Fred's Fusor

Control Systems

Contents of this page

construction helmet


This webpage describes control systems that are used to operate the Fusor. These control systems as such are not essential for operating the Fusor but they provide automatic control of equipment in the Fusor system or are required due to the properties of some of the parts in the Fusor system, e.g. vacuum valves operated by pneumatic air.

In the original setup of the Fusor website the paragraphs of this webpage were part of specific pages describing the particular equipment, which require these control systems, but it was recognized that having these control systems extensively described on the specific equipment pages would lead to increased loading times of these pages due to their lenght and the amount of images that needed to be downloaded when opening the page.

A major control system described on this webpage is the pneumatic control system that became essential when compressed air operated vacuum valves were obtained. Should we have obtained mains operated vacuum valves than a pneumatic control system should not have been required.

Pneumatic Control system

Pressure converter

For your convenience we have added to this page a pressure converter in order to enable convertion of pressure units mentioned on this page into units which might be more familiar to you.

Instructions: put the amount in the top left "From:" box, choose the known unit in the left listing box, choose the required unit in the right listing box and read the result.


Unit Converter



Pneumatic operation of components is very common in industrial facilities. Because most of our equipment is obtained from surplus supply and/or auctions, a realistic chance exists that the equipment acquired has been designed for pneumatic operation. Indeed, quite a number of acquired vacuum valves appeared to require pneumatic control. This fact made it necessary to study the principles of pneumatic operation theory, which is called fluid power control. "Fluid power" sounds somewhat peculiar because we work with compressed air. However, not much difference exists between hydraulic and pneumatic systems since the behaviour of gas is not different from fluids in fluid power and motion control.

Tackling the theory and practice of pneumatics reference 1 was found to be very helpful as well as reference 2.

The pneumatic control system consists of:
  • Compressor with pressure regulator
  • Shut-off valve
  • Filter
  • Regulator
  • Control Valves
  • Electrical Connections
  • Vacuum Connectors
  • Vacuum Tubing
The compressor with the main pressure regulator should be able to produce compressed air with a pressure of 0.8 Mpa (8 bar) and preferably have a large pressure tank to avoid that the compressor runs nearly constantly, producing loud noises.

The compressor is connected to the Fusor by means of a long, flexible tubing, connected to a shut-off valve. The shut-off valve is connected to the combined filter/regulator, which can be set to the required pressure for the system. By means of one or more dividers, the filter regulator is connected to the control valves. Connections are made with polyurethane tubing that can be obtained in diameters of 4, 6, 8, 10 and 12 mm and with push-in type connectors, which are available for the same tubing diameters and with different threadings. Connectors are available as straight and angled connectors, as dividers, as chokes, etc. (images 1 through  3):

angled connector  regulated choke  divider
Images 1 thru 3: Angled Connector (left), Regulated Choke (centre), Divider (right)  (Source:  suppliers)

The filter and pressure regulator can be combined in one single unit (image 4) and the control valve in our system has five ways with two positions (image 5):

pressure regultorcontrol unit
Image 4 and 5: Filter regulator (left) and bidirectional valve (left) (Source: Suppliers China)

The specifications are as follows:

SFR 400 Air filter regulator: input/output " BSP; max. pressure 1.0 Mpa; test pressure 1.5 Mpa; temperature range 5-60C; nominal filtration rate 40 m; recommended lubrication No.1 turbine oil ISO VG32; max. dimensions: 230.4x80x96.5 mm; weight 570 g.

BLCH Model 4V210-08 pneumatic solenoid valve: type 5 ways 2 positions; power consumption 24V DC 3W; voltage range 21.6-26.4V DC with an ED of 100%; operating pressure 0.15-0.8 Mpa; ports inner dia. "; hex connector inner dia. "; dimensions 120x68x23 mm; weight 223 g.

