Examples of Applications of Industrial Control Systems (PLCs)
for Vacuum Equipment
R. Gavaggio P. Strubin
CERN - LHC division
1211 Geneva 23, Switzerland
Abstract
This paper describes some developments in the domain ofvacuum controls, using industrial control systems(Programmable Logic Controllers or PLCs). After showing
the different advantages of the PLC for vacuum
applications, when compared with a specific solution, wemention the main points that led us to make this choice.
Then, we describe some realisations (pumping groups andtest benches for vacuum chambers) using a PLC and therelated fieldbuses to interconnect these controllers to theupper layer of the control system. Finally, we sketch out
one of the possible solutions to control some vacuum
equipment of the future LHC machine.

shows the following main advantages:- robustness (massive use in industry),- easy to use (powerful developing tools),- easy hardware modifications (modularity),- reduced number of spare parts,- reduced maintenance,- connectivity to at least one fieldbus,- MMI programmes available,- long lifetime and long-term support from themanufacturer.
This solution has therefore been adopted for the control of
the two applications describes below.
3 Examples of applications

1 Introduction
In recent years, PLCs have been more and more used in
the control systems of accelerators and physics
experiments. This situation is the consequence, on one
hand, to their intrinsic qualities and, on the other hand, ofthe current trend to integrate industrial equipment insteadof 'home-made' developments and to go toward global
industrial control solutions [1]. For these various reasons,and after a complete study of the different possible
solutions, we have decided to use PLCs for two
applications in the vacuum field: the control of vacuum
pumping groups and the control of a set of two test
benches for the vacuum chambers.
2 Using PLCs for vacuum applications
The vacuum system of accelerators and physics
experiments require the control of a large number ofequipment (valves, gauges, pumps, etc.) coming fromdifferent manufacturers (e.g. more than 1800 vacuum
devices in the LEP, more than 800 in the PS Complex [2]).
To control this equipment we use devices supplied by thevacuum manufacturers or specific controllers developed atCERN and assembled in industry (e.g. G64 chassis for thecontrol of valves, pump power supplies, etc.).
In both cases we are faced with the same drawbacks andthe same constraints:- specific controller for one family or one type ofequipment,- incompatibility between manufacturers,- large number of different controllers to maintain,- no fieldbus interface or only a serial interface (RS232)
with specific protocol,- difficulties to implement hardware or software
modifications after initial installation.
The PLC solution avoids most of these problems and3.1 Vacuum pumping groups
Vacuum pumping groups are used in large numbers inaccelerators for the pumping of the beam pipe, down to apressure of some 10-9 mbar.
A typical pumping group is composed of a mechanicalroughing pump, a turbomolecular pump with its own speed
controller and 4 or 5 valves (for isolation, venting, leakdetection, ...). In addition other auxiliary devices, likepressure gauges or switches, heating element and coolingsystem may be found (fig.1).
The controller must manage all these devices to satisfy
the different operational modes required by the vacuum
technician. The pumping group is usually used in a standalone mode, via a local control panel, but it also can beremotely controlled when connected to a fieldbus.
Until now our choice was to buy a complete pumping
group on the market with its own control system or to buy
all the components separately from different vacuum
manufacturers, integrate them , and develop a specificcontroller. This practice has lead to the situation where wefind ourselves with tens of different pumping groups (withnearly the same functionality) with as many different typesof controllers!
The need for new pumping groups provided theopportunity to use the PLC solution to develop a'universal' controller for all pumping groups whatever theirorigin or their configuration.
3.1.1 PLC selection
The main criteria of selection are:- Technical: CPU power, input/output modules, fieldbus
connectivity, limited size (installation inside a 3U Europachassis), adequate development tools.
- Others: quality/price ratio, European origin, technicalsupport from the manufacturer and inside CERN, etc.

Field BusVACUUM CHAMBER

PLC CONTROLLER
Penning GaugePPirani Gauge

R

Turbomolecular Pump

I/PTMP

To Leaks
Detector

O/P

Remote Control
PanelGauges PowerSupplies

Local Control
PanelPr.

TMP SpeedController

Heating jacket

Pr.

Pres. Switch
MainsRP

Power

Pres. Switch & Gauges

RP

PUMPING GROUP

Fig. 1 - Pumping Group

Fig. 2 - Pumping Group Controller

Roughing Pump

The PLC selected for this application belongs to theSimatic S7/300 family of Siemens. We use the following
modules: one power supply PS307, one CPU313, one 32
input and one 16 output digital modules. A pre-prototype
had been realised before with the previous Simatic family
S5-95U [3].
3.1.2 System description
The PLC is installed inside one half of a 3U Europachassis. The remaining half is reserved for the speed
controller of the turbomolecular pump. There is a control
panel on the front used for 'remote' operation, as thepumping group can be located at a distance of up to 300m
from its controller. There is a 'local' control panel and amains distribution box near the group itself (fig.2).
The input module of the PLC is connected to the signals
coming from the various components (pumps, valves, etc.),from the control panels and from the gauges.
The output module is connected to the different actuators(valves, power breakers, etc.).
3.1.3 Operating modes
A pumping group is an ideal application to use a PLC.
The main phases of operation are the following:- starting sequence,- pumping at nominal or reduced speed,- leak detection,- stopping sequence.
All these operating modes can be clearly defined withsequential logic. There is one programming bloc dedicatedfor each component of the group (object). The program isstored on an EEPROM card which is very easy to change
to match the program to the type of group or to its
configuration.
3.1.4 Dual-controller
For smaller pumping groups we have integrated 2 speed
controllers for turbomolecular pumps inside the same 3U

