1. ICALEPCS 2005 Advanced uses of the WorldFIP fieldbus for diverse communications applications within the LHC power converter* control system Quentin King Converter Controls Power Group CERN * A CERN “power converter” = everyone else’s “power supply”

2. ICALEPCS 2005 Q. King 2 Context CERN is building the Large Hadron Collider (LHC) LHC will include 1712 magnet circuits, each driven by a power converter Each power converter will be controlled by an embedded computer → Power Group will use a total of 280 man years and 86 MSF to power the LHC Converter Controls section will use ~50 man years and 7 MSF to provide the controls 1400 out of 2000 controllers have been produced 100 have been installed

3. ICALEPCS 2005 Q. King 3 Control the 1700 power converters in the LHC  Spread around a 27km machine  Tolerate radiation (<10 Gray/year)  Send commands and receive responses  Maintain synchronisation to better than 1ms  Support real-time control for feedback of beam parameters  Support transmission of start/stop events  Support status publication  Support remote diagnostics  Support remote software updates We have been able to meet these challenges with the WorldFIP fieldbus The Networking Challenge

4. ICALEPCS 2005 Q. King 4 In the 1970s… Communications used enormous connectors and parallel data buses  Very expensive  Unreliable

5. ICALEPCS 2005 Q. King 5 In the 1970s… Communications used enormous connectors and parallel data buses  Very expensive  Unreliable

6. ICALEPCS 2005 Q. King 6 In the 1970s… Communications used enormous connectors and parallel data buses  Very expensive  Unreliable  Lots of wire wrap  More than 350 converters are still controlled this way today!

7. ICALEPCS 2005 Q. King 7 Then in the 1980s… LEP was built  800 power converters  One control computer per converter  Huge step forward in networking: MIL1553 fieldbus  Separate timing network

8. ICALEPCS 2005 Q. King 8 And in the 1990s… LHC was started in 1996  1700 power converters  One control computer per power converter: The Function Generator/Controller (FGC) In 1997 a survey of fieldbuses was conducted:  WorldFIP was identified as particularly interesting

9. ICALEPCS 2005 Q. King 9 Why WorldFIP? What is WorldFIP? Industrial network similar to Profibus  Uses 150 Ω twisted pair cable  Long distances: 500 m at 2.5 Mbps 800 m at 1 Mbps 1900 m at 31.25 kbps  Excellent noise immunity  Transformer coupled for galvanic isolation  Inexpensive components So nothing special so far!

10. ICALEPCS 2005 Q. King 10 WorldFIP components 150Ω Field Drive FullFip 150Ω Z=150Ω Field Drive μFip Gateway FGC

11. ICALEPCS 2005 Q. King 11 WorldFIP Synchronisation Field Drive FullFip CPU Timing Receiver Timing Network Ethernet Synch Gateway 150Ω Z=150Ω

12. ICALEPCS 2005 Q. King 12 No need for a timing network! All traffic is controlled by the FullFip device in the gateway Each transmission cycle is triggered by the synchronisation signal The first transmission is a broadcast so all FGCs receive a synchronised interrupt request from their uFip chips All FGCs can synchronise their local real-time clocks – so no timing network is required!

13. ICALEPCS 2005 Q. King 13 Time distribution FullFip Timing Gateway FGC μFip Timing Receiver 50 Hz Synch ms Period 50 Hz IRQ 1 kHz Gateway: Time broadcast Synch μFip IRQ 450 μs ± 3 μs PLL Clock PLL + local clock required so that FGC can run autonomously in case FIP traffic stops for a while Drift < 1ms after 1000s (1 ppm error)

14. ICALEPCS 2005 Q. King 14 WorldFIP cabling for FGCs 30 out of 200 FGCs in our reception and test lab  The green cables are WorldFIP fieldbuses  One gateway can support up to 30 FGCs

15. ICALEPCS 2005 Q. King 15 WorldFIP cabling for FGCs

16. ICALEPCS 2005 Q. King 16 FGC Gateway

17. ICALEPCS 2005 Q. King 17 50 Hz Synch Time distribution FullFip Timing Gateway FGC μFip Timing Receiver PLL Clock ms Period 50 Hz IRQ 1 kHz Gateway: Time broadcast Synch μFip IRQ 450 μs ± 3 μs

18. ICALEPCS 2005 Q. King 18 FGC Gateway connections 50 Hz Synch FullFip Timing Gateway Timing Receiver

19. ICALEPCS 2005 Q. King 19 Time distribution FGC μFip PLL Clock ms Period 50 Hz IRQ 1 kHz

20. ICALEPCS 2005 Q. King 20 Gateway: Time broadcast Synch μFip IRQ 450 μs ± 3 μs PLL Clock ms Period 50 Hz IRQ 1 kHz

21. ICALEPCS 2005 Q. King 21 How does the PLL work? If the CPU includes the necessary timer functions (input capture and output compare for Motorola devices), the whole thing can be done in software In the paper I explain how the PLL can be implemented in three lines of C The PLL disciplines the period of the local real- time clock, which can be implemented in ten lines of assembler The same functionality can also be implemented in a small piece of VHDL

22. ICALEPCS 2005 Q. King 22 But does it work?

23. ICALEPCS 2005 Q. King 23 PLL Error data Error = PHASE_REF - (IC - OC)

24. ICALEPCS 2005 Q. King 24 Proportional-Integral PLL data Clock Period = Integrator + GAIN x Error Integrator += Error

25. ICALEPCS 2005 Q. King 25 And the frequency? So the PLL captures nicely, but what is the frequency error? Is the drift < 1ms after 1000s?

26. ICALEPCS 2005 Q. King 26 And the frequency? So the PLL captures nicely, but what is the frequency error? Error = 0.8 μs in 40 s

27. ICALEPCS 2005 Q. King 27 And the frequency? So the PLL captures nicely, but what is the frequency error? Drift = 0.8 μs in 40 s 0.02 ppm or 2 in 10 8

28. ICALEPCS 2005 Q. King 28 Comments This is a tribute to the amazing stability of cheap quartz oscillators It is also an excellent result from a tiny amount of software combined with a bit of control theory This is not an lucky result, repeating the test has similar results everytime However, low drift over a minute does not prove that the drift will be less than 1 ms after 1000 s because the oscillator has a temperature coefficient of >1 ppm per degree

29. ICALEPCS 2005 Q. King 29 Conclusions WorldFIP is an excellent networking choice for the LHC power converter control system The real-time behaviour has saved us the need for separate timing and real-time control networks With more than 1700 systems, this is huge saving in connectors and cabling  Big financial savings  Improved reliability Protocol supports all our diverse communications needs with one twisted pair cable

30. ICALEPCS 2005 Q. King 30 Thanks to: My colleagues in AB-PO-CC  Stephen Page, Philippe Fraboulet, Philippe Semanaz, Alex Frassier, Denis Hundzinger, Gilles Ramseier, Daniel Calcoen The excellent collaboration from my colleagues in AB-PO and AB-CO To you for listening!