The five ways, two positions control valve permits two single acting vacuum valves to be connected, operated in opposite actions, or one double acting vacuum valve. Image 39 shows on top of the control valve two ports marked A and B, which are connected each to a different PVPK valve. The air pressure line is connected to the middle port on the bottom of the control valve, marked P. The left port on the bottom is marked R and the right port is marked S. In the rest position of the solenoid actuator port A is connected to the pressure line and the vacuum valve connected to port A is closed, whereas port B is connected to the exhaust port S and the vacuum valve connected to port B is open. When the solenoid is actuated port A will be connected to exhaust port R and the valve connected to port A will open, whereas port B will be connected to the pressure line and the valve connected to port B will close.

For independent control of a number of vacuum valves, multiple control valves are usually combined on a central base in order to reduce compressed air line connections and air outputs. The four control valves on a central base in image 6 individually would have needed four separate compressed air lines (with the base only one) and eight silencers on the air outputs (with the base only two).

control valve island
Image 6: Multiple Control Valves on Base with push in Connectors and Silencers ( Assisi Electric UK)

Single Action Actuators

Single Action Actuators, or spring return actuators, require compressed air for just one action. In the case of a single action vacuum valve this valve is normally closed by means of a spring and introducing compresssed air into the valve causes the valve to open by compressing the spring. When the air pressure on the valve is released, the valve closes again by pressure of the spring.

The basic layout of a single action pneumatic control system is shown in image 7:

basic pneumatic layout
Image 7: Basic layout of a pneumatic control system with a single action vacuum valve ( FRS 2014)

The layout in image 6 has been drawn for the connection of one single action vacuum valve and the control valve is of the 3/2 type, i.e. three in/outputs and a bidirectional operation (image 8). When powering the solenoid of the control valve with 24V DC, the piston moves out and compresses a spring; ports are opened or closed (depending on the type of controller) and when the power to the solenoid is cut off, air pressure is released from the control valve, the spring in the controller decompresses and moves the piston to the rest position closing or opening ports.

When an appropriate directional control valve is selected, two vacuum valves can be operated in tandem with one actuation of the 24V DC coil (reference 1). For our Fusor an operating voltage of  24V DC
has been chosen for the solenoid voltage but this can also be 12V DC or 230V AC. Our choice for 24V DC has been made because the signalling microswitch of the vacuum valves is rated at 24V and because all electromagnetic ventilation valves also operate on 24V DC. Therefore one single 24V DC power supply will be suitable for all low voltage applications in our Fusor vacuum system.

Image 8: two positions, three way control valve ( Assisi Electric UK)

The layout of a pneumatic control system operating two valves on one 5/2 controller is shown in image 9. Both vaccum valves operate in tandem, one open and the other one closed and vice versa, controlled by a pneumatic controller of the 5/2 type. In the schematic drawing vacuum valve No.1 is closed (A port connected to pressure P) and vacuum valve No. 2 is open (B port connected to exhaust S):

final control system

Image 9: Schematic layout of the pneumatic control system for two valves in tandem ( FRS 2014)

The sound made by the pneumatic controller when blowing off pressurized air can be absorbed by inserting a sound absorber into orifices R and S (image 10):

sound absorber
Image 10: Festo Sound Absorber ( Supplier)

Double Action Actuators

Double Action Actuators require alternating compressed air in one of two ports to either open or close the valve. Usually this is the case with high vacuum sliding valves which move in two directions, each direction operated by putting compressed air on one port (one side of the psiton in the cylinder) and by opening the other port (releasing air to the environment from the other side of the piston in the cylinder) or vice versa.

An example of a sliding high vacuum valve, in this case a vacuum isolating linear gate valve, is shown in image 11:

gate valve
Image 11: Example of pneumatic VAT linear gate valve (source: supplier Germany)

Instead of the sliding motion of the valve in a linear gate valve, also a sytem exists where the valve is swinging into position (image 12). The swinging mechanism is also operated by a double acting pneumatic actuator and such a valve is also called a pendulum valve.

