.
The most puzzling problem of high precision measurementof analog signal is of shielding from the affection ofcommon-mode interference.
HIRFL contains a lot of high precision and powerful
distributed power supplies which use floating ground output
mode according to the need in work. It causes the continuousvarying of potential between one equipment and anotherequipment or ground which leading to serious commonmode interference in signal measure. Generally, the mosteffective method for solving the problem is to use ADC

alone with which the digit signal is converted fromanalogous signal and transmitted through photoisolator. That
control system needs much investment, and both theaccuracy and the stability of measurement are notsatisfactory as ripple voltage and affection from environment
temperature to ADC. Another method is to use relay contact
gating and removing far-end common-mode interference byisolated amplifier, then together with native power supplies
to measure the signal(difference input) by multiplex ADC
module KSC-3516. In order to eliminate the affection ofripple voltage, digital filter method in processing program
has been adopted. The results are very satisfactory. The third
method is that the analog signal is gated by relay contact andconverted to digital signal by 7075 digital voltmeter. Thismethod will be adopted in HIRFL control system. Of course,according to actual needs, isolated amplifier will be alsoadopted. Because of high input resistance of 7075 digital
voltmeter which can eliminate the affection of generalcommon-mode interference, the converting time of 100ms
has been selected to overcome the affection of ripple
voltage. It is important to use isolated amplifier for themeasure and regulation of DC high voltage power supplies,
if not, the control system can not work properly.
4 Conclusion
Because of the variety of control fields and the difference
characters and requirement of control equipments, it is hard
to reach a uniform work model. To built up a set of reliable
and rational computer automatic control system and to reachthe expected aim, technical staff must analysis and compare
different schemes again and again with the rational
processing method for digit and analog signals. However,using isolation technique is inevitable to assure the reliable
work of control system.