Microprocessor Automatic Control System
for Control of Physics Plants Parameters
A.A. Jelezin, I.M.Koltsov, A.A.Komarov, V.M.Rybin
Moscow State Engineering Physics Institute (Technical University)
31, Kashirskoye shosse, Moscow, 115409, Russia
Abstract
A universal modular system for control of physics plants
parameters is presented in the paper. The developed systemis especially intended to expand possibilities of old
operable distributed data processing control systems. The
system can greatly increase the performance of dataprocessing without high cost. This effect is achieved byapplication of the new approach to the object control and to
the synchronization of peripheral devices. As the result, thedataflows in the fieldbus of the system significantlydecrease. The developed system is particularly suitable inthe cases there the narrowband communication channels
are available, such as telephony. This paper describes indetail the essence and distinctive features of the applied
control method and presents an example of application of
the system in the experiment of thermonuclear plasma
synthesis. Also we give here the main characteristics of thesystem.
1 Introduction
The automatic control system was specifically developed for thermonuclear research. Because of universality andexpandability, it can be used in any large experiment where
the fast synchronous control on a base of many parameters
is required. Let′s illustrate the operation algorithm of thesystem by way of example of its operation with our physics
plant.
As the object of automation the plasma synthesis plant(see fig.1) is a closed chamber, filled by composition ofdifferent gases. The most significant properties of plasma,such as its lifetime and stability, depend on how precisely
the composition of gas medium is maintained inside thechamber. During its lifetime plasma exhausts a part oforiginal gas components and we must continuously
regenerate these components. The energy emitted during

Experimental Hall

1.1 Method of preliminary transferring.
Va lve bl ock
M ixerValvesGas mediumGassources

PressuregaugesTranceiver

Tranceiver
Control Center

the thermonuclear reaction is partially absorbed by the gas
medium and can change its chemical composition. Also
one must change forcibly the composition for control ofplasma parameters. The theory that would describe thebehavior of gas medium and could precisely calculate theoptimal control mode is very complex and it can not yet becompletely developed. Therefore for plasma stabilization
we can use only empirical data.
As shown in fig.1 for control of gas medium parameters
blocks of gas valves are used (each block consists of up to
16 gas valves). These blocks bring gas medium
components in the different parts of plant work chamber.
For checking of gas medium condition the set of pressuregauges is used. The valve control is accomplished byapplying of high analog electric voltage to the valve drives.
Experimental data show that when regenerating of thegas medium is absent, the lifetime of plasma is about 10ms. During this time plasma goes through the several
stages of its life; for each stage the distinctive specificcomposition of gas medium is inherent. Always the plasma
conditions don′t significantly change during the timeinterval of 1 ms or less. That′s why we decide to make theperiod of control signal equal 1 ms.
Taking into account the large amount of control valves
and necessity of data receiving from the pressure gauges
simultaneously with control of valves, the overall amountof data, transferred from the control computer appears tobe quite large (it′s about 80 kbytes per second). At thesame time we cannot use any data channel between thecentral computer and the plant but analog data acquisition
optical fiber line that provides safe transferring of digital
data at a rate lower than 2.4 kbits per second. This
contradiction forced us to start the development of the newsystem.
Taking into account the possibility of system expansion
necessity of searching for a new object control strategy
becomes evident. This method should allow to reduce theamount of information. We have found two such strategies.

Duplex analog fiber-optic line

Fig.1. Schematic diagram of the plasma synthesis plantIf during the experiment one observes how the pressureof one or another gas component is changing in time, thetypical forms of time dependencies that are shown on fig. 2
appears there.
The theory (so-called theory of experiment planning)
exists, that allows to predict before the experiment begins
how, by what rules we must open gas valves duringexperiment. The typical forms of control functions arepresented in fig. 3.

PPPt0t0t0Fig. 2. Typical dependencies of gas component partial pressure on time.