Image 12: Vacuum Isolating Pendulum Valve (source: supplier USA)

An interesting fact relating to the pneumatic operation can be observed in both images. In image 11 we see that the length of the pneumatic actuator (cylinder) is much larger than the length of the cylinder in image 12. This is due to the fact that the distance to be travelled from fully open to fully closed and vice versa is by far larger in a linear (sliding) valve than in a pendulum valve. When we assume that the mass (the weight) of the moving parts in both vacuum valves is equal than with a shorter distance to travel more kinetic energy will be required for the action. Therefore the diameter of the piston/cylinder needs to be increased, which we can see  in image 12: a "fatter" pneumatic cylinder.
Conclusion: a linear gate valve has a longer and thinner pneumatic cylinder than a pendulum gate valve, which has a shorter and fatter pneumatic cylinder.

A totally different type of high vacuum isolation valve with pneumatic operation is the butterfly valve (image 13). In this type of valve the part that closes or opens the valve is a disc with an O-ring lining which is mounted on a rod over the diameter of the disc. The disc rotates a quarter turn from the open to the closed position. The disc is always present in the flow and therefore causes a reduction of the initial flow.

butterfly 1
Image 13 Butterfly Valve (closed; top view)

Image 14: Butterfly Valve (bottom view with rotating axis)

The butterfly valve also has a double action pneumatic actuator, which is connected to a mechanical construction (image 14 the red box and image 15 inside the red box) that transfers the reciprocating linear motion into a quarter turn rotational motion.

butterfly mechanism
Image 15: Butterfly Valve Mechanism (inside the red box) ( FRS 2015)

In all three types of vacuum isolating valves the fully open and/or fully closed position of the valve is indicated by means of electric contacts.

The schematic layout for operating a double action actuator, controlled by a 5/2 valve controller, is similar to image 9 and shown in image 16:

double action actuator
Image 16: Schematic layout of double action actuator with 5/2 valve controller ( FRS 2015)

The complete vacuum system consists of one double action butterfly valve, to separate the vacuum chamber from the oil diffusion pump, two single action vacuum valves, one foreline valve and one roughing valve, and two air admit valves. The air admit valves are not pneumatically operated (like all other valves) but they are normally closed and activated to open by means of a 24V DC solenoid. The complete pneumatic layout of this vacuum system is shown in image 17, including the layout of the 24V DC circuit.

complete system
Image 17: Combined pneumatic control system and 24 V DC system ( FRS 2015)

The two single action valves and the butterfly valve have microswitches in the valve body, which are closed or opened depending on the position of the valve. Green and red LED's indicate the opened or closed postion of these valves, yielding real time information  about the valve status.
The two air admit valves do not have microswitches and instead it is only monitored whether the solenoid is under power or not, which is an indirect way of signalling the status of these valves.

Unfortunately for our Fusor concerning the butterfly valve we do not only need feedback from the system to indicate whether the valve is closed or open, but also we would like to have the possibility to set the butterfly valve in a partially open (or closed) position.

The reason for this requirement is that the most precious material in the operation of our Fusor is Deuterium gas, which is "consumed" in the process of producing fusion, but also which is pumped out at a high speed by our vacuum pumps.

The goal in feeding Deuterium gas into our Fusor is to keep it there as long as possible and to loose it only in very small amounts through the pumping system. Therefore it will be required to  minimise pumping once the Fusor system has reached its final low vacuum. Lowering the pumping capacity directly on our vacuum pumps is not possible and therefore we will need the butterfly valve to act as a choke. This will require a control on the position of the butterfly valve, which unfortunately is not incorporated into the butterfly valve. Moreover we will need a feedback control and a regulating system in the pneumatic control system.

Normally, in industrial systems quite intelligent solutions exist to enable control of a double acting pneumatic actuator, but the price of such a system is not quite in line with our available budget.
We considered it a challenge to find a simple solution, within our budget, and sufficiently sophisticated to fulfil our requirements within reasonable accuracy, i.e. maintaining more or less a controlled, choked vacuum flow in our Fusor.

