collimators md: low-level point of view ab/atb/lpe 18/12/2006

Collimators MD:Low-level point of view

AB/ATB/LPE18/12/2006

Collimators Control Review, 18/12/2006R. Losito, AB/ATB 2/37

Authors The real work has been done by:

Alessandro MASI Jerome LENDARO Arnaud BRIELMANN Mathieu DONZE Pierre GANDER Michele MARTINO FSU!!!


OUTLINE Introduction LSS5:

Architecture Problem with EM Noise Results

TT40 Architecture Position Reading


INTRODUCTION We prepared two different architectures:

LSS5: Old LEP motors, Old 2004 sensors New control system (National Instruments PXI) Integrated into FESA

TT40 New non rad-hard motors New LVDTs Control system based PC (production Testbench). Algorithms for position reading equivalent to what will

be used in LHC No integration into FESA (controlled through remote

desktop)


LSS5 Architecture

Control system based on National Instruments PXI

Power driver PARKER Gemini: will not be used for collimators but for TDI. Characteristics similar to what specified for collimators. Little bit more noisy.

Driver control based on FPGA: 5 volts TTL Installation started the same day of MD

(Oct. 31st )


LSS5 Noise Problem:

Motor current and end-stroke switches in the same cable.

Local cabling (2004) very poor quality: no shielding, cables tight together and twisted.


LSS5


LSS5 Noise Problem:

Motor current and end-stroke switches in the same cable.

Local cabling (2004) very poor quality: no shielding, cables tight together and twisted.

Result: too much noise on switch signal (>5 Vpk)

Solution: Decouple switch signal using optocouplers, excite (and

read) switches at 24 volts. Noise shorted to ground with capacitors.

It took 6 hours to find the components (AB/RF, AT/MTM), mount the circuit and bring it to operation level.

It worked perfectly, no more noise at all on FPGA input.


LSS5 Lessons Learned (1/2):

As foreseen, position sensors gave unreliable reading.

Reasons: Quality of GAP LVDT (poor linearity) Sensor type (potentiometers) not adapted to

precision measurements over long cables Fast cycle reading

Basically, there is nothing we can do about it. If we want better measurements, we should install baseline LHC sensors.


LSS5

Measured during test in LSS5 (Oct. 31st)


LSS5 Lessons Learned (2/2):

PXI was stable for nearly one month.

No crash, no lost connection (during crash of CMW, PXI still accessible with LabView RT)

Don’t worry, in LHC access through Labview RT will only be able to check whether the system is alive or not, no possibility to change the program or any parameter “on-line”.


TT40 Architecture

Control system based on Windows PC, equipped with National Instruments motor controller and DAQ cards

Power driver PARKER Gemini. Driver control still on 5 volts TTL Proper cabling (all shielding properly done)


TT40


TT40 Lessons Learned:

Our strategy for the LHC has given excellent results concerning accuracy (see coming slides).

EM Noise is perfectly under control. No need to put optocouplers and go to 24V to get clean signals (However we will do it in the LHC to prevent even further any problem).

Remote Calibration working fine. For the LHC, we will not need to access the collimator to re-calibrate the sensors !!!!

Position reading algorithms we developed robust. A simple windows PC is sufficient to get 1 µm sigma on the measurement!!!


TT40

-35.000

-30.000

-25.000

-20.000

-15.000

-10.000

-5.000

0.000

5.000

10.000

0:00 0:28 0:57 1:26 1:55 2:24 2:52 3:21 3:50

time

Jaw

pos

ition

[mm

]

Position UP LVDTPosition UP step counter


TT40

3.980

3.985

3.990

3.995

4.000

4.005

4.010

4.015

4.020

2:08 2:15 2:22 2:29 2:36 2:44 2:51 2:58 3:05

time

Jaw

pos

ition

[mm

]

Position UP LVDTPosition UP step counter


TT40

3.980

3.985

3.990

3.995

4.000

4.005

4.010

4.015

4.020

2:08 2:15 2:22 2:29 2:36 2:44 2:51 2:58 3:05

time

Jaw

pos

ition

[mm

]

30.0

35.0

40.0

45.0

50.0

55.0

60.0

Dow

nstr

eam

tem

pera

ture

[ C

]