Europa chassis. With the addition of 2 extra input/output
modules and of a second control panel we can control, withthe same PLC, two pumping groups in an totally
independent way.
3.2 Test benches for vacuum chambers
The second application is the rejuvenation of two test
benches for the vacuum chambers.
The following tests are executed:- leak detection before and after bakeout,- measure of the degassing rates,- measure of the limit pressures,- residual gas analysis.
The two test benches are identical. They are equippedwith a 6m long measurement chamber connected on one
side to four pumping groups and on the other side to thedevices to test (DUT) via six isolation valves.
The measurement chamber is equipped with 3 gauges, agas analyser and a ion-pump. On every output we find alsoa gauge an a ion-pump (fig.3).
The rejuvenation consists of replacing the oldest
equipment (pumping groups, gauges, etc.) and, in a second
step, to install a supervision system for the remote controlof the test benches.
3.2.1 Description
For the new pumping groups we have used the dualcontroller describe in 3.1.4 . For the supervision of the test
benches we have chosen the following solution (fig.4). We
use as main controller a Siemens PLC type S7/400 forreasons of compatibility. It is connected to the pumping
group controllers via the MPI fieldbus.
This serial bus (RS485) is integrated in every CPU
module and can be used with a maximum length of 50m at
187.5 kbit/s. It is very cost effective for small applications
because we do not need additional communication module.
The 20 analogue inputs from the gauges are connected tothree 8-input modules with a resolution of 13 bits . For thecontrol of the 12 separation valves we used two distributed

DUT 6

DUT 5

DUT 4

DUT 3

DUT 2

DUT 1
VGI

VPI

VGI

MEASUREMENT CHAMBER

Ion Pump

VGR

VGP

Gas Analyser

PUMPING
GROUP#4

PUMPING
GROUP#3

PUMPING
GROUP#2

PUMPING
GROUP#1

4 Control of vacuum equipment for the LHC

Fig. 3 - Test Bench for Vacuum Chambers
Ethernet

Supervision PC

WinCCMain PLCController

GAUGES

Simatic S7/400
MPI / Profibus

Profibus DP

VALVES

Distr. I/ODistr. I/O

Simatic ET200M

Simatic ET200M

VALVES

PLC Controller forGroups 1 & 2

PLC Controller forGroups 3 & 4

PLC Controller forGroups 1 & 2

PLC Controller forGroups 3 & 4

Simatic S7/300

Simatic S7/300

Simatic S7/300

Simatic S7/300

TESTS BENCH # 1

TESTS BENCH # 2

Fig.4 - Test Benches Control Layout

32-input and 16-output modules connected via Profibus,
using the DP protocol.
3.2.2 Operation
The main PLC is used as master and works in pollingmode. The data transmission with the pumping groupcontrollers is made periodically by exchange of data blocks
between master and slave PLCs. The remote control of thevalve signals is seen as 'normal' input/output, after theinitial configuration of the Profibus DP protocol. Finally,
all the data of each test bench are stored to be accessed bythe supervision system.
3.2.3 Supervision

The selected MMI program is WinnCC (Version 3.1)
from Siemens. It runs on a PC under Windows 95 orWindows NT. The PC is connected to the main PLC
either via the MPI or the Profibus fieldbus, according to
the selected interface. The representation of the system ismade using hierarchical view derived from photographs ofthe test bench down to the detailed synoptics of theequipment. The program also provides function modules
for graphic display, messages and archives.

Considering the good results obtained with these two
applications, the use of PLCs and distributed I/O connected
via a fieldbus such as Profibus, could be an interesting
solution for the control of the numerous vacuum devices
that will be installed in the future LHC accelerator. Oneway to do it would be to install, for every LHC octant, amain PLC connected, via a Profibus line to either, otherPLCs acting as local controllers or, directly to distributed
inputs/outputs interfaces. All the 8 main PLCs could beconnected to a local supervision system and also to theupper layer of the general control system.
5 Conclusion
We have seen with these two applications that the slow
control systems used in the domain of vacuum foraccelerators and physics experiments can use and integrate
PLCs instead of specific or 'home-made' controllers, withall the benefit of industrial equipment. It is a first step to a
global approach of a complete industrial solution to ourrequirements.
References[1] M. Rabany, Industrial Control Solutions in ResearchLaboratories, ICALEPCS’95 Chicago.
[2] R. Gavaggio, P. Strubin, The New Vacuum Control
System of the CERN PS Complex, ICALEPCS’95
Chicago.
[3] R. Gavaggio, Utilisation d'un API pour le Controled'un Groupe de Pompage, CERN Note technique
LHC-VAC NT96-07.