Initially we found that a double acting actuator can be position controlled by a 3 position 5 way solenoid control valve, though not accurately, with a number of disadvantages (such as drift) and that it is more difficult to control with a microprocessor. Such a 3/5 solenoid valve can be obtained in several configurations for the mid position but in our case the configuration with the mid position setting both actuator cylinder spaces open to outlet is the most preferred one. The reason is that both actuator chambers have different piston surfaces and different chamber volume characteristics due to the fact that one chamber contains a variable "amount" of the piston rod (depending on the position of the piston) and the other chamber has no piston rod at all. This makes it the more difficult to maintain the piston at a fixed place with both chambers pressurized. Moreover, a pneumatic system is never fully airtight and a 3/5 solenoid valve configuration with both chambers pressurized at rest will start drifting due to small leaks in the system. However, the disadvantage of a
3/5 solenoid valve configuration with both chambers open to outlet at rest is that it fully depends upon the mass inertness of the actuator components to stay in the set at rest position.

We had to look for a different solution for which we have read a paper describing a closed loop pneumatic positioning experiment with a double acting actuator (reference 3). This paper learned us that we had to add a linear 100 kOhm potentiometer for reading the position of the moving piston in the actuator. Another very helpful paper (reference 4) made us understand the requirements of such a closed loop servo system for controlled positioning of the pneumatic valve.

As can be seen in image 15 not much space is available inside the butterfly valve housing for adding a large sliding potentiometer and, moreover, the linear stroke from the piston rod appears to be a swinging motion as it powers a rotating motion on the valve axis.
The easiest solution would be to add a rotary potentiometer to the valve axis. However, the principle of using a sliding potentiometer with a sliding movement (stroke) on the resistor surface which is equal to the displacement of the piston rod will than be abandonned. The advantage of that principle is that the highest accuracy in position reading can be achieved. The disadvantage of the rotary potentiometer is not only that the resistor surface of it is usually shorter than that of a sliding potentiometer, but also that the actual movement of the valve from the closed to the open position is only a 90 turn, whereas the resistor surface covers a 270 turn in the rotary potentiometer.
With other words, we will use only one third of the available resistor value of the potentiometer!


Wiring Diagram for the Cylindrical Fusor

The Cylindrical Fusor, prototype 1, has been designed with a manual override switches panel on the frame of the reactor trolley. The purpose of these switches is to operate the fusor manually and/or to switch off certain components or closing or opening valves manually in case of emergency.
The panel has control lights, which indicate the status of the valves. The colors have been chosen for the valves in the normal operation situation to show all indicator lights in green (except for one valve).
In addition to the valve control swiches, also two on/off switches have been added for the cooling fans for the air cooling of the foreline pump and the turbo drag hybrid pump.

Wiring Diagram

The wiring diagram is shown in image 18:

wiring diagram
Image 18: Wiring Diagram for the Cylindrical Fusor, Prototype 1 ( FRS 2017)

The wiring circuit for the Cylindrical Fusor, Prototype 1, makes use of two power supply units with 230V AC input and respectively 24V DC and 12V DC output, each with a maximum current of 5A.

The 12V DC power supply unit powers two 12V DC fans, used for air cooling the two vacuum pumps. The circuit is a simple power on/off circuit with a green LED indicating power on.

The 24V DC power supply unit powers six solenoids, operating vacuum valves in the Fusor system. The vacuum valves consist of three direct acting solenoid valves, used for air admittance or turbo pump venting, and three pneumatically operated vacuum valves.

Under normal operation of the Fusor direct acting solenoid valves (all for introducing air into the system) are in the normally closed position (NC) and draw no current, except for three green LEDS indicating that the Fusor is in the operational mode.

The three pneumatically operated valves draw only current when changing the position of the valve and during keeping that changed position. During operation of the Fusor, the normal position for the foreline valve is NO (normally open), for the roughing valve it is NC and for the Butterfly HiVac valve it is NO.
All three pneumatically operated valves have integrated micro switches, which will be connected to green or red LEDs as indicated in the wiring diagram, indicating red when closed and green when open. The switches situation as shown is in the valves closed psoition.

Current limiting series resistors are connected to the LEDs to set the current at approximately 20 mA. Our LED's were measured to have a voltag drop of 1.8V and therefore we will need
1110Ω for the 24V DC circuit (which results in a standard resistor of 1k2 at 1 W) and 510Ω (or a standard resistor of 560
Ω at 0.5W) for the 12V DC circuit.

