UPDATION OF ECR POWER SUPPLY CONTROLS TO DISTRIBUTED PC
ENVIRONMENT
Tushar K. Das, Amitava Roy, Sushanta K. Pal , S. Dasgupta
Variable Energy Cyclotron Centre, Calcutta 700 064, India

Abstract

2 HARDWARE ASPECTS

Controls of the ECR source and the beam-handlingelements for injection of the heavy ions into the cyclotron,
are being shifted to the central control room, in phases.
The work constitutes a part of the retro-fitted distributed
computerization of the Cyclotron. A Pentium, Win95 PC
working in the ECR front-end takes care of the above
power supplies controls. Existing CAMAC crate, several
ADC & amp; DAC modules have been put to use, afterin-house development of Windows compatible CAMAC
library functions. VB callable hardware In/Out functions
have been used in the libraries, by incorporating available
freeware from internet. Several graphic bit-map icons,
specially suited for the purpose, have been prepared andused in the VB MMI form. The Client-Server mode
implementations of the distributed controls work using
SocketWrench-VBX socket control on Windows-95.

1 INTRODUCTION
The Variable Energy Cyclotron (VEC) has recentlybeen upgraded with Electron Cyclotron Resonance Ion
Source (ECRIS) for increased scope of research. TheECRIS subsystem along with its manual control console isphysically located on the high bay above the cyclotron
vault. The separate control console located at a great
distance from the cyclotron control console is logisticallyinconvenient from the control perspective as well as
deployment of man power. Therefore, to partly reduce
this inconvenience computerized control has beenplanned for ECRIS operation. It was decided that one of
the computerized consoles of ECRIS would be located inthe cyclotron control room as a remote console. This has
generated the work on the computerization of the ECRIS
parameters and remotely operable control software.
In this paper we describe various schemes we have
explored for control of the ECRIS power supplies fromPC with the help of the existing and easily procurable
hardware. Since none of the power supply (except twonumbers) has any computer interface our tasks are todevelop, appropriate hardware to make the power supply
suitable for remote SET and MONITOR operations, thecomputer interfaces and the I/O libraries for theinterfaces.

There are altogether 32 power supplies in the ECRIS
subsystem including injection line, puller and bias supply
and the ion-source itself. At present it is planned tocomputerize only the injection line power supplies whichare 22 in numbers with ratings from 0-1A 0-30 V DC to0-350A 0-20V DC and tolerances from 0.01% to 0.05%.
All these power supplies are operating in current
controlled mode and are electrically floating and isolated.
None of these power supplies has any form of computerinterface.
In this project, as far as the hardware aspects areconcerned we have basically explored two schemes tocontrol the power supplies: in one, the DAC-ADCs werekept outside the power supply and in the other, theconverters were integrated within the power supplycabinet.

2.1 SCHEME 1
We started the computerization with a 0-1A 30 V DC
power supply which was fortunately available as spare atthat point of time. The control circuit was studied andsuitable amplifier circuit using low cost OpAmps wasdesigned to replace the potentiometer reference control
with DAC controllable reference and the monitoring point
was also properly buffered. The schematic diagram isshown in Figure 1.
+VPoweron+

Rectifier&filter

0VAttenuater-DAC-V

220 V

Amplifier CAMAC
ADC

Rectifier&filter

0.5 ohm

LOA
DFigure 1: Schematic of control circuit connection.
The power supply was controlled by a 12-bit DAC andmonitored by a relay multiplexer followed by 12-bit ADC

CAMAC modules. The CAMAC system was organised inserial configuration. The control PC was connected to aPARALLEL BUS crate controller and situated close tothe PC. The remote crate located at an electrical distanceof 250 meters was accessed through a Serial Highway
Driver module in the local crate and an L2 crate
controller at the remote crate. The DAC, ADC, and relay
multiplexer CAMAC modules were put in the remotecrate. The power supply reference and monitoring point
was connected to DAC O/P and relay multiplexer I/P by
10 meters of twisted shielded cables. Figure 2 shows thehardware architecture of the control system.
U CCSHDC o n tr o l P C

L o ca l C r a te

L2 CCDACADC

MUX

R e m o te C r a t e
P ow erS u p p ly

Figure 3: Histogram of the measured O/P voltage
In this configuration interfacing circuits are also
required at the power supply and PC ends. At present wehave designed and developed a parallel field bus system,
as it could be easily built with low cost and available ICs.
The total length involved is also within few meters. Thissystem consists of a PC add-on I/O card, parallel bus
driver and for each power supply a parallel bus interface.
The parallel bus driver initiates a bus transaction when acommand (READ / WRITE) is written on it through thePC add-on I/O card. We can connect a maximum of 64
power supplies in this method. The schematic is shown inFigure 4. The parallel bus circuit design and construction
is in advanced stage of completion.