VoutVoutt0

Voutt0t0Fig. 3. Typical forms of control voltage on time.
The zero moment on figures corresponds to start ofexperiment and start of plasma lifetime.
The Method of preliminary transferring is based on thetransferring of control ‘ image’ through slow data channel
into a buffer memory before the experiment starts and on
output of this ′image′ in real time during the experiment.
For this a microprocessor module with buffer memorymust be installed near the plant, the possible structure ofthat presented in fig.4.
Preliminary transferred ′images′ of the control areplaced into the buffer memory as arrays of digital data.
Before the experiment the central computer sends out to all
peripheral modules the command ′get ready to start′. After
execution by all modules of this command any change ofthe voltage level in the fieldbus starts an output of control′images′ to the gas valves. At the same time thesynchronization of internal clocks of peripheral modules
with the central clock of the system is occurred.
Notice that the evident disadvantage of this method isthe finite time of experiment, dependent on the size of theperipheral buffer memory. This disadvantage can beremoved by using the next method.

1.2 Method of alternated ′images′
For this method to be realized, we must slightly
complicate the structure of peripheral microprocessor
module (see fig.5).
Now in each of peripheral modules the two microprocessors with the device of buffer memory page control areinstalled. The first microprocessor continuously executes
output of control ′images′ to the digital-analog converters,and second processor controls the first by substituting partsof the ′images′ to it from the image library. For simplifying
of work with data arrays the buffer memory is divided into
pages, which the special device-page selector-moves andswaps in the address space of the first microprocessor. The
second microprocessor also provides the data exchange
through data channels.
In this method the complicated function of the control
process is divided into the simplest pieces (see fig.6), theform of control action in which can be derived from thestandard library. This library may be formed by calculatingon the base of current condition of the object of theoptimum control. The calculation may be performed, forexample, with the theory of experiment planning.

Internal clock

System central clock

BuffermemoryOutput High
voltage
amplifier

Digital/Analog
converter

Input/output
microcontroller

From the centralcomputerFig.4. Schematic diagram of the simplest peripheral microprocessor module.

Internal clock

System central clock

BuffermemoryOutput High
voltage
amplifier

Digital/Analog
converterPage
selector

Input/output
MCUCPU

From the centralcomputerFig.5 Schematic diagram of the peripheral microprocessor module.
•Voutt0T

3T

4T

5T

6T

7T

Fig.6. Division of control process into simple elements.
If the size of the library ′image′ is presented by N signal
samples, then amount of information, transferred throughdata channels, is reduced by N times. Moreover, from thecurrent condition of the object one can define further
control even of valve blocks (see fig.1). Thus in this casethe data rate is reduced by N•m times, where m- theamount of valves in a block. Typical value of N is 1000,and m is 4. Then, for 16-bit control of 32 valves data rate
will be equal
2002 byte /s ∗32 v a l v e s= 16 byte /s
1 0 0 0 s a m p l e s * 4 b l o c ks

This is more than enough even for very bad datachannels, for example for connection through oldtelephony.
Notice, that in this method signals of peripheral clock
synchronization generate in the moments 0, NT, 2NT, andso on. If peripheral module clocks are fast, its microprocessor extrapolates the output signal by using a special
prediction table until the signal of the clock synchronization will appear. By this way the precise synchronization of
all peripheral devices in the system is achieved.
2 System hardware
The sample of microprocessor module was developed
and tested by us. It has the following characteristics:

Central processor - Zilog Z80 with clock frequency 8MHz;• Size of the buffer self-power memory - 128 Kbytes;• Microcontroller of input-output channel - Intel I8751;• Amount / resolution of the analog output channels 20/10, expanded up to 40/10;• Amount / resolution of the analog input channels 8/10, expanded up to 16/10;• Amount of the digital object control data lines - 120;
• Sampling interval of the output analog signal- 1 ms;• Data rate in the channel between the module andcentral computer - 300 bytes/s;• Period of the clock synchronization signal - 1s
The microprocessor module is manufactured as block ofstandard dimensions and can be mounted into a tower case.
There are a mini keyboard and LED display on the front
panel. On the back side connectors for gas valvesamplifiers, analog gauges of pressure, external digital
devices and central computer data channel are placed.
3 Summary
A universal control system was developed, that can use
all the possibilities of narrow band data communication
channels by the way of the new approach to object control.
The example of system peripheral microprocessor module
was manufactured with its software. It was tested in ourlaboratory and may be recommended for using in a physics
experiment.
References[1] Azizov E. A., Koltsov I. M., Rybin V. M. The
microprocessor-based system for exploratory physicalinstallations control. Pribory i systemy upravlenya,
1997, no.1, p. 25-28.