Diodes have been applied as flyback diodes (1N4007, 1000V/1A), except for the turbo vent valve which already contains integrated series opposing (anti-series) Zener diodes.
The diodes for the fans could be replaced by Schottky diodes (1N5818, 30V/1A) when we want to regulate the speed of the fans with PWM from a microprocessor, measuring with a tempearture sensor the housing temperature of the pumps.


Turbo Pump Controller Control System


Because our turbo pump controller, a
Varian TV 70 model 969-9507-3003 controller, lacks a control terminal or the remote hand held terminal and because no RS 232 connector is present as an option, we will have to construct a separate control terminal making use of the P1 input connector and the J2 output connector in order to operate the controller and the pump.
Fortunately the matching counterpart connectors were present with the controller.

Control Terminal

All wiring from the connectors to the control terminal are made with AWG 24 (0.24 mm2) wires.
The following additional hardware is required:
  • a sheet of aluminium (1.5 mm thick, dimensions at choice) as base for the panel when the controls will be panel mounted or an aluminium box when we prefer a handheld terminal,
  • 4 single on/off switches for 24V/2A,
  • 5 LEDs (colour as preferred) with 5 resistors 1.2kΩ / W,
  • Digital voltmeter 3 digit 100 V DC,
  • stickers with text.
The wires are connected from the connectors to the terminal panel according to the schematic in image 19. Placing of the components on the terminal panel and colour of the LEDs is arbitrary.
All input and output connectors to the turbo pump controller are optically isolated from the controller internal circuit and when powered the outputs on J2 are 24 V and 60 mA.

Image 19: Schematic layout of the turbo pump control panel ( FRS2015)


Turbo Pump Vent Control System


Venting a turbo pump is the procedure of admitting a dry gas into the turbo pump. When a turbo pump is switched off and the rotor comes to a standstill, oil contamination and condensates from the foreline pump seep into the turbo pump and into the vacuum chamber contaminating walls and pump parts. By admitting a dry gas into the vacuum pump and the vacuum chamber contamination is excluded. The
minimum pressure to be attained is 10 to 1000 mbar.

Usually a turbo pump is equiped with a manual venting valve, which is opened when the pump is slowing down after stopping pumping. The roughing valve, the foreline valve and the high vacuum valve can be closed manually when the vacuum process is to be halted, isolating the turbo pump and the vacuum chamber from the foreline pump. However, when the foreline pump stops unexpectedly due to malfunction or overheating no time is left for manullay closing the valves and venting the turbo pump. Therefore, we describe in this chapter a simple automatic vent control system.

Vent Control System

The sensing element for initiating an action at a sudden drop in vacuum pressure is a pressure switch or a vacuum gauge with switching functions. A contact opens or closes when a chosen or fixed setpoint is passed. For converting such an open or closed contact signal into a signal that can be understood by a microprocessor we have developed a simple circuit or number of circuits, shown below:

turbo vent layout
Image 20: Turbo Pump Vent Control System Layout ( FRS 2015)

The schematic layout of image 20 consists of a number of control circuits, coupled or separate. The basic setup in the first circuit (centre of the image) is a 24 V DC power supply with an impuls switch, connected to two LED's for indicating the switch position, which powers the solenoid of the 5/2 control valve for closing or opening the pneumatic vacuum valve. The impuls switch is connected to a push button for manually closing or opening the valve and to a 5V DC relay, which is connected to a microcontroller system. The relay comes into action when activated by the microprocessor and changes the current position of the impuls switch in order to close the vacuum valve.

Note: In our initial vacuum system setup we had manual switches to open/close the vacuum valves. With the introduction of the automatic vent valve system we had to replace the manual switches by inpulse switches (or bistable relays). Operation of the vacuum valves is now either by a pulse from a push button on the control panel or by a pulse generated by the relay in the vent valve system when this system comes into action. In image 20 the complete schematic for the inpuls switch has not been entered. It is just shown a a "black box" by the dotted lines.