Position UP LVDTPosition UP step counterDownstream Temperature


TT40

3.980

3.985

3.990

3.995

4.000

4.005

4.010

4.015

4.020

2:08 2:15 2:22 2:29 2:36 2:44 2:51 2:58 3:05

time

Jaw

pos

ition

[mm

]

30.0

35.0

40.0

45.0

50.0

55.0

60.0

Dow

nstr

eam

tem

pera

ture

[ C

]

Position UP LVDTPosition UP step counterPosition DN LVDTDownstream Temperature


Collimators’ requirements Position Readout and Survey

LVDT systems (LVDT+signal conditioner) from the leading companies (Schaevitz/MSI, Sensorex, Penny & Giles) have been tested.

The results for the full system were very deceiving from different points of view:

Temperature stability is bad. Few degrees of change in temperature of the electronics may result in 200 to 300 µm change

Maintainance and portability very difficult. Each conditioner has to be manually calibrated with trimmers. We will have ~720 sensors installed in LHC.

They are all based on linear approximation of the sensor response. To go down to 5 µm resolution one would need a linearity of ~0.01%. Standard sensors are at the level of 1 to 10% linearity.

No real immunity to noise and to interference with other sensors at the input of the conditioner.



All the companies contacted were ready to produce a dedicated signal conditioner to address all these points.

The first offers were very expensive and incompatible with our budget. The risk of not getting at the end what desired was also not negligible.

We therefore decided to proceed ourselves with the development of a conditioning strategy that could be conveniently applied to such a huge system.


Collimators’ requirements

LVDT:



After investigation on several different solutions, we chose to go for high speed sampling of the signal, and real-time processing of the data in the CPU to get the position information.

That is different from standard approach, where an analog front end electronics treats the signals before sampling



SI NE WAVEGENERATOR

LVDT

.

FRONT-END

DAQ P ADC DAQ PROFI BUS PLC



DETECTOR

E1-E2+NOISE+DRIFT

noise

E1-E2 E1-E2+NOISE



To increase the immunity to Noise and Drifts, both secondaries are brought to the electronics rack.

DETECTOR

(E1+NOISE+DRIFT)-(E2+NOISE+DRIFT)=

E1-E2

noise

E1E2

E1+NOISEE2+NOISE



•DETECTOR

(E1+NOISE+DRIFT)-(E2+NOISE+DRIFT)=

E1-E2

•

noise

Noise is reduced by proper cabling



Measured during test in LSS5 (Oct. 31st)



Measured by P. Gander during test in TT40 (Oct. 31st) in remote!!!!

LVDT Calibration Repeatability test (TT40)36 repetitions

0.95

0.955

0.96

0.965

0.97

0.975

0.98

0.985

0.99

0.995

1

1.005

1.01

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35

distance [mm]

Nor

mal

ized

pos

ition

[mm

]

< 20 µm

~ 25 µm mechanical play



This result is obtained with: 250 kS/sec simultaneous sampling of secondaries 1000 points per acquisition Demodulation through sin-fit algorithm (IEEE –

1241) No additional filtering



A small parenthesis on Sin-fit Algorithm Defined by standard IEEE – 1241 as recommended

method for sinus wave demodulation Synchronous Demodulation: Allows relaxing

sampling specs by using the KNOWN information about frequency of carrier (less bits, less speed).

Frequency response is a SINC: allows to have all the sensors in the same cable without interference from one to the other, and without additional filtering!!!!! (Calculated by M. Martino, University of Naples)



FREQUENCY RESPONSE OF SIN FIT



A small parenthesis on Sin-fit Algorithm Frequency response is a SINC: allows to have all the

sensors in the same cable without interference from one to the other, and without additional filtering!!!!! (Calculated by M. Martino, University of Naples)

That allows to transmit in the same cable, without individual shielding of the twisted pairs, all the LVDT signals.

Savings on cabling are in the order of SEVERAL 100KCHF!!!!!!


Conclusions PXI robustness demonstrated in LSS5

Accuracy of position reading demonstrated in TT40

Strategy chosen for Low-Level system successful !!!

collimators md: low-level point of view ab/atb/lpe 18/12/2006

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