Figure 2: Schematic of Hardware architecture
The distribution of the measured O/P values indicated a
FWHM of 0.085 % of full scale. The distribution of themeasured O/P is shown in Figure 3. This result shows that
we can even use a remote DAC and ADC if the 0.1 % isacceptable.
In this experiment the reference and monitoring points
were however not isolated. At present we are developing
an amplifier circuit with high quality isolation amplifiersand OpAmps.

To other power supplies

DACBusinterface
ADC
INSIDE PS CABINETDACBusinterface

2.2 SCHEME 2
As the above scheme is not suitable for a measurement
accuracy, as well as stability, better than 0.1 %, weundertook the design of the coupling circuit using highprecision DAC and ADC chips. In this design 16-bit DAC
with stable reference, 16-bit ADC, isolation amplifiersand high stability OpAmps were integrated in a single
board. This would be placed close to the analog control
circuit of the power supply inside the power supply
cabinet. The design of the circuit is complete and thecircuit fabrication will start soon.

PowerSupply
2

ADC
ComputerBusdriverPowerSupply
1

Isolation
amplifierFigure 4: Converter connections in SCHEME 2
The parallel bus method, however, is being pursued asa temporary solution. It has been planned to replace thiswith a serial field bus. A prototype design with Intel 8251
microcontroller with RS 232 interface has been tested byconnecting it to the COM port of PC. Work is now being
initiated however, thinking of using a 16-bit
microcontroller Intel 8796. The serial line protocol has
not yet been finalised. Relative merits / demerits of amultidrop and star protocols are being studied. We mayeventually decide in favour of a standard serial field bus
e.g. CANBUS at a later stage.

3 SOFTWARE ASPECTS
The initial version of the control software with Human
Computer Interface has already been developed by othercolleagues [1]. In the present project we have developed
the low-level functions for the hardware access from thecontrol software. The necessary modification of thecontrol software for remote or distributed operation are
also being carried out.

augmented with more dialog boxes and display windows
for the power supply control and monitoring. This part of
the work is being done in close collaboration with theother colleagues who have developed the initial version of
the control software.

To Other PCs/
Hub/Switch

PC in ECRISControl Roomwith CAMAC etc.
HUB

3.1 LOW-LEVEL FUNCTIONSIn the case of Scheme 1 we have developed the lowlevel functions for CAMAC I/O using a downloaded
freeware dynamic link library VBASM.DLL, as the basic
port I/O functions are not available in VB 3.0. Each of thefunctions are basically sequence of port I/O operations tocarry out the CAMAC module READ/WRITE in a serial
CAMAC architecture. The DAC write function writes on
the DAC input register of a particular DAC channel in theDAC module. The ADC read function first selects thedesired channel of the relay multiplexer module, initiates
conversion command in the ADC module and reads theconverted data after the conversion is over. There are twomore functions for setting and reading a specific bit in theCAMAC I/O register module. The last two functions areused for switching on the vacuum pumps and reading theinterlock status and is not directly used for power supplycontrol. All these functions are clubbed together in a VB
module file and are called by the control software.
Similar I/O functions have been developed for theparallel I/O interface of the Scheme 2 and are about to betested with the interface hardware on their completion.
Low level functions for the serial I/O have not beendeveloped so far.

3.2 REMOTE/DISTRIBUTED OPERATIONThe control software is being modified for remote or
distributed operations. The schematic of the distributed
environment is depicted in the Figure 5. The control
software residing on the PC on which the I/O hardware
has been installed would act as server and also as client
for local operation. In any other PC in the LAN e.g. PC in
the cyclotron control room, the control software would act
as client. The control software has been modified in sucha way that the same software would auto-detect its role asserver or client. If the client has proper authentication
then it can do the same operation using the identical MMI
as if the client is operating from the local PC. The clientserver communication has been implemented using
another downloaded freeware SocketWrench VBX socketcontrol. The client-server version has already been tested.
Now a protocol is being thought of, for co-operative
access from multiple clients. The software is also being

PC in Cyclotron
Control RoomFigure 5: Distributed operation

4 CONCLUSIONSThe present project is one of the important parts of thecomputer control activity of this centre. The difficult areain this project is to make the power supply of different
ratings and different manufacturer, computer controllable,
mainly because the power supplies are already in theoperational condition with the ECRIS system. The otherparts are relatively straight forward and progressing at areasonable pace. The experience to be gained in thisproject will be potentially useful in the Superconducting
cyclotron control system.

ACKNOWLEDGEMENT
The authors deeply acknowledge the co-operation of
the other colleagues of the Computer Group, VECC. We
extend our thanks to Prof. Bikash Sinha and Mr. S. K. De
for their interest in the computer control activity.

REFERENCES[1] Tapas Samanta, C. D. Datta and D. Sarkar, “HumanComputer Interface for the Computerised Control ofElectron-Cyclotron Resonance Ion Source (ECRIS) atCalcutta”, ICALEPCS’97, Nov. 3-7 1997.