A simple solution for the impulse switch was found in a tiny circuit, a flip-flop latch switch module (image 21):

Image 21: Flip-Flop Latch Switch Module ( Yonggang81's shop)

The flip-flop latch switch module can be operated in a range of 3 - 24 V DC. The standby current is < 2 A and the continuous output current
is 5 A at 5 - 24V DC, 4 A at 4 - 5 V DC and 2 A at 3 - 4 V DC. The dimensions are 16 x 10 x 7 mm with a pin pitch of 1 inch.
With an inductive load, which is the case with our solenoid valves, a diode is required in parallel with the load (image 22):

Image 22: Flip_Flop Latch Switch Module with Inductive Load Schematic ( FRS 2015)

A module with the possibility to switch higher loads makes use of a relay (image 23):

Image 23: Bistable relay module ( Gadgetinfinite)

The electronic module in image 23 needs a 12 V DC power input and the relay opens or closes when a pulse is received from a pushbutton. The relay is capable of switching loads of 30V DC at 10A as well as 250V AC at 10A.

Image 19 shows four individual 24 V DC power supplies, but that is only for keeping the drawing simple. In real life we can use one single 24V DC power supply for feeding all circuits and solenoids. An extra power supply is, however, required for the microprocessor unit, which requires 9 - 12 V DC. This can also be created with an additional simple circuit powered by the 24 V DC power supply.

A second circuit can be found above the pneumatic vacuum valve in image 20. This circuit signals the position of the valve optically by means of two LED's and additionally also electronically by generating a high signal (+ 5 V DC) to the microprocessor when the valve is in the closed position.

The third circuit is in the top left hand corner of image 20. This circuit generates a high signal to the microprocessor when the pressure switch trips to a closed contact.

A fourth circuit is shown in the right hand bottom corner of image 20 and it consists of a 5V DC relay that opens the turbo pump vent valve when a signal is generated by the microprocessor.

It should be noted that the first and the second circuit are present in triplicate because for venting the turbo pump we will need to close three vacuum valves: the roughing valve, the foreline valve and the high vacuum valve. Therefore we will also need three input ports of our microprocessor and three output ports for the relays. It may be possible to combine the three relay output ports into one output port serving three relays at the same time because the action required is the same for all three valves: closing.
Another input port will be required for the pressure switch signal and another output port will be required for the vent valve relay.

In order to separate the 24 V circuit from the 5V logic circuit we have chosen for the CNY17 optocoupler, which has a forward voltage of 1.39 - 1.65 V and a minimum CTR (Current transfer Ratio) of 40%. With a CTR of 40% and an input current of 10 mA we will get 4 mA output. For 24V over R4 and R5 we get a value for these resistors of (24 - 1.5 V)/0.01A = 2250
Ω or the nearest value of 2k7 Ω. The output resistors R3 and R6 will have to cause a voltage drop of 5V at 4 mA and their value therefore is 5 V / 0.004 A = 1250 Ω. In order to be at the safe side we take a value of 4k7 Ω, which limits the current to 1 mA. In the current configuration of the in/outputs at the CNY17 we have a high signal. To reverse that into a low signal the in/outputs Vcc and Vout will need to be reversed.

For the microprocessor we have chosen for an Arduino Mini Pro (image 24), simply because quite a number of them were lying around in our toolkit. They cost about EUR 2.00 each and they have 14 digital I/O ports, of which 6 provide PWM output, and 6 analog input pins. When we lack sufficient I/O ports and when we would like to have a standard LCD display connected for status messages than we can upgrade to the larger Arduino Mega, which can be bought for about EUR 15.00. However, by connecting the LCD display through an I2C interface the number of ports can be reduced to two: a data line SDA connected to analog port A4 and a clock line SCL connected to analog port A5. A power connection from the LCD goes to Vcc and to GND on the Arduino. On an Arduino Mini Pro analog port A4 is the pin hole above A2/A3 and analog port A5 is the pin hole above A3/Vcc (image 22).
Connecting an external power supply ranging from 5 - 12 V DC to the Mini Pro can be done through the RAW pin (Vin).

Image 24: Arduino Mini Pro with pin layout

When using the Arduino as the microcontroller for the turbo pump vent controller system it should be noted that a push button is required on the vent controller panel (connected to RST to bring that to low) for resetting the microcontroller, as well as an override push button, setting an input port low or high as required, to prevent the microcontroller from venting the turbo pump when the vacuum system is starting up from ambient pressure. The override action can be performed with a few lines of programming by setting a delay time for the venting action when an override input is received.

We have chosen for relays instead of solid state switching devices because 2, 4, 6, 8 and 16 relay boards (image 25) are cheap to obtain and they can easily be connected to an Arduino. However solid state relay boards for the same application are also available, though at a higher price.

Image 25: Relay boards ( SainSmart)

The relay is to be connected with a 5 V DC power source and it switches when the IN-pin is connected to ground. The current drawn is at the IN-pin about 4 mA and the coil draws about 70 mA with a coil resistance of about 70
Ω. The contacts have a power handling capacity up to 30 V DC at 10 A or 250 V AC at 10 A. This is more than sufficient for our purposes because a solenoid of a solenoid operated vacuum valve draws a current below 0.5 A at 24 V DC.

Image 26: Relay connected to Arduino ( MAKE Flickr pool)

Image 26 shows a basic setup for the relay schematic layout. In theory it would be possible to control up to four relays directly and fully from the Arduino's Vcc because each relay draws minimally 70 + 4 mA and an Arduino is capable of providing a current of 400 mA in total. However, this is not a good idea because it applies only when an Arduino is connected to an USB port and not when the Arduino is running on an external power supply (due to limitations of the Arduino on-board voltage regulator, which accepts a maximum current of about 70 mA). Therefore we prefer to apply an external 5V DC power supply, which offers minimally a current of 1 A, such as shown in image 27. This tiny power supply has an input range from 85 - 230 V AC at 50/60 Hz, incorporates an EMI filter and a temperature and short circuit protection. The output is 5 V DC 0.2V at 1000 mA, an efficiency at full load of 85% and a ripple of 150 mV.

power supply 5V DC 1A
Image 27: Power Supply 5 V DC, 1 A (source: Supplier)

For this purpose the schematic from image 26 is used. Diode D1 is a flyback diode (1N4004) for clamping voltage/current spikes produced when the coil is switched off. Resistor R1 has a value of 10 k
Ω and is connected to the base of transistor TR1, for example a BC847. When the Arduino digital pin goes high a voltage of 5 V flows through R1 to the base of the transistor and a current of 500 A turns TR1 on. The transistor connects the 5V line through the relay to ground and a current of about 70 mA flows, which causes the relay to switch the contacts.
The combination of the relay with the diode, the resistor and the transistor is usually sold mounted on a printed circuit board and is called a relay brick. Other configarations are also possible, such as an extra optocoupler in the circuit to separate the circuits or a reed switch instead of a relay.

When using a separate power supply in the switching circuit of the relay an optocoupler relay brick is preferred over a standard relay brick (image 28).

Image 28: 8-Relay Brick with Optocouplers and Jumper

Image 28 shows the actual relay brick that we will use in our Vent Control System. It has 8 relays, optocouplers and a jumper (image 29) to enable an external power supply. The price for such an 8-Relay Brick is just below 11 EUR.

Image 29: Jumper on the 8-Relay Brick (right under in image 24)

For connecting the 8-Relay brick to the Arduino and the external 5V power supply we use the following contacts:

The external 5V power supply goes to
  • JD-VCC (jumper removed)
  • GND
The Arduino goes to
  • Relay board Vcc to Arduino Vcc (+ 5 V)
  • Arduino signal pins to IN1 through IN8 (image 30)
input pins
Image 30: 8-Relay Brick Input Pins

The pins IN1 through IN8 on the 8-Relay brick are active low. This means that setting a relay pin low, turns the relay on. The advantage of having an active low relay setting is that when the system is powered up or a reset is given no relay(s) will turn on but they will activate only when the system program requires it.

A simplified schematic layout of the 8-Relay Brick is shown in image 31:

8relay schematic
Image 31: Schematic Layout of the 8-Relay Brick (See source: reference 5)

Programming the Vent Control System

A sequence of actions is required for approriate functioning of the Vent Control System:
  • Switch on the Vent Control System module; start the microprocesssor or reset the microprocessor;
  • Receive an external input override signal and apply a sufficient delay time before checking the signal from the pressure switch (the manual input signal overrides the system for a chosen period during start-up);
  • Check the protection switch status until a signal is received indicating that the switch has tripped at 5 mbar, due to a pressure drop in the vacuum system, e.g. the foreline pump has stopped deliberately or unexpectedly or the vacuum has sprung a leak.
  • The microprocessor issues commands for the roughing valve, the foreline valve and the high vacuum valve to close. The program, waits for an input signal from the valves.
  • When a signal has been received that all mentioned valves have been closed, the microprocessor issues a command for the turbo pump to switch off, as well as the foreline pump (if not stopped already due to malfunction or by choice).
  • The microprocessor issues a command for the vent valve to open. A dry venting gas (or air) is entered into the turbo pump before the turbo pump rotates lower than 16,000 rpm. In order to protect a turbo rotor still running at high speed the microprocessor can progressively open and close the vent valve for admission of dry gas by means of pulses with increasing duration.
  • Finally, all mentioned valves are opened manually and remaining venting or air admittance valves are opened.

Main Computer System

As a main computer system in the Fusor operating console we make use of an industrial Siemens Simatic 19" rack PC, model 840, part no. A5E00163324, with Intel Pentium III 1266 MHz processor, 512 MB RAM and 2 x 80 GB IDE HD (image 32 and 33; the manual can be found in reference 6).

simatica simaticb
Image 32 and 33: Siemens Simatic 19" Rack PC, Model 840 ( Siemens)

The rack PC dates from 2004 and originally runs on WIndows NT Workstation Embedded, but has been upgraded to Windows XP professional 32-bit OS. The system unit has the following adapters on board:
  • Creative Labs Sound PCI Card CT4810
  • Sony SMO-F551 Magneto Optical SCSI Drive 5,2GB 5,25
  • CD-ROM 5,25"
  • Floppy Drive 1,44MB 3,5"
  • Matrox Graphics Video PCI Card 16MB 908-07 Dual Monitor G2+DUAL-PL Rev A
  • 3Com Ethernet PCI Adapter
  • Adaptec 2940AU SCSI PCI Controller
The main computer system is used for on-the-site software programming of the Arduino microprocessor controllers in the Fusor operating system and for data acquisition and processing from the monitoring equipment, such as the ADC's, as well as process and measurement control by means of LABVIEW software.



engineering works
Ion Source


Ref. 1:
Introduction to Pneumatics: http://www.clippard.com/downloads/PDF_Documents/Application_and_Training/Intro_to_Pneumatics.pdf

Ref. 2: Hydraulics & Pneumatics; Directional Control Valves: http://hydraulicspneumatics.com/other-technologies/book-2-chapter-8-directional-control-valves

Ref. 3:
Pneumatic System Closed-Loop, Computer- Controlled Positioning Experiment and Case Study: http://engineering.nyu.edu/mechatronics/Control_Lab/Criag/Craig_RPI/SenActinMecha/S&A_Hydraulics_Pneumatics_2.pdf

Ref. 4:
Novel cylinder positioning system realised by using solenoid valves: http://www.scad.ugent.be/journal/2011/SCAD_2011_2_1_142.pdf

Ref.5: Controlling power with Arduino: https://arduino-info.wikispaces.com/ArduinoPower

Ref. 6:
Manual for Siemens Simatic 19" rack pc model 840 : http://usedplcs.co.uk/manuals/siemens/PC/RackPC840/hbrackPC840_b.pdf

Last Updated on: Thu Jul 6 12:42:02